Burning oil and compression test results
 

Good localtime forum friends,

I created a post a couple weeks back (http://67-72chevytrucks.com/vboard/s...d.php?t=733313) regarding my 64 C20 (283), and how she appears to be burning oil to the tune of a quart every 50 miles or so. I performed a compression test this weekend on a cold-ish engine and here are my results:

1. 120 PSI - 6 revs
2. 125 PSI - 6 revs
3. 125 PSI - 6 revs
4. 130 PSI - 5 revs
5. 125 PSI - 5 revs
6. 125 PSI - 5 revs
7. 130 PSI - 6 revs
8. 120 PSI - 5 revs

I performed the above test with a couple of squirts of oil added to the chamber, and the numbers were similar, though it often took 8-10 revs to max out pressure.

So my question is, do these number make sense if I am burning oil? I thought for sure I would be low on a cylinder or too, but these numbers look pretty awesome. I have white smoke coming out of my pipe when I drive her around and I do not seem to be leaking a lot of oil. What could be the culprit?

I learned this weekend that I def have matching numbers, and I know that doesn't matter so much for old trucks, but I would like to fix my stock 283 instead of throwing in a 350 crate.

Re: Burning oil and compression test results
 

pull all the plugs and redo the test with 3 second cranks or 3 revolutions. maxing out is not accurate. and no oil squirts either.

Re: Burning oil and compression test results
 

I also noticed the plug #2 was completely different than all the other plugs, see attached. I am assuming it is a "performance" plug the previous owner had and just threw in.

Re: Burning oil and compression test results
 

4 revolutions is the norm. You can crank it ten times and it won't show any more than the normal four.
Use oil for a wet test to check for rings sealing.

Re: Burning oil and compression test results
 

Your numbers look low (due to your elevation)but are all within 10% of each other.
The important number is the first crank. You like to see at least 75-80.
Your wet test shows your rings are good.
Oil leaks.
One oil drip every 100 feet equals a quart in a 1000 miles. Multiply yours.
What do you have for a pcv system?

Re: Burning oil and compression test results
 

I did both dry and wet tests for each cylinder. I had my wife turn the engine over until the pressure was no longer increasing, but the difference between the 4th, 5th and 6th cycle was about 10 PSI max (maybe 8 from 4-5 and a couple from 5-6).

My shop book says I should be at 140 PSI or so.

Re: Burning oil and compression test results
 

Not at your elevation.
Air density effects it.

Re: Burning oil and compression test results
 

Makes sense. I know I had to re-jet my bikes to get anything remotely resembling power out of them sense we are at about 6700 feet.

Re: Burning oil and compression test results
 

And what do you have for a pcv system?

Re: Burning oil and compression test results
 

I have no idea, I will have to check when I get home, though just about everything on this truck is stock.

Re: Burning oil and compression test results
 

Take pics!!
Air cleaner off so we can see the whole motor.

Re: Burning oil and compression test results
 

A coworker of mine just mentioned that I am probably burning oil from valve stem links.

Re: Burning oil and compression test results
 

Maybe!!
But could be from excess crankcase pressure too!

Re: Burning oil and compression test results
 

Attached are my images

Re: Burning oil and compression test results
 

Appears you have an inline pcv off the road draft connection and a breather on the intake so likely not a crankcase pressure problem.
So your coworker could be right.
If your sparkplugs are all oil fouled then your valve seals could be the culprit.

Re: Burning oil and compression test results
 

They were pretty oily.

Re: Burning oil and compression test results
 

Likely you had o-ring seals that are toast now.
Maybe a head refresh is in order. New guides and seals and a valve grind.
Or replace the heads.
You'll need the casting number off yours to decide what to replace them with.
The casting numbers are between the rockers. Easy to find.

Re: Burning oil and compression test results
 

I'd put a wrench on the intake bolts and see if they are loose?
valve seals would be my next guess..
or a stuck ring..
Might be worth putting a 1/2 to 1 qt of marvals in the engine and run it for a week then drain and new oil and filter..

Re: Burning oil and compression test results
 

Any other leaks like crankshaft seal? If so maybe worth it to pull for an overhaul.

Re: Burning oil and compression test results
 

Agree...the intake leak (gaskets), can pull the oil up....the marvel might take care of the sticky rings? But I had one, with a fresh top end, that used 14 quarts, from mid Ill to the southern point & back. My bud said bad heads....but the same shop had done my heads for yrs. The same heads went on the fresh bottom end, & used 1 pint of oil in 2000 miles on the break in! A stuck oil ring, will give you some problems....even tho you have good compression/good power.....longhorn

Re: Burning oil and compression test results
 

Diesel fuel, I've heard let it idle for some minutes before dumping it. I've also heard of using transmission fluid. Another guy swears by revving it fast like almost wide open and pouring a liter of water down the carb. Apparently that frees stuck rings. What have you got to lose?

Re: Burning oil and compression test results
 

If you play with the water "trick", be careful....water does not compress! I have set an engine to 1800-2000, & misted , or dribbled water in to clean carbon deposits. Just dont let the engine choke down or die! This will clean carbon from the combustion chambers/pistons/valves, but a soak in Diesel or Marvel... let sit, may do more for sticky rings. Longhorn

Re: Burning oil and compression test results
 

I will try the marvel first and see what happens. Eventually I want new heads, new exhaust headers, new intake and 4 barrel carbs (and also engine compartment painted) so I might end up putting some money aside for a while and doing that all in one fell swoop.

Re: Burning oil and compression test results
 

If your gonna pull heads....pull the motor and go through it. Why put a new top end on a 50 year old engine? If the cylinder walls are in good shape a quick honing and new rings will only be more cheap insurance. If your gonna spend all that money on head rebuilds, intake, and carb....may as well make sure the bottom end will hold up long enough for all of that.

SBC parts are cheap so I'd be looking at standard bearings, oil pump, timing chain, and rings. If your gonna do an engine...make sure the whole thing is internally fine or you'll just have more problems down the road. 50 year old rings are 50 year old rings weather it has good compression or not. :chevy:

Re: Burning oil and compression test results
 

I may do that some day, but for now, the main reason is ... best I can tell the bottom end is in great shape and I have too many projects to spend money on currently.