Compression Test Results 160/210/210/210/210

da7 · Post by **da7** » 13 Jun 2011, 10:27

Hi Guys and Gals, while troubleshooting my fuel economy problems, I'd thought I'll go and do a compression test... I knew I should've done it before I went ahead to spend hours and $1500+ on other things... now I'm worried...

the Haynes Manual suggests Rings and/or Camshaft Lobe...

I don't think it's rings, as I never noticed any puff of blue smoke, not losing oil... other cylinder seems to be in top condition at 210... teaspoon of oil in spark plug hole didn't seem to make any difference...

do you think Camshaft Lobe wear is possible? The car have probably been neglected previously for oil change... haven't taken the rocker cover off yet... hoping I don't need a re-cond head, as the camshaft will probably cost more.... engine supposedly have 80,000 miles....

any chance that it will be something simpler? Somehow it seem to have gotten up to 200-210 when I first did the compression test, but I had to crank it about 10 revs, but after I went through the cylinder #2,3,4,and 5, and back to #1 for a second run, it refuse to go above 160 no matter how many times I crank it.... any ideas? Any comments will be greatly appreciated! Thanks...

Post by **JRL** » 13 Jun 2011, 12:06

You can't have 210, that's just too high

Post by **erikv11** » 13 Jun 2011, 12:34

No, if his gauge is off just a little, 210 is totally normal for an NA, check his sig/nameplate. 200-205 is typical for an NA in decent shape.

Now, about the OP's actual question: one hopeful possibility is a sticky valve. You could try one of the cleaning methods, seafoam in the intake for example. More likely is the exhaust valve is burning/cracking due to leaky valve stem seals.

Post by **JRL** » 13 Jun 2011, 13:01

Well 160 is nothing to sniff at either
I would try a SEAFOAM treatment before you do anything else.
It may just help whatever may be stuck in that cylinder and for 10 bucks and a 1/2 hour of your time, what have you got to lose?!

da7 · Post by **da7** » 13 Jun 2011, 20:49

thanks Erikv11 and JRL, I was hoping for the same thing, that it can be fixed by cleaning... but I sort of did some treatment to it couple months ago... and was wondering if it's got to do with the fact that cylinder #1 is the hardest to reach to via the intake manifold, I want to try cleaning it again via the left most vacuum connection, but it may be a bit hard to reach to... but if I can't reach it, I'll do the cleaning again via the manifold and test for compression again later...

so do you think 160 is something I should be worried about? so assume the gauge is slightly off,and the actual readings are 150/200/200/200/200, then cylinder #1 is about 25% lower than the rest, there is a slight rough idle more noticable while cold, but engine still got decent power....

what I don't get though, is if the camshaft lobe is worn, how does it affect compression? As I thought the camshaft is only there to push against the spring to open the valves? If it's worn, shouldn't the only effect be that the valve doesn't open as much? Rather than not closing properly?

Post by **Ozark Lee** » 13 Jun 2011, 21:43

I have never heard of a bad lobe on a cam on the white block engines - I'm sure it has happened to someone but I have never heard about it.

I had, as my fuzzy memory recalls, a B-20 (FI) engine on my 142GL that had a couple of lobes that were completely round but that engine was a completely different animal. I bought the car from Don Pepe who was Aristotle Onassis' personal chef on his yacht before he opened a restaurant next door to my apartment in Kansas City. I think he worried more about that nights menu than he worried about oil changes.

It was an interesting night when I started to change the cam at around 5:00 PM and I had to be in class at 8:00 AM the next morning for my differential equations class. Thank God it wasn't for an exam that morning. I made it a habit of showing up for all exams through college wearing a coat and a tie along with a pair of wingtip shoes. That morning I was covered from head to toe in grease and oil wearing a set of "work on the car clothes" that were riddled with holes since I finally got the timing right and the car would run at about 7:15AM.

...Lee

copandengr · Post by **copandengr** » 13 Jun 2011, 22:33

I can't comment on other causes for your bad compression results except for the following, which is universal among all piston engines...

Putting oil into the cylinder will temporarily raise the compression if the problem is worn or broken piston rings. The fact you are not seeing smoke is irrelevant. If the oil does not raise the reading then the problem is not the rings.

Think of a worn cam lobe like a garden hose with the nozzle partly closed off.... You are not going to get the maximum amount of water from the hose that it is capable of flowing... The same thmg is going on with a worn cam lobe... It is not opening the intake valve enough to allow all the air into the cylinder, therefore you will have a lower compression reading. There was not enough air in the cylinder to compress to the proper pressure.

I'm afraid you have a bad head. That is going to be a major repair.