Sealing heads

[neilca]

I built a 100mm x 66mm type 4 engine. I had lapped in the cylinders to the heads and yet 3 out of the four leaked. I have pulled the engine apart again. Now, how do I get these heads to seal?

[Dave at Pelican Parts]

Make sure they're round, for one thing. Make sure the ends are parallel to each other, and perpendicular to the bore, for another. Check that the registers in the head are flat and co-planar with each other. And check that the surfaces in the case that the cylinders seat to haven't started shifting or collapsing.

The large cast-iron cylinders are not known for being super-high quality, BTW. That's why measuring them is critical.

--DD

[neilca]

My cylinders are birals, heads have been resurfaced. I will check the deck next. What about copper Orings for head gaskets.

[Dave at Pelican Parts]

Copper O-rings will crush and need to be re-torqued. Possibly periodically. They are not usually recommended any more; they were slightly better regarded about 20 years ago but not now.

Birals do not guarantee a quality product. Some of them have had mediocre QC, while some have been of good quality. I'm not aware of anyone who makes them at the current time for 914s. It seems like the Nikasil-plated cylinders don't cost an immense amount more to make, and don't have to worry about proper crush fit and so forth. If all the case and head measurements pan out, it might be worth considering getting a set of Nickies...

--DD