maggiesadie8525

Just took a compression test on a 66 327/350hp, we are having trouble with our rebuilt motor with about 1,2000 miles on it. The motor smokes and we are trying to figure out whats making it do that. I might add this is the second rebuilt in the same amount of miles and it's doing the same thing. We took a compression test this morning and here are the results: We did not take a compression test on the first one. Here are the results:

c-1 160 c-2 170
c-3 155 c-4 170
c-5 160 c-6 150
c-7 150 c-8 150

Would you consider these readings correct for that motor, or is something not right with the internals? My main concern is the 20 lb and the 15 lb difference in some of the cylinders or is exceptable? All responses are welcome Thank you

Mr D.

Not sure what the "official" reading should be from a +/- standpoint but those numbers look fine to me.

Found this;

When checking your cranking compression you should be looking for inconsistencies between cylinders. Don't focus simply on how high or low your figures may be, unless all the cylinders are extremely low, (less than 100 psi), which could indicate you're doing the test incorrectly, or your engine is about 7 cylinders shy of a full power plant. A good thing to watch for is repeatability between cylinders. That means that with same number of starter revolutions, each cylinder should build pressure within about 5 percent of the others.

Mr D.

What was done to the heads between the two rebuilds?

Geralds57

I don't think you have a compression problem. You didn't say if it smokes only during startup or all the time. If it smokes all the tme I would think you have a broken oil ring on the piston.

maggiesadie8525

It smokes sometimes at start up go figure. Thank you

maggiesadie8525

They were machine during the first rebuilt. Thank you

Geralds57

Scratch the broken ring then. it sounds more like a bad seal on one of the valves or a bad valve guide.

Mr D.

I agree with Gerald, sounds like valve guides but you would think this would have been caught during two trips to the machine shop.

65tripleblack

It's possible that there's a problem with 1 or more oil scraper rings. That will cause oil burning and still show good compression.

Also, ask the engine builder what he used for piston to bore clearance. I assume he used Speed Pro L2166F pistons.

Another possibility is intake port seal problems. This will show more dramatically during closed throttle higher RPM coasting (very high manifold vacuum).

Pull all 8 plugs, photograph and post.

new vette 62

I would try a leakdown test this will help you locate where you might have a problem. With just a compression test you don't know if it's valves or rings.

67vetteal

If you are using Synthetic Oil in your new engine this could cause your problem. These older engines need Organic Oil during the Break In period. Synthetic is too slick to allow the Rings to Seat properly. I'd change your oil to Dino stuff and take the car out and Beat the Snot out of it for a little bit. Maybe 50-100 miles. This "May" Seat the Rings and cure your problem. Also, put some Marvel Mystery Oil, (MMO), in the gas at 1 ounce per two Gallons of gas to lubricate those new Guides in the Head. Al W.

devildog

Maury,

This is a very rare situation, but since it occurred on your TWO rebuilds, please consider. It happened to me, my aluminum intake manifold had a crack on the bottom of the intake. It was hidden by the the oil plate on the bottom of intake manifold.

It would suck oil mist from the gallery and foul the plugs after several hours runtime. Some intermittant smoking. I welded and continue to use with no problems.

Joe

Westlotorn

Compression on any new rebuild should be equal, post what rings were installed, Moly, Chrome or Cast Iron. Moly rings will seat right away, usually by the end of a first pull on a dyno. Ask the machine shop what final hone was used, he should describe it exactly.
Start up smoke does point to valve stem seals. 1200 miles should have everything seated in, unless you drive it with no load pampering it all the time.

maggiesadie8525

Thank you Joe I'm starting to think tht is the problem. Maury

maggiesadie8525

Thank you

Mr D.

I second that, it will give a better picture of what's going on.

midyearvette

also..was the choke and throttle held open during the test?......

maggiesadie8525

No they weren't

JohnZ

All plugs should be out, engine warm, and throttle held wide open for a proper test.

midyearvette

do it again preferably after a slight warm up.....choke open and throttle too.....maybe this will give a more consistent reading

oil consumption is probably a guide or seal or intake leak......good luck....