Just put new rings in my 300trx(has a 10:1 85mm piston) and a web 40b cam. I am running it with no base gasket for a little added oomph. Last night i got finished putting the top end back on and everything. Started it and let it idle for a few seconds, sounded great. However as soon as it gets above idle it has a really loud knock. I am at wits end. Do you think I need premium?

 

I went from a 9.2:1 stock piston on my quad which is not a 300ex to a 11:1 piston and a race cam and it was recommended to run atleast 108 octane race fuel. I would definatley try a higher octane gas might not need that high but its better to have too high of octane then not enough.

 

Do ya think that might be a problem??? Just so I'm sure, you are refering to the gasket that goes between the cylinder and the cases, correct?

 

Unless the timing is way off, a motor isnt gonna knock from spark unless theres a load on it. reving in nuetral, isnt a load. add some octane booster and see if it goes away, but im thinking it wont.
When the head was off, did you see how far up the piston went? Is it possible the piston nows goes too far, because the base gasket is out?

 

i'm with hondabuster on this, i'd say that yer piston either slapping the head and might bend a ring land as a result, or you might be hitting a valve, both not good, before running the motor without that base gasket i would've done a clay-ball clearance test between the valves and the head to make sure they don't touch, with the higher compression piston the dome is probably higher and near hitting the valves anyway, so either way you cut it, take it apart, check the piston dome for marks, check the ring lands for bent sections, and check the valves to make sure you did'nt bend them, the 10:1 piston should have enough oomph, if not i'd look to swapping engines for a 400ex. but for your motor, at best, no damage, at worst, bent valves or cracked piston domes and bent ring lands. good luck...... josh....

 

I just went to Web cams website. The 40b cam is for the 350x. It has a quarter inch more lift than the big 300ex cam. I think that is your problem. The valves are crashing ito the piston.

Did Web sell you that cam?

 

Guys, I never said I have a 300ex. I have a 300 TRX. this is the old-school 2-valve motor. The 10:1 compression piston I run is a flat top. before I took the top end back off I checked the piston/valve clearance using a piece of solder. Besides, a 350x cam wont fit in a 300ex. Today I am gonna put the cylinder back on, check the timing, and put some octane booster in it.

 

You are gonna put the base gasket back on this time, right?

 

Im not gonna run the base gasket. There is plenty of clearance.

 

How are you getting it to seal between the top of the cases and bottom of the cylinder? I bet if you put it on, problem will be solved!