Valve Appearance - 496 BBC - Impala Tech
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post #1 of 10 (permalink) Old 01-12-2020, 04:20 PM Thread Starter
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Valve Appearance - 496 BBC

Hello all,
While I had the intake off my 496, I noticed something odd. All of the valves look gummed up with blackish brown goop; something is not right....I think. At first I thought that maybe some oil that hadn't drained out had worked its way past the intake gaskets when I had the engine upside down to replace the oil pan gasket. But this stuff is sticky and doesn't wipe off easily. All 8 intake runners at the valves look like this. See attached pic; is this normal or are my valves gummed up already for some reason? Less than 1000 miles on her. Thanks for any replies.
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1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #2 of 10 (permalink) Old 01-12-2020, 06:47 PM
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Looks like your valve stem oil seals are not sealing. Could be the wrong size oil seal for the valve used (0.3415" in. stem versus the stock 0.3750" stem). Would be really bad if some one installed high performance 0.3415" in. stem valves in a 0.3750" stem valve guide. You would not only have the oil leak you see but the valves would never fully seal and will wear/burn at an accelerated rate. Or it could be that the person who assembled your head left the valve stem seals off all together for unknown reasons.

Big Dave
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post #3 of 10 (permalink) Old 01-12-2020, 07:22 PM Thread Starter
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Dave,
Wouldn't it smoke like crazy if the valve stems weren't sealing properly? It didn't smoke at all in the thousand miles I drove it before yanking it the engine. As I mentioned before, whatever it is it's sticky; not what i would expect from oil...

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #4 of 10 (permalink) Old 01-12-2020, 10:10 PM
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Do you have any idea hot hot the valves are when the engine is running. Oil running down the stem turns to varnish before it reaches the seat. You wouldn't see the oil that makes it into the engine burn as it is a very small amount compared to blow by with bad rings. Just think how frequently you topped off your oil. Probably didn't even register on the dip stick, but you can see evidence of oil in the varnish and tar that remains.

Anything running down the exhaust valve would burn in the exhaust pipes without affecting performance. But if oil gets into the combustion chamber it lowers the octane rating of the fuel resulting in knocking, which forces you to retard the spark and loose possible performance.

All of this is speculation without a further examination.

Big Dave
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post #5 of 10 (permalink) Old 01-13-2020, 08:08 AM Thread Starter
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Thanks Dave. No affect on dipstick readings, which I check frequently. Any chance this could be insufficient crankcase ventilation?

ETA: I might be able to test this by cleaning the intake runners, adding oil to the crankcase, and using the oil pump primer to circulate oil throughout the engine. If the runners are oily again, I think this would be a good indicator that they're is an issue with the valve stem seals. Works in theory I guess.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac

Last edited by 68WASAGOODYEAR; 01-13-2020 at 08:25 AM.
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post #6 of 10 (permalink) Old 01-13-2020, 09:07 AM
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Valve stem seals wipe off excess oil from the oil squirted out the push rod tubes to lubricate the rocker ball and to cool the valve springs. There are a lot of factors determine how much of the oil actually gets on the valve stem. Don't think a staic test will work. A flash light and an inspection mirror would allow you yo look inside the valve springs to see the seal.

I use white nylon with a stainless spring Perfect Circle valve stem seals that require machining the top of the valve guide. I bought a special cutter years ago and machine the valve guides in my drill press, then press them on by hand. The factory used a rubber umbrella for a seal that may not fit well inside high performance springs (double wound or conical). If the rubber seals don't fit, then a lazy builder would leave them off entirely, rather than address the problem.

Either way you can see the seals or the lack of them if you look.

Big Dave
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post #7 of 10 (permalink) Old 01-13-2020, 09:55 AM Thread Starter
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OK. I will take a look tonight and see if I can see the seals.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #8 of 10 (permalink) Old 01-13-2020, 05:41 PM Thread Starter
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16 valve seals, all matching the ones in this link, present and accounted for:

https://www.summitracing.com/parts/cca-518-16/
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1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
68WASAGOODYEAR is offline  
post #9 of 10 (permalink) Old 01-13-2020, 05:57 PM
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Those are Fel-Pro valve stem seals. Made of rubber instead of plastic but should last for 70K miles at least.

Don't know whose heads those are but even new heads require work as opposed to bolting them on. This is one of about nine videos on machining a head that illustrates my point:


Big Dave
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post #10 of 10 (permalink) Old 01-13-2020, 06:26 PM Thread Starter
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Quote:
Originally Posted by Big Dave View Post
Those are Fel-Pro valve stem seals. Made of rubber instead of plastic but should last for 70K miles at least.

Don't know whose heads those are but even new heads require work as opposed to bolting them on. This is one of about nine videos on machining a head that illustrates my point:


Big Dave
The cylinder heads are by Dart.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
68WASAGOODYEAR is offline  
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