Testing Compression while hanging from engine crane, need help
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Testing Compression while hanging from engine crane, need help
I have a 7.3 hanging from a engine hoist, I hooked-up starter and batteries (4 of them for good measure and fast crank).
Using a known working digital diesel comp. tester, I was unable to get readings on this engine though I can hear/feel the engine sucking and pushing air (glow plugs out).
Being that this engine timing runs off a CPS, am I ever going to get any reading (same thing that happens when cps goes out on the road).
Number one, two and four cylinders show some small movement of valve springs, the rest just lay there like a dead dog.
I was able to get number one hole to push my gauge to 46 psi. Two injectors are currently removed, but can't see how that would affect comp in other holes.
I just wanted to see if this engines rings/valves held any psi and what kind of life it may have left before I go to the trouble of dropping it into a vehicle.
Any help or tips would be great.
Using a known working digital diesel comp. tester, I was unable to get readings on this engine though I can hear/feel the engine sucking and pushing air (glow plugs out).
Being that this engine timing runs off a CPS, am I ever going to get any reading (same thing that happens when cps goes out on the road).
Number one, two and four cylinders show some small movement of valve springs, the rest just lay there like a dead dog.
I was able to get number one hole to push my gauge to 46 psi. Two injectors are currently removed, but can't see how that would affect comp in other holes.
I just wanted to see if this engines rings/valves held any psi and what kind of life it may have left before I go to the trouble of dropping it into a vehicle.
Any help or tips would be great.
Elder User
Joined: Dec 2009
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From: Fort Campbell, KY
The timing you speak of is for fuel... the intake and exhaust valves are set. Sounds like your cam is broke if your not getting any valve movement toward the rear of the engine. As far as 46pis 
, Napalm wouldn't ignite with that little pressure.
If your hearing a good "air pump" sound, perhaps your gauge is messed up.
, Napalm wouldn't ignite with that little pressure.If your hearing a good "air pump" sound, perhaps your gauge is messed up.
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Used an air compressor to test that the gauge was working. And have oil pan off and watched the crank spin smooth, plus using shop light the cam looked fine along with the timing gears on the front. Any other thoughts?
Elder User
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From: Fort Campbell, KY
Bent push rods, galled lobes on the cam???? If the valves aren't moving, you got some major issues. Try removing a couple rocker arms and press the push rod down on the cam while turning the engine over. If it still doesn't move, your not getting any lift from the cam. Either it's not turning, or there is no lobe.
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From: Kamloops, BC
A little trick to test compression is to take out the glow plug, get a rubber end on a hose and connect it to your air compressor. Now take that rubber tip and push it into the glow plug hole enough to get a good seal. Now inject air into your motor.. When you pull your air hose off the glow plug hole you should get that air that you have just pumped in back out of the hole.. If it just disappears into the crank case and you don't get that air coming back out your glow plug, that cyl is the one you have a problem with ! Follow ??????
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I will look closer, but when I was out there, I could see cam lobes when spinning. Plus, I feel/hear the air pushing and sucking out the GP holes. If the cams are flat, wouldn't that drop my valves shut completely and give me top compression...
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A little trick to test compression is to take out the glow plug, get a rubber end on a hose and connect it to your air compressor. Now take that rubber tip and push it into the glow plug hole enough to get a good seal. Now inject air into your motor.. When you pull your air hose off the glow plug hole you should get that air that you have just pumped in back out of the hole.. If it just disappears into the crank case and you don't get that air coming back out your glow plug, that cyl is the one you have a problem with ! Follow ??????
I am trying to find out why all holes are giving no love. Am I overlooking something obvious here?
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From: Kamloops, BC
Ya you would think you would get something out of one of the holes.. Try the air method just to rule out a gauge or a connection problem with the gauge ???? Just a shot in the dark.. I know my way works.. I just found a dead hole in mine that way !
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From: Fort Campbell, KY
Now with the valves perma-shut, the GP trick with pressure will work for sure, no matter what. You could do this real quick and ascertain if ALL the valves are closed at the same time. Then you'd know, "Houston, we got a problem!"
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So aside from pumping air into the cylinders(which I am heading out to do now), is there any way to get these valves moving so I can run the traditional compression test? Or does anyone else have a way to verify engine health from the rings down?
Elder User
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From: Fort Campbell, KY
Check for oil pressure, make sure there is enough oil in it, and since the GP's are out, let it turn over a bit. Get some oil flowing through the gallies and see if your valves "wake up"
Senior User
Joined: Nov 2006
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From: Raleigh, NC
Have you thought about trying a leakdown test? It may work better for you right now, and give you more useful information if you are wanting to know about piston/ring condition.
Won't tell you if the valves are stuck closed or not, but like said above, i'd bet it has something to do with hydraulic lifters....
Won't tell you if the valves are stuck closed or not, but like said above, i'd bet it has something to do with hydraulic lifters....
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