Low compression cylinders 2 & 3

[REHolder]

Been having problems with my 77 Spider so I pulled out my 40 year old compression gauge. Cylinders 1 and 4 read 150 PSI, cylinders 2 & 3 only read 50 PSI. Is this a blown head gasket?

[Nut124]

Since it is two adjacent cylinders, the most likely cause would seem to be a head gasket failure thru the narrow land between bores 2 and 3.

[SteinOnkel]

Spray some lubricant ( like Fluidfilm) into the bores. Try to get as much as you can onto the outside, you really want to coat your cylinder walls. Then let it run down for a few minutes and crank the engine by hand so it will end up around the rings.

Now recheck compression. If it goes up significantly (like +20-30psi), your rings are shot.

I've got a similar issue on my other car. Compression from 1-4 is 225, 60 (!), 185, 215. #2 goes up to 90psi with above mentioned treatment. 99% sure it's due for a rebuild.

Only way to know with absolute certainty on both our engines is to do a leakdown test OR pull the head. At which point you need a new cylinder head gasket anyway and your question becomes moot. Mine is in a car that is raced and the bottom end has 140k hard miles on it (Autobahn and Trackdays), so I'm just going to rebuild the whole thing.

Cheers
Steiny

[REHolder]

Thanks for your comments and pictures! Just wanted some validation from other Spider owners that my hunch was on target.