'65 exhaust smoking. - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 06-06-2012, 07:15 AM Thread Starter
 
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'65 exhaust smoking.

Hi Guy's,

I have a qwick question, that I am hoping the more experienced members can help me with. I have a '65 with an '68 400cid that has a '66 Tri-power set-up. When I bought the car, the previous owner could not give me any real info on the engine internals, as he didn't have the info. The only thing he was told was it had a mild cam after it was rebuilt in 2004. The motor has less than 5000 miles on it since then.

When I first got it home and started driving it, the idle was a little rough and it would bog when you put your foot in to it. It's a 4 speed manual, so I changed the oil, flushed the block and rad, changed the fuel filter and changed the oil in the Muncie.

I had a local classic car shop adjust the Tri-power, not my area of knowledge yet, and also set the timing. Now it runs like a champ, good idle, easy starts hot or cold and great wot. The problem I am seeing now is: when I am down shifting and letting off the throttle, I can see exhaust smoke in my rear view mirror. It's not white smoke, more like a light gray colour. I only get this when I let off the go pedal and down shifting, and not always from both exhausts, most of the time it seems to be from the drivers side exhaust. The car sat for a long while before I bought it, the previous owner only drove it about 3000 miles in 10 years.

Do I have a problem? or am my just being overly cautious? Thanks for any insight and comments.
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post #2 of 12 (permalink) Old 06-06-2012, 08:14 AM
 
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It's probably not a major issue, but if you're like me you won't be satisfied until you know for certain what causes the smoke.

It could be a number of things; valve stem seals/guides, rings not properly seated, a clogged crankcase breather or PCV valve (I don't know if you've got a PCV valve on your engine...IIRC, they started using them in 1965).

It could also be completely normal and nothing to worry about if you're not using any oil...

You can learn a lot with a vacuum gauge. This web page has some good information and a number of "Scenarios" that demonstrate the effect of various engine issues on vacuum gage behavior. It's a simple diagnostic tool that can tell you a lot about your engine without touching a wrench. How to Use and Interpret a Vacuum Gauge

You could also run a compression test (wet and dry) to look for valve and/or ring issues, but I'd start with the vacuum gauge.

1968 Pontiac GTO
1983 Pontiac Bonneville (G) wagon
2008 Pontiac G8 base

Last edited by jmt455; 06-06-2012 at 08:15 AM. Reason: clarity
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post #3 of 12 (permalink) Old 06-06-2012, 08:58 AM Thread Starter
 
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Thanks for the reply. I'll start with checking the vacuum as I have a gauge. I hope it's nothing to worry about as well, just want to make sure I don't have something more serious happening.
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post #4 of 12 (permalink) Old 06-06-2012, 05:52 PM
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Grey/blue smoke on deceleration is indicative of worn or hardened valve guide seals or possibly worn valve guides. High manifold vacuum on deceleration pulls oil past the guides/seals and into the combustion chambers. You can replace the valve seals without pulling the head(s).
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post #5 of 12 (permalink) Old 06-07-2012, 05:32 AM Thread Starter
 
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Thanks geeteeohguy, kinda what I was looking for. When I have time I'll do the vacuum test and then have a look at the seals. Would there be any problem driving it while I get the seals replaced?
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post #6 of 12 (permalink) Old 06-07-2012, 12:15 PM
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No it won't hurt if it's the valve guide seals. I would expect it to blow alittle smoke at start up after it sits from a hard run if it was those as well. Synthetic oil could also slip past the seals easier. You could try to change the oil and add some LUCAS oil stabiliser, that should slow it down.
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post #7 of 12 (permalink) Old 06-07-2012, 12:34 PM
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I agree. The only thing you'll hurt is your wallet if it's using a lot of oil. Actually, you're getting extra top cylinder lubrication the way it is now....no worries at all about hurting anything.
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post #8 of 12 (permalink) Old 06-07-2012, 01:49 PM Thread Starter
 
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Thanks guy's for the replies, it puts my mind at ease. Was a little worried that I had a bigger problem. I do have the dreaded rear seal leak, so I get a few drops of oil on the garage floor, if she's sitting for a couple of days. I plan on pulling the motor and doing a refresh after this season is over anyway.

I did just put some some Lucas oil stabilizer/seal renew in last week. It did seem to help with the rear seal leak, I think the whole problem stems from it not being driven very much, before I picked it up. That's not a problem any more, as I drive it every chance I get.
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post #9 of 12 (permalink) Old 06-22-2012, 05:45 PM Thread Starter
 
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Hi Guy's,

Just alittle update on my exhaust smoke issue. While I am sourcing new valve stem seals, I decided to add some Bardahl No-smoke oil additive. It stopped my exhaust smoke problem immediately. I have no gray smoke on acceleration or down-shifting anymore.

I went for a good run today and afterward I checked my oil level, now my fairly new oil, 700 miles since changed, is completely black. Level is good, but before I added the Bardahl, the oil was still looking like new. Is there something else to this or is it just because I added the Bardahl to new oil? When I changed the oil I added a seal renewer, Lucas I believe, to slow down the rear seal leak.

Have I put too many additives in my oil? Just looking for advice from the group. By the way, the '65 is running great, lots of power, smooth idle and no problem with the response when I go WOT. Have a big ass grin everytime I take it out of the barn.
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post #10 of 12 (permalink) Old 06-22-2012, 06:55 PM
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I'm not a big fan of oil additives, personally. Stopping the smoke doesn't mean you've stopped the leakage anyway. Like others have said, it's not a huge problem or 'dangerous' to your engine. One thing that will happen is it will tend to form carbon-ish deposits on the back sides of your intake valves that, if left unchecked, will eventually get large enough to affect performance becuase they'll be affecting airflow into the motor. The stuff is fairly easy to clean off, but you have to pull the heads and valves to do it youself so keep that in mind. I'd recommend getting some fresh valve stem seals on it at your convenience, and lose the additives.

Almost forgot... on the issue of your idle mixture screws not having any effect. Grab youself a copy of this book:
How to Rebuild and Modify Rochester Quadrajet Carburetors - Cliff Ruggles - Google Books

In there you'll find a section on adding "idle bypass air". That should take care of the problem.

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