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| pepperami |
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pepperami
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 Posted: 18:03 - 20 Jul 2012  Post subject: CZ`s & MZ`s and all that |
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This is one for the two-smoke pundits on here.
Bear with me and you`ll see where I coming from.
Many moons ago I had the pleasure of spending time riding a CZ 250 moto-cross bike.
The grin factor was off the scale and it was a BRUTE  .
I also had A CZ 125 that we mildly tweaked , ie roller small end bearing rather than the bronze bush that was in there, a clean up of port edges, a bigger carb, and reduce the restriction from the baffles.
It made a noticable differance but it was never going to compete with a Jap 125 two-smoke.
When I was in Germany, I saw MZ`s that were so much better that what we see over here, and we all know that there was/is a race series just for MZ`s
So why is it that that MZ`s and CZ`s road bikes just dont measure up to the expectations of thier off-road cousins.
It would be dead easy to just say "they`re crap" but I believe that there`s more to it than that and this is where I would like some opinions.
Is it the size of the ports? or the length of the stroke ie long? is it the weight of the pistons? are Jap cranks lighter and therefore easier to spin?
What do you think two-smoke pundits? 
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Shaft
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| Posted: 20:47 - 20 Jul 2012 Post subject: |
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I think the answer is a combination of all those things.
I came close to buying a very tidy, low mileage Jawa 350 a little while ago, with the intention of applying my long unused tuning skills to produce a bit of a sleeper.
I did have a really good look at it and it didn't seem terribly badly built; the finish was pretty poor, but the bare materials were OK, if incredibly basic.
You realise you're up against it though, when you compare some raw figures:
1974 RD350
39 bhp @ 7500 rpm
162 Kg total weight
1993 Jawa 350
27 bhp @ 5500 rpm
166 Kg total weight
So no power, no revs, single carb and a 4 speed box, will seriously limit what you can do, without some pretty extreme mods.
On the other hand, you don't have to try too hard to get a lot more from the Yam and it can handle it.
It still would've been an interesting exercise and I wish I hadn't missed it, but I reckon there was a lot of work needed to get the motor really singing, plus issues with suspension and braking to overcome.
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| MarJay |
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MarJay
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| Posted: 21:37 - 20 Jul 2012 Post subject: |
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I've thought about this problem a lot, and I used to own an ETZ301.
Remember though, eastern european bikes aren't designed in the way that Japanese strokers were. For the Japanese, win races on the sunday, sell bikes on the Monday was always the rule. This meant that the goal was power power and power, at the expense of low end rideability.
With Eastern European bikes, they were designed to get Vladimir and Boris to work in the foundry, not to allow wannabe Kenny Roberts win at proddie racing. Not only this, Eastern European metallurgy and machine tools lagged behind western factories. Not to mention the need to be maintained with a hammer and a crowbar.
So, with a tune designed for rideability in all conditions, poor metallurgy and machining, the bikes really weren't that great. Plus, the loss of the genius Walter Kaaden from the Motorrad Zchopau when he defected to Suzuki lost a lot of good design like Expansion chamber mathematics.
I'm sure a Jawa or MZ could be tuned to make good power, but it would be a lot harder and give a lot less result than tuning, say an RD350 YPVS.
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Shaft
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| Posted: 22:13 - 20 Jul 2012 Post subject: |
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I still fancy having a go at a Jawa, it's the sort of challenge I quite enjoy and they have the advantage of being substantially cheaper than an LC.
Once I've got the Zed how I want it, I'll probably revisit the idea.
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| hmmmnz |
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hmmmnz
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| RhynoCZ |
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RhynoCZ
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Posted: 23:19 - 20 Jul 2012  Post subject: |
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The 1st thing you should know is, that communists had strict rules for production motorcycles in czech republic. CZ and JAWA couldn't built 4 strokes for road use anymore, because some idiot said so and communist claimed that motorcycle is outdated old school way to transport comrades, so they said no improvments in this segment anymore. Every motorcycle made in Czech republic, I mean road legal pruduction, had to be simple and cheap. Sport use was different and quite supported, when mister Pudil invented V4 engine for his CZ race bike, communist said enough and sent him to motocross/enduro bikes, where he also made some incredible machines. The last communist general manager of CZ was a hairdresser that was a cousin of high-ranking communist politician I think, not sure about who's cousin he was. But he destroyd the factory and sold it to Cagiva, that ruined it.  Also, Japs were coming here to learn, how to make a bike, that's why their 2 strokes are quite similar to CZ and JAWA bikes.
Race bikes were high tech though and whole world just stare at it and couldn't believe this, check some czech race history, you'd be surprised. We had the very first four stroke V4 engine in the morocycle, japs could copy that about 18 years after us 
They claimed, that czech republic was a motorcycle country number 1, that supplied motorcycles to the whole world, in fact we were just flooding the world with outdated 2 strokes, we're one of the reasons why EU said NO to new 2 strokes for road legal use.
If you want a bike, get MZ, more stable and reliable bike, Jawa 350/640 is quite close to MZ.
If you're into weapons, check history of CZ, they invented semi-auto 9mm weapons, communist were stupid and made bad copywright on it, so every one copied it, fells sad just to talk about how stupid this era was 
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| Teflon-Mike |
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Teflon-Mike
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| Posted: 08:20 - 21 Jul 2012 Post subject: Re: CZ`s & MZ`s and all that |
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| MarJay wrote: | the loss of the genius Walter Kaaden from the Motorrad Zchopau when he defected to Suzuki lost a lot of good design like Expansion chamber mathematics. |
It was His chief technician & development rider/racer Ernst Degnar that jumped the wall, sponsored by Suzuki, taking a lot of Walters Know-How with him... including Disc-Valves that turned them from an also-ran to a Championship winner in one season.
Suggestion was that Walter was frustrated by the lack of support he got for the race-program, and the refusal of the soviet-ministry-of-supply to let him have 'western' made components, specifically ignition parts, or better grade materials, or more exotic materials.
Some of the anecdoted I have read suggest he was a victim of his own success, and the East German Authorities told him 'It Doesn't Matter - your bikes are winning races, you don't need it"
Others recount that Ernst was winning pole grid position & setting lap-records in practice, but Walter was struggling to fix his bike for the actual race, due to poor quality components, and other teams were often 'loaning' bits to help see him to the grid!
And that, some of the western factories, even donated unwanted 'spares' like ignition systems, to 'help-out'!
Officially, Walter wasn't implicated in aiding and abetting Ernsts defection... if he had been... he'd probably have been SHOT!
But the amount of MZ Technical data, and Walters research notes Ernst toook with him, suggest that it was NOT entirely without Walter's 'blessing'.....
But, soon as Ernstz' absconding was reported; the MZ works GP program was terminated, I believe Walter was put under effective 'house arrest', and they refused permits for entries in races outside the iron curtain.
The factory's efforts were re-directed then at the major International Multi-Day Trials.... now Enduro's... and I seem to recal they exploited a 'loop-hole' of Soviet regulations.....
The East German ISDT 'Teams' were not 'factory' teams, they were 'National' teams, and the riders, were serving members of the East-German Armed Forces...... Conveniently, by exploiting the 'National Service' scheme, and 'the Reserve Lists'....
The entire MZ 'Works' Enduro-Team, were, scheduled for thier annual militery service, the weeks of the major international events.... then 'seconded' to represent the nation in the 'entry'!?
Walter's 'genuis' in two-stroke development was extensive. far more than 'Kaaden-Effects' and resonance tuning to create the 'expansion chamber exhaust' (An Idea Joe Erlich for many years claimed credit for 'inventing')
The basis of his work was the pre-war DKW RT125, itself a piece of design genius, distilling 'the engine' down to the minimum possible number of moving parts, and producing a design of almost 'fool-proof' assembly..... Laterly built in Britain as the BSA Bantam, in 125cc guise, it produced around 6bhp, which was typical for piston ported two strokes of the era.
At the time, that 'specific' power output was about on a 'par' with conventional four stroke technology; BUT until Walter came along, it was about the limit for the two-stroke engine, and if you wanted a higher-performance engine, you really had to look at the four-stroke.
The 'trapping efficiency' of the piston ported two-stroke engine was probably the main limitation.... using the piston skirt to open a hole into the crank-case through which charge could be sucked from teh carburettor as the pistoin rose... meant that hole was also open when the piston fell, and in thoery.... ought to have been pushed straight back out again, so the engine would never run!
Reason it DID was due to 'lag', and having been sucked in, it was loath to turn around and flow back out..... But, to get more charge in the chrank case you needed a bigger port.... bigger port lets more 'in' but also lets more back out!
Lots of work was done using 'tuned' induction, and the long swan-neck inlet manifold was popular on the P-P 2T for a loing while, tapering from the carb to the port, it provided a smooth flow 'in' but offered a more restrictive path 'out' helping trapping efficiencty, while length also helped prevent 'triple charging'..... air sucked through carb drawing up fuel to make mixture once, then flowing BACK through carb drawing second mixture of fuel, then as flow turned around and went back again drawing a THIRD charge of fuel into the air stream.... a problem that made carburation rather 'sensitive'!
However.... with very poor trapping efficiency, the P-P 2T had a very poor 'pumping-efficiency', 125cc piston might suck 125cc of charge into the engine on the up-stroke, but they were lucky to keep half of it IN the crank case and get it into the cylinder to burn it....
BUT, making a combustion cycle every revolution, as opposed to every other revolution, that 'half charge' meant they could just about pump the SAME amount as a four stroke, with a more efficient, 'pumping efficiency'... but a 'redundant' revolution where no power was made.
Yamaha's reed valve; adapted from bellows or reed organ 'flap-valves', was essentially a re-invention of the 'Atmospheric Inlet Valve' used on early four-stroke engines, before the benefit of the mechanical operated poppet valve, allowing 'advanced' valve opening was realised.
'Flap-Valve' works by having a flap in the inlet tract; when there is vacuum on the down stream side, it swings open, when there is positive pressure its pressed shut.Fitted to the inlet tract of a P-P 2T, it did what the swan-neck inlet manifold tried to... but more 'positively'
However, charge will only start to flow when there is enough vacuum to move the flap, and until there is significant vacuum, the flap acts as a 'choke' restricting flow.
The Disc Valve, a simple disc covering an apature, with a cut-away opening and closing the 'port' will allow flow whenever the window is uncovered, much like the cam operated poppet valve on a four-stroke, this allows for 'advance' port opening.... timing of the disc can be set so that the port is fully open BEFORE the piston reaches bottom dead centre, allowing full, unimpeded flow from the moment the piston starts to rise.... the window can also be held open BEYOND top dead centre, allowing 'inertial charging' from the momentum of still moving gasses, as the piston lingers at top dead centre and slowly starts its decent. Many argue, that this gives the 'advantage' to the disc valve over the reed, and provides a greater scope for extreme tuning to be exploited.
However, THIS innovation, was significantly what helped Walter Kaaden reveal the true potential of the two-stroke, and allow a full cylinder fill of charge on EACH stroke, almost doubling its specific power-output in one shot. Suddenly that 125cc engine could deliver around 12bhp, almost as much as four-stroke engines twice the size....
BUT with the greater trapping efficiency in the crank-case, came the problem of getting that charge into the cylinder, and having got it THERE stopping most of it being 'wasted' being mixed with exhust gasses.
Now getting a more significant amount of charge into the cylinder, Kaaden had the problem of, first stopping it flowing straight out of the still open exhaust port.
Solution to that one was to look at 'jet-streams' and flow paterns, and try and create a port arrangement that directed the incloming charge from the transfer ports somewhere other than at the exhaust port!
Solution was 'opposed' porting, with two directly opposed transfer ports, directing incoming charge over an almost flat-top piston, so that the jet-stream met in the middle and was defected almost vertically in a 'fountain' jet-stream up to the centre of the combustion chamber, where it could flood the cylinder from above, chasing exhast gasses 'down' the bore and out of the exhaust port.
NEXT, having stopped the fresh charge going straight down the exhaust, he had to look at the turbulance of these jet-streams, where fresh-charge was 'mixing' with the spent charge.
If the engine pumped a full 125cc of charge through the transfers, every cc of exhaust that mixed and retained in the fresh charge meant that there was 1cc less charge to burn, and that cc of fresh charge must have gone down the exhaust port, unburned, reducing efficiency from direct loseses, as well as 'indirect' efficiency losses from the exhaust gasses 'damping' the burn of fresh charge.
SO, turning his attension to THAT one.... he deviced 'multi-porting' using more than two directly opposed transfer ports, four, or six, and setting them not 'quite' directly opposite, so that as the jet-streams met accross the piston, instead of meeting directly head on, and bumping into each other and going straight up, they met sort of 'shoulder to shouler, so that they were 'twisted' creating a 'vortex' swirlm but like a tornado, going uo the middle of the cylinder, which kept 'turbulance' much tighter, minimising mixing of incoming charge and exhaust gasses, while as the incoming charge flooded the cylinder from the top, the 'swirl', would slow down, but increase in pressure, so that it better pushed exhaust gasses down the barel, but also, made them rotate AROUND the barel, so that more was washed past the exhaust port, where with pure 'fountain' effects, charge coming in the transfers, fountaining to the combustion chamber, pushing exhaust gas straight down, would create a 'dead-zone' opposite the exhaust port and over the transfers where exhaust gasses would be trapped, and NOT be scavenged... 'swirl' helped 'spin' them past the exhaust port, minimising this dead zone.....
The 'Spannie' was almost the last thing he considered.... and it was only becouse he had got SO good at filling the cylinder, and so good at scavenging the cylinder, he was starting to loose fresh charge out of the exhaust ports, chasing the exhaust gasses.....
The Expansion chamber exhaust, and the Kaaden effects named after the genuis that invented it, which it exploits, uses the resonance of the exhaust to create a harmonic pressure wave, traveling in the oposite direction to the exhaust gasses....
So... exhaust gasses flowing out, BUT a pressure wave traveling through the exhaust gas BACK towards the exhaust port, faster than the exhaust gas is traveling forwards... TIMED so that that pressure wave reaches the exhaust port just before the piston closes it, and pushes any escaped charge BACK into the cylinder.... Sort of 'tweeking' the port timing, to allow the port to be held open longer, without letting too much fresh charge escape.
With these breakthroughs, each leading to the next, he tool the 125cc two stroke, from a humble 6bhp 'commuter' machine, to a respectable 12bhp machine to rival the performance of contemprary 250 four-stroke 'road' bikes, and from THAT pushed the limits up into the 20's suggesting 160+bhp per-litre specific power out-put potential, the same specific power as the then contemprary, 'most' exotic four-stroke Double Over Head Cam race bikes, the Gilera and later MV 'Fours'... which were punting around 75bhp from 500cc....
I seem to recall, that when Suzuki set out to build the original RG500 'square four', 197?4 thier target was 90bhp, that MV Claimed from the 'four' and they believed to be at least 5bhp 'optimistic'..... and using basically Kaaden's 'technology' as provided by Ernst Degnar, knew that they could be fairly 'concervative' in thier tuning to achieve it...... Last of the RG500 GP bikes being run by Galini and Heron, I think about 1983/4, were claiming 'over' 140bhp, from the same engine design, with revised porting and improved carburation.... suggesting around 300bhp per litre was within the grasp of Kaaden's 'Technology', or almost double what Kaaden had achieved, with what REALLY has to be viewed as 'Garden Shed' techniques, tools and materals, and a budget that the average 'clubbie' would have probably considered, 'restrictive'!
He HAS to be given credit, for being the 'father' of the high-performance two-stroke engine; he really was the chap that did 'most' to unlock the engine's potential, and he has to be given so much MORE credit for the circumstances under which he DID IT!
ANYWAY.... as for the ISDT bikes Peppers.....
Rhino can probably elaborate more on teh CZ's in terms of what they built. From my recolection; I was a school-boy, drooling over T&MX every week from 1979.... CZ imports were a bit 'patchy & batchy', we got the 350 twins, and 250 singles, as well as 175's and 125's.... and it was almost as though they filled a container with however many bikes of whatever type they had to hand.... MZ supply was rather more consistant..... it was a 250 single.... that was IT!
The MZ ISDT replicas, were quite desirable, and I seem to recall were AS expensive in UK show-rooms as Suzuki PE250, if not more. IF you could get one. T&MX remarked that the UK was 'allocated' a certain number each year, and most were ear-marked for dealer-backed competition riders or 'worthy' privateers. It was a HANDFUL of 'genuine' ISDT bikes that 'escaped' captivity. LOADS of replicas were constructed though.
Looked at it a couple of times over the years, when I have had 'THOSE THOUGHTS'....
As I recall, the earlier ISDT machines were more 'closely' related to the road-bikes.... I am rather hazy, and cant recall all my previouse research... I know that later ISDT bikes had 'unique' frames... VERY desirable bikes now; they are 'Evolution Era' eligible, and dont have to be converted to T-Shock like the Kawasaki KX's or later Suzuki PE's, and in thier day were as competative as the Jap mono's! Earlier ISDT's I'm sure had tube frames also, BUT I am hazy as to thier relation to the road-bikes, which I kow, at least on later models had pressed steel spines.
Engine wise, recall that there was some experimentation with disc-valving, and Yamaha style reeds, but that may have only been on works proto-types. Pretty sure all the IDST bikes remained Piston Ported and in fairly humble state of tune, throughout, though there was a 'Moto-Cross' barel kit, ISTR. They tended to win on reliability rather than outright power; but they weren't THAT far off the pace; or behind the times, the Montesa's, Bultaco's & Miaco's they competed against were all PP2T as well; I dont think that 'all' the Suziki's were disc valve either.
Actual specs of the variouse models over the years are all 'out there', and I'm pretty sure that the ISDT bikes shared bore & stroke with the road-bikes; not sure about pistons & porting, but wouldn't be surprised if the early ISDT machines were pretty much 'hopped up' road motors with little more than a higher compression ratio and bigger carb.
When I pondered it, I investigated what the Bantam club were 'up to' for the MZ series, and in the late eighties and early 90's, I think they were changing some of the rules, as the series had effectively evolved two classes; one was running to the 'spirit' of the regulations, using pretty much 'stock' MZ motors, with a few tweeks, like a skimmed head and cleaned up barel; other was running to the letter of the regs and shrinking Yamaha YZ liners into the barels, and milling them to take TZ reed-blocks and carbs, and 'stuff'....
Conclusion was... whatever the actual spec of ISDT motors, 'scope' was there to mimick whatever they had, OR go silly, using Yamaha reeds and MX porting!
What vexed me, was fact that potential donor bikes were always pressed-spine MZ-ETZ's and the ISDT bikes had tube frames.... which meant it was always going to be rather more 'involved' than taking a road bike, swapping forks for something off a Jam MXer, and fitting longer Betor gas shocks to the back, and plastic acerbis tank!
Little research into contemprary MX & Enduro entries threw up some interesting ideas......
Pretty sure I came accross a few references to a 'Cheeney-Zundapp'...... and that the project had more than a little Clews involvement... Clews later CCM Scrambles bikes used Cheney frames and B441 motors, but looking for two-stroke power he turned to Zundapp, before getting into bed with Rotax and the Can-Am group through the Armstrong deal.... leaving it to Cheney to 'do something' with it.....
Also recall some 'kit' specials, using MZ or CZ engines in Cheney or Rickman frames...... Which offered inspiration
Although! Classic-Trialing, keep bumping into Greeves..... and looking at that forged aluminium head-stock/down tube..... and 'pondering', IF you took a stock MZ pressed-spine roadster.... WHAT IF.... you braced it, a-la Greeves?.... not exactly an ISDT rep... but something sort of 'period-special' esque....
Which is a departure from original Q....
| pepperami wrote: | So why is it that that MZ`s and CZ`s road bikes just dont measure up to the expectations of thier off-road cousins.
It would be dead easy to just say "they`re crap" but I believe that there`s more to it than that and this is where I would like some opinions. |
EXCEPT that I think that the difference between the MZ road-sters and the ISDT bikes was probably due to a number of factors...... the different chassis probably the most significant... the tube frame was almost certainly lighter....... or at least the rolling chassis was! Just swapping those heavy valences steel mudguards and oil-drum petrol tank for the plastic mudguards, tank and side-panels of the ISDT bikes would probably have halved the weight! Think that some of the cases were also Mag, rather than alloy or steel.
Engine wise....... as said, dont think that internally they were hugely different.... BUT I suspect that they had a lighter fly-wheel.....
My Cota has a 'secondary' flywheel on the crank, weighs about three pounds, and is mounted on the outside of the primary drive pinion. Was supposed to smooth the power delivery and make the bike more 'plonkable' in the days of 'long trial' for which it was originally built.
Had a mess a number of yeard ago, and the notion of trying to get a 'spare' and milling it down to make it lighter, for better response in modern 'short section' events...... but never really persued it.... DID take the thing off entirely and do some back to back comparisons.....
Makes absolutely NO difference to the power the bike makes, its just 'mass' on the crank.... BUT...... difference is astounding! You would SWEAR from the way the bike 'revs up' without the flywheel, it had 30% more power! Simply from the 'response' and the power delivery, giving that greater 'urgency' and sense of 'shove'......
With that in mind, the roadsters had pretty hefty generators and flywheels; the ISDT bikes minimal electrics the MX machines JUST an ignition..... Halve the all up weight of the bike from minimalist equipment and bodywork, and a few lighter weight components like alloy handlebars and yokes..... wouldn't take MUCH tweeking of the motor to make it 'feel' a completely different animal, and a LOT more 'lively' than the roadster, WITHOUT actually giving it a huge amount of extra power.
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| RhynoCZ |
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RhynoCZ
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| Posted: 11:22 - 21 Jul 2012 Post subject: |
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| hmmmnz wrote: | cool post RhynoCZ
i was even reading it in a czech accent  |
So it sounded russian as always 
I don't know if they are any books or sites in english about this era and especially about Frantisek Pudil, who stood behind CZ's best ideas. Interesting fact, on CZ 860 Bohumil Stasa, could even keep up with Agostini on his MV, which was the best bike and rider on the grid back then. That's how great the bike was and they made it all in one factory. Other ''brands'' were making just the engine and frame, rest of it was bought, suspension, brakes, wheels and so on.
There's even a funny story about one race, I think it was Assen, where CZ's mechanics were preparing the bike for the race on a blanket out side of their bus. They tuned timing and rebuilting carburetors and so on. People were coming around and could belive what these mechanics are doing, because it was even back then, a ''custom'' to have a big truck full of parts and ''mobile'' workshop on the wheels. Some one from big brand asked them, where they get suspension and wheels and so on, and when they heard that it's all made in CZ factory, their jaws fell down.
Just to add what ''Golden czech hands'' means, Czech's can do something from nothing at low budget, german's need precise tools to even start thinking of doing something. If Czech mechanic needs a tool, he makes it. It was like this in every house hold with a workshop during communist era.
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| nowhere.elysium |
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nowhere.elysium
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| Posted: 11:28 - 21 Jul 2012 Post subject: |
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I always find it funny when people point the finger at Czech cars and bikes and say "they're crap", without accounting for the fact that it was the Soviet Union's fault for making everything shit. The Russians seemed to have an understanding of precision engineering that's alarmingly close to the American standard; precision being "to within an inch or two" - OCC being the best example on TV for this sort of thing.
Whenever I've been in the Czech republic, I've always been impressed by the technical competence of the people I've been working with over there - there's a really strong analytical work ethic going on, and it's a joy to work with the Czechs, in my experience.
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| stinkwheel |
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stinkwheel
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| Posted: 21:26 - 22 Jul 2012 Post subject: |
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They're crap.
The offroad models were specially fettled and tuned for competition use to prove a point to the decadent capitalists in European competitions (MZ dominated trials competitions for years).
The road ones were made a cheaply as possible and in as high a volume as possible.
There were also shortages to consider. So for a few years they might have used a bronze bush where there really ought to be a bearing but there was a bearing shortage. Or the alternator windings might be too thin because there was a copper wire shortage.
It goes on and on.
They could do some amazing things but the work ethic and top-down controll of production meant they weren't allowed to.
That said. Nobody would ride Jawas type 673. A 500cc liquid-cooled V4 making 80bhp at the back wheel in 1971. Which confirms that the Japanese never really ever came up with anything new.
https://100percentmotorcycle.files.wordpress.com/2010/08/jawa673.jpg
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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temeluchus
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RhynoCZ
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| Posted: 23:17 - 22 Jul 2012 Post subject: |
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| stinkwheel wrote: | They're crap.
The offroad models were specially fettled and tuned for competition use to prove a point to the decadent capitalists in European competitions (MZ dominated trials competitions for years).
The road ones were made a cheaply as possible and in as high a volume as possible.
There were also shortages to consider. So for a few years they might have used a bronze bush where there really ought to be a bearing but there was a bearing shortage. Or the alternator windings might be too thin because there was a copper wire shortage.
It goes on and on.
They could do some amazing things but the work ethic and top-down controll of production meant they weren't allowed to.
That said. Nobody would ride Jawas type 673. A 500cc liquid-cooled V4 making 80bhp at the back wheel in 1971. Which confirms that the Japanese never really ever came up with anything new.
https://100percentmotorcycle.files.wordpress.com/2010/08/jawa673.jpg |
Sir, you are wrong it wasn't like no one would ride a 500cc V4, it was like Ivan said, let's built something that costs nearly nothing and can survive in various conditions. But yes Japs came here learned and then produced, they were called clever copiers back then. If anyone here was like a honda and said, well we built this bike, it costs 20 000 pounds, it has 80bhp, goes 260, great machine. If they built something like this, they would end up in the jail. You're way wrong sir. And if you want to talk about I don't know, 500cc 4 strokes, they were forbiden to invent something that could be road legal and had 4 stroke engine. After velvet revolution, Ivan said, alright start with 4 stroke programe, they started and made some prototypes, some of them with rotax engines, BUT Ivan also said, that none of the parts can be built out of soviet union and Jawa couldn't built, I think it was a head seal. So stop for this one boys. They could buy these in europe for bargain, but Ivan said no, we don't need them. Designers and engineers had so many projects that you even can't imagine, not only in motorcycle industry, cars, machines, planes and so on, but Ivan was tough and who said no to Ivan spent live as a sweeper and his kids were banned at every university in the soviet union or you could be in the jail if you really pissed them off with saying what you actually think about them
BTW that JAWA what you've picked, was problematic and very difficult to ride. Yes it was crap, but CZ was always number 1 in the world where ever they appeared.
I'd say, CZ was top factory in the country and let's face it, in the whole Soviet union, but Ivan sold it to cagiva. Cagiva never wanted to work with CZ, they just wanted to control it and practically destroy it in which they've succeeded. 
Edit: you'd might be right in some things, I've just came out of pub, so I will read it again in the morning and edit it
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stinkwheel
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| Posted: 23:57 - 22 Jul 2012 Post subject: |
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The Jawa I pictured was a killer, precisely because they made the engine using inferior metal leading to high-speed engine seizures.
Nobody would ride it because it killed any riders who had tried.
It perfectly illustrates my point of good new ideas being let down by poor execution.
The design was years ahead of it's time but it was so poorly made it couldn't possibly work. I can't think they would have had a tight budget for the race bikes, after all "Ivan" had a point to prove to the West that Communism was superior. As such, there was no real need to use inferior metal.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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RhynoCZ
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| Posted: 00:29 - 23 Jul 2012 Post subject: |
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| stinkwheel wrote: | The Jawa I pictured was a killer, precisely because they made the engine using inferior metal leading to high-speed engine seizures.
Nobody would ride it because it killed any riders who had tried.
It perfectly illustrates my point of good new ideas being let down by poor execution.
The design was years ahead of it's time but it was so poorly made it couldn't possibly work. I can't think they would have had a tight budget for the race bikes, after all "Ivan" had a point to prove to the West that Communism was superior. As such, there was no real need to use inferior metal. |
Sorry If I offended you, well even race budgets were tight and that thing that everything had to be done by comrades made it even tighter. But with really tight budget I ment production motorcycles, that's why they look and ride as they do. Production bikes were ment to be like, from Prague to Moscow and beyond, desert, rain forest, with screwdriver and a hammer. I'd say quantity over quality would be right expression here.
Roads were poor-quality and still are if you go to poland or leave today's Schengen area, well somewhere they even don't have a road. And these bikes were supposed to be for every working man and woman. Japs and european factories had customers that had nice roads in their area and could get enough money to buy whatever they build. Here, smart people were poor and in jails, not that bright people who could hold a shovel were overpaid So shitty 2 strokes for our roads it is
In defense of that JAWA, only 1 rider died when he ran on the bike with no helmet just to say hi to spectators in free practice.
JAWA is really bad example, it was ran by politicians from the beginnings. CZ wasn't, but after some big successes, communist did what I was talking about and sent Frantisek Pudil for his bikes to another job.
EDIT: I just found, in 1969 JAWA 673 was second in the championship right behind Ago with his MV, the rider was Silvio Grassetti. Jawa was also the fastes bike in GP that year. In 1968 Frantisek Stastny finished 3rd in Brno and Bill Ivy 2nd in Hockenheim behind Ago and they both overtook every rider there twice
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Shaft
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| Posted: 01:03 - 23 Jul 2012 Post subject: |
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Just a little hyperbole there.
It was a 350, lots of people did ride it (it achieved several podium finishes) and although Bill Ivy was killed as a result of it seizing, it might have helped had he been wearing a helmet at the time.
It was also finished by the end of 1969 (when the rules were changed) but I will agree the Japs rarely come up with anything new; they copy and improve with consummate skill though.
And I think it's a little harsh to single out this bike for criticism, pretty much every hi-po 2 stroke was prone to seizing; if you read Barry Sheene's biography, he spent his entire career with his fingers hovering over the clutch lever, waiting for the big lock up.
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pepperami
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| Posted: 09:41 - 23 Jul 2012 Post subject: |
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Some VERY interesting stuff there folks, Thank you  .
So what do you think peeps, could a Jawa 350 twin/CZ 250 twin be fettled to top the ton without destroying itself?
Or is the stroke/port size/ lumpyness of the piston/diddy carb going to prevent this?
I suppose the first thing that needs to be answered is , could the crank, con-rods, and pistons cope?
Bearings & carb/s could be changed for better ones, but somehow I doubt very much that anybody produces better quality aftermarket engine internals for either of those bikes ?, unless you know different?.
Has anyone on here ever had any experiance fettling these?
Someone must of tried?
I wonder what the likes of Stan Stephens would make of theses engines?
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stinkwheel
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Posted: 10:42 - 23 Jul 2012  Post subject: |
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| pepperami wrote: |
So what do you think peeps, could a Jawa 350 twin/CZ 250 twin be fettled to top the ton without destroying itself?
Or is the stroke/port size/ lumpyness of the piston/diddy carb going to prevent this? |
Possible but not without a LOT of work. I got 80mph out of mine on the flat once.
| Quote: | I suppose the first thing that needs to be answered is , could the crank, con-rods, and pistons cope? |
They certainly COULD. They are extremely heavy-duty and the crank has a centre main bearing. It also has needle roller small-ends. I think the major issue would be how round and balanced everything is and dissipating the heat. They run very thick liners in an alloy barrel.
| Quote: | Bearings & carb/s could be changed for better ones, but somehow I doubt very much that anybody produces better quality aftermarket engine internals for either of those bikes ?, unless you know different?. |
They don't but the bearings are totally standard sizes. There is no reason you couldn't use a mikuni carburettor. The bearings would be a major point because the originals are far from round and true.
| Quote: | Has anyone on here ever had any experiance fettling these?
Someone must of tried? |
I tried after a fashion and gave up. It was very much a case of trying to polish a turd. It took me all my time to get the squish bands equal, never mind tuning them. One side landed up with two head gaskets, the other side with none because there was a full mm differrence between the two sides.
I polished the squish bands on the head and thinned down the base gasket to bump the compression up.
I used an electronic ignition.
I had the crank pressed apart, Japanese bearings fitted and it reassembled and balanced.
I fitted oversize (+2.5) pistons with a chamfered edge and cut-down skirts.
I also did a little, fairly inexpert messing with the baffling so I had a single baffle plate and varied the distance into the exhaust I had it until it sounded best.
Then I got to polishing the inlet tract, came upon the point where
they'd drilled the hole for the inlet manifold stud so close it was actually protruding into the inlet and gave it up as a bad job. (as in, if you removed the carb and looked down into the engine, you could see part of the stud threads sticking out into the inlet port).
I geared up the end result by four teeth on the front sprocket and it would still rev out in top. I'd guess in the region of 80mph but the speedo runs off the gearbox and was never all that accurate anyway.
I think if I was going all-out to tune one. I'd replace the mains. balance the crank. Skim the barrels for equal and smaller squish-bands. Weld up the inlet stud holes and re-drill them to take a mikuni manifold with a reed valve. Polish the inlet port and cylinder head. Take the burrs out of the transferr ports.
I would also arrange for a PROPER expansion chamber exhaust. The exhausts are shit. In an ideal world, I'd use two MZ ES175 or TS125 exhausts.
| Quote: | I wonder what the likes of Stan Stephens would make of theses engines? |
He'd lock himself in the toilet crying.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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RhynoCZ
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| Posted: 10:47 - 23 Jul 2012 Post subject: |
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I've seen a documentary about this jawa and the engine is so complicated, that it seems that, it had to be broken all the time. It's got 4 separated crank shafts, crankshafts that were in line was connected via grooved coupling/clutch and these 2 lines one above the other of crank shafts were connected with cogwheel. These shafts could be dismantled while the engine was in the frame, also 7 speed gear box could be removed. They practicaly knew it would have some difficulties. Heads and cylinders were duplicates so It doesn't matter which is where.
To stop this topic and answer some relative questions:
If you want something to ride as a road legal machine, go for anything built here in Czech rep. The best bike you can get is JAWA350/640, but thera are many bikes that, if you care about them they would go for ever. Also JAWA 660cc series is good, very comparable with modern production. JAWA 650 production needs good old FIAH, Finish it at home, poor wiring mostly. Every bike made here, I mean before '70, Would be quite the same as the whole world were producing back then, 2 strokes of course. Parts are cheap and its construction is made for screwdriver and hammer, so you could rebuilt it even with no manual, If you've got some experience.
Many factories even produce improvements for these bikes, like modern contactless ignition, two-chamber mufflers, better this and that, and these parts are quite cheap to get and easy to get it on the bike.
MZ - these bikes are better, slightely but they are, parts are also very cheap, but the look of the bike seems quite odd. A friend of mine just bought MZ150, he's about to start to be a stunt rider and this is the best starter bike he says. This MZ150 is capable of 110km/h, has 5 speed gearbox and if you don't mind the look of it, than it's the best way.
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'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor |
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stinkwheel
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| Posted: 11:36 - 23 Jul 2012 Post subject: |
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I'd like to have any one of the following eastern block 2-stroke bikes:
Simson S51.
DKW RT125.
Minsk 175.
The VERY early ETZ251 with internal oilways but they are rare as rocking horse poo).
MZ ES300.
MZ BK350.
Jawa 559 twinport.
Jawa 593 "Supermaster".
IZH "Springbock".
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Old Thread Alert!
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