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MG MGA - How much compression

I went over to a friends house to help him get his MG to run. He has been having trouble getting the car to run properly. Now it will not start at all. It is getting spark and fuel so the next thing I did was check the compression. He has only 92 pounds in each cylinder. Is that enough for the car to run? When I checked one of my cars last it had 130 in each cylinder. He claims the car has been running ok but not well but why would it now not run at all? He is not sure of the mileage but he thinks it is over 100,000 miles. My question is how much compression does a car need to run?
GK George

The engine is probably flooded so badly that the cylinder walls are washed down. Oil the cylinders, recheck the comp it should come up, then try to start it.
I have seen cars so fuel fouled that the oil was 2 quarts over full with gas. These cars needed a oil change before they would start.
Typically the limit at the bottom is 100 psi any lower wont start or run well.
R J Brown

Hi GK. 92 pounds of compression is a bit low, but the engine should run, especially if the weather is warm. An engine needs fuel, compression and properly timed spark to run. You say the engine has fuel and spark. It also seems to have adequate compression. So it SHOULD run. Being Devil's advocate: Is the fuel fresh? Is the fuel actually reaching the carburettors? Is the spark occurring at the correct time? If the distributor has been removed or rotated, the ignition timing could be way off, which would keep the engine from starting. Before doing anything else, try installing a new set of spark plugs and a new distributor rotor. THese parts are inexpensive but often cause starting problems. These would all be good things to check before digging further. Cheers, Glenn
Glenn Hedrich

I agree that 92 psi should get 'er running provided it is 92 across the board. The engine probably won't run strong being so low.

Dry plugs, a shot of oil in each cylinder and a "light" shot of ether at the carbs should get it to fire provided everything else is in order. Too much ether could cause cylinder wall damage but it sounds like it is time to re-ring at a minimum. If it won't stay running, it is a fuel problem. Drain the bowls and check the quailty of the fuel coming from the tank.
Chuck Schaefer

This thread was discussed between 18/08/2009 and 19/08/2009

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