Valve stem seals - advice

[Duke W.]

Re: Valve stem seals - advice

Hi Duke,

Thanks for your input. A quick update - Last week I took my '67 to a local mechanic who's familiar with older Corvettes as the engine wasn't running right. He found the #2 spark plug oil fouled. I had replaced this same spark plug about 1,500 miles ago to resolve a similar rough-running issue. Once the fouled #2 plug was replaced the engine ran sharp again. The mechanic said the oil fouling is most likely caused by oil leaking down the #2 valve guide. He said to fix this would require the heads to come off and the valve guides rebuilt with new seals installed. I'm noticing oil consumption at about 500 miles to the quart. I get blue smoke on start-up, I don't see smoke once the engine has warmed up/ on the road.

My questions:

1. What would I be looking at in terms of hours labour/parts to re & re the heads to rebuild the valve guides? Note my car has factory A/C. It's a stock 300hp small block.
2. Is there a way to diagnose if only the valve seals need replacing? Doing that would not require the heads to come off. But, that might be a short term or inadequate fix if the guides themselves are worn, correct?

Thanks

First, what spark plugs are installed. Especially with oil consumption you need "hot" spark plugs to burn off the oil deposits. What brand/number is installed?

Oil consumption due to deteriorated valve seals or worn guides is primarily a nuisance issue. Usually engine performance does not suffer, so you have to ask if it's worth spending what will likely be a $1500-2000 job if done by a shop. It would be much cheaper if you did the head R&I yourself and have a machine shop rebuild the head, including new valve guides.

Oil consumption of 500 per quart is high, but livable. If #2 plug if fouling it's likely letting more oil pass than the other cylinders, so you can just add oil, change the #2 plug more often, and even consider running a hotter plug in #2.

My Cosworth Vega never did better than a quart every 600 even when new. By the time I quit running track events it was using a quart every 300, but still ran strong. By the early 2000s it was down to about a quart every 100 and was putting out blue smoke on overrun like long downhill grades, so I finally bit the bullet and pulled the head for new guides and seals as I previously described. I was hoping new seals would do the trick, but when I removed the first spring, dropped the valve a quarter inch, and wiggled it I knew it was off with the head for a rebuild. In your case I would go on the assumption that you will need to do the same, but there's no way to tell that the guides are bad versus just seals until you drop a valve and do the wiggle test.

Duke

[Duke W.]

Re: Valve stem seals - advice

Alexander------



By the way, if you replace the seals with stock-type "o-ring" seals, make sure you use seals made of Viton, not neoprene or other rubbers.

Absolutely agree! Viton will outlive conventional nitrile rubber seals by at least 2:1, BUT I've never found set up the special "square section" SB valve seals that are Viton rather than nitrile.

Do you have a brand/part number for Viton SB valve seals?

Duke

[William F.]

Re: Valve stem seals - advice

Oil getting into combustion chambers increases chance of detonation, I believe.

[Joe L.]

Re: Valve stem seals - advice

Absolutely agree! Viton will outlive conventional nitrile rubber seals by at least 2:1, BUT I've never found set up the special "square section" SB valve seals that are Viton rather than nitrile.

Do you have a brand/part number for Viton SB valve seals?

Duke

Duke------

The current GM valve seals have the correct "square cross section" configuration. I believe these seals are Viton but I have, so far, not been able to confirm that. The part number is GM #10214034. They currently GM list for $1.60/each so I hope that implies a better material than neoprene.

[Alexander D.]

Re: Valve stem seals - advice

First, what spark plugs are installed. Especially with oil consumption you need "hot" spark plugs to burn off the oil deposits. What brand/number is installed?

Oil consumption due to deteriorated valve seals or worn guides is primarily a nuisance issue. Usually engine performance does not suffer, so you have to ask if it's worth spending what will likely be a $1500-2000 job if done by a shop. It would be much cheaper if you did the head R&I yourself and have a machine shop rebuild the head, including new valve guides.

Oil consumption of 500 per quart is high, but livable. If #2 plug if fouling it's likely letting more oil pass than the other cylinders, so you can just add oil, change the #2 plug more often, and even consider running a hotter plug in #2.

My Cosworth Vega never did better than a quart every 600 even when new. By the time I quit running track events it was using a quart every 300, but still ran strong. By the early 2000s it was down to about a quart every 100 and was putting out blue smoke on overrun like long downhill grades, so I finally bit the bullet and pulled the head for new guides and seals as I previously described. I was hoping new seals would do the trick, but when I removed the first spring, dropped the valve a quarter inch, and wiggled it I knew it was off with the head for a rebuild. In your case I would go on the assumption that you will need to do the same, but there's no way to tell that the guides are bad versus just seals until you drop a valve and do the wiggle test.

Duke

Hi Duke,

I'm running AC-45S plugs. Is this the right heat range for an L-75 type motor? I corroborate your assertion: my engine runs very well, despite the smoke on start up.

As you've characterized this problem as a "nuisance issue", I'm now less concerned about addressing it immediately. Adding oil, and changing the fouled #2 plug is certainly cheaper, for now.

The plug that shows the most fouling is #2, followed by #4 with slight fouling only. Is it a coincidence that two adjacent plugs are showing the most fouling?

Cheers,
-Alex

[Duke W.]

Re: Valve stem seals - advice

AC heat range "5" or equivalent in another brand are the best choice, so those plugs are okay. It's not unusual that one or two cylinders are ingesting more oil that the rest... can't say if there's any correlation other than random that 2 and 4 are ingesting the most oil.

Duke