Valve stem seals - advice

[Alexander D.]

I have a '67 coupe. Recently, when I start my 327-300hp stock original motor (rebuilt in the late 90's but only 20k miles on it since then), I sometimes see blue smoke. Once it warms up there is no blue smoke, as far as I can tell. The engine runs strong and doesn't seem to burn much oil. I drive the car maybe 1,500 miles a year.

I understand the smoking at startup can be caused by valve guide seals. Could it be anything else? Is this something that should be fixed right away?

Is there some type of oil additive that might help restore the seals to reduce the smoking on startup?

If I want to replace the valve seals, what are the recommended type to use?

I would likely hire a mechanic to do this job. How much time, roughly, would it take to do (hours) and more or less what should I expect to pay for a job like this? I realize labor rates vary across the country, but a ballpark idea of time and parts cost would help.

For your info, my car has factory A/C, and does not have K-19 (A.I.R.).

Thanks,

[Joe L.]

Re: Valve stem seals - advice

I have a '67 coupe. Recently, when I start my 327-300hp stock original motor (rebuilt in the late 90's but only 20k miles on it since then), I sometimes see blue smoke. Once it warms up there is no blue smoke, as far as I can tell. The engine runs strong and doesn't seem to burn much oil. I drive the car maybe 1,500 miles a year.

I understand the smoking at startup can be caused by valve guide seals. Could it be anything else? Is this something that should be fixed right away?

Is there some type of oil additive that might help restore the seals to reduce the smoking on startup?

If I want to replace the valve seals, what are the recommended type to use?

I would likely hire a mechanic to do this job. How much time, roughly, would it take to do (hours) and more or less what should I expect to pay for a job like this? I realize labor rates vary across the country, but a ballpark idea of time and parts cost would help.

For your info, my car has factory A/C, and does not have K-19 (A.I.R.).

Thanks,

Alexander------

What you describe does sound like valve stem seals or, possibly, the valve guides, themselves. If you have worn guides, new seals will do little to correct the problem. Most likely, though, it's just a case of the seals.

Assuming it is configured as original, your engine uses "o-ring" type seals installed on the valve stems. Over time, these harden and deteriorate. However, they can be replaced without the need to remove the heads. I'd say it's about a 2-3 hour job for someone with the right tools and expertise. Positive type seals can be installed and are superior to the stock type. However, this requires removing the heads and machining the valve guide bosses to accept the seals.

If I were you, the first thing I would try is changing the oil and using motor oil labeled for "high mileage" vehicles. This contains additives which might "rejuvinate" the seals to some degree.

[Gene M.]

Re: Valve stem seals - advice

I’d bet that when the engine was done they never did the guides. They should last longer the 20k miles.

[Duke W.]

Re: Valve stem seals - advice

I have a '67 coupe. Recently, when I start my 327-300hp stock original motor (rebuilt in the late 90's but only 20k miles on it since then), I sometimes see blue smoke. Once it warms up there is no blue smoke, as far as I can tell. The engine runs strong and doesn't seem to burn much oil. I drive the car maybe 1,500 miles a year.

I understand the smoking at startup can be caused by valve guide seals. Could it be anything else? Is this something that should be fixed right away?

Is there some type of oil additive that might help restore the seals to reduce the smoking on startup?

If I want to replace the valve seals, what are the recommended type to use?

I would likely hire a mechanic to do this job. How much time, roughly, would it take to do (hours) and more or less what should I expect to pay for a job like this? I realize labor rates vary across the country, but a ballpark idea of time and parts cost would help.

For your info, my car has factory A/C, and does not have K-19 (A.I.R.).

Thanks,

If you drive it 1500 miles per year you should have a pretty good handle on actual oil consumption. If it's more than about 600 miles per quart, don't worry about it... just add oil in half-quart increments as needed. With the small four-quart oil pan I would not it get a quart low before adding oil and running a half quart over is no problem.

If it gets down to 300 per quart time to replace the valve seals or rebuilt the guides. Whenever tackling a valve seal change the first thing to do once the spring is removed is drop the valve down about a quarter inch and wiggle it. A good guide should have barely any perceptible wiggle.

A quicky valve guide rebuild is done by knurling and reaming to size, but it's only good for about 20K miles. Maybe that's what was done 20 years ago.

Use 15W-40 CK-4 oil.

Duke

[Gene M.]

Re: Valve stem seals - advice

As Duke say knurling thing is a “quicky” and there is no assurance it will be true to the valve seat.

Knurling still allows oil thru and not assured it’s true with seat, that’s why it’s a “quicky”.

A car guy does this correctly with valve seats too all on a machine that insures everything is in line and seats correctly.

[Duke W.]

Re: Valve stem seals - advice

After knurling and reaming, the valves were usually reseated or at least lapped in.

When I had to install new guides in my Cosworth Vega's engine about 15 years ago I didn't want to reseat the valves because it would have sunk the valves enough to require reshimming all 16 valves. I wasn't sure if I had enough shims in my collection to cover any changes, and shims were getting rare.

Fortunately, I had the work done by a Cosworth Vega owner who owns an engine shop in San Clemete that did a lot of work with aluminum head engines, so he had a big industrial oven to heat up the head to swap the guides. The stellite seats were perfect, but the 21-2N exhaust valves had tiny burn spots. After the head cooled down and he reamed the guides to size I spent the next hour or more lapping the hell out of the exhaust valves until nearly all the little black spots were gone with a little lapping on the inlets to get a good seat pattern. Then I installed the valves and mounted the cam carrier with the tappets and shims, and all the valve clearances were right on - no change.

Duke

[Gene M.]

Re: Valve stem seals - advice

I don’t know anything about a Vega. But SBC heads are cast iron and require boring out guides, fitting and pressing, and in the end ream to size. To insure the valves are traveling the same path the seats need attention too same as Duke outlined above. But with new guides vs knurling with new guides entire diameter of the guide fits the valve stem not just the high spots. Thus better oil control.

[Alexander D.]

Re: Valve stem seals - advice

If you drive it 1500 miles per year you should have a pretty good handle on actual oil consumption. If it's more than about 600 miles per quart, don't worry about it... just add oil in half-quart increments as needed. With the small four-quart oil pan I would not it get a quart low before adding oil and running a half quart over is no problem.

If it gets down to 300 per quart time to replace the valve seals or rebuilt the guides. Whenever tackling a valve seal change the first thing to do once the spring is removed is drop the valve down about a quarter inch and wiggle it. A good guide should have barely any perceptible wiggle.

A quicky valve guide rebuild is done by knurling and reaming to size, but it's only good for about 20K miles. Maybe that's what was done 20 years ago.

Use 15W-40 CK-4 oil.

Duke

Thanks Duke for your solid advice.

I'll monitor the oil usage and top up with 15W-40 CK-4 oil. If the car starts using more than a quart every 300 miles or so, it'll be time to replace the valve seals / rebuild the guides.

Cheers,
-Alex

[Edward D.]

Re: Valve stem seals - advice

The seals are relatively easy, the heads do not have to be removed, you move the rockers aside and hold the closed valves in place with compressed air thru the spark plug hole and use a valve spring compressor to compress spring, remove keepers, pull off spring, replace stem o-ring. Valve guides are a whole different matter. Heads must be removed and the work done by a competent machine shop. While doing, if the valves seats were never replaced with hardened seats this ought to be done as well. The lead in the old gas not only boosted octane, it lubricated the valve seats cut into the cast head. If redoing heads for valve guides it makes sense to have new hardened seats and alloy valves installed at the same time.

[Jim L.]

Re: Valve stem seals - advice

While doing, if the valves seats were never replaced with hardened seats this ought to be done as well. The lead in the old gas not only boosted octane, it lubricated the valve seats cut into the cast head. If redoing heads for valve guides it makes sense to have new hardened seats and alloy valves installed at the same time.

Just keep in mind that machining a perfectly good set of heads for hardened valve seats comes with the risk of cutting into the water jacket.

If that happens, you've got a set of very pretty, Chebby engine orange doorstops.

[Duke W.]

Re: Valve stem seals - advice

While doing, if the valves seats were never replaced with hardened seats this ought to be done as well. The lead in the old gas not only boosted octane, it lubricated the valve seats cut into the cast head. If redoing heads for valve guides it makes sense to have new hardened seats and alloy valves installed at the same time.

Installing hardened valve seats is NOT a good idea and unnecessary. The internet if full of stories about cutting into the water jacket and dislodged seats, including plenty of discussions here.

Vintage Corvette engines rarely operate under high load, so the valves remain relatively cool and there is little seat erosion. The are still plenty of OE engines out there... heads never removed... running unleaded fuel for decades and no problem.

Valves and seats should both be dressed with a 45 degree stone, then thoroughly lapped in. Don't use the one degree "interference" angle in the service manuals and let the valves pound out their own seats.

Duke

[Roger W.]

Re: Valve stem seals - advice

Back in the 60's, Amaco unleaded gas was popular. Nobody seemed to worry about valve seat wear then.

[Dick W.]

Re: Valve stem seals - advice

Duke is right, unless you are racing, engine is in a boat, or you are building a heavy duty truck engine, you don't need hardened valve seats

[Alexander D.]

Re: Valve stem seals - advice

If you drive it 1500 miles per year you should have a pretty good handle on actual oil consumption. If it's more than about 600 miles per quart, don't worry about it... just add oil in half-quart increments as needed. With the small four-quart oil pan I would not it get a quart low before adding oil and running a half quart over is no problem.

If it gets down to 300 per quart time to replace the valve seals or rebuilt the guides. Whenever tackling a valve seal change the first thing to do once the spring is removed is drop the valve down about a quarter inch and wiggle it. A good guide should have barely any perceptible wiggle.

A quicky valve guide rebuild is done by knurling and reaming to size, but it's only good for about 20K miles. Maybe that's what was done 20 years ago.

Use 15W-40 CK-4 oil.

Duke

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

[Joe L.]

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

Alexander------


Mitchell's Guide gives 9.2 hours for cylinder head removal and replacement. This does not include valve guide replacement or a valve job.

The only way to diagnose if the problem involves only the seals is to disassemble the valve spring assemblies and try to "rock" the valve stem. There should only be the very slightest movement. Badly worn valve guides will be obvious. If you replace the seals and do not replace worn guides, your repair will be short-lived, if not imperceptibly short-lived.

GM never recommended the replacement of valve guides. Instead, GM SERVICE procedures called for the guides to be reamed out and the installation of new valves with oversize stems. Three different valve stem OD's were once available from GM. This is actually the best way to correct worn guides but the oversize stem valves are no longer available from GM and I don't know, off-hand, if they are available in the aftermarket.

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.