Engine Knock

[Pmcg]

Finally got to put some hours on the new motor and have noticed a pretty loud knock when warm.  I had Todd redo the top end to run premium pump gas but am wondering if the compression is a bit too high.  Engine details are:

88mm bore
wossner windowed piston
lectron carb set a bit rich if anything
Vforce II reeds
Fatty exhaust
Power Dynamo ignition set at .86 BTDC


I can source some race gas locally but don't want to have to do it all the time.  Any thing else I should check?

Thanks

[Foxx4Beaver]

is it actually pinging?....or is it more like a KIPS rattle?

I would definitely try a 50/50 mix of pump gas and C-12 if you believe it's pinging.
Todd did mine as well...and he figured 25% C-12 to 75% pump would be ok for mine...but I actually ended up going 75% C-12 to 25% pump, cause I was getting a decent amount of pinging as well.

[Pmcg]

It's a pronounced knock. Not the Kips. At first I thought my helmet strap was unfastened and slapping on the helmet. What is c12?  Where can I get it? 

Thanks.

[umberto]

It comes from VP Drag Racing Fuels.  You can go to this website and they have a dealer locator.

http://www.vpracingfuels.com/vp-drag-racing

[sandblaster]

Doah no.... Sounds like a crank rod... When you had the top end off, did you measure the side play in the crank?

[Pmcg]

Todd rebuilt, balanced, and welded the crank. I really hope that's not the issue. I only hear it when the bike warms up. Which makes me think pre detonation.

[Foxx4Beaver]

It's a pronounced knock.

ugh...I asked, cause you didn't really give a clear description in the original post.

Doah no.... Sounds like a crank rod...

unfortunately, I agree...the bottom end needs to be investigated, unless of course by some miracle, you find something whilst removing the top-end.

I could be mistaken, but I thought you had a new crank in this thing?

[Pmcg]

It's a pronounced knock.

ugh...I asked, cause you didn't really give a clear description in the original post.

Doah no.... Sounds like a crank rod...

unfortunately, I agree...the bottom end needs to be investigated, unless of course by some miracle, you find something whilst removing the top-end.

I could be mistaken, but I thought you had a new crank in this thing?

Crank is new. I would think the bike would knock all the time if it was a bad crank not just when warm.

[Foxx4Beaver]

Todd rebuilt, balanced, and welded the crank. I really hope that's not the issue. I only hear it when the bike warms up. Which makes me think pre detonation.

if Todd did it...it should be good....
try some race fuel, see if it goes away....but if it doesn't, plan on disassembly.

[sandblaster]

+1