Valve seals

[eventhorizon66]

What are your opinions on using seals only on the intake valves?  Some say the exhaust valve needs all the lube it can get and the engine will not smoke without exhaust seals if the guides are in order.  Others say, positive rubber seals on the intake and umbrella on the exhaust.  Thoughts...opinions???

[VileZambonie]

What type of guides are we talking about and what's the guide clearance?

[eventhorizon66]

Cast iron.  Maybe 0.0015" intake / 0.002" exhaust clearance.

Also, how would you approach the situation if the guides were bronze?

[VileZambonie]

Personally I would run the positive seals. Just lube the valve stems upon assembly by dipping them in clean oil and soak the valve seals in clean oil.

[SUX2BU99]

Speaking of valve seals, was this the cause of the infamous puff o' blue upon start-up that I would see on almost every SBC-equipped GM product made in the 70's and 80's when I was in high-school in the early 90's? It was a real badge of honor if you had a SBC-equipped vehicle that didn't smoke on warm start-up. We always said it was valve guides in the heads. Why was that such a problem?

[eventhorizon66]

I think GM used umbrella seals on these engines.  They work more like "shields" than seals, making them less than optimal for oil control.  But I think the main reason was infact the guides, because cast iron really is not an ideal material in terms of wear resistance.  Well that's my take on it anyways.

So Vile, just to make sure I understand, your advice is rubber positive seals for both intake and exhaust regardless of guide material?

[VileZambonie]

If you want to avoid the infamous POOF yes.

[eventhorizon66]

Gotcha, thanks.