Leaking intake question...

avanti-176 · #1 (**permalink**) 09-27-2003, 09:04 AM

Hi guys,
quick question, I have developed a pretty good knock(detonation?) on the passenger side of the engine and have a pretty good amount of smoke coming out of the passanger side exhaust, I know that a leak in the intake gasket allowing some oil to be sucked in will cause it to smoke but would it also cause a knock?

It is okay at idle but once you start giving it some rpm's it starts knocking.
any input is appreciated.

Thanks,
Dan

p.s. I have tried messing with the timing and retarding it seems to
help a little but it is still there.

wilf leek · #2 (**permalink**) 09-27-2003, 09:38 AM

Burning oil can give rise to detonation, most of the old clunkers I had when I was much younger proved that to me!

Some investigation, starting with a compression test on that side of the engine sounds in order.

Does the thing smoke all the time, or just under acceleration, or after a period on overrun?

avanti-176 · #3 (**permalink**) 09-27-2003, 10:39 AM

Thanks Wilf,
Compression test is right where I headed after my initial post.
175 psi across the board on that side.
so maybe the intake is leaking or another thing I am thinking is a couple of bad rod bearings throwing oil up on the cylinder walls since it does not smoke too bad on startup but gets progressivley worse the longer it idles. Does that sound viable?

well gotta go got a 1:30 tee time.
more tinkering later.

have a good one,
Dan

wilf leek · #4 (**permalink**) 09-29-2003, 02:43 PM

If it smokes after a period at idle (max engine vacuum) I might go look at the valve stem oil seals???

Do you get a puff of smoke when you re-apply the throttle after being on the over-run? If so, that would tend to confirm my valve stem oil seal idea.

You would have to have very worn bores and rings to see the smoke as the effect of excessive oil slung out of the crank IMHO.

I'll come right out and say I don't know enough about sbc engine architecture to know if an intake leak can give you excessive oil into the exhaust port. Just working from general principles here.

HTH

Wilf

Mr.Fixit · #5 (**permalink**) 09-29-2003, 03:02 PM

What do the sparkplugs look like? If you are sucking oil, one should be oil fouled, if that cylinder is also detonating, the insulator may very well be cracked too. Burning oil will cause detonation problems, it isn't a very good fuel, and it causes carbon buildup which causes detonation.

KraZMechanic · #6 (**permalink**) 10-06-2003, 06:36 PM

oil has a lower flash point than the air/fuel mixture, so it can cause premature ignition...but that's pretty much already been said. your valve seals may also be leaking - a much more common problem than blowing your gasket. also, get your A/F ratio checked. there may be oil in the cylinder (causing the smoke), but the detonation might simply be an extreme rich condition.