rand5204

I have a 70 BBO that I had professionally rebuilt about 7 years ago. It was never started and run until just recently. It starts right, up runs smooth and seems to have plenty of power but it smokes from the left tailpipe at startup. I'm guessing that it's one, or more, leaking valve seals. Short of tearing it down, are there any tricks to help solve the problem?

Vintage Chief

First, I'd want to know if it is in fact burning oil. Lots of variables in your post. How do you know it's burning oil and not water moisture emanating from the left tailpipe. A vehicle sitting for seven years which wasn't started in that period of time and just recently is going to have lots of moisture in the fuel tank, engine, oil pan, fuel pump, you name it. If it runs fine, I'd drain all the old fuel, I'd drain all the old oil and replace both with fresh fuel & oil then take it on a lengthy drive of 50+ miles then evaluate if there remains smoke emanating from the left tailpipe at startup.

Change the spark plugs and during the spark plug R&R perform a compression test - both wet & dry and determine any deltas in compression test between wet & dry compression numbers.

You don't state exactly what was done during the rebuild seven years ago. Did they replace pistons & rings? Heck the rings may not even be seated yet. The valves may not even be completely seated. I'm suspecting if the rebuild was professionally done and the vehicle runs fine, it's most likely a ton of water moisture in the system burning up each time you start-up; but, it's a crap-shoot at this point. I wouldn't necessarily suspect valve seals straight off. Whenever a rebuilt is accomplished (depending on what was done), you should have a period of 'burn-in' in which the engine is run for select number of miles w/in select framework of speed variations.

I certainly wouldn't consider a tear-down until you get some compression numbers and change out the plugs, fuel & oil firstly.

Olds64

If you determine that it is indeed the valve guide seals leaking then you don't have to tear the engine apart to replace them. You can put compressed air in the cylinder at TDC to keep the valves from dropping when you remove the valve keepers. Better yet, feed nylon rope into the cylinder through the spark plug hole near TDC and compress the rope against the valves by rotating the engine with a breaker bar. Then you can remove the springs and replace the valve guide seals.

cutlassefi

Agree with above except valves don’t need to “seat” like rings do.

rand5204

I should have been more clear in my description. Engine was built 7 years ago from the bare block up. Everything in it is new. It was never installed in a car and has been on am engine stand the whole time. It was just installed in a car that that I am redoing so everything, fuel and fuel tank oil, water, is fresh. It is smoking blue smoke from left exhaust at startup, nothing from the right side. It doesn't seem to smoke after that. From the blue color and the smell, I am assuming oil but I could be wrong. It has been through the cam break in process but beyond that, has been run at idle only. Maybe my complaint is premature and it just needs some miles on it?

oldcutlass

Have you run it long enough to burn all the residual crap that usually finds its way into the exhaust system? It usually takes a good ride to clear that up.

rand5204

oldcutlass,

probably nit but I will take care if that as soon as it stops raining when I am at home so I can drive for a few miles

Ozzie

I agree that a bit more running may be in order. Get a good diagnosis before any dismantling. If it's only at start-up, it may not be anything serious.