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Northern Monkey |
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Northern Monkey World Chat Champion
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BusterGonads |
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BusterGonads Trackday Trickster
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steve the grease |
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steve the grease Crazy Courier
Joined: 26 Jan 2018 Karma :
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Posted: 00:11 - 22 Jun 2018 Post subject: |
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The thing about the CG 125 is that it was downspecced from the earlier OHC 125 singles (CB and XL for example). A pushrod engine s fitted not an OHC one , the cam followers are designed so the loadings are very low, which results in a bike with low lubrication requirements, for the valve gear at least. Combine this with lazy valve timing, a small carb and restricted inlet tract and you have a machine that will stand thrashing all day. Don't believe me, see what Honda themselves have to say:
https://world.honda.com/history/challenge/1975cg125/index.html |
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BusterGonads |
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BusterGonads Trackday Trickster
Joined: 18 May 2018 Karma :
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Posted: 10:18 - 22 Jun 2018 Post subject: |
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steve the grease wrote: | The thing about the CG 125 is that it was downspecced from the earlier OHC 125 singles (CB and XL for example). A pushrod engine s fitted not an OHC one , the cam followers are designed so the loadings are very low, which results in a bike with low lubrication requirements, for the valve gear at least. Combine this with lazy valve timing, a small carb and restricted inlet tract and you have a machine that will stand thrashing all day. Don't believe me, see what Honda themselves have to say:
https://world.honda.com/history/challenge/1975cg125/index.html |
Thanks Steve the grease.
That's interesting. I've heard bits of that story before - the part about the Honda people going to SE Asia and the Middle East to see how motor cycles were being used. Great read that.
The over-square crank design lowers piston speed too which is why it can rev like a wasp and not wear too much. Obviously, it isn't the most revy motor around, but even at about fifty mph it is topping 6000 revs which is a hundred turns a second.
When I was a lad, my uncle who was a mechanic gave me some old brown hard backed text books about auto motive engineering. I don't know where they are now, but they were of 1930s vintage and they were talking about 'high speed engines' doing as much as 3000 RPM. They were full of formulas and thermodynamic equations and stuff like that. I read them all and understood as much as I could get to grips with. This thread questioning the thrashing of the CG is rooted in that set of old books really. They were full of technical explanations of why high speed engines wear themselves to destruction. Chalk and cheese of course, those old side valve grafters and the modern motorcycle engine.
Cheers... |
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Teflon-Mike |
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Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
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Posted: 11:53 - 22 Jun 2018 Post subject: |
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tony1951 wrote: | Chalk and cheese of course, those old side valve grafters and the modern motorcycle engine.. |
Not nearly so much actually.
The long stroke motors of the pre 195o's, worked 'well' for what they were mainly bvecause of the 'blended' alchoholo petrol of the era....
Oooooh E~Fuels!!!! It's something we seem to be heading back towards! Lol
As mi grandad was want to say, you can always trust the yanks to re~invent stuff, fifty years after the event, stick a new lable on it and flogg it to the world as all thier idea... like the fluid flywheel!
Thing with alcholhol fuels, is that they tend to have a high octane rating, which is why ethanol grasstrack or speedway bikes can run almost deseasil compression ratios in the order of 14:1.... however they also have a lower calorific value... so burning them wont release the same amount of energy, so you have to burn more to get it... which is why grasstrack bikes had thier main jets reemed out with a 1/4 inch drill, and mpg is pretty dire! But curiousely, they have a very slow 'burn', so as long as they have time to burn, they can actually release quite a lot more of thier potential energy.... but that does beg a slow speed, deseasil rpm motor.
BRAZIL!!!! More legacy of the CG, honda had diverted almost all of its engineering R&D to the Civic car project circa 197o.... the Honda self publicity has to be taken with a very large pinch of salt.... they count Montessa's World Trials championship of 198o in thier accolades.... even though they didn't even own a share of the company until 1982, and didn't buy it out completely, until I think 1986!!!!
However, Honda had bought the US plant in the late 6o's early 7o'sm initially as a local marketing and import export office, but a view, as US imposed trade tarriffs on Japan to limited manufacture for US market.
I have an inkling that the Brazil plant was packaged in there some~where, in a land deal that bought up some parcels Ford had aquired in the 194o's with ideas of an un unionised Bornville like manufacturing utopia... where Henry was judge, jury and god!!! However....
US trade deals with south america gave them favourable access to US market, and more favourable than SE Asia... curiouse how Brazil was also one of the largest importers of Montesa, before Honda took them over.....
The Brazil factory, then was established, with a lot of Brazil gov't incentive, and contractual obligations on Honda, not only to employ Brazilians, but also export brazilian made goods....
Interting again to note the Honda official gloss over the project, that was it seems quite a failure; The factory didn't get the CG production line as intended for nearly ten years, and suggestion is that large areas of the factory didn't get production line, but stock~piled unsold CG's, because rest of world actually DIDN'T want them.
Not very surprising really; as a low cost, low maintenance commuter, it wasn't much of either. Here in the UK the few CG's we were offered from 77 to 82 ahead of the 125 learner laws, were marked up at a more expensive price than the Over Head Cam Honda CB1ooN which was slightly more ecconomical on fuel and significantly cheaper to insure. And when Honda gave in to the two stroke, and offered the H1oo, that too was cheaper in the catalogues, whilst also being faster, and, needing little more maintenance than checking the 2T oil tank was full, WAS the bike the world wanted when Honda deviced the CG.
Its remarkable how the CG has survived, against the odds, and big part of that is pure serendipty. Had it not been for the punartive contract clauses with the Brazil Gov't that made it cheaper to keep paying people to make bikes to stock~pile bikes that didn't sell, it would have been almost dead in the water. When Brazil was brought on stream... oooh isn't it coincident that Honda had bought out the best selling motorcycle in the country at the time, Montesa!? And like killing thier world champion trials endevour to give Eddy Lejeun and the fourstroke TL25o an unsporting chance..... Momtesa no longer made a {TwoStroke} road bike Brazil might want... only Melody mopeds... giving the unsold CG's a clear run at the local market!!
When the CG made it out of Brazil in any quantity, it was due to ever tightening emmission controls giving it a better chance against the two~smokes, but it was still a much higher maintenence motorcycle, and still not 'cheap' UK and then EU 125 licence law revisions, that un the UK demanded a full 125 for test, then gave it another bite at the cherry, and UK Bike schools bought them, as they were a lower maintenance and higher reliability bet than say an OHC Suzuki GS125 or Yamaha SR125, and in the mid 9o's revisions to the insurance groupings conceded the low performance they had compared to the 2T 1oo's.
The CG's survival is incredibly flukey, and more by dint of circumstance and chance of regulations than it was in any way by design....
The design, was a rush job, based on the CB/SL OHC single, that was want to eat its own cylinder heads; and the main genius of the design was in a lot of over engineering to make it tough and rugged in the face of poor anticipated service levels, with the main novelty the manufacturing cost cutting of a single, common cam lobe for both inlet and exhaust.
What is quite curiouse about the design, is that even with that much 'retro' engineering... it actually ISN'T much if any more durable, rugged or lower maintenance than the C7o cub moped of a decade and a half earlier..... which used a laydown OHC single four stroke engine... and a C9o isn't a heck of a lot less powerful, and bored as common now to 11o or 125cc or more for some of the pitbikes, STILL isn't much if any less reliable of robust.
However... post the OPEC oil crisis, Brazil went Ethanol.... Locally made VW's had thier main kets bored out and thier timing advanced, and they were the mainstay of South americal transport for my life time. Honda let Brazil do likewise to the CG, which gave us the CG15o, bored out to compensate for the lower grade fuel a bit..... and again, locally made, sold because of import tarriffs and difficulty making more finikity two~strokes run on the stuff.
Back to old JAP and Pantha thumpers; owe thier heritage to the DeDion 'Buscuit Tin' engine of the turn of the 2othC. DeDion concieved the 4 stroke much as we get in the text books today, after getting frustrated with his Benz autocarriage and deciding to simplify the contraption a bit. Very simple engine, it used a buscuit tin crank case, with a hole drilled in the tin and the lid to take a bronze bush and a three part pressed up crank almost any one could make on a lathe.
The legacy of that engine was the bain of the Britbike in the 6o's, the twins often using a pressed up three journal crank like a single, just with extended 'pin' to take two conrods, as they had on earlier V~twins in the 2o's. Running on bronze bushes, essentially splash lubricated, they sort of did the job, and it was cheap and easy to make.
The modern forged one piece crank was an innovation cars quickly exploited; the crank could be stronger and better supported on split 'shell' bearings, but that demanded a high pressure lubrication system; rollers remained cheaper and more reliable, and less demanding of complex lube, hence why pressed up cranks remained the norm on two strokes till the end. So for bikes, the forged one piece crank was not adopted because it was expensive, and expensive to tool up for.
CG uses a pressed up three piece crank like an old Panther or JAP..... and with roller bearings, like a two stroke to reduce demands on a high pressure oil supply, actually has far more in common with those engines of the pioneering era than it does anything else of the last half decade, that almost universally has a car type forged crank running on split shells with a high pressure oil supply.
Its almost square bore stroke, isn't particularly remarkeable; many Britbikes of the 5o's were as close, and a short stroke motor, has lower piston hence piston ring speeds for any given RPM, and burning more 'exiteable' fuels can exploit the faster burn to get the power from it.
Which is all to rubbish a lot of CG lore, as ever I am sure annoying CG afficionado's... but it remains the most remarkeable thing about the CG has nothing to do with any design feature, but simply the fact that it existed at all, and survived as long as it did, pretty much by 'fluke' rather than design.
Doesn't mean that its bad design, just its no where near as great as so many, Honda's own propaganda included try and make it.
And far too many try and endow the design with far far more than it has ever had the potential to realise, or site features of its design as being the key to the alledged greatness its supposed to have.
It really is a pretty mediocre bit of design, and was a rush job taking the CB/SL OHC single motor, and retro~engineering it to use push rods and that common cam lobe, to try and make it a bit more rugged, a bit cheaper to make, and a bit more reliable in the face of the air cooled two stroke singles, that beat it on almost every count bar the smoke screen!
Boiling it down, "Can you thrash a CG?" answer is YES, that is what they were built for! And those beefy roller mains, and low pressure lube and rockers that can almost live with just an occasional smear of grease, coupled with a reletively square bore/stroke, means that you can pretty much rev the pants off one, where a longer stroke old brit on bronze bushes would probably shake itself to bits; but main reason is just the fact that it only makes 1obhp, it doesn't make enough power to do itself seriouse harm, and that common libe cam, is incredibly soft compromised on lift and timing to open both valves, it will simply run out of puff long before it reaches the sort of revs that the rest of it is at any great risk of damage, so LONG as there is oil in the dang thing.
But C9o comparison bears more than a glance... that engine makes the same sort of power, doesn't use any more fuel, doesn't rely on push rods or a common cam lobe, or demand much if any more maintenance of oil changes....... and with one cam chain instead of a pair of push rods and couple of extra rockers, its actually even simpler and cheaper to make! So there's little in the CG's design that endows it with any more toughness or greatness than other bikes or engines. ____________________ My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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BusterGonads |
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BusterGonads Trackday Trickster
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ThatDippyTwat |
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ThatDippyTwat World Chat Champion
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Teflon-Mike |
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Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
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Posted: 00:34 - 23 Jun 2018 Post subject: |
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tony1951 wrote: | On the point about cost: I bought a brand new CG in 1990 on my first return to biking after riding for years at the end of the 60 s and early 70s on an L plate |
Interesting.... you've had your full licence about as long as me then.
199o CG125 cost £13oo, Same year, I bought my AR125 to get to and from uni placement. £1425 OTMH. Sensible choice was KH125, which was £11oo, the smarter choice but for impending test regs was a KH1oo at £999. An MZ125, was advertised at £599 OTR, and the lads grumbled that the 'must have' TZR was just shy of £2ooo depending whether you had the fairing.
Like I said the CG was a curious choice; twice the price of an MZ for about as much performance and arguably less maintenance. A third more than a KH1oo, that was faster and lower maintenance.
What made you buy the CG over say a CB125 Super~Dream that was about the same price in the show~room or an SR125 or a CB1ooN, or a C9o or even a Hoo or other two~smoke commuter? ____________________ My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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BusterGonads Trackday Trickster
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Chuffin Nora |
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Chuffin Nora World Chat Champion
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BusterGonads |
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BusterGonads Trackday Trickster
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