XR650R cam timing weirdness, or Are the valves hitting the Piston?!

[BasketCaseSensitive]

Hi All,

A friend came by today with the plans of replacing the piston in his '04 XR650 with a Wiseco 11:1. I had downloaded a manual off of here for an '01, I think, believing it would be close enough.

Anyway, we pull down the engine. Everything looks pristine. Tons of cross-hatch on the cylinder walls. Slight wear on the skirts of the stock piston. No doubt it was still within specifications. The new piston installs easily. everything is going great.

Now, the book says to turn the engine over until the "T" mark on the magneto aligns with the mark inside the cover, and the two timing marks on the cam gear should align with the head surface. No problem, everything lined up. We triple checked it. Put the bike together and kicked it over and TAPTAPTAPTAPTAPTAPTAPTAP! Something sure as hell isn't right. I pull out my borescope and have a peek inside. It looks almost as if the intake valve is beginning to open just as the piston arrives at TDC, and the two get awfully damn close. I couldn't see contact, but it looked probable.

We tore the head cover back off. depending on how you look at it, the timing marks don't line up quite exactly. Certainly not a tooth off, I thought. But well, it could sorta be interpreted as maybe the cam could possibly be advanced a tooth to correct it. So we did. And it sure looked like it was a mile off. But that bike fired right up and ran fantastic. Big increase in low end torque, and it seemed to rev freely throughout the rev range. Easily shot up to 95 mph with more to go (this particular bike is street legal).

Does anyone have an explanation for what we witnessed? The timing by any account is off, but you can't tell by the way it runs. Do Wiseco 11:1 pistons hit stuff? Was the book wrong? Was there a difference between the model in the book and this one? Why can't I get laid daily?

Thanks!

[weskc35k]

Stretched cam chain,evil spirits geez i don't know.

You haven't been laid lately because you have questionable grooming habits?

[scalejockey]

ah yes....a stretched chain sounds sounds like the answer to both yer problems.

[Maroast]

Why can't I get laid daily?

Have you considered lowering your standards? Prostitution?

I don't know much about the wiseco 11:1...but I do know that ANY piston should'nt "hit stuff"

[rdahl]

Did you check the cam positioning with the chain tensioner tight? I had the same issue "less the clicking noise" and when the tensioner was on the timing marks lined up with it off they were slightly off. Any chance you adjusted the valves with the auto decomp ingaged?

[martinfan30]

Have you considered lowering your standards? Prostitution?

I don't know much about the wiseco 11:1...but I do know that ANY piston should'nt "hit stuff"

legal here in nevada!LOL!

[BasketCaseSensitive]

Did you check the cam positioning with the chain tensioner tight? I had the same issue "less the clicking noise" and when the tensioner was on the timing marks lined up with it off they were slightly off. Any chance you adjusted the valves with the auto decomp ingaged?

Yes. Well, we checked it both ways, and the marks always seemed to be pretty darn close. Just to reiterate, the marks initially were about as dead on as you could get, and something was hitting. Advancing the cam a tooth made everything look obviously wrong, but that's where it runs well.

The decompression mechanism wasn't the culprit, either.

[BasketCaseSensitive]

Well, it seems that when you put the piston in backwards, things can touch. Who knew?

More amazingly, even after denting the top of the piston slightly, not a single valve had bent, and we were able to tear it down, turn the piston around, put it back together, and go riding.

The mixup occured when I was reading out of the Honda manual. It said to put the mark on the piston toward the intake side. The Wiseco manual on the other hand suggested the opposite.

?

[Maroast]

legal here in nevada!LOL!

HAHAHAHA took me a second to get that! ?

[bosshog]

So it was in backwards. Can't belive you got away with no damage, cool. Friend of mine once did that on a 2 stroke but wasn't so lucky. I guess all's well that ends well. So do you think not knowing how to put it in correctly is causing your other proplem aswell??

[motopsycho650]

The 11:1 piston is and "interference piston." Which means, the piston moves into space that was occupied by the open valves. If the timing is off, due to a stretched timing chain, the piston can hit the valves. I'm not saying that is your problem, but it is possible. Just because the piston & valves are close, does not means they are hitting.

I would say, get rid of the easy problems first. Make sure the valve lash adjustment is correct. If the valves are too loose, lots of tapping sounds will occur.

When you lined up the "T" mark, did you use the kick starter, or did you turn the fly-wheel? Removing the fly-wheel cover, and turning the fly-wheel to find TDC is the most accurate. I found that out while adjusting valves. The kick starter in not the best way to turn the engine over.

[BasketCaseSensitive]

Well, there wasn't actually a problem with the cam timing. Just that when it was timed right, things touched. Amazing that it ran as well as it did with it a tooth off.

[rdahl]

Glad you figured it out. So you said it ran better in one of your earlier posts....now that the pistion is in correctly how is the performance? That would be pretty classic if it ran the best with the cam off a tooth and the piston in backwards.