951 Cylinder Decking


Active Member
I have two 951 carb engines I am assembling, and both are about .090 squish with a head gasket installed and no base gasket. I think the spec is .067 to .091. One has a WSM crank, the other is SeaDoo. Pistons in both engines are WSM. Based on what I know, I need to deck them about .030. This sounds odd and seems to be a lot of aluminum would need to be removed. Thoughts?
The few times I've done squish tests they are always out of spec. I got .68" on my first 787. Compression was great when measured and the ski runs great. If you tighten up the compression you are gonna load the engine more. My theory on WSM pistons is the dome shape may be different resulting in a different squish reading but the same compression result (just a guess on my part). I'm always at are above 150psi when I do engine tests. I complain more about the ring gap not being spot on but I guess that is a growth issue. Compression is always good so I don't worry about at all.

You'll never notice it and you'll save yourself time and money.