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Hey folks,
Im going to try this one again as I received no response the first time: Does anyone know what the " normal" or "standard" compression on a '78 Spider should be? Nothing in any of the manuals I have list the compression.
Thanks for the help.
 

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Bill -
I'm not sure of the "normal" compression, but I think in the range of 150-170 would be about right. Compression will vary, of course, with the condition of the motor. The most important thing is that the cylinders are relatively even. Within 10% of each other seems to be accepted norm. The compression in my engine (74 2000cc) is 140-150, which I believe to be about "normal" for it's mileage. A newer engine will probably be more. A badly carboned-up engine may be higher as well. Do a compression check, engine hot and throttles wide open with a fully charged battery and spark plugs out. Then try it again with a bit of oil squirted into the cylinders. If the compression improves dramatically, then the rings are probably worn.
 

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If you get much below 120, that a pretty good sign that a rebuild is coming. The "wet" cylinder test can perhaps help pinpoint the primary problem to valves or rings. If the compression is really low and wetting the cylinders doesn't help much, it's probably leaky valves, probably exhaust. To check for sure, you have to remove the cylinder head, turn it upside down, and fill the valve areas with gas or kerosene and see if they hold liquid. Of course, by the time you get the head off, it's probably best just to have it redone. Usually you'll need all new guides and seals, and new exhaust vavles, plus a clean up on surfacing.

Be sure to meet the conditions I set out above, especially throttle WIDE OPEN, or you'll get a low, and false, reading.
 

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Trained (ex)Professional, , 1953-2018 RIP,
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I would also recommend that if the car is fuel injected, either Spica or Bosch, to pull the fuse or relay that powers the fuel supply pump. Eliminates a possible explosion hazard.
 

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Good point Jim. On a SPICA system you can pull up the trunk mat and disconnect the connector to the fuel supply pump. I've never had too much trouble with excess fuel being shot into the intakes, but disconnecting the fuel supply pump is quick and easy. No reason not to for the additional safety it affords.
 
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