beginning the evaluation: compression

[o0sara0o]

We're a couple of Spider newbies. Just yesterday posted our story in the Intro section.

1979 Spider 2000, carburetor. Neglected for years, abused when it was running. How do I know this? You should see it--you just know. (Craziest evidence so far: exploring front brakes, we find only one pad on the right side. Wear pattern shows caliper squeezed directly on the pad-less side of rotor for quite a while. Alright. Next, left caliper comes off and three--THREE--pads tumble out. Prize to anyone who can explain this.)

Anyway, first engine diagnostic (after verifying spark, of course) is compression test. First day, it's 120-120-50-120. Pour oil in #3, goes to 80. Darn. Couple days later, we try again--I desperately do NOT want to do a major rebuild here. Now, #3 goes to 180! How is that possible? Other three are all over the place, 120 to 160. Now I question my compression tester, wonder if I should get a new one. We pull off the camshaft covers to check the action under there. Everything seems to be fine, shafts are spinning, lobes are pressing, we check the alignment marks on the timing belt--seems very close, if not right on. Today, a week after pouring the oil into #3, all four cylinders are showing around 140-150.

In an engine with an unknown and dubious history, are we naive to think we DON'T have to pull off the head and at least visually inspect the condition of the valves, seats, and pistons? And what explains the high compression results? Isn't 120 about where we should be? Do compression tests vary when all the plugs are out and the camshaft covers are off? Or does this all point to a couple or 8 burned valves?

Thanks for any advice.

Andy (and Sara) in Bluffton, OH

[manoa matt]

As with any test, the accuracy of the results depends on the frequency of the input data = the more more compression tests you perform the more accurate your results will be. You can check the accuracy of your compression tester with an air compressor set at a regulated PSI.

Have you been running the engine at any time?

"left caliper comes off and three--THREE--pads tumble out. Prize to anyone who can explain this.)"

They used rear caliper pads as they are about 1/2 as thick as the fronts. Do the pads have a small nub on the back side?

[majicwrench]

If your compression is all relatively even no need to do anything. NOthing wrong with 140-150.
Why the low cylinder initially?? Who knows, anything from stuck valve to bad gauge to improper testing.
Does this thing run??

[SLOSpider]

Anyone that has owned a Fiat knows its common practice that if your brakes pull to one side to remove that pad and put it on the weaker side to compensate.

If not running for awhile then the rings could be stuck shut or some debris/rust may have been on the valve seat that remained open #3 while sitting. Best thing is to check your valve clearance and if that is ok and compression is 120+ your should not need to pull the head. I would recommend a new timing belt before its ran for too long.