Deck height question with JE 90mm 9.5:1 Pistons.

tornik550 · 01-02-2015, 11:17 AM

I am changing my setup from 2.7l pistons/cylinders to JE 90mm 9.5:1 Pistons. I have a 2.7l crank. I am basically using the same heads as I had previous except the heads I will be using have been flycut .20mm LESS than my old heads. I do not know how much they have been flycut from stock.

With the previous setup, I had 3x .25mm cylinder base gaskets. I mocked everything up and placed some acid core solder on the Pistons as described in dempseys book. I started with the 3 base gaskets that I previously had installed. I tried to crank the engine to crush the solder however I wasn't able too. the solder was completely smashed on the flat part of the piston. Obviously I need more shims. Has everyone else had to increase the amount of shims when using the 9.5:1 Pistons?

Also, do I measure the deck height on the domed part of the piston or the flat part or whichever is thinnest?

VFR750 · 01-02-2015, 12:50 PM

Many variables at play here. Was the case machined too?

Rods compatible? Not too long?

Take a picture with the head off, and the piston at TDC. What does it look like?

The clay method was suggested as a poor alternative to the solder, but maybe for you, clay might give an indication as to how bad it might be.

I think competition engineering a sells thick cylinder base gaskets.

3literpwr · 01-02-2015, 03:01 PM

If you are running JE domed pistons, you should be checking from the outer lip of the piston. I was not able to get an accurate measurement with the solder method and just used calipers. My deck ended up being 1.1mm on my 10.8:1 pistons. My actual comp ended up being 10.65:1 with 91cc heads

snbush67 · snbush67's Garage

Use thicker base gaskets, go up in increments of .25 until you can at least turn the motor over without solder.
If you have to use over 2mm to get the right clearance and the right deck height than something else is likely wrong, piston pin spacing, wrong pistons, etc.

tharbert · tharbert's Garage

I kinda asked this question a while back. One thing that was suggested to me... You don't want to use more than a couple shims. Find shim height you need and get custom shims made.

tom1394racing · 01-03-2015, 06:03 AM

Don't confuse deck height with piston to valve clearance.

Measure deck height with the head off using the depth gage feature on your vernier caliper. Measure along the piston edge at four locations 90 deg apart around the perimeter. Use a dial indicator to ensure the piston is at TDC. You should also measure the dome and combustion chamber volumes to check the CR. This will tell you the base gasket thickness needed.

Measure piston to valve clearance after the heads and cam towers have been assembled and the cams have been timed. Use the method described in Wayne's book where the valves are screwed in until they make contact with the piston.

tornik550 · 01-03-2015, 11:27 AM

So I was able to get a deck height of 1.45 with 8 x .25mm shims. The only two things that have changed with my setup is the pistons and cylinder heads. With 2.7 cis pistons and my old heads, there were only 2x .25mm heads. Does this sound right or scream out any problems? Fyi- I have JE pistons pn 261663

Also, what are my options for shims? Only place I am aware of that has thick shims is competition engineering.

tornik550 · 01-03-2015, 11:29 AM

Also- I have a 2.7 crank, 2.7 rods and cylinders. My case HAS been machined.

VFR750 · 01-03-2015, 11:39 AM

Sounds like you need a 1.9-2mm thick shim.

If it were me, I'd do some more checking on the case, cylinder, head, and cam housing.

The concern would be: will the hole (and cam shaft seal) in the cam chain box line up with the end of the cam?

It's tough without knowing all of the measurements that make up the assembly.