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Engine compression tester

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AutoAnglaise

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Hi !

I do not know if the better place for this topic is "Tools" forum or this "Austin Healey" forum. It is for an Austin Healey so I post here, sorry if it is the wrong place.

I would like to check the engine compression of my BT7 1960. I have the tool and I would like to have advices from persons who have already done the operation.

Thank you !
 
The compression check should be done with an engine that is warm. So if you can run it, get it to temperature, and then turn it off. Remove all of the spark plugs. Put the compression tester in the first spark plug hole and being careful not to let the fan catch anything, crank the engine for 4 or 5 seconds (a good battery helps here), do this with the throttle wide opened, so as not to restrict the intake air. (You can do this with the starter solenoid button in the engine bay if you have one, and open the throttle by hand on the linkage). Your tester should have a check valve in it so it will hold the highest pressure reading you get. Do the next cylinder and so on. There are threads on this site, if you do a search for compression test, that will help you interpret the readings you get. All cylinders should be within a few PSI of each other, and you like to see readings over 130 PSI. You should read the other threads for more information. Hope this helps.
 
Here is a trick if you have a low cylinder or you want to check the rings in all cylinders. After you have taken a reading in a given cylinder squirt an eye droper amount of oil in the test cylinder and if the reading comes 10#s or more you have leakage blowing by the rings. If the cylinder is still low then the valves are in question. What is the reason for the test?
 
roscoe said:
do this with the throttle wide opened, so as not to restrict the intake air.
Click to expand...
Would holding the throttle open on CV carbs make a difference? Seems like the pistons would still be down with the engine only turning at starter speed.
 
Greg,
probably not, but if I hadn't mentioned it someone would have said "be sure and have the throttle opened when you do this". I honestly don't know, and most of the time I do a leak down test because I can.
 
Curious is a good thing. If you are really curious a differential or leak-down test can tell you much more.
 
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