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ossaman55 · Posted: Wed Aug 09, 2006 5:37 am Post subject: Smoking 931

I just got my 1980 931 back together after replacing the turbo. It was smoking before but i thought it was due to bad seals in the turbo. It now lets a large puff of white smoke out on startup. At first i thought it might be burning up the rest of the oil that was pumped into the intake when the turbo shaft broke. Now im not so sure. I think it might be the valve guides. Is valve guide wear a problem on these cars. Also does anyone have any suggestions as to what might be causing the smoke on startup.
Thanks
Darren
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Darren
1980 931
1984 Maserati Biturbo
1978 Triumph Spitfire
1986 Camaro Z28

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

white smoke = coolant = headgasket

But, since you have the head off, you might as well have the valve guide seals replaced too.

Pick up a $30 compression gauge from your flaps. You'll probably see one cylinder (or two) very low when cold, and probably closer to the others when warm.

You can also pull the spark plugs out when you start to see the smoke. The leaking cylinder will be smoking out of the spark plug hole.

ps - the turbine shaft broke?? yowch!

Lizard · Posted: Thu Aug 10, 2006 1:21 am Post subject:

yes white smoke is coolant, though if it only happens on startup on moist days it could just be condensation in the tail pipe.
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3 928s,

clawless · Joined: 06 Nov 2006 Posts: 14 Location: Stafford, VA

I am having the same problem as ossaman55. I had the headgasket / valve guides replaced. it smokes the same, (maybe a little less) even when they started it the first time, but only at startup for about 30 seconds. its oil smoke, no doubt. my next though was turbo seals, but why only at start up?

As a side note:

The large hose going into the air filter housing (comming from that puroilator canister thing <- yes its a technical term), I was making a new air intake, I plugged that hose and it smoked like MAD like it did when I started it. Opening it back up stopped that smoking. I connected it to my new intake. Yesterday I was running it hard (redline hard) and the bottom hose that goes to that puroilator canister on the firewall side (i dont know where it comes from) blew off the canister and a noticable amout of oil blew out. I repaired it, cleaned it, and ran it again, it was fine. This morning I did not notice any smoke, could that hose have been restricted internally some how and i blew it out? kinda like when i plugged it? I will see what happens tomorrow morning, if there is any smoke...

Lizard · Posted: Mon Nov 06, 2006 1:44 pm Post subject:

that is the air oil seporator. 1 lint to crank case breather, 1 line to oil pan and 1 line either to atmo or back into the crank case.
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3 928s,

clawless · Joined: 06 Nov 2006 Posts: 14 Location: Stafford, VA

Ahh Yes air oil seperator, found that in another post later. - thanks

Made no difference, same smoke. Although tonight when I left work there was no (or very little) smoke. It seems to make a difference on how the car is parked. Front higher than back, little or no smoke, back higher than front, lots of smoke.

turbo rebuild in the spring....
_________________
Clawless

'80 931 M471, Audi Throttle Body, 11PSI for now
'97 Volvo 850R (The other woman)

'85.5 944 SOLD - 175,000 mi most reliable car EVER
'79 924NA RIP

Cedric · Joined: 27 Aug 2004 Posts: 2807 Location: Sweden

Maybe its time to do a leak down test on the cylinders. I´ve seen a couple of 931´s with broken piston rings. On my engine the top ring was broken on all cylinders..

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1980 924 Turbo
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emoore924 · Joined: 13 Apr 2004 Posts: 2822

I too had that same smoke thing happen when blocking off the purolator. Stupid mistake on my part. Blew *lots* of smoke out the rear. Way too much crankase pressure pushing oil up past the rings. That being said, once corrected, luckily no further prob's.

To add to the story, I recently dyno'd the car with a cone filter (which is why the stock air cleaner had been replaced and why the puro had nowhere to go...). The hp was up 10 but the tourque was WAY down up through 5300 rpm, attributable IMHO to the removal of the stock airbox. I'm trying to set up another run with the stock airbox replaced (head work done in the meantime), but have not been able to schedule at this point. Hopefully will do so in the next month or so...

Paul · Posted: Wed Nov 08, 2006 3:16 pm Post subject:

Maybe due to hotter air entering the intake????
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
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Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

clawless · Joined: 06 Nov 2006 Posts: 14 Location: Stafford, VA

I have a cone filter and a rubber 90 deg. elbow on mine, did not feel any drop in performance (only gain) but would I? never dynoed it...interested to know if the stock box performs better than the cone.

my smoke shows up after 30 - 45 seconds after its started. Like oil is sitting in the bottom of the turbo, just waiting to be burned when it gets hot enough...if the turbo seals are bad i am guessing oil can drip into the housing?
_________________
Clawless

'80 931 M471, Audi Throttle Body, 11PSI for now
'97 Volvo 850R (The other woman)

'85.5 944 SOLD - 175,000 mi most reliable car EVER
'79 924NA RIP