My buddy has a '09 Street Glide with a 103" kit with dome top pistons and stock heads yielding 10.25 to 1 compression (according to the builder). He is having a set of heads done, and the guy doing the heads knows the motor has dome top pistons and Screamin' Eagle 251 cams.

The machinist guy is going to move some material around, install bigger valves, better springs and add compression releases and titanium retainers. He's also going to shave a few thousanths off the heads to get to 10.5 to 1 compression, using .030 Cometic head gaskets.

My question is, how the heck will he know what the final compression is without seeing the fit of the piston and jugs? Is he just basing his calculations of the stock head dimensions? I asked the machinist guy, but he wasn't very forthcoming with information. Just spouted off about his 140hp FXR...

I'm still trying to learn this stuff, so please educate me. I can't seem to find the answers I'm looking for, even though I've read LSR's site, Big Boyz, Head Quarters, GMR, Deweys, Nightrider, and some other websites I've not mentioned by name..

 

When the piston is at top dead center. you measure the amount that the piston is down in the bore compaired to the top of cylinder. This is done best with a dial indicator.

 

JC,

You're doing this secondhand! It's not YOUR bike that is being reworked. How close are you to what your buddy has discussed with HIS builder? Is your buddy worried about this? I have no idea what deck height is either, but if I was paying an expert to work on MY motor I would probably leave him to get on with it! Or ask him in person.

 

My procedure during last build:



Also works on the edges for domed/raised pistons!

 

http://www.bigboyzcycles.com/showthread.php?t=92