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HDshiny
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Joined: 24 Sep 2017
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PostPosted: 20:02 - 24 Sep 2017    Post subject: engine swap bike Reply with quote

So i wanted to buy a road legal bike and engine swap it.

Yamaha wr 125 x as the frame and then a 160cc pitbike engine.

Would this be do able or would it be very hard work ?

How reliable would the pitbike be for everyday use
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c_dug
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PostPosted: 20:09 - 24 Sep 2017    Post subject: Reply with quote

It's a pretty easy job, just a couple of bolts usually.

Worst case you might need a different exhaust and a red powerband.
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barrkel
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PostPosted: 00:11 - 25 Sep 2017    Post subject: Reply with quote

No.

This would be much more feasible: https://www.motorsportgoetz.com/Yamaha-WR-125-R-X-125-to-183ccm-cylinder-Big-Bore-Kit

But if you have to ask, no.
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pepperami
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PostPosted: 07:26 - 25 Sep 2017    Post subject: Reply with quote

I smell a sock!
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P.
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PostPosted: 08:58 - 25 Sep 2017    Post subject: Reply with quote

It would not work.

The big bore would be best option.
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G
The Voice of Reason



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PostPosted: 09:06 - 25 Sep 2017    Post subject: Re: engine swap bike Reply with quote

HDshiny wrote:

How reliable would the pitbike be for everyday use

Much less so than a physically bigger Japanese engine - especially if ridden hard.
And there's little point in going to that effort and making use of it.

You've got more power in a smaller space with worse quality control and more cost cutting.

You then put it in a chassis that's heavier, so it has to work even harder.

I've had the gears go on at least one of my pitbike engines - you shouldn't use the engine braking it turns out because they just can't hack it.
And for similar reasons you can only reasonably get a 4 speed - the expensive 5 speed is too fragile because they can't fit enough metal in the small space to make it durable.
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Wheezybiker
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PostPosted: 09:30 - 25 Sep 2017    Post subject: Reply with quote

I'm assuming you have the correct licence to ride a modified bike and the insurance and mot will be allowed
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G
The Voice of Reason



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PostPosted: 10:19 - 25 Sep 2017    Post subject: Reply with quote

Wheezybiker wrote:
I'm assuming you have the correct licence to ride a modified bike and the insurance and mot will be allowed

Why would you assume that? Seems a pretty silly thing to assume! Wink

I'm assuming that the OP is too young to have anything more than a low powered 125 and wants more power.

Of course, that begs the question; why not just get a DT125, or other 2 stroke?
Less money, more reliable and a lot less hassle.

Hell, I've seen competition KTM125 2 strokes on L plates - I don't think they are legal for 47hp restriction (power to weight), never mind a restricted 125cc!
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Wheezybiker
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PostPosted: 12:56 - 25 Sep 2017    Post subject: Reply with quote

G I can see why you are labelled the voice of reason

You are absolutely right I was thinking like I would if it was me doing this

It won't happen again lol
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HDshiny
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PostPosted: 16:03 - 25 Sep 2017    Post subject: Reply with quote

so best thing to do is to just buy a 2 stroke. have the haste of buying a 160 engine and fabricating it on a frame ?
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HDshiny
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PostPosted: 16:06 - 25 Sep 2017    Post subject: Reply with quote

barrkel wrote:
No.

This would be much more feasible: https://www.motorsportgoetz.com/Yamaha-WR-125-R-X-125-to-183ccm-cylinder-Big-Bore-Kit

But if you have to ask, no.


so would this be a better option than buying a roiling frame and putting a 160 engine into it
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HDshiny
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PostPosted: 16:20 - 25 Sep 2017    Post subject: Reply with quote

G wrote:
Wheezybiker wrote:
I'm assuming you have the correct licence to ride a modified bike and the insurance and mot will be allowed

Why would you assume that? Seems a pretty silly thing to assume! Wink

I'm assuming that the OP is too young to have anything more than a low powered 125 and wants more power.

Of course, that begs the question; why not just get a DT125, or other 2 stroke?
Less money, more reliable and a lot less hassle.

Hell, I've seen competition KTM125 2 strokes on L plates - I don't think they are legal for 47hp restriction (power to weight), never mind a restricted 125cc!





so best thing to do is to just buy a 2 stroke. have the haste of buying a 160 engine and fabricating it on a frame ? and im 20 with a A1 licence
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Teflon-Mike
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PostPosted: 16:51 - 25 Sep 2017    Post subject: Reply with quote

If you are over 19, just go do your A2 licence, and get a big bike if you want more power.

There's bog all point piggng about spending time and money to try and make a slow 125 a bit less slow.

Buying a 2-stroke 125?!?! Well, if you are a masochist carry on... they are barely much less slow, or more reliable, especially since none of them are close to being a spring chicken any more.

Lets look at this... the fastest of the fast sports 125 two-strokes were the Cagiva Mito and the Aprillia RS, which both via different accrediting bodies managed, with specially prepared 'homologation-special' variants of the models made in very very small numbers for Italia domestic 'production' racing managed to be clocked at just over 100mph.... that is the very best of the best street-legal 125's..... which were not particularly cheap, or reliable or 'low maintenance' or every day 'practical', and now likely twenty years old, even less every day practical or reliable!

To put that into context, they made about as much power and were just about as fast as a Honda four-stroke 250 from the end of the 250 learner-laws over thirty years ago!

Here and now.... get out of the L-Plate arena, and there are bikes like the much maligned ER5, critasised by so many folk with licences to ride'em for being dull as ditch-water, and so under-valued they cant give them away when they need a pair of tyres and a C&S kit for an MOT, yet, still have to be 'restricted' by a couple of bhp for A2 licence rgs, and offering 50bhp likely offer twice the oomph even a 'good' two-smoke 125 will likely deliver for very long...whilst being cheaper to insure, less nickeable and probably no less unreliable....

For dirt iron, if you buy some sturdy locks to detur the tea-leaves these so attract, choice of naturally A2 complaint machines and easily restricted to A2 bikes is pretty good; and all are likely cheaper to buy, insure, and maintain than a not so slow 125.

Absolutely no sensible reason to try beat the system trying to tune a 125 to go faster than is legal on A1 or L-Plates.. just go do the tests and get a bigger bike!!! It' just making life hard for yourself, buying hassles to make a slow bike a tiny bit less slow, whilst spending money to make it less valuable and likely less reliable.. A-N-D get you nicked by interested plod for some obvious crime.. especially if you try exploit the bit less slow you may get!
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G
The Voice of Reason



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PostPosted: 17:41 - 25 Sep 2017    Post subject: Reply with quote

Teflon-Mike wrote:

Buying a 2-stroke 125?!?! Well, if you are a masochist carry on... they are barely much less slow, or more reliable, especially since none of them are close to being a spring chicken any more.

I think most would be find maybe half the 0-60 time of a 90s/00 2 stroke to a modern 4 stroke a bit better than 'barely much less slow'.
Faster than a lot of expensive cars - maybe about the sort of pace a £20k Fiesta ST that would probably cost a young person as much again to insure.

Being cheap to rebuild, you could easily factor that into the price and have a rebuild and service completed straight after purchase.

Personally; I'd suggest a bike like the NSR125, which hundreds on here have used as regular commuters.
You'll get over 90mph on the GPS, sensible service intervals with relatively cheap maintenance.

Considering modern 250s haven't really upped the stakes much - I'm sure plenty would be happy with a 125 that matches a 250s power output!

However yes; if the option of a bigger bike is available and makes sense for licensing (vs say, having to redo your licence a few months later); I'd definitely go with that.
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Rogerborg
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PostPosted: 18:19 - 25 Sep 2017    Post subject: Reply with quote

You made me agree with Mike. Tut Tut

You're not a kid, stop fiddling with your tiddler.
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stevo as b4
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PostPosted: 18:49 - 25 Sep 2017    Post subject: Reply with quote

A properly done 180cc conversion on the Yamaha/Minarelli engine can actually make as much as 19-21bhp at the wheel, if you really go to town on the head, big valves, cam, throttle body, ECU's and uprated internals and cooling/oiling systems.

You'd be into a std engine for over £2k to do it though.

Not saying a well built and tuned big bore converted YZF/WR engine is a shit thing, or that it wouldn't be useful in some situations, but it is crap for VFM.

You'd need to be a shed nerd, with a shop full of engines and machine tools to make it a project worth it for your own satisfaction.
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G
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PostPosted: 20:19 - 25 Sep 2017    Post subject: Reply with quote

For posterity Smile:
https://i.imgur.com/sBA3RC0.png

And I thought those 'end of the world' things were all just conspiracy nut jobs!
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HDshiny
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PostPosted: 01:16 - 27 Sep 2017    Post subject: Reply with quote

Teflon-Mike wrote:
If you are over 19, just go do your A2 licence, and get a big bike if you want more power.

There's bog all point piggng about spending time and money to try and make a slow 125 a bit less slow.

Buying a 2-stroke 125?!?! Well, if you are a masochist carry on... they are barely much less slow, or more reliable, especially since none of them are close to being a spring chicken any more.

Lets look at this... the fastest of the fast sports 125 two-strokes were the Cagiva Mito and the Aprillia RS, which both via different accrediting bodies managed, with specially prepared 'homologation-special' variants of the models made in very very small numbers for Italia domestic 'production' racing managed to be clocked at just over 100mph.... that is the very best of the best street-legal 125's..... which were not particularly cheap, or reliable or 'low maintenance' or every day 'practical', and now likely twenty years old, even less every day practical or reliable!

To put that into context, they made about as much power and were just about as fast as a Honda four-stroke 250 from the end of the 250 learner-laws over thirty years ago!

Here and now.... get out of the L-Plate arena, and there are bikes like the much maligned ER5, critasised by so many folk with licences to ride'em for being dull as ditch-water, and so under-valued they cant give them away when they need a pair of tyres and a C&S kit for an MOT, yet, still have to be 'restricted' by a couple of bhp for A2 licence rgs, and offering 50bhp likely offer twice the oomph even a 'good' two-smoke 125 will likely deliver for very long...whilst being cheaper to insure, less nickeable and probably no less unreliable....

For dirt iron, if you buy some sturdy locks to detur the tea-leaves these so attract, choice of naturally A2 complaint machines and easily restricted to A2 bikes is pretty good; and all are likely cheaper to buy, insure, and maintain than a not so slow 125.

Absolutely no sensible reason to try beat the system trying to tune a 125 to go faster than is legal on A1 or L-Plates.. just go do the tests and get a bigger bike!!! It' just making life hard for yourself, buying hassles to make a slow bike a tiny bit less slow, whilst spending money to make it less valuable and likely less reliable.. A-N-D get you nicked by interested plod for some obvious crime.. especially if you try exploit the bit less slow you may get!


booking my A2 asap haha
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andyscooter
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PostPosted: 08:19 - 27 Sep 2017    Post subject: Reply with quote

G wrote:
For posterity Smile:
https://i.imgur.com/sBA3RC0.png

And I thought those 'end of the world' things were all just conspiracy nut jobs!



I haven't really just spent two minutes trying to close that screen down Embarassed Embarassed Embarassed
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HDshiny
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PostPosted: 12:36 - 27 Sep 2017    Post subject: Reply with quote

Always thought that 2 stokes were quicker than 4 stokes.

Is that not the case with 125?
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stevo as b4
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PostPosted: 18:30 - 27 Sep 2017    Post subject: Reply with quote

I think 'were quicker than four strokes' is more appropriate today.

If the obsolete two stroke your looking at is a liquid cooled one that's been artificially limited to 12-15bhp for European legislation, but was based on 20-30year old motocross or race bike engine design, and was engineered to make much more than the 9kW UK limit, then yes they are.

Its all a bit of an irrelevance to today's young and coming want to be bike owners, as the bikes are old, harder to find, and either knackered after lots of thrashing and bodging, or getting expensive way beyond economic sense.

Add to that, I'd say most if not nearly all non engineering and classic motorbike mad 17-19yr olds really don't have a clue how to maintain them, keep them running, and repair them. The knowledge isn't there or being taught or passed down, as millennials probably have never encountered or seen many two stroke engines period. Its very common for such an owner to not know what two stroke oil is, where to put it and how to mix it or check it's level etc.

That sort of caper happened in the late 80's- early 90's when we were coming up to 'my first road bike' age. What chance have kids got today?

Back then alot of us had off road bikes, field bikes, or were into other hobbies with two stroke engines as kids, as games consoles and computer gaming and video/media wasnt up to much. You had to have real hobbies and many were outdoor pursuits.

If you were a teen in the 70's-80's you won't have had any problems, as two stroke bikes were everywhere, and you probably had an older brother or mate or dad that knew exactly what they were doing and could pass it on to you to learn how to fix things and make them work etc.

Back to two strokes being faster than four strokes, well yes they often are at the same cc, but they are not long lasting by comparison as a very general rule. The brightest star burns for the least time and all that.

Also two strokes from a purely engineering point of view are a pretty crap way to make an engine. The Volumetric efficiency is dreadful as are the emissions. They shouldn't work nearly as well as they do on paper. But they are light, simple and have a very good power to weight ratio making them useful in some situations.
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Ste
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PostPosted: 18:58 - 27 Sep 2017    Post subject: Reply with quote

There's not many good options for NSRs to buy on eBay right now. Sad

An NSR125 project: https://www.ebay.co.uk/itm/Honda-NSR-125-Full-Power-Streetfighter-Bike-/122722941299?hash=item1c92db7973:g:sXkAAOSw4P1Zx8ma

An NSR125 which just needs a front wheel and a rear brake lever: https://www.ebay.co.uk/itm/Honda-NSR-125-RR-1994-Free-Delivery-UK-Mainland-/263218890166?hash=item3d491185b6:g:lAUAAOSwKcdZwkor

An NSR125 monstrosity: https://www.ebay.co.uk/itm/Honda-nsr-125-Motorcycle-is-registered-in-UK-and-its-100-working-/263225042580?hash=item3d496f6694:g:sLgAAOSwXvNZtXFu

Some of the ones which sold recently could have been alright purchases: https://www.ebay.co.uk/sch/Honda/9806/i.html?_from=R40&_nkw=NSR125&LH_Complete=1&LH_Sold=1&rt=nc&_trksid=p2045573.m1684

Until there are four stroke 125 bikes that'll do 90mph or more then a two stroke is still the fastest 125. And there's the acceleration as well. Wink
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HDshiny
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PostPosted: 20:31 - 27 Sep 2017    Post subject: Reply with quote

mainly looking for a 125 supermotor.

could anyone suggest any good ones. been looking at the Yamaha wr125x and the Yamaha dtx.

thanks
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G
The Voice of Reason



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PostPosted: 21:04 - 27 Sep 2017    Post subject: Reply with quote

5 ok looking ready to go NSRs on gumtree.
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Teflon-Mike
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PostPosted: 22:27 - 27 Sep 2017    Post subject: Reply with quote

HDshiny wrote:
Always thought that 2 stokes were quicker than 4 stokes. Is that not the case with 125?

It's not the case regardless of capacity.

The conventional two-stroke is a fantastic bit of product engineering, evolved from the NSU RT125 motor. In the 1930's there were many different arrangements of two-stroke engine, like the 'split-single'.

The Otto-cycle, that describes the combustion process, says that you have to have four 'phases'; suck, squash, bang, blow.. or Induction, Compression, Power and Exhaust.

The conventional four-stroke reciprocating piston engine, completes each phase in a chamber above a single piston, in a single cylinder, on a separate 'stroke' of that piston in the cylinder, ie gong up or going down. Hence it takes four strokes, or two crank revolutions to complete a single combustion cycle.

The two-stroke engine, 'cheats' and completes one cycle on one crank revolution and two piston strokes, one up, compression, and one down, power.. getting the charge 'in' to the engine has to be done by some other sort of pump.. usually by sealing the crank-case and using the under-side of the same piston, but could be a super-charger or another piston; 'exhaust' is usually just left to its own devices, to escape by its own inertia from a hole in the bottom of the cylinder wall.

The DKW two-stroke, then, was conceived in the 1930's, in Nazi Germany; The VW 'people's car', wasn't quite the Ford-Model-T any-one could afford, it was supposed to be; and the clamoring masses were a little disappointed they couldn't have their own personal motorized transport.. The DKW tackled this by distilling the internal combustion engine down to the fewest possible moving parts; one crank-shaft, one piston, and no valves. With one combustion cycle completed per revolution, it didn't require a complicated ignition system, nor intricate assembly; the few individual components could be made fairly cheaply, and put together by essentially untrained labour. Installed in a rudimentary cycle frame, it provided a very 'cheap' motorized personal transport 'product' to mollify the masses with their name on a twenty year waiting list for a Volts Waggen!

Performance was not a particularly high priority! Nor was efficiency. The main 'problem' with the engine was that lacking valves, it relied entirely on piston-porting; control of gas flow in and out accomplshed by the piston opening and closing 'windows' cut in the cylinder wall as it passed them.

I Theory, the piston-ported two-stroke, should NOT work!!!! Using the underside of the piston as it rises on the 'up' stroke, to suck charge into the crank-case..... when the piston falls again on the down stroke.... it should shove it all back out the way it came in! (not into the combustion cylinder!) Fact that it does, is perverse, and relies on curious flow effects, mainly making the forward flow easier than backward, so that 'some' charge hangs around in the crank-case to get shoved up into the combustion cylinder.

However... that little niggle aside.... it is still 'cheap', better still, lacking valves and stuff, there's not a lot to wear out or go wrong, and when it does, well, there's very little to 'adjust', pull it to bits and replace the worn parts, its nie on sealed for life, and will keep running till its scrap.

The DKW RT125 made about 5bhp, and could achieve about 45mph, and the low maintenance and consequently relative high reliability meant it offered very good low cost, low maintenance 'utility' transport, and it's design was widely licenced or simply copied around the Nazi world, significantly Italy and Spain, before the design was appropriated by 'War Reporations' after WWII and licences granted to BSA in the UK who built it as the BSA Bantum.More significantly a Licence was granted to Yamaha by the Americans, in thier post Hiroshima guilt to 'reconstruct' Japan....

Meanwhile! A chap called Walter Kaaden, at the old DKW factory, left in the Easter Russian sector and renamed MZ, had hoped to go racing... and four-strokes ruled.... with positive valves, they could typically produce around 60bhp per liter, even in moderately low states of tune. Under Soviet control, though, MZ were expected to make low cost utility machines.... and derivatives of the old two-stroke RT125 was all that was required... but 5bhp from 125c was 40bhp per liter.... surely one could be tuned? So Kaaden set about the challenge.... and soon discovered it was a little bit more tricky!

Problem was that piston porting and the clever tuning it relied on to stop charge sucked into the crank-case leaving the way it came. More audaciously he tuned the engine, the more charge he got sucked in... more want it was to bugger off again... and even if he did get it to hang around, it made the engine ever less 'tractable', making more power higher up the rev-range, with ever less low down.... for a race engine, that he could live with.. to some degree BUT to solve the problem he did away with piston porting, and provided a mechanical 'disc-valve', to open and close the crank case, so as piston rose, charge got sucked n; as it fell, the disc closed, to keep it there, and transfer ports saw it pumped into the combustion cylinder.

At a stoke, he more than doubled the trapping efficiency of the two-stroke, and saw power increase from around 5bhp to 10 or more.

Although, 'artesian' porting, using fountain effects to effect cylinder 'scavenging' incoming charge directed to the top of the pot to 'chase' exhaust out the bottom, with minimum contamination, and 'harmonic' (expansion chamber) tuning of the exhaust to stop or push back fresh charge following exhaust down the pipe helped enormously.

Meanwhile in Japan.. Yamaha tackled the same problem from a different approach, and rather than use a disc-valve to keep charge i the crank-case, they used a flap-valve, like they used in the bellows for the musical organs they made. Bit like a clarinet with a below instead of a fella puffing.... key ingredient was a 'reed' hence a reed-valve.

Both working on essentially the same base engine, the DKW RT125, they each managed to get the engine to deliver around 12-15bhp relatively reliably and use-ably from just 125cc.. and suddenly the 'Hi-Po' two stroke offered around 100bhp per litre, almost twice what could be achieved from even a well tuned four-stroke...

It gave rise to the suggestion that twp-strokes were 'twice' as powerful because they went bang twice as often.. which is hugely over simplistic...they made more power by pumping more charge.. but same end.

BUT now we have a polarization. At one end of the spectrum you have the simple piston ported two-stroke. Still 'cheap' to built, still low maintenance, still ideal for low cost utilitarian machines, but also still not very powerful or efficient. At the other, you have the 'Hi-Po' two-stroke, that with positive valved crank case could make an awful lot of power for it's displacement and or weight.

Building on Kaaden's breakthroughs in porting, two-strokes went from having just one or two transfer ports to maybe seven or nine! Now stopping piston rings from 'pinging' into the holes as they passed became a problem; but advancing the port timing by raising the ports, like making a four-strokes cam more lumpy was easy enough, but made the 'power band' ever more peaky.. whilst as power rose, reliability fell. And on a two-stroke there's bog all to 'adjust'... so when things wear they need replacing....

On something like a piston ported MZ250, which makes about 15bhp, you keep chucking in pre-mix petrol and oil, and it will possibly run, with little more than a new spark plug every 10ooo miles or so, for best part of 100ooo miles.

On a Honda RS125 GP bike.. that will make around 50bhp, that will run for oooh.... maybe twenty hours! Before the bits that are worn out need thrown away and replacing... those will e the piston rings, the piston, the cylinder, and oh yeah, the crank.... ie MOST of the motor! Same deal, really, t is from the off, 'sealed for life'and wll run till it falls to bits... only making that much more power... its not for so very long!

That book-ends the spectrum; at one end low cost utility machines of decidedly not very inspiring performance, but long lived and low cost; at the other incredibly high performance machines, of very short lived mechanics.

In between.. well, the hey-day of the two-stroke was little more than a decade, the 1970's.

They came to the fore in the early 1960's in racing when Kaaden's MZ's showed they could challenge the four-strokes, and there were plenty of 'cheap' utility two strokes, like the BSA Bantum for amateurs to mess with in their sheds.

The Japanese making two-strokes for the consumer market were quick to champion them in racing, yet, it aught be noted that the four-strokes managed to hold off the challenge, in track and dirt racing for a very long while; it wasn't until 1975 that Yamaha took a 500GP world title with a two-stroke!

In 1980, Yamaha launched the immortal RD250LC; it was far from the 'first' liquid cooled 'production' two stroke... and before any-one yells "Suzuki GT750 Kettle"... I'll just say 1908 Scott!... The RD250LC brought the Hi-Po 2T to the mass market; The RD350YPVS of '83 that added a valve to dynamically tune the harmonics response of the expansion chamber exhaust, was pretty much the pinicle of Hi-Po 2T evolution.

The 'thing' is that by the time you have added crank-case valving, water cooling and exhaust resonance control... you no longer have a very 'simple' engine. Can still be relatively light weight, but its not that simple; especially if you start adding more cylinders. It's now a case of swings and roundabouts; and for ultimate performance, the two-stroke is starting to loose out; the original advantages of it's 'simplicity' are being lost to all the 'complexity' added to get the performance.

And the big 'niggle' with the conventional crank-case induction two-stroke, is that the charge has to go through the crank-case, which mans you cant easily use a positive pressure recirculating lubrication system, as is common in a 4-stroke.. the engine would tr and suck its own engine oil into the combustion chamber. Hence the need to use pre-mixed petrol and oil for fuel, which makes for a less efficient 'burn' as well as more noxious emissions, but probably more damning, is that it denies the use of 'solid' shell bearings, that can stand a lot of load and speed; and begs more convoluted 'roller' bearings, that are more tolerant of lesser lubrication, and more 'open' to let low pressure lube get to the bearing surfaces of their own accord.

The practical limits of the Hi-Po two stroke seem to be at around 200bhp per litre; and at that level, the loading on such open bearings and the rather less stiff pressed up cranks that are needed to use them, mean that component lifes are short, and for a road bike those emissions have been unacceptable in most western markets for decades.

If you look at the BMW S1000R... you have a four-stroke production bike, that out the crate, is delivering 200bhp per litre.... as much as the last of the 500cc two-stroke GP bikes... and suffering similar problems of managing that, begging sophisticated electronic rider aids to do so! But still.... It shows how in the last twenty five years, four-stroke technology has evolved, to the point that it can achieve the same power levels as ever the two-strokes could have, and yet do it with consumer levels of durability ad reliability AND eviro-mentally tolerable levels of 'emmissions'. Mostly because the charge doesn't have to go through the crank case, and stiffer cranks and stronger bearings can be used.

As to the matter of the smaller displacements? The 'optimum' displacement for a four-stroke cylinder, is somewhere around 400-500cc, but it's a fairly 'flat' curve. The optimum doesn't drop off too much as you get much bigger or much smaller. It do with a two-stroke! Their optimum cylinder displacement is probably around 150-175cc. Much bigger or much smaller and the performance and efficiency drops off sharply; 125cc is probably the most common displacement due to legacy and regulation, both for licence or tax or public roads or classes in racing.

And ts that 'legacy', really that saw them live as long as they did.

Within a year or to of the Yamaha RD350YPVS in the early 80's providing a Hi-Po two-stroke for the consumer market, bikes like the Kawasaki GPz600R heralded the modern era of four-strokes that offered the power, and the reliability and the handling earlier two-strokes had suggested, but not often delivered, and did it whilst meeting ever more stringent emission controls.

The 'sports' two-stroke 125's were something of an anomaly; exploiting the ability of a two-stroke to make relatively big power per cc, where licence or taxation regulation denied anything larger.

Interesting to note that in the mid 90's, bikes like the Cagiva Mito and Aprilia RS125's, cost as much in the show-room than bikes like a Kawasaki GPz500s, and did NOT sell well, brand new in countries that didn't favor them with tax or licence breaks! Most of the Hi-Po Italians in this country of that era, were actually grey-imports, brought into the country as 'scrap' having been written off in Italy where they were sold new, when their contentious taxation laws made them too expensive to keep on the road!

So ultimately, what's 'quicker' is pretty much independent of anything; there's two-strokes that are less powerful than four-strokes of the same cc, there are others that are more powerful; meanwhile there are 125 two-stroke race bikes that set lap times better than 600 four-stroke race bikes... yet RIDERS on 4 stroke 500 singles that set lap times better than folk on 125GP bikes....

Which is hint that it is the RIDER that has most influence on how quick a bike goes than anything.....
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