So about a year ago, I had to tear the engine down for a sudden knock. Turns out it was one of the gears in the clutch side.. lost a tooth. It knocked out a couple of other things as well, but I spent time replacing all the broken pieces and such.
I figured since I was in the engine I would inspect the piston/rings. Understand, this truly is a lower hour, well maintained extremely clean machine. The stock bore was pretty clean and I measured it with (calibrated) ID mics. I bought a 11:1 Wiseco and measured it as well. I measured everything 10 times to make sure I got consistent numbers. I got 0.0025" clearance between the piston and cylinder, which is what Wiseco wants.
I reassembled everything. It runs great but I am not 100% convinced that I don't hear some piston slap. Are the 660 motors perfectly quiet? Or do they all make "some" noise. It also has a stage I cam. Valve lash is good. I am 100% certain it is not top end, loose valve noise. It is a little deeper than that, but not crank deep. We (my buddy and I) checked out the crank bearings and felt zero play. The cam chain tensioner is about 1/2 out so I don't believe it is cam chain noise either.
Does the higher compression piston make a little more noise? I am 99% certain I measured everything correctly, but it's also hard to believe that a 12 year old machine still has a good stock bore. I just don't want piston slap and loose a piece into the crankcase. It seems easier to nip it now and bump up to a clean 686, or now I see there is a 693 kit.
It's hard cause it runs good and I run it 2-4hrs a year. So right now my "new" piston has 6-8hrs on it.
Is everyone's motor dead quiet? Can I truly check piston slap by turning the crank back-n-forth and listening for the piston hitting the cylinder? I would think that a good 686 install would be just as reliable as a stock bore, if done correctly? Anyone try the 693 (team alba racing)? Yes, going to 693 means that I would have to get a new cylinder but at the rate I ride it could take 10-15 years before I need a rebore! If not longer!
I was able to post a vid:
If you could check it out that would be great guys!
Thanks
Dan

 

To me it sounds ok. They are noisy engines in my opinion.

 

Anybody else have an opinion. Yes another just said nature of the beast, especially with a cam (stage I).

 

I compared mine. That’s normal to me. Ride it!