engine smoking

[6768chevylover]

If my 383 engine is smoking on acceleration and deceleration, does that mean the piston rings are shot or is it still a possibility that the valve seals are shot pretty bad? I've always heard if it smokes on acceleration its the rings and on deceleration its the valve seals. Then again is that a true fact? Compression test was done a that was fine but was thinking the oil rings are shot..

[68gmsee]

Could be both. Most of the time when I've had valve stem seals go bad, the engine will smoke on startup after sitting for a period of time like overnight. It's not always the case though but they are the easiest to check and/or replace. The last engine I was working on the seals were so bad they crumbled when I removed them for replacing. They were hard and brittle.

You could also try some of the oil additives to see if it can loosen the oil rings if you suspect they are causing some of smoke.

[GRX]

My instinct says rings. Oil being sucked past eight 0.3438" valve stems is insignificant compared to eight 4.000" rings.

Smoking when letting off the accelerator while going down hill with truck in gear is classic sign of rings since you are essentially creating a high vacuum situation in the cylinders.

Using a bore scope to observe carbon wash patterns on the pistons would be very helpful here.

[Coley]

noting that everything wears out....how many miles are on the motor?
Was it a pro-build?...crate or?

Coley

[Alex V.]

Smoke most of the time, heavier under load pretty much means rings.

[6768chevylover]

its got about 35000 mile on it. it was pro-built engine when I first got it years ago. smokes more when let of the pedal. but smokes a little bit on acceleration. When I say a little bit, it smokes but not a fog left behind me.

[mattfranklin]

That's not a lot of miles for a smoking problem. Most motors are just getting properly broken in at that point.

So it was good and didn't smoke at all when you first got it, but now is starting to smoke? I'm assuming it's gray/blue oil smoke, and not steam or carbon.

Was there one event that made it suddenly start smoking a lot more, or was it gradual over the years?

[WorkinLonghorn]

Sounds like both but I would pop a valve cover off and look. Poke a few to see if they are hard. It's really easy to replace these. Check the guides too while you're in there. -BA

[6768chevylover]

Its definitely blue/gray smoke. I had a bad over heat one day forgetting to click my fans on sitting in a parking lot b.sing . That was alittle over a yr ago. Its been gradually getting worse since then I guess. I'm starting to think you guys are right and that the rings are shot. I was hoping it wasn't that..

[6768chevylover]

anyone know a ball park on a rering job?

[mattfranklin]

I just saw your location. Hopefully you’re all ok there in Napa. We could smell the fires way down in Richmond.

I thought this video on overheating and piston failure was interesting. My guess is that yours are probably not as bad as the ones shown because the failure was at idle rather than at WOT.

https://m.youtube.com/watch?v=aCr9iltAx2w

Could it be valve seals only? Small probability. Less than 5% based on the event that triggered the smoking. There are methods to change the valve stem seals with the heads staying on. I have not done that myself, but it looks easier than changing pistons. If you do it yourself it might be a good decision. But if you have to pay to have it done then the cost and risk trade off leans toward pistons. Depends on if you want to do it yourself or how tight your time is.

If I had lots of time and mechanical ability, I’d try the valve stem seals first, knowing it’s more likely the pistons, but hoping for an easy fix. If that didn’t do it then I’d dig deeper and pull a few pistons.

[68gmsee]

Originally Posted by mattfranklin

.....If I had lots of time and mechanical ability, I’d try the valve stem seals first, knowing it’s more likely the pistons, but hoping for an easy fix. If that didn’t do it then I’d dig deeper and pull a few pistons.

^ Agree. It's cheapest and fairly easy to do if a person has the necessary tools: small air compressor and spark plug adapter (auto parts part), valve spring compressor, small mechanics magnet. Took me a few hours in my front yard to do.

However, I will say this is a temporary fix to minimize oil burning. For an engine that's high mileage, tired and worn down it's best to rebuild the whole engine and be done with it.

[AcampoDave]

My engine developed a smoking habit when the intake gasket went bad. I thought it was something more serious and was just beginning to tear things down when I discovered the gaskets just soaked with oil. May not be the case with you but hopefully so, because it was easy and cheap to fix.

[70K10Hunter]

Originally Posted by 6768chevylover

anyone know a ball park on a rering job?

you can get a rering kit from summit for like $120 for a SBC. It will come with the cheap o-ring valve seals but just buy the umbrella style extra.

[6768chevylover]

I might put that into consideration for the valve seals and try it. also for the intake gasket. To add to my issue, I noticed that I am losing about 3/4 of a pint of oil every 60 miles. 30 each way for work for me..

[GRX]

3/4 of a pint = 12 ounces. Not good but have seen much worse.

When buying valve seals consider type. Factory style o-rings will do nothing if the stock sheet metal oil shields around the springs have been removed. Being a 383 good chance the heads have been reconditioned, or after markets installed. Hopefully they can accommodate positive valve seals that fit tightly on the guides and do not move up and down. Viton are best material here.
Umbrellas, which ride with the valve stem, and not as desirable as positive seals, are another distinct possibility. When going that route be sure their size allows them fit inside the springs without interference.
Hope that helps.

[70K10Hunter]

The umbrella style valve seals that I'm talking about are the ones that are held to the valve guide with a steel split ring and DO NOT ride on the valve stem, they are a tight seal around the valve stem and do not move. sorry I'm old school with some of my terminology.