i got a brand new top end for my fxef stroker 93 cid. Having issues with compression new parts include: new jugs bored 10 over,new pistons & rings,new cam,heads were lapped with new guides and valves. In the end 45 psi in back 55 in front. There pistons are high compression as well. I did some measuring today and i found out my new pistons are oval on one side by .023 thou. i checked my old pistons there are the same . Is this an s&s thing? or did i get a dud set of pistons?

 

all pistons are what is called cam ground, and that is the skirt bottom is measured @ 90 degrees from the wrist pin and one inch up, is the ONLY location you can measure a piston / BECAUSE it is cam ground --- the cylinder wall to piston distance should be .0035 to .004 for an S&S piston

you need to understand how to do a leak down test, i believe you have a valve issue not a piston one but i am not looking at the parts - Do you have a leak down tester or do you now someone who does you need to do that -- First

 

I have 1 jug off right now, when i turn the motor over by hand i can hear air going past the rings down too the connecting rod.I measured the bore it was about .06 for piston to wall clearence. The head was done new valves and guides its all new and triple checked due too having issues with compression. I put the motor together myself once and i took it too a harley tec. too get checked out and he took it apart and everything seems cool. He put it back together and this is where i am at right now

 

it doesn't make sense too me a piston should be perfectly round. What is the prupose behind making a out of round piston>?

 

I understand now about cam ground.Learn something new everyday, but something isnt right with this motor.

 

the .06 is 60 thousands i believe you ment .006 < that is too loose

remove the piston rings and re install the piston in the jug than with one hand pust it to the top like TDC and slide a feeler gague along the side of the piston and the jug and see what you get

i do not know what you are hearing so i cant respond to that

i think you should bring the pistons and jugs to a race shop in your area and ask the guys to check it for you - that would be the best way to determin what is going on

 

my bore reads 3.625 and my piston reads 3.623 +/- a few. as for what i'm hearing its the air going by the rings in the other jug i have a spark plug in it.so the compression is by passing the rings and coming out the bottom of the piston. The top end was done at a race shop all checks out according too them. I have a kicker only on this bike i dont know if that will make a difference. when i kick it over it turns 360 on the crank and thats it.

 

They didn't line up the ring gaps did they? The gaps should be staggered or you will not get good compression.

 

ring gaps are cool and measured

 

Please explain COOL and measured

Filthy has a real reason for asking - it the location of the rings ???? it is the spicific location of the piston rings - please answer how you did it and what you did