I have an 1987 cylinder with an 88 prolite piston in it, and i have 120lbs of compression, how much should i shave my head, or is it not worth it ? The bike has an .80 over bore on it as well. Also is any body haveing problems with there base gasket leaking in the front under the exaust valve, mine does and the motor is fresh, with new gaskets, it did this before too and sugustions.

 

i was also wondering the same thing(85'lt).the base gasket leaks on mine to.and i havent really got a good answer to the shaving on the head so i just got it done(.020) so i will see how well it works.

 

120 lbs is pretty low compression on a fresh top end. Mine is like 170. You will see some power gains taking a little off that head.

 

Maybe its becasue of the 87 cylinder with the 88 prolite piston, everyone says the 87 pistions are differnet form all the years, but how

 

let me know how u make out with the head Id really like to know, i can get it done really cheap so hey why not

 

170 lbs of compression, how it your bike set up, what do you have done to it, how much more compression do u think ill get by shaving the head .020

 

hey f250r, i'm also guessing that the 88 prolite in a 87 jug is why you're compression is so low. If you could get the ring clearence specs for a 87 from the dealer and then check you're ring clearence. Post the result here, i can't find a prolite for my 87 and was debating on getting a 88 prolite piston.

 

the ring clearence is the same from 87 -91 but, i think the pistion has a longer stroke in a 87, i dont think the pistion comes up high enough to get the compression, i was reading from another person in this forem, and he seems to know the diff, but i coundnt find the thread it was. that is why im wanting to shave the head, but Im not sure of this theory?

 

If the 87 rod truly does have a longer stoke then maybe replaceing you're rod with an 87 will be a better fix not to mention the longer stroke may give it a bit more torque. A crank switch might also be part of this and then it just gets too expensive, i guess you'd have to research it. But yes milling you're head is an easy fix but you should also rechamber it to get the proper cumbustion chamber shape since you are going to have to mill it enough to bring the compression up to around 180lb.

 

The stroke comes from the crank. They are the same. A longer rod will give you the same stroke, but require a different piston pin height which affects the compression ratio. Before shaving your head way down I might be more inclined to get the right piston so you end up with proper deck height and more efficient combustion.