Newbie at Compression testing

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RamHead72

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Hey guys a couple of weeks ago i made a post asking about the price for rebuilding a slant six. This time i need feed back on compression testing. I have 1986 D100 w/ .225. I was told it was possibly the rings by a mechanic, that i should probably just do a complete rebuild. He didn't do a compression test, dont know why he didnt do one haha. This sucker is burning a quart of oil in 60 miles. The PCV valve is new so its either the rings or the valves. I am just wanting feed back on these readings. Thanks!
DRY- 1) 150, 2) 150, 3) 150 ,4) 155, 5) 150, 6) 150
WET- 1)155, 2)155, 3) 155, 4)160, 5)150, 6)155
 
Dang I wish my 273 had those numbers.

If you are going through that much oil I would assume that there would be a cloud of smoke behind you.

Any oil leaks?
 
Your compression numbers suggest something besides oil getting in the combustion chambers. What did the spark plugs look like?
 
Was this done with the engine warm up first or cold? All plugs were pulled and WOT on the carb during the test? Honestly not bad numbers.
 
Those numbers look good... I don't see a need to rebuild...

Don't go back to that mechanic...
 
When exactly does it smoke? With oil consumption that bad, you must be sprayin the neighborhood for skeeters. Does it smoke hot? Cold? Is one worse than the other? Does it smoke on acceleration? Deceleration? Help us out a little more.
 
I will say this. Those saying it doesn't need rings could well be wrong. If the rings are worn, every compression test he does is a wet test. The rings will be sealing better since they are that worn. That's why his numbers are high. No slant has those high numbers like that stock. Naturally, his wet numbers would be higher anyway, because he's adding even more oil on top of oil already there. That's my theory anyway. A leakdown test will tell the story.
 
RustyRatRod said:
I will say this. Those saying it doesn't need rings could well be wrong. If the rings are worn, every compression test he does is a wet test. The rings will be sealing better since they are that worn. That's why his numbers are high. No slant has those high numbers like that stock. Naturally, his wet numbers would be higher anyway, because he's adding even more oil on top of oil already there. That's my theory anyway. A leakdown test will tell the story.
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That makes sense to me, especially since his wet numbers aren't really much higher than the "dry" numbers.
 
any oily residue in tailpipes?like rrr says, get a leakdown test done, not that expensive and a good tool to have. i had a leaky 340, ended up being the cam thrust plug at back of block
 
As RRR said, those compression numbers are pretty high for a stock used engine. I would confirm they are correct, by using another compression tester, and/or doing the leak down test.
 
RustyRatRod said:
When exactly does it smoke?
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I got talking to a woman in a bar the other night and she asked me if I smoked after sex.... :D

I said that I don't know, I've never looked... :eek:

But I have smelled burning rubber a few times.... :rolleyes:
 
RustyRatRod said:
I will say this. Those saying it doesn't need rings could well be wrong. If the rings are worn, every compression test he does is a wet test. The rings will be sealing better since they are that worn. That's why his numbers are high. No slant has those high numbers like that stock. Naturally, his wet numbers would be higher anyway, because he's adding even more oil on top of oil already there. That's my theory anyway. A leakdown test will tell the story.
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Learning here as usual. What does testing wet mean?
 
Troub said:
Learning here as usual. What does testing wet mean?
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Putting two or three squirts of oil from an oil can in the cylinder before testing... Always test dry first, then wet...

The oil will fill the gaps between the pistons and rings and if the numbers increase with the oil in the cylinder, then the rings are most likely the culprit that needs to be replaced....

If the readings are the same or real close from wet to dry on the same cylinder, then look at the valve seats and seals for the leak....
 
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