64 Ford 289 leak down test

callbald

callbald

Senior Member
In reading various instructions on doing the test, I do not see anything about engine temperature. Should the engine be warmed up?

As to why i am doing the test, I have oil on the spark plug threads and the valve cover seals are not leaking. Thinking it may be valve stem seals, I want to do a health check to see if there are more problems before diving in.

Some one thought I could be seeing fuel on the treads, but there was no fuel smell. Side note, I did have one massive backfire this past summer with raw fuel getting into the muffler and blowing it apart.
 
I do differential compression tests all the time on the aircraft engines. They are generally better if the engine has just cooled down a good bit from a run up. I do them cold but if a cylinder is low on pressure then I have to run it and recheck it warm so I try to do it warm to begin with.

I would suspect a power valve problem when I think of internal carb leakage but it depends on which carb a person is running.
 
I generally do a leak down test after the engine is warmed up. After a drive and engine has cooled enough where you can work on it comfortably. Leave all plugs in engine except the cylinder you are testing and try to have that piston TDC. 15% is or less optimum very much over 20% or more may be cause for concern.There may be as much as 10% difference between cylinders. Just like a compression test is performed on a warm engine I feel a leak down test should also be performed on a warm engine.
One thing you may check that I have seen on higher mileage Ford engines is the oil return holes on the back of the head can get gummed up and cause oil to run down the valve guides
 
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If the leak down goes good, I'm going pull the valve covers and clear out the oil return drains, which is no problem since the valve cover gaskets are steel enforced and go from there.

I did a compression test on the 289 getting 168-175#'s across all cylinders and the spec range is 130-170.
 
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