69 911 with strange engine smoking problem

[rngpc]

I recently purchased a '69 911S with a strange engine smoking problem. The former owner told me the engine was rebuilt in the 80s and it ran fine until he took the car to a 10 min oil change place. He had the oil changed and the car came back smoking like a train. He parked the car and it had not been driven for some time (at least a year). The first time I saw the car, it was not smoking at all. We let it idle for at least 15 min while looking at it and no smoke whatsoever. I went back a couple of weeks later - started it and ran around the block and came back and it was billowing smoke at idle.

A leak down test performed showed all cylinders between 4-6% . I went ahead and made a deal on the car. The shop initially thought the oil tank was overfilled and it was burning oil which had accumulated in the exhaust system. The oil was changed and some other general maintenance items taken care of. The oil is at correct level. The car has been run several times while at the shop and it still periodically smokes. When I picked up the car, I was told it could possibly be valve seals or worn oil ring(s). It this were the case, wouldn’t it smoke more regularly?

Here are the current symptoms:

1. After picking up, I drove about 5 miles to get gas - no smoke. I let idle for a few minutes - no smoke at all.

2. Within about 5 minutes of driving down the highway at around 3000 rpm, it started smoking like a train. When I got home, I let it return to idle again and it was smoking so bad the neighbors called the fire dept. (not really)

3. Here is where it is getting strange - I then let the car sit for about 3 hours or so. I started it and let it idle for about 10 min. - no smoke at all. I revved up the engine several times thinking it would start puffing, but no smoke.

Any thoughts or suggestions what this could be? I would think that excess oil, if any, would have burned out of the muffler by now. I have not pulled the plugs to see if any are oily yet.

I posted a similar posting on the Early 911S Registry.

Thanks in advance for any thoughts.

Robert

[copper]

First thought I had was an overfill, that would have explained the no smoke at idle, but the smoke with motion, once it started moving around.

Could still be remnants of an overfill.

Does it do it consistently at any particular time? Such as during a hard decelleration? Could be a sticking valve allowing oil through or a worn guide.

But it seems like there isn't any consistency to it. Strange.

Check your plugs. See if there's oil on them, note whether one or more cylinder is heavier than the others. Clean them, put them back, drive it, and recheck. If you got lots of fresh oil, then there's most likely a problem with that cylinder on the intake side allowing oil through, which would generally be valve related.

Jim

[Fishcop]

You might have an oil leak at pressure. That is, a seal doing it's job at idle to 3000, but failing at 4000+. Maybe rocker shafts dripping on to exhaust at higher revs?

[Early_S_Man]

Robert,

Pull the plugs, and if clean ... pull the muffler. Rinse out muffler with Varsol or similar solvent and let air dry. Chances are that oil remaining in muffler was the source of the smoking, and that a good one - two hour drive on the highway after reinstalling muffler will end the smoking problem!

[jluetjen]

I hope that you got a good deal on the 911S. This could be just the type of problem that allows a knowledgeable buyer to get a good deal.

[rngpc]

The saga continues:

Pulled all plugs - black and sooty (running rich) without any signs of oil

Pulled muffler - sat it up for a few hours with outlet down, no oil

Let car idle for 30 min with revving up of engine - no smoke at all

Drove car - within 1-2 minutes, car smokes like train while accelerating, appears problem clearly surfaces when engine under load. Nothing really significant either way when decelerating in gear. I didn't drive for considerable amount of time, probably 15 minutes.

Very strange since nothing at idle, even after car sits idling for long time. Wouldn't it blow smoke when cold or hot if rings were bad? Why would driving it cause it to suddenly blow smoke? I guess valve guides/seals may be possibility.

Any new thoughts would be appreciated. Thanks.

Robert

[Redlineshftr]

Im interested to see what you find because I have a very similiar smoking problem...

[Grady Clay]

I’m inclined to agree with Warren – oil in the muffler. It only smokes under load when there is seriously hot exhaust gasses in the muffler. Let it cool – no smoke. Start cold and idle – no smoke.

See if you can borrow a clean muffler and try it.

Best,
Grady

[Early_S_Man]

Robert,

Doesn't sound like worn rings to me with the good leakdown numbers you got!

Smoking under power at mid to high rpms ... could be sucking oil into the intake ports past worn valve guides and/or bad seals on the intake valve stems. You could pull the intake valve covers and check for intake valve guide wear on each cylinder with lift at 10 mm ... push/pry spring retainer with large-blat flat screwdriver ... significant deflection would be a bad sign.

On the richness issue:

What condition is the hot air tube [double 25 mm corrugated tube, black plastic over aluminum] to the injection pump thermostat in ... any kinks or crush damage??? At idle after warming up ... significant volume of hot air should be coming out of the thermostat exhaust air outlet, continuously.


On checking the muffler for oil ...

The two inlets are what should have been down to allow for draining. The outlet is too far from the oil source, and a muffler has to be really full of oil to drip out the outlet!

[rngpc]

Warren:

What about oil control ring?

I will pull the covers and see if I can check the valve guide wear - never done this before but doesnt' sound too difficult. If there is not much deflection, then is there any way to check the seals?

The hot air tube appears to be in good condition. I don't know about air coming out the thermostat, but will check it.

Thanks for the reply.

[rngpc]

I don't think there is oil in the muffler because none came out, but I could be wrong - I may try swapping out muffler also.