hello, i have two questions here. i am a little worried about this. i was riding my 98 300ex today and if i am cruising in the last 2 gears and push on the gas some, it start making a high pitch knocking from under the cam cover. it sounds like detonation or something.once it starts getting up to speed in those gears it goes away. i just put a new timing chain and guides on it last saturday, it runs nicely, it is not out of time. one of my questions is: WHAT DOES THE STOCK PISTON LOOK LIKE, IS IT FLAT,DISHED OR DOMED. i got this off a friend that said he had a wiseco piston put in. he does not know if it is a high compression piston or not but it is domed. i just put some 87 octane gas in it, i am going ot drain that and try 93 tomorrow and see what happens. the 2nd question is: HOW MUCH PSI WOULD I GET IF I TESTED THE COMPRESSION WITH A HIGH COMP. PISTON AND NEW RINGS. or can this even be answered. i also had to adjust the exhaust valves. they were pretty loose and tapping before the timing chain replacement. it does not do it at idle or slow acceleration but only on fast acceleration if going a little slow in a top gear.anybody have any good news for me. what else could it be. it is from the top.

 

first off i would try the 93 octane. aslo, maybee your bike is not jetted correctly? Has this only happend recently? Take out your sparkplug and see what color it is just to check your getting the correct fuel/air mix. If he has a high compression piston you need to run premium, and that might be your problem.

 

i am not sure if it just started today or not as my chain was loose and was rubbing against the chain guard which was loud and the exhaust doesn't help much either. i tightened the chain today and that is when i noticed it.how would i know if it is jetted out enough or not if the 93 does nothing for my problem. when i had the head off this weekend the plug looked black but not sooty, could probably be very old.

 

anybody else have any ideas

 

well i found the problem. i have some stripped threads for the rocker cover and oil comes out of them. but i didn't think it was coming out that fast, i check it a lot. it was low, i filled it up and it stopped the noise, but it started again after a while. so now again i will take the top end off and have all the holes retapped. and spend another 40 buck on a damn top end gasket set.