03 yz450f stroker crank?

I need to put a new bottom end in my 03 yz450. I'm looking for a stroker, but only finding them for 06+. Can anyone point me in the right direction? I'd like to use my factory piston with it?

Why. Stokers usually only produce bottom end and take it off the top. By the time you put a big enough cam in it to make it rev the rod speed is too fast on the bearings. They usually are not too reliable when reved high.

Your better off with a big bore and a cam than a stroker.

If all of that were true, the 450 should be less reliable than the 426, since it is basically a 426 with a 3mm stroke increase.

Generalizing too much.

If all of that were true, the 450 should be less reliable than the 426, since it is basically a 426 with a 3mm stroke increase.

Generalizing too much.

From the stroker cranks I've seen they usually move the pin out.

On factory bikes they use the pin in the same place with a longer rod and taller cylinder.

From the stroker cranks I've seen they usually move the pin out.

On factory bikes they use the pin in the same place with a longer rod and taller cylinder.

Please tell me you are joking???

Please tell me you are joking???

Well it could be your a aftermarket stroker fan and able to explain things a lot better.

Edited by stevethe

Why. Stokers usually only produce bottom end and take it off the top. By the time you put a big enough cam in it to make it rev the rod speed is too fast on the bearings. They usually are not too reliable when reved high.

Your better off with a big bore and a cam than a stroker.

 

 

The main reason is because I don't "need" to replace the piston and cylinder. I "need" to replace the crank. It already has hot cams in it.

The main reason is because I don't "need" to replace the piston and cylinder. I "need" to replace the crank. It already has hot cams in it.

If it was me I would go with a stock crank. Then put about 1/2 point more compression on the piston to bring the torque back from your cam.

If it was me I would go with a stock crank. Then put about 1/2 point more compression on the piston to bring the torque back from your cam.

I'm assuming stock compression is 12.5? 

From the stroker cranks I've seen they usually move the pin out.

On factory bikes they use the pin in the same place with a longer rod and taller cylinder.

 

Increasing the rod length is done for an entirely different reason (the same reason the cylinder was offset forward starting in '10), and has no effect whatsoever on stroke.  Only changing the distance between crank axle and crank pin does that.

Increasing the rod length is done for an entirely different reason (the same reason the cylinder was offset forward starting in '10), and has no effect whatsoever on stroke.  Only changing the distance between crank axle and crank pin does that.

 

Reasonable info on stroker cranks. http://en.wikipedia.org/wiki/Stroker_kit

 

I am not a fan of them. I owned a TT600 - 680cc bored and stoked with a Carrillo rod. I believe the bore only TT600 had more HP. The only stroker I have seen that really hauled was a KTM 250 bored and stroked to 350 with a big cam. It spun some very high RPM's. The only problem with the bike was the crank went out every season.

Edited by stevethe

Reasonable info on stroker cranks. http://en.wikipedia.org/wiki/Stroker_kit

 

 

 

Reasonably wrong, much of it.  For example, they state an engine with an increased stroke will produce more power that a similarly sized engine without one.  The horsepower gain from a stroker kit comes specifically from the increased displacement.  They fact is that otherwise similar engines of any given size that are more over square (bore larger than stroke) will produce more power because of their slightly increased ability to turn up higher RPM than engines that are under square (stroke longer than the bore dimension), or square (bore and stroke equal), or simply less over square.  Increasing the stroke with no other changes will cause the engine to produce a larger portion of its power at lower speeds. 

 

Compensation for the increase in YZF's is done by spacing the cylinder upward by half of the stroke increase.  The piston pin cannot be raised in the OEM pistons any farther than it already has been, and shortening the connecting rod is counterproductive to power output. 

 

You cannot directly compare experiences with an XR600 or a KTM to what you expect from a Yamaha. Again, if the stroke would reduce power and reliability, the 450 would be slower than the 426 and be less reliable.  It is neither.

Couldn't find a stroker, so I went with a Wiseco factory style replacement.

Good luck with that.  They've historically had rather bad luck with their replacement cranks.  They have changed vendors, though, so...

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