2004 Yam R6 - Engine knock?? (not bearings??)

Anyone have any experience with an '04 R6 engine making a very distinct "rod-knock" sound, only to tear it down and find all bearings are OK?

Details:

Only happened after it sat for a while. Temperature of engine did not matter. Once oil pressure built up the sound went away. (if the bike was cold it did it. if the bike was hot it did it. the only variable was how long since the bike was previously running. if greater than 8-10 minutes, it knocked. if less, it was smooth with no sound)

Was very noticable at low RPM acceleration. Holding RPM and it was only barely audible. Rapping the throttle from idle to 3 or 4k and it sounded like a rod-bearing going.

The sound was distinctly lower than the rod/crank, and seemed to be coming from the transmission more than anywhere else. (more to the rear of the bike, not in the head/crank area)

The motor was a 100 or so mile street motor - transmission was sluffing off metal into the oil but nothing worse than all street bikes. shifted good, made good power, no other signs of doom.

Shift drum, both primary and drive axles and gears, as well as both shift forks look like I expect them too. nothing obvious.

main and con-rod bearings are basically perfect.

clutch basket is not missing teeth, nor do any of the tranny teeth/crank teeth look damaged in any way.

oil pump spins freely by hand, although has yet to come apart.

no major signs of crud in the oil screen, and the oil pressure relief valve is operating correctly with nothing obstructing it.

no signs of piston to valve/head tapping. can not be 100% sure this was not the case, but absolutely no marks are on the head, valve, or pistons.


In other words - the motor looks basically brand new inside, but the tapping was loud enough that it could be heard as I exited onto pit road from a spectator area.

Anyone have any similar experiences?

The only two things I can come up with is something in the tranny is letting go (although not visually obvious just yet) or I am floating a valve into the piston, although very lightly and not leaving a mark. How exactly either one of these is tied to oil pressue is not obvious at this point either...

????

-dave

 

I had a similar sound in one of our R6's when we were running this really light oil. It would make this rod knock noise below 3-4k rpm. With 10w-40 in it, it doesn't make the noise though.

 

...I spent like 4 hours inspecting this motor, and finally was actually able to find something "wrong" with it, although I really don't believe it to be the cause of the knock.

Main bearings came out looking perfect (as did the rod bearings)...but the main bearings were one size larger than what "should" have been used if following the numbers on the crank/case.

Case numbers are 66665.
Crank numbers are 22222.

That leaves 44443 (minus 1) which is 33332.

3332 is "Brown/Brown/Brown/Brown/Black".

It had "Green/Green/Green/Green/Black" installed from the factory.

I have yet to plasti-gauge, although take little stock in its abilities. I do not have a bore gauge so I can not say for sure what the deal here is, but in quite a few years of messing with Yamaha engines I have yet to see the color coded bearings different than the crank/case numbers on the outside.

So, I am just as confused with this as when I started. The clutch and transmission look perfect, and I assembled the motor to check squish without detecting anything out of the ordinary. I am willing to bet that after I put the whole thing back together a final time it will knock again...:/

 

...and FWIW, I run the 10/50 Silkolene Pro4 (of whatever the red colored race oil is...) in all my motors.

 

R6

The main bearing color codes are correct.Read the shop manual.
You are supposed to include an "extra" 1 in your math caculations.
Check the piston skirts. A loose piston will knock like hell untill it heats up and the skirt expands.If you don't have a dial bore gauge and external mikes,borrow some ribbon guages,they still work pretty good,for "go-no go" measurements.

 

Did you check the small end of the rods and piston pins?

 

put the center back in the head gasket

 

...small end was perfect.

New pistons/rings went in just because I couldn't find anything else to replace.

24.8 thou is the tighest piston/head clearance with well over 62 thou being the tightest piston/valve clearance. (I dont think the stock yammie gaskets have "centers" like I hear the Suzuki's do... )

Good ideas though - keep 'em coming.

 

What exhaust do you run? Are all the springs on the spigiots? we have a M4 and it knocks if one of the sprigs breaks or is loose as it gets hot the noise goes away..Yes Yamaha has 3 piece gaskets..The newer r6 engine is real close piston to head needs stock clearance..