Compression Test Results
Thread Starter
|
New User
Joined: Jul 2000
Posts: 15
Likes: 0
Compression Test Results
Ran the test earlier today on the '77 351M with 106k original miles. It's been sitting in a field for years, but supposedly ran OK when parked. It sounds pretty decent, but smokes badly (sometimes). Anyway, here's the score:
cyl. max.psi. comment
1 100 leaks down fast
2 125 leaks down fast
3 100 leaks down slow
4 100 leaks down slow
5 125 leaks down fast
6 125 leaks down slow
7 125 leaks down slow
8 125 leaks down fast
This is different from any I've run before- by leaking fast, I mean gauge drops to almost nothing within 10 sec. after cranking. Would this be an indication of worn rings, or valves? Is there any way of knowing without full disassembly? Strange how the max. psi does not seem to be related to the leakdown rate.
Any ideas or comments? I'm still hopeful that some running might free a frozen ring or two, or maybe a lifter, and start running well enough to avoid a rebuild. Any chance?
Bob A
'77 F-150 4x4 "the project"
cyl. max.psi. comment
1 100 leaks down fast
2 125 leaks down fast
3 100 leaks down slow
4 100 leaks down slow
5 125 leaks down fast
6 125 leaks down slow
7 125 leaks down slow
8 125 leaks down fast
This is different from any I've run before- by leaking fast, I mean gauge drops to almost nothing within 10 sec. after cranking. Would this be an indication of worn rings, or valves? Is there any way of knowing without full disassembly? Strange how the max. psi does not seem to be related to the leakdown rate.
Any ideas or comments? I'm still hopeful that some running might free a frozen ring or two, or maybe a lifter, and start running well enough to avoid a rebuild. Any chance?
Bob A
'77 F-150 4x4 "the project"
Senior User
Joined: Apr 2000
Posts: 192
Likes: 0
Compression Test Results
When an engine sits ( in a field ) moisture will set in and cause some surface rust on the internal parts of an engine. You probably have some rust on the valve seats where they were open while sitting. I think if you get some kind of cleaner to pour in the gas tank to see if you can clean the valve seats (without removing them) that it will start running better. Just driving around can sometimes clean them up also. What ever you do dont try and clean out the engine with anything like Marvel mystery oil, or the like because with an engine with alot of miles you could possible clean it to good, and cause it to start knocking ( personal experiance ). I also think that by running it will free up stuck rings. Put some fresh oil in and drive it, just see if it clears up. I hope to help, good luck. Rob
Elder User
Joined: Dec 2002
Posts: 639
Likes: 0
From: not mass
Compression Test Results
the techtron is suppose to be the best
but you would be better to put air pressure, a tank should work if not near compressor, if the engine doesn't turn by hand you can loosen the rockers to close the valves if with the engine holds with the valves closed and the sprk plugs in and doesn't come out of the oil fill or water fill neck pull the ajacent plugs to check the head gasket
this should tell you where the leak is may have to fill a tank more than once if using a compressor keep it as far away as possible to keep the noice down
but you would be better to put air pressure, a tank should work if not near compressor, if the engine doesn't turn by hand you can loosen the rockers to close the valves if with the engine holds with the valves closed and the sprk plugs in and doesn't come out of the oil fill or water fill neck pull the ajacent plugs to check the head gasket
this should tell you where the leak is may have to fill a tank more than once if using a compressor keep it as far away as possible to keep the noice down
Posting Guru
Joined: Dec 2002
Posts: 2,003
Likes: 2
From: chicago burbs
Compression Test Results
doesn't your gauge hold it's reading with a shrader valve that you have to release to reset the gauge for the next reading? i've never heard of a compression test gauge giving leakdown readings.
