cam chain loose?

[kyleschonert]

When i was racing last night, (and when i have practiced at larger tracks a for the past couple of weeks) when i was in 3rd gear and it was reving that high, i heard a rattling sound that sounded like it was coming from about the head of my quad. It has done this before at a 3/4 mile practice track i run, so i guess it gets hotter quicker. If that has anything to do with it. Because it didnt do it last night until the last moto of the night, and I ran 2 classes, so i had one practice and 4 motos overall. So I dont know if it running hotter has anything to do with it. When I came off the track, some guy told me that it sounded like my cam chain was coming loose. Now my dad is calling our mechanic tom. and I may run it up there after work, and hopefully it will be done before my next race which is friday, should i save the time, gas money, repair money, and all that jazz and try it my self? How hard is it? If someone could give me detailed instructions it would be greatly appreciated. Also, we have a new stock steering stem and bearings for it in the mail, how hard is it to change out that bearing? Ive heard it was a pain. Thanks, kyle.

[kyleschonert]

bump

[GPracer2500]

How much compression does the engine have and what kind of fuel are you running? "...in 3rd gear and it was reving that high, i heard a rattling sound that sounded like it was coming from about the head of my quad..." That could easily be detonation you are hearing. Being a sporatic thing that seems to come and go with varying temperatures would also suggest deto as a possibility.

Does it only happen when you are hard on the gas; when you're putting a big load on the engine?

Try running a higher octane fuel and see if it dissappears. If it does than you've discovered the minimum octane limit for your engine.

[kyleschonert]

We've been running 93 in it, and it happens when I'm hard on the gas, and when in 3rd gear, it feels like it should be bogging, but it makes that noise. And the compression is whatever the piston that FST sells for the 330kit. Which I think is 11:1, but im not sure.

[GPracer2500]

I'm thinking what you are hearing is deto. You say "...it feels like it should be bogging, but it makes that noise...". That's more verbage that could be describing deto. Detonation robs power--possibly causing the feeling that it should be bogging [shrug]. Pick up some race fuel and mix it 50/50 with 93 and I bet it dissappears. Your engine will thank you.

I run a 50/50 mix of 91 pump and VP-110 in my 10.8:1 engine. It knocks a fair amount with straight 91 (the highest available around here)--even at 6000 feet it will still knock with 91. Just tooling around it's fine. But once the engine heats up and I start putting big loads on the engine (hill climbs, hard accelerations, etc) it begins knocking/pinging.

This is what happens to ring lands if deto is severe enough or goes unchecked for too long. The errosion of piston material in the upper right corner is what I'm referring to:

http://www.logicalwebhost.com/images/660_piston_top.jpg

[GPracer2500]

If you run race fuel and it still makes the noise then that should eliminate deto as a concern and you can move on to troubleshooting other things. But I'd definitely eliminate deto as a cause FIRST.