compression test question

[matt gineo]

Is it possible to get an accurate compression test reading on cold engine that has only been started a few times in the past 15 years? 76 targa 2.7 The valves have not been adjusted in 15 years either. My mechanic did the compression test and said one cylinder was 85. Engine has not been started yet.

[yelcab1]

Not really. When things sit that long, it is really not conclusive what the results are. You should start it up, drive it a few hundred miles, and test it to see if you are lucky or not. If not, well, you have not lost anything. Getting it to start may be difficult.

[911pcars]

MHO. Valves don't wear when they sit. However, if the chamber was subject to dampness, rust could form and prevent an open valve from closing correctly. If stored indoors, less likely for that to happen.

Usually, the lube on the cylinder walls isn't sufficient. Try squirting some oil in the spark plug hole, then retest. This doesn't preclude corroded rings that stick in the ring lands, negating their primary function.

In addition, make sure the engine rotates at normal crank speed. A tired battery or starter motor will crank the engine more slowly and decrease the compression readings.

Sherwood

[HawgRyder]

Also...when making the test...wedge the throttle plate open with a tool or piece of wood so that all the cylinders will get the same amount of air.
I have seen tests done where the guy in the seat pushed on the gas pedal sometimes and not for others...the readings were all over the place.
And...plugs out...all cylinders....once again...for continuity for all cylinders.
The oil thing is ok...but I would try with it dry the first time...and then spray a littl oil into each cylinder as you test that one.
If the numbers go up...it might be the rings are not sealing properly.
It's a judgment call with this test...everyone has their own method.
Bob

[matt gineo]

Thanks for your replies, great info!!