Lack of compression

Kelly914 · 04-29-2008, 03:54 PM

I have a 914/4 2.0l with Webber carbs. I bought it last October and ran it for about 100miles no problems. This spring I took it out of storage and changed the oil, oil filter and spark plugs. It ran fine for about 30 miles, then slowly began to stall at idle with the engine either cold or hot, then suddenly it began to backfire, and seemed to run on three cylinders. I did a compression test and am running 120, 90, 90 & 70 psi with the engine cold and the throddle wide open. While doing my compression test I found a rag in the fan rotor! I'm afraid I may have fried the engine. How little compression is too little compression? Has anyone else had a similar experience? I tried starting then engine with one ignition wire unplugged at a time, and it doesn't seem to run any worse with either the 1, 2, 3 or 4 cylinder unplugged. Could it be as simple as an ignition problem?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Re-do the test with the engine warm. If you still have cylinders under 100 PSI, and you're not in Denver, you're probably looking at a top-end rebuild to get the compression back up again. A 50 PSI difference between highest and lowest is also not a great sign, but see if it improves when the engine is warm.

Check your valve adjustment as well. And make sure the battery is charged, and the starter is cranking at its "normal" speed. Those will all affect compression test numbers as well.

--DD

Kelly914 · 04-30-2008, 06:00 PM

Thanks for the reply Dave. I can't check the engine warm, because when it starts it runs like a bag, and backfires big time. Right now I'm looking for a cheap leak down tester. This week end I'm going to try and drain the engine oil, and fill it back up with 80W90 gear oil, then do the compression/leak down test again. When I drained the oil during my maintenance, then engine was warm, but still I remarked that the oil was thick. I suspect the previous owner filled it with super heavy weight oil to keep it running, and sell it. If the 80W90 boosts my compression, then I know I need rings. Thanks again for the reply!