Compression Service Limit

[brinks]

Can someone verify the expected compression test result for a stock '76 2.0 with a 7.6 compression ratio? Also, what would the lower service limit be before considering a rebuild? Thanks...

[Dave at Pelican Parts]

The exact compression pressures vary with things like the state of charge in the battery, the health of the starter, the altitude, etc. So you'll only ever have a rough idea of what the numbers "should be".

Mr. Haynes tells us that the lower limit is 100 PSI. I think I remember that a typical "fresh stock engine" number is around 145 PSI, but I'm much less sure on that.

--DD

[brinks]

DD: Thanks for your feedback...

The seller states: "All are within spec. Brand new they should be about 105psi. These are all in the mid 90's except number 2 which came in at 92."

So what am I missing? This is a '76 2.0, which has a 7.6 compression ratio, which is less than other 914 engines at 8.0 CR. Could this explain the difference in the Haynes manual that you reference?

In your opinion, is this 2.0 a candidate for rebuild? Top end/bottom end, or both?

[76912E]

My '76 912E Porsche Workshop Manual for the 2.0 L engine (7.6 to 1 compression--same engine as the 914, different FI system) states the compression pressure (with open throttle and engine at operating temperature, all spark plugs removed, practically no blowby with gauge in spark plug seat, engine cranked by starter motor) is:

New: 121 - 156 psi

Wear Limit: 92 psi

Difference between cylinders: max. 21 psi

Depending on the test conditions (as stated above), I think that engine is at the low end of its service life and may be due for some sort of rebuild.

Fran

[Dave at Pelican Parts]

I'd say that it's a candidate for at least a top-end. But once you've taken it apart that far, it's not that much more work to tear it down the rest of the way. And while you're in there....

--DD