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cowboyona426

Opinions on stroked 426

44 posts in this topic

I know YZDAD1 used to have a stroked 426, but has anyone else tried stroking their bike? What other type of work did you to (high comp piston, overbore, headwork etc)? Worth the money or not? My bike is an 00 426 with a 450 cam and Thunder Alley pipe, otherwise stock motor. Any input would be appreciated :cry:

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I went with the 13.5:1 piston. It seems to have some more punch to it right off idle. I don't like the way it sounds though, it has some piston slap that the factory piston did not have. If you can get by the noise, then its worth having. As far as big bore kits and stroker motors..... Your money is probably better spent with buying new tires or suspenion work. (Unless you last name is McGrath or Reed)

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I know YZDAD1 used to have a stroked 426, but has anyone else tried stroking their bike? What other type of work did you to (high comp piston, overbore, headwork etc)? Worth the money or not? My bike is an 00 426 with a 450 cam and Thunder Alley pipe, otherwise stock motor. Any input would be appreciated :)

Chase you just need to ride the one you have...forget about hot rodding it!! :)

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You're right, Satch, most of us can really get along fine with the big YZFs just like they are. But there is something very cool about really BIG thumpers! Years back, I got a chance to ride a CCM MXer with a 600cc BSA Victor in it. Very impressive. Not the rev forever kind of power we have now, but massive low end punch. Short shift the thing and it would climb the hill at Carlsbad in 34 thumps. Recently I got to take a spin on a 570 some cc KTM. That was an eye opener, too! :)

So, I think it would be really cool to own a 500cc YZF. Trouble is, I can't afford it. See what I mean?

Makes my mouth water, though. :)

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426/450 is all ANY of us NEEDS.

If he's got a baby coming, it's all either of us can AFFORD. :)

...And in more ways than one. :p:)

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after reading that website and your opinions it makes me wonder about a slight overboring... which would be a better bennifit...

a) overbore it

:) stock bore just use a high compression piston

will the gain be the same between the two'

is one better than the other

Im just trying to do as much research and as as many questions as possible before i dump a wad of cash into my bike.. :)

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those prices are for a 450. i talked to them a while back and for a stroker crank for a 426, the mods will cost $750. that will give you 466cc with stock bore. with a big bore kit, it brings it up to 488cc and depending on what you want with the big bore, it can range from around $400-$1100+. not too bad but thats doing all the disassembly and assembly yourself. but if you have a baby on the way, then :) . some things are are more important than your bike(not many tho).

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after reading that website and your opinions it makes me wonder about a slight overboring... which would be a better bennifit...

a) overbore it

:) stock bore just use a high compression piston

will the gain be the same between the two'

is one better than the other

Im just trying to do as much research and as as many questions as possible before i dump a wad of cash into my bike.. :)

Overboring usually produces a straight up power gain more or less equivalent to the percentage gain in engine size. Expect from one to three, I would guess. The larger piston will increase the loads on the crank slightly, because it's heavier. The rpm range will be roughly the same.

Stroking the engine will do a number of interesting things besides add to the power output. Increasing the stroke will increase the piston speed at any particular rpm, and because there's a limit to how fast the gasoline will push the piston, stroking tends to lower the peak rpm and slide the whole power curve downhill a bit. Not by 1000 rpm, but some. If the combustion chamber volume stays the same at TDC as it was, a stroked engine will have a higher compression ratio because the volume at BDC will be greater. Loads on the crank are increased here as well. Boring gives you the same engine you had, but bigger. Stroking tends to make it more of a moose, if you know what I mean.

When stroking an engine, something needs to be done to correct for the fact that the piston will be going farther up as well as farther down. The options are, raise the cylinder with a spacer, or make a new, taller one; make the rod shorter; or move the wrist pin farther up in the piston.

Raising the cylinder seems like the simplest thing to do, but then you would need to find a custom timing chain to reach the extra distance, and the top engine mounts would need to be modified. Carb clearance, exhaust alignment, and other problems could arise.

Shortening the the rod is often the only practical choice, but there can be problems with it. A shorter connecting rod bears on the crank at an increased angle, and by doing so, increases loading on the crankpin. There is a proper range of rod length to stroke that should be adhered to, but I don't know how closely the stock or shortened YZF rods conform to this, or whether the shortened rods Falicon is using are anywhere near the short end of that range. They seem to work, so I won't worry about it. Generally, a shorter rod is more beneficial to producing low speed torque than high speed power, so it sort of fits in with the whole nature of stroking an engine anyway.

The ideal approach would be to move the wrist pin higher, but here we run into a problem with the YZF because the pin is already very close to the oil ring as it is. I have seen stroker pistons for V8s that used machined plugs over the ends of the piston pin to bridge over the cut out section of the oil ring groove, but that's a pretty extreme solution, and frankly doesn't work that well.

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Chase you just need to ride the one you have...forget about hot rodding it!! :)

Satch, I'm not talking about NOW, I'm talking about later in the year when I'll actually have MONEY! :p I know I won't be getting a new bike anytime soon, so I was just exploring options to make the current ride more fun/powerful. Suspension is a good idea, but I'm going to learn how to adjust my stock stuff before I go for fancy new suspension.

In short, just wishful thinking :)

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so the safer bet for longevity would be overboring...

w/ the three instances you mentioned on setting up a stroker could pose major problems down the road and or a lot of work to get it properly done.

either a) a piston splits because the wrist pin has been moved

:) you trash a crank because the shortened rod has increased angles

c) you deal w/ modifiying everything on the bike while using a spacer.

if you just do a overbore everything stays the same except the piston.

I can see a problem w/ this as the cylinder walls are a little thinner now and w/ extreme pressure some sort of detonation backfire or something bad happens to cause extreme pressure you can kiss the jug good by as it blows a hole thru it...

hmmmmmm.....

i think ill go w/ the overboring it seems easy practicle and i will still get a gain out of it...

now what about a high comp piston?? any bennifit to those or just stick w/ a stock compression piston w/ the overbore

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so the safer bet for longevity would be overboring...

w/ the three instances you mentioned on setting up a stroker could pose major problems down the road and or a lot of work to get it properly done.

either a) a piston splits because the wrist pin has been moved

:) you trash a crank because the shortened rod has increased angles

c) you deal w/ modifiying everything on the bike while using a spacer.

Not necessarily. If the crank work is properly done, it should hold up fine. But anything you do to make an engine run more fuel/air through it is going to result in some kind of extra strain on it. Those are just things to consider. The 350 Chevrolet is a stroked 327, which is a stroked 302, all with the same rods. Chevy did it by moving the pin higher in the piston. The 302 was the most failure prone of the three because of the revs it was capable of.
if you just do a overbore everything stays the same except the piston.

hmmmmmm.....

i think ill go w/ the overboring it seems easy practicle and i will still get a gain out of it...

now what about a high comp piston??

Big bore kits are very much less expensive, but there's a practical limit to it, as you note. The people producing them are quite conscious of this, and don't generally offer products that would cause excessive grief. For example, there was a 302cc kit available for the YZ250F that was recalled from production by the maker because the heavier piston had an unfortunate tendency to pull the rod in half. Nobody needs the kind of trouble you can get by selling something like that.

High compression is always a good way to get a little extra from a four-stroke, and the power gains are across the rpm range. Idle quality will actually improve, and even fuel economy will get better, but of course, the way we ride, we won't notice that.

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you have been very helpful... thx..

Now to find a reputable company to supply the bigbore kit and re-nikasil the cylinder.. :)

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Does anyone know of a reputable company to have this kinda work done... just overbore and re-nikasil the jug... i live in vegas and could ship to just about anywhere..

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Raising the cylinder seems like the simplest thing to do, but then you would need to find a custom timing chain to reach the extra distance, and the top engine mounts would need to be modified. Carb clearance, exhaust alignment, and other problems could arise.

I rode YZDAD1's stroked 426....we did a +2 mm over stock stroke and we had no need for a "custom" timing chain, the stock one worked with a 450 exhaust cam. the top engine mounts did not need any modification. the carb bolted on just like normal, along with the airbox boot. the exhaust alligned perfectly like stock....it was a Thunder Alley full exhaust. And finally, no other problems arised :)

and just like he said, it turns it into a "moose" but i called it a tractor.

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Well lsts put It this way we have all kinds of people on here that think they know a lot .But It's like this, powroll does a stroker on the 426 that 426 rod ,an piston with only a trim on the dome for the stroker crank.With no other work to be done .My 400 has been a 450 sents 98.

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I used the Poweroll +2mm stroke crank mod ($394) with a JE +2mm piston (std.compression) along with porting the head, Thunder Alley Exhaust and 450 exhaust cam. Makes a 459cc engine with great power and torque and zero reliability issues after 2 seasons of use it's still going strong! I actually sold the engine to a fellow TT'r and as far as I know he's still riding it.

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YZDAD, do you think the head porting was necessary or would the motor do fine with a stock head? Also, did Powroll provide the cylinder spacer or would that be additional $ to have one made up?

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