Hi guys,


So up until recently I've only ran my 350 for probably about 15 seconds or less whilst I was nutting out issues, now that I've ran it for extended times to get it up to temperature here is what happens.

After about maybe 15 seconds smoke starts coming out of both side pipes (see video) --> https://imgur.com/NKFJR5A

At first I thought it was white and I had a coolant leak however I'm starting to think it may have a blue tinge to it

It's an 80-85 truck 350 with a 4 speed, it starts pretty much straight away and runs easily (Havent had the chance to actually rive it yet.) but there is no water in the oil and visa versa.

I've done a compression test which ranged from 125 - 135 PSI in all cylinders. 6 out of the 8 spark plugs have a tiny amount of oil on the threads.

I've also just started doing a leak down test,#1 cylinder had just below 20% leak down. #8 had just below 30% however got to number 4 which showed 55% leak down, I had a hose over the dipstick tube and can definitely hear the leak, I did the test cold because I hear mixed review on the difference between warm and cold, I can't imagine 55% in one cylinder will magically become lower than 20% when warm.

So now I know the motor was tired but now I'm thinking it's going to be coming out for a rebuild, I'll be retesting the motor in the next couple of days and do all the cylinders so I know the results but I'm thinking the cause of my smoke is oil being drawn up past the rings a burnt, would that be a fair assumption?

 

Oil in the combustion chamber can come from worn oil seal rings and/or worn valves/valve guide seals. A compression test is addressing the compression rings, not the oil control ring although if the cylinder is badly worn, both types of rings are less effective.

 

Bottom line. Cylinder leak down past 20 percent is pull it down time. In my line of work I do leak down tests fairly often. The factory requires this before any warranty work on engines. Most good engines have 8 percent leak down or less. 20 percent seems to be the standard line in the sand. So, if I were you. I'd be pulling it apart. no need for further tests.

 

fill it with coolant and drive it. stay close to home. beat on it a little. stuck rings could free up a bit. worst case, you will know the diff between a dying dog and a fresh engine in the end...

 

 

What have you done to properly seat the rings.
15 minutes of run time on a fresh motor just idling is not a proper way to seat the rings.
What type of cam are you running?
How did you break in the cam?

 

Would it be useless to switch to 10w 40 ...just to see if the smoke lessens and the leak-down test improves?

 

Not a fresh motor mate, it's unknown conditions, didn't run when I got it

might try the wd40 trick but won't that give a false resdibg?

 

You can smell the difference between oil and anti-freeze burning. Oil smells like that old toy train with the smoke option and anti-freeze smells sweet.
Usually if your valve guide seals are leaking you'll see the blue smoke at startup and it may not be noticeable when running. If it's the rings then your oil consumption will go up. Are you having to put oil in it a lot?

 

I haven't had it out on the open road yet as it was a mess when I bought it so it's hard to tell

It doesn't have a sweet smell, this coupled with what I've found with the results from the tests I would say its probably rings but could even be a combination of both to be honest, it's an old motor, most likely tired.

might be a good excuse to make it a 383

 

Now you're thinking clearly.

 

UPDATE:


So, I decided to re test what I had as I believed that much pressure loss the motor would be running like poo.

So I re tested all cylinders and when I had 60 % loss the exhuast valve was SLIGHTLY opened creating a loss, closed the valve and got much lower results. My results are below:

1: 25%
2: 23%
3: 15%
4: 24%
5:23%
6:24%
7:19%
8: 20%

So, it's not as catastrophic as i originally thought however this tells me the motor is '"Tired" I would say.

Back to the smoke, I think it would create a little smoke and I can hear the pressure at the dipstick tube however there will always be a little bit, I don't think it would blow as much smoke as I can see.

So now I'm thinking valve stem seals or possibly a leaking intake manifold (leaking coolant into combustion chamber.) The smoke appears white but in a different light my eyes can play tricks on me.

The question is how far do you go with it before you just bite the bullet and do a rebuild, as the block number is 14010207 and the head numbers are 14079261

I can see myself going 3 ways,


Replacing valve stem seals/guides and removing intake + asses and re seal.

Removing heads and replacing with better heads, replacing camshaft and rocker gear, poss new intake.

Removing motor asses, possible re build hot 350 or 383

 

15% is the it is a dying pos number. ONE cyl is only 15% fill it with coolant and beat on it. it will not have enough power to break the rear. then start thinking about what you want for a motor.

 

Are you sure the valves are adjusted properly. If you used a 'faulty' method for setting them...but you did that repeatedly for all valves...you could end up with the condition you now have. If you haven't done any adjusting on the valves, you have a very tired engine. If you have changed oil and filter, operating the engine probably won't do any (or much) damage. You could use it as a 'test bed' to learn/practice how to tune and maintain a working[??] engine...and have a little fun in the process. Or you could just get down to it....

Good luck with it. It's a Chevy engine. You can make it into about anything you want with some planning, some parts, some money and some 'elbow grease'.