MTFCA Forum

My second engine Ive built for my 21 touring ( damn broken crankshafts) was rebuild by someone decades ago and shelved, So naturally I go through it to make sure its was built well. Well it wasn't, cylinder clearance too tight, bearings too tight but Ive sorted that. However the 0.080" Pistons seem to stand proud a good amount more above the block deck than my last two engines at TDC. So much that the Z head ive put on that past two engines hit the pistons with about 0.120" of interference, Way too much to grind from the head chamber.
I put the Pistons on my mill and shaved 0.100" off the tops and re balanced them, still piston 2 and 3 hit the head, so ive ground the chamber about 0.030" and checked with some Playdoh for what my quench is. About 0.25" between the pistone top and the chamber. Engine runs well but sounds like there is a Bit of Pinging if the advance lever is more advanced than level with the floor.

I'm not comfortable with taking more off the pistons or head, another option is to cut and shorten the rods I suppose, I am a professional fabricator but it seems extreme. Is there an extra thick head gasket available or could I get away with adding another Copper gasket? I know doubling up any gasket is generally a No No. Have you gotten away with this?


Thanks - Wolff

In my experience, the Z head has inconsistent combustion chambers & require a bunch of milling to fix. That & their propensity to corrode quickly, I would get rid of it & get a Prus head. You are putting a lot of effort to use a lousy head. Shortening the rods is a silly idea.

If you have .025" clearance BEFORE the head gasket, you are fine.

To answer your question, I have not doubled a T head gasket. We are after more compression, not less.
I have doubled up on a vintage harley head gaskets for clearance issues. Much higher compression. Still running after 20 years, so I dont see a problem doubling on a T.
Again, I would reconsider the use of that head.

The pinging could be from an over advanced condition. Recheck your timing.

If you are getting detonation, back off on your spark advance. Your .25 clearance should be plenty. How much total advance are you running now? If much more than about 25 degree,s timing might well be your problem.