lost rpm

[Simplespeed]

would not pull the Rpms ???

 

[Doowithblue]

Is there a way to tell that it skipped a tooth without pullin valve cover off?

 

[KnappAttack]

Is there a way to tell that it skipped a tooth without pullin valve cover off?

No.

 

[sideshowBob]

I am curious as well to why some of the 998 Turbos cam chains have skipped a tooth.
I have been running four stroke bikes, four wheelers, outboards, and sleds for a long time and have never encountered this issue.
Other then the reported potential issue of rotating the engine backwards what else could be causing this issue?
Is it isolated or common?
Could launch control be an issue?
The engine guys out there should have some insight.

 

[74Nitro]

If the exhaust cam advances one tooth it will lose peak RPM HP

 

[Simplespeed]

What I was wondering if rolling the motor over while working on it is the cause of jumping one tooth, or self adjusting chain tensioner, or even chain stretch from stress over time ?

 

[KnappAttack]

What I was wondering if rolling the motor over while working on it is the cause of jumping one tooth, or self adjusting chain tensioner, or even chain stretch from stress over time ?

The chain adjuster does not ratchet up quick enough to the next level before the chain gets too loose and allows the exhaust cam to skip if turned backwards even the slightest amount.

If the tensioner is tight enough it won't happen.

 

[max rolph]

when the engine is slightly turned backwards it pushes all the slack up to the cam and pops over one tooth, the tentioner is on the oposite side and that side stays tight, Yes it was found by TD when they did the tear down, they were baffled 3 weeks before why it wouldnt pull RPM when they put the adjustable wastegate on and were testing , it only reved 86-8800 but they only ran it for 150 yrd pulls. it idled good. thats why during the stage 6 we did manual adjuster ... it wont alow the chain to skip there is a video i have seen that demonstrates how it skips REAL easy... i cant remember where it was.

 

[74Nitro]

Retarding the exhaust cam was an easy mod to gain peak HP and RPM on the YFZ 450's.

YFZ450 Exhaust Cam Mod

I haven't seen anything useful about this. For the people that have this quad, this is the best engine mod you can do for it, period. It's all gain. The WR and YFZ have the same cam profile as does the YZ450F. The difference is in the cam timing. Whereas the YZ use a 102.5 deg lobe...

ty4stroke.com

 

[Simplespeed]

Ok Thanks Guys… I think we need to engineer a faster chain tensioner Mike… or one that will prevent this issue…

 

[Turboflash]

Ok Thanks Guys… I think we need to engineer a faster chain tensioner Mike… or one that will prevent this issue…

While your doing that, please re-design the engine to put the tensioner somewhere where we can get at it without disassembling so much stuff to tip the engine forward!

 

[Simplespeed]

While your doing that, please re-design the engine to put the tensioner somewhere where we can get at it without disassembling so much stuff to tip the engine forward!

I think the days we had room to work on things are long gone … But thats also the difference between sleds that top out at 70 and sleds that go 140 or more .. I agree with you and if it was designed correctly there would be no need to get at it in the first place. Spinning a clutch the wrong way should never have this happen in the first place…