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Compression test


ricksrb
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You can probably get buy for a while. From what I have seen others post about compression, it seems that when it gets down to about 95 is when they want to quit running or run and start poorly. You probably need to start to look for a gap in y our life in which you pull your engine. If you get underneath it and tear out the frame member that keeps you from getting the oil pan off like I have, then you can rering it without pulling the engine. Replace the frame member with a goog tough bolt in member, Since I did mine, I have had my pan off several times and once its done your glad you did it for ever more. The last time I pulled my transmisson, I also did so without pulling the engine. Just slid the engine back about 3". Saved a lot of time. What oil do you run.

Lenny

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so it does sound like the rings to you? i did a search earlier and read about you doing that to the cross member. So i guess i can order the all i need from JMC right? I have been running mobile 1 oil.

didn't silverbullet work on your motor not to long ago?
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Okay, a bit puzzled now. I did a leak down test last night. I found that on #3 i have air coming from exhaust and nowhere else so that tells me exhaust valve. On #4 which on compression test showed 120 lbs same as #3 i could not hear any air coming out anywhere. I checked exhaaust, intake, oil fill on valve cover, and radiator for bubbles. In fact pressure was building up so much it started leaking air from fitting going into spark plug hole. Just to make sure i repeated 4 times with same results. Any thoughts?

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Are you doing the leak down test with the exhaust manifold removed. The intake should be treated the same so you can positively issolate each port. Sounds like valves will need to be worked based on #3. The complication with doing valves is the shims. You may be able to have your valve guy cut the valve stem the same amount he seats the valves farther in. Other wise you will have to have the shims replaced, correct replacements could be difficult to find, or regrind their thickness. When I put in the torque cam,I reground the thickness on mine. I was able to use some of the original shims because they were either rtight or needed to go thinner. On the rest, I used standard 25mm shims that were thick enough to grind to size. Having the machine shop make a custom collet to hold the shims in the lathe is real simple. A surface grinder with a magnetic chuck would work too. You could redo the valves and put the head back on, run it a bit to seat the valves and recheck the compression. If you have to tear it down, taking the head badk off and putting it back on is not too bad now that your valve shims are set to go. Just be sure to keep track of what went where. Still havn't found pictures for the under engine frame change but will. Going out of town for the weekend. Leaving about noon today so I'll do it when I get back.

Lenny

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one when you did the compression test did you make sure the compression gauge fitting was tight on all four holes? the smallest leak can give you major different readings... second when u pressure tested number 3 was the piston at TDC? the exhaust valve may have been open... on a compression test all cylinders should be within 10% of each other

Josh

No Limitz

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Goingdeep. are you doing your compression test turning the engine manually to TDC? When I do mine, I crank the engine over with the starter and let it pump up the gauge. For those that arn't familuar with a compression tester, thsy have a valve stem type check valve in them so they can be pumped up and will hold the pressure. With a leak down test, you of course would turn it manually to TDC or close to it.

Lenny

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try and answer all at once.

Lenny,

No it was with exhaust manifold on. I hate the thought of messing with the shims from all i have heard from you guys.

goindeep,

yes i made sure it was tight. I did compression test on all cylinders two or three times. On the leak down test i made sure it was at tdc each time i did it.

nocturnalsixer,

yes, i also made sure throttle was wide open.

whats puzzleing me is the #4 now.

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did you try a wet compression test or just a dry ? BTW if you ane not sure what a wet is I will explain. First off are you disconnecting the fuel pump relay ? If you leave it in the injectors can wash the cylinder down.

Try a wet test, jake a cap full of oil,or the old oil cans with the pump and tip and squirt a few shots of oil and then spin it over with the gauge in it. Th oil will seal up the rings.

Also a compression test should be done at operating temp due to expansion, mind you I have done them cold also. You could warm it up then recheck it

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