'69 silver BB

I have a 69 coupe, 427/390, 85,000 mi, #'s matching, survivor. Runs great, looks great. Smokes a fair amount at startup and a lot at acceleration. Uses a quart of oil every 60 miles. Drips a little oil while parked, seems to come from belly pan and valve covers. I've only had it one year, former owner says engine never been rebuilt. I doubt it has hardened valve guides or rods. So, to get it right, it probably needs surgery, but minor or major? Anyone with the same experience? Any suggestions for the fix and associated cost? Also, once the incision is made is there anything else recommended while we are in there? I expect to keep this bad boy for the long haul. Thanks.

Fevre

Do a leak down test to see if your rings are shot. You prolly need to valve stem seals no matter what if they are orig, that might be a cheap way to try to fix it but a full head job is prolly in order.

'69 silver BB

Thanks for the advice Fevre. Sorry for the ignorance, but I never heard of a leak down test. Are we talking pulling the heads and putting oil in the cylinder?

bigvette1

Take a look in the JC Whitney or Summit catalogs at the leak down testers. They will basically inject air pressure from your compressor into a cylinder that is at TDC say 100 psi and you read a gauge to see how much is blowing or being lost somewhere ie. 80psi which equates to a 20% leakage rate. YOu can then listen to where the air is escaping, carb, valve covers, exhaust etc and deduce what is going on. This with a compression check will tell you the health of the lower end and the heads and what needs to be done.

'69 silver BB

Thanks, I'm learning as I go. Knowledge and experience are wonderful things. I'll check out the testers.

Fevre

Best adv I can give is to get a book or two on rebuilding big block engines, there is a lot of useful info in them even if you don't catch on to every detail and most will have a trouble shooting guide to follow when trying to diagnose a problem such as you are experiencing.

LemansBlue68

The part of your description about smoke at startup and smoke on accel would lead me to believe it MAY be worn out valve guide seals but the 60 mi/qt really concerns me. To get only 60 mi/qt you must be blowing blue smoke all the time and fouling plugs! My own experience is that leakdown tests aren't always fool proof. I've seen some pretty worn out motors make good leak down numbers. A compression check may also give some clues, but again, not always fool proof. Look for inconsistency among cylinder readings more than absolute numbers. You may narrow the problem down to a bad cylinder, but even so I think you'll be pulling the heads at a minimum.

Considering the leaks and oil burning it may be rebuild time. I rebuilt my 427/390 recently and the machine work and parts came in around $2200 and that was pretty much for the whole works. I assembled the motor myself.

clem zahrobsky

back in the 60s the ring package they used from the factory were not the best. i owned new 65 and 66 big block corvettes and 600 miles was the max on a quart of oil. :chevy

bigvette1

All area talked about are right on. Oil burning can only come from 3 places, guides, rings and being sucked into the intake. Run your compression check and see the numbers. If they are within norm and no great spreads the engine rings and valves are pretty good. That leaves you with the guides and intake. Take your carb off and see if the floor of the intake has an oil resideue on it. Also the bottom of the carb. If it is oily you are sucking oil in the intake runners from a bad gasket. That would be the best of all worlds. Check out all areas before pulling.

R 73 454

Does it foul ALL the plugs? Mine is now fouling #4 really bad and #6 slightly less. I have a feeling it's the valve seals and/or guides. I had the heads off, and my machinist said the guides looked O.K., he told me this by trying to wiggle each valve assembly in the head. I assumed trying to feel for excess clearence in the valve stem/guide. I'm not convinced that was an effective test. Also a vacuum guage reading is nowhere near steady. My car doesn't use THAT much oil, but the puff is definately there. The worse thing is that the engine "breaks up" during spirited acceleration. A true buzzkill! :U :banghead: :nonod:

LemansBlue68

:iagree:

I definitely agree!! Ring technology has come a long way since the '60's. If you go for the rebuild go for a plasma moly top ring. Don't go with a low tension ring pack or any of the gapless top ring BS unless you've gone all out on everything else and want to get that last little bit of power back from friction and blow-by. Definitely have the block honed with a deck plate. If a shop insists that they can do as well without the deckplate, look for another shop. The deck plate hone will assure that the bores are round in the assembled state. Round bores are by far the most important consideration for proper ring seal and oil control.

I forgot about the leakage from a bad seal with the intake. Good call. If this is a problem you might also see abnormally low manifold vacuum.