When measuring deck height, how do you accomodate for piston rock? The pistons are KB 107's (flattops) and sit below the deck around .020 while measuring above the pins. (*Ill get a better reading when I bring my depth mics home from work*) But the pistons are alot closer to the deck on the lifter valley side and/or outer block edge as the piston can rock in the bore. Trying to decide on a head gasket with closed chamber heads..

You would check the piston as close to the bore as possible on the valley side , that is the part of the piston that is closest to the closed part of the chamber. Push on the piston 180 degrees from where you have your dial indicator , that should rock the piston upward , if you push down on the side you have the dial indicator that should show you how far it's going to drop ...

I'm sure someone has a better idea ???

http://www.speedtalk.com/forum/viewtopic.php?p=121141

There is no perfect way it seems, most like to rock the piston and take an average.

The quench number is usually a static number - in your case .040 - which allows for piston rock. In other words, If you rock the piston and take the highest point and add .040 to it, you will have too little quench. If your goal is .040 and your slugs are .020 in the hole, you want a head gasket as close to .020 as you can get.

i.e. my slugs are .016 above the deck. I use a .051 gasket to yield .035 quench. Piston rock is not considered in the equation, its expected that the .035 will accommodate the rock.

FWIW I don't want to argue about "my" quench. It is what it is and I ain't changing it now. If someone doesn't particularly like my tight quench, keep it to yourself. Let's stay focused on the OP's issue.

I use a deck bridge and move the Dial Indicator stub to different positions on the piston while rotating the crank. I check all 8 pistons,especialy when building an engine with tight quench. I have seen crank indexes and inacurate rod lengths out by .003".

good info guys...very helpful.. It looks like the piston sits .012 beneath the deck above the pins just using feeler guages (not .020 like my og post--brainfart ).. and looking at that speedtalk post it looks like an "average" reading from the rocking will be real close to an above the pins measurement. Ill get better readings with good tools on Monday..

So, if I have .012 reading in the hole...and run a MP gasket which has a compressed thickness of .024 to .028, that will give me between .036 and .039. Or run the felpros (.039 compressed) and get a .051.

I seriously doubt this will be a pump gas engine with a 55cc head, but which gasket will make it more pump freindly? Ive heard the larger the piston to head clearance is the MORE chance of detonation is, which seems backward to me.

Shoot for .040 frm the highest part of the piston after rocking over in all four directions, I use a narrow thin bladed screwdriver between the top of the piston and the cylinder wall to move the piston tops over when checking deck hieghts

I shoot for 0 deck and use the .039 Felpro head gasket on my 493. As said I rock the piston and take alot of readings but I prefer to use the reading that puts the piston closeast to the head. So if I get a reading from -.001 to -.008 below the deck for my piston deck height I will use the -.001 reading. That way I know my quench is from .040 (.039 head gasket and -.001 deck height) to .047 (.039 gasket to -.008). I can get better more accurate redaings to get it closer but I prefer to be on the higher amount of quench when dealing in .001 to .005 of variation as I would rather have a tad more quench then worring about a piston hitting the head. I ended up with my pistons about .006 average down in the cyl on my 493 and with the .039 gasket my avreage quench is .045. But it could vary from .042 to .048 going to the highest reading anywhere on my pistons. In other words I wont run .038 quench nowing with some varyiation it could be as tight as .033. Thats why I run it a tad looser. A profesional eng builder that builds many engines over years every day may run it tighter as they know what they can get away with. Ron

Your shooting for .035 - .045 on it... so get it close
and call it good.... most are putting WAY TO MUCH into
it... take a reading over the pin centerline and call
it good