1966 l-36 needs valve job

[Jerry S.]

I am burning oil in my C-2 equipped with an L-36 engine. Just had a compression test done and all is well. The leak down test indicates the problem is most like poor seating with the valves. Wondering if anyone has dealt with this issue and what I can expect for a general estimate on time and cost. Not expecting to have to pull the engine to do this job right? If you are familiar with the Phoenix area, maybe you could recommend a great service facility to do the work.

[Joe L.]

Re: 1966 l-36 needs valve job

I am burning oil in my C-2 equipped with an L-36 engine. Just had a compression test done and all is well. The leak down test indicates the problem is most like poor seating with the valves. Wondering if anyone has dealt with this issue and what I can expect for a general estimate on time and cost. Not expecting to have to pull the engine to do this job right? If you are familiar with the Phoenix area, maybe you could recommend a great service facility to do the work.

Jerry-------


Poor seating valves will not cause an oil consumption problem. There is no relationship between poor seating valves and oil consumption. Poor seating valves will cause loss of power and low compression readings.

High oil consumption is usually caused by the following:

1) worn piston rings or pistons

2) worn/deteriorated valve stem seals

3) worn valve guides

4) malfunctioning PCV system

[Jim D.]

Re: 1966 l-36 needs valve job

Over the last 50 years, I've found that the majority of oil burning big blocks has been caused by worn valve guides.

[Mike T.]

Re: 1966 l-36 needs valve job

Jerry - Can you fill us in on some of the details such as how many miles on your L36? And, what kinda numbers did you get with the compression test and leak down test? If the valve guides are worn, they can be repaired while leaving the engine in place but it might be worthwhile to pull the engine and go through it all at the same time.

[Jerry S.]

Re: 1966 l-36 needs valve job

Good information to know. And here are the readings from the compression test. #1) 175 #2) 160 #3) 180 #4) 150 #5) 180 #6) 175 #7) 170 #8) 170. And the Leak down test #1) 6% #2) 15% #3) 11% #4) 15% #5) 11% #6) 6% #7) 12% #8) 5%. I really can't say how many miles are on this engine but I've owned it for 3 1/2 years and have put about 2800 miles on it. On a side note, my service report also mention a slight delimitating of the hood from the frame. Another issue I will look into fixing.

[Jim D.]

Re: 1966 l-36 needs valve job

Jerry, my suggestion for the oil issue is to pull the heads and have the guides fixed and a valve grind. As far as the hood issue, which is very common, here's a link to a prior thread on this issue. I have used the DAP product on several hoods and it works perfectly. https://www.forums.ncrs.org/showthre...mdrop-Adhesive

[Chris H.]

Re: 1966 l-36 needs valve job

Jerry on my L71 the oil burning culprit turned out to be disintegrated intake manifold gaskets.

[Joe L.]

Re: 1966 l-36 needs valve job

Jerry on my L71 the oil burning culprit turned out to be disintegrated intake manifold gaskets.

Chris------


Yes, this can be another culprit that I forgot to mention. Besides deteriorated/failed intake manifold gaskets, this can occur due to misalignment between the manifold and cylinder head. The root cause of this is deck surfacing of the cylinder heads without concurrent machining of the intake manifold mating surface of the cylinder head.

If the above is the source of the problem, the intake ports of the cylinder head will be wet with oil while the intake manifold runners will show no signs of oil. If the source of oil is a malfunctioning PCV system, the cylinder head ports and the intake manifold runners will both be wet with oil.

[Bill M.]

Re: 1966 l-36 needs valve job

Jerry when you rebuild your heads and install new gaskets the top end of your engine will be tight as a drum. If your piston rings are worn or used to the loss of pressure you could develop a lower end problem. This happened to me when I was young. we swapped a nice set of rebuilt heads on my Chevelle. the motor only lasted a week. The machine shop told me this happens all the time. I would go the extra yard and rebuild the whole engine.

[Mark F.]

Re: 1966 l-36 needs valve job

Jerry when you rebuild your heads and install new gaskets the top end of your engine will be tight as a drum. If your piston rings are worn or used to the loss of pressure you could develop a lower end problem. This happened to me when I was young. we swapped a nice set of rebuilt heads on my Chevelle. the motor only lasted a week. The machine shop told me this happens all the time. I would go the extra yard and rebuild the whole engine.

Hi Bill,

Just curious - what exactly happened in your case?
Thrown/broken rod?

and why does rebuilding/replacing the head cause lower end problems?

[Duke W.]

Re: 1966 l-36 needs valve job

I am burning oil in my C-2 equipped with an L-36 engine.

What is the rate of oil consumption... miles per quart?

Duke

[Jerry S.]

Re: 1966 l-36 needs valve job

I would estimate that I'm getting about 400 to 500 mile per quart. I'll pay closer attention to that going forward. This is in town driving and I usually don't go more than about 50 miles at any one time. I should also mention that there is no oil leak under my car when parked.

[Bill M.]

Re: 1966 l-36 needs valve job

Mark at least one piston lost its rings. With new heads and gaskets the compression remains as it was designed. When the valves are worn pressure can escape through the worn parts. So the new tight upper end will cause the older piston s and rings to have hold the compression pressure. If any are weak or worn they can let go This is what happened to me.

[Duke W.]

Re: 1966 l-36 needs valve job

I would estimate that I'm getting about 400 to 500 mile per quart. I'll pay closer attention to that going forward. This is in town driving and I usually don't go more than about 50 miles at any one time. I should also mention that there is no oil leak under my car when parked.

That's on the high side, and you do have somewhat high leak down in some cylinders, but what's your SOTP impression of how the engine runs. If it runs okay for the way you use it, it's a lot easier and cheaper to add oil every few hundred miles.

And then there's good old "project creep". If you remove the heads for a refresh you should measure cylinder taper and if you have cylinders with more than .003" taper it may be time to refresh the block, which means you're into a full engine rebuild that could cost up to $10K or more if you just turn it over to a shop to do.

If the engine has no annoying operational issues and you just use the car for pleasure driving I suggest you leave it alone. Just check oil frequently and add as needed.

Duke

[Joe L.]

Re: 1966 l-36 needs valve job

I would estimate that I'm getting about 400 to 500 mile per quart. I'll pay closer attention to that going forward. This is in town driving and I usually don't go more than about 50 miles at any one time. I should also mention that there is no oil leak under my car when parked.

Jerry-------


One other tip: remove the carburetor and inspect the plenum below it. If it is wet with oil then the problem is related to the PCV system.