924Board.org

[-nick]

Argh! Pulled the plugs yesterday and found #2 plug is wet with coolant. I think that what I thought was the turbo burning oil sometimes (happens if I shut down the engine before the car has fully warmed then restart- see earlier thread on the topic) is really steamy coolant coming out of the exhaust. I hadn't put my nose up to it before yesterday and that was definitely coolant. If this is what the smoke was all along then the gasket must have blown shortly after the rebuild - within 3k miles.

I'm also getting pressure from the coolant after the car has completely cooled = compression blowing into the coolant.

I have to say, I'm a little surprised. I'm using Raceware studs torqued correctly and a new headgasket. I did have a short overheating episode around the time that I began getting the smoke cloud- the cooling fan switch on the rad had one of the two wires come loose in traffic. I pulled over shortly after the temp gauge needle crossed into the red- but it must have been enough. The coolant tank did puke up quite a bit.

Grr. What a pain. I'm just venting a little here... I'm not going to have a chance to replace it for a few weeks but it seems like driving on it isn't hurting anything if it has gotten me this far (~8k miles already). I'm not looking forward to this!

-nick

[Paul]

Drain the oil and check for coolant, and I'd stop driving it immediately.

[wdb]

deffinitly change the oil , try retorqueing the head bolts , it should have been done at 1000 miles IIRC ,using stock bolts , the alum head ,steel bolts ,and iron block have different heat cycles and will settle in at different times . it cant hurt and might get it and save you some time and money .

[-nick]

Yep, new mobil1 change over the weekend too. The old oil looked amazingly clean after 5k miles. So I don't have any oil/coolant mixing at least.

I retorqued the head per raceware's directions (after the first heat cycle). I also just blindly checked them over the weekend while I adjusted the valves to make sure the nuts were all tight with a ratchet- and they were.

It's still odd to me that I only get smoke if I shut off the car before it has completely warmed up then restart. If I shut it off hot and restart, there are no problems whatsoever. All I can think of is that when the engine is cold there is a break between the #2 cylinder and a water jacket and when the motor warms up the break seals up too. Thus when the engine is cold the cylinder is pressurizing the coolant and if I shut the car off when cold then the coolant flows into the cylinder through the break, which doesn't happen when I shut it off hot. Sounds fairly reasonable.

Next test will be to check the compression hot & cold. That may be telling. Might shed some light on why cyl #1 looks like it's burning lean too.

-nick

[wdb]

be sure to retorque them before major surgery if it seems neccessary . (back off the nuts then torque, just to be sure its right , also old torque wrenches can be out of specs , I think sears has a service/calibrator , if not call around the part stores .

[Paul]

Raceware has different torque specs for dino oil and Mobil 1, which did you use?

[-nick]

I'll retorque them to double check, but I'm not expecting any miracles- once there is a gasket break is pretty doubtful that retorquing will seal it up.

Paul- raceware only has torque specs using dino oil to lube the threads. That's what I used for the first & second torques. So it should all be up to snuff.

thanks,
-nick

[Paul]

Raceware had 2 torque values when I installed mine 5 or 6 years ago.

The value for Mobil 1 was quite a bit lower since the nut supposely turned with less friction against the washer. Using the dino oil spec with Mobil 1 could crush the head gasket, I guess. The guy I talked to (5 or 6 years ago) seemed to be more concerned about stripping the nut, than crushing the gasket, however.

I emailed them today asking that they send me the specs again.

[Racing]

Nick.
After having swapped 6 gaskets since last october...
The basic truth is that the OEM style one won´t take any what so ever detonation.Period.
Dunno if you remember,but my gun had a somewhat larger compressor housing and even at boosts as low as 1,3 bar i would have the gasket go awol if i weren´t COMPLETELY ontop of what was going on.

As far as i´m concerned the 931 engine really needs to have a copper gasket and some forged pistons if and when you start playing around with it.
Problem lies in the sealing propertys of a copper one.
Frankly speaking the easiest way to do this would in my opinion be to seek one of the old Crane "o-ring" cutters out.
This old tool-that i´m not even sure can be had from Crane anymore-centers on the individual cylinder and from there on is run by hand to cut a relief at a set distance from the cylinder per se.
The mere relief will be seeked out by cylinder pressure,while it will also let the copper head gasket "creep" into the cut making for a vastly more secure seal.
If need be and arises you can also make up stainless steel wire inserts for said cut which in that case will increase pressure on the copper gasket to a point where you can basically forget about sealing problems from the cylinder.

None the less...
I would NOT under any circumstance install a CU head gasket on the stock pistons,cause that would be the same as putting an adress note on them for the nearest junk pile as they in that case would take all the beating the engine could muster in a heartbeat.

Installing the cheap "generic" forged Mahles i did works like a charm.
It is however a project as the engine needs to come out and have the small ends of the rods redone to 22mm piston pins.

My take is that the stock head gasket and the stock cast pistons of the 931 engine is the only weak points of it,but they indeed are some serious weak points alright.

[Paul]

Here's Raceware's answer:

Hi Paul,

All of our tightening torques are specified using 20W-50 regular petroleum engine oil. We do not provide tightening torques for any of the slippery lubes like synthetic oil, Moly or cam lubes as these all vary by brand, lube, etc. The proper tightening torque for your 924 HSK is as follows:

Use 20W-50 regular petroleum engine oil to lube the top stud/nut threads. Do NOT use slippery lubes like synthetic oil, Moly, cam lube etc. as these require a lower tightening torque.

step 1 = 20 ft/lbs.

step 2 = 35 ft/lbs.

Final Torque = 50 ft/lbs.

Run engine to full operating temp, allow to cool to room temp then re-torque to 50 ft/lbs. again as all head gaskets compress after they have been thermally cycled.

If you are using synthetic oil in your engine as a lube from initial start-up (which usually isn't a good idea as the rings need to seat in before using synthetic oil), we recommend that you do NOT exceed 35 ft/lbs. on the RE-TORQUE after the engine has been run to full operating temp and allowed to cool to room temp. You still assemble the HSK with regular 20W-50 petroleum oil only however. The reason for a lower tightening torque on Re-Torque is that the synthetic oil will migrate into the HSK threads when the engine is run, thus reducing the turning torque when you re-torque the nuts. If you tighten the nuts to 50 ft/lbs. with synthetic oil you will likely strip the threads or stretch the stud as synthetic oil can lower the tightening torque by as much as 30%.


Regards,

Randy Hubbard
RACEWARE Engineering LLC

[Joes924Racer]

there torqued to a lower value than the stock 78 ft lbs
porsche has em at.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[Paul]

Due to their design of the threads, nut, and washer, these lower torque values actually result in a higher clamping force than the stock setup and torque values.

[numbbers]

Well, no offence to anyone, but I think, if I was having headgasket problems with Racewares recommended torque values. I would try replacing the raceware studs with a new set of stock headbolts, torqued to factory specs, before I would go back into the engine.
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1980 924 Turbo

[CMXXXI]

Just curious... is it a matter of finer thread pitch = lower torque value instead of higher/coarser thread pitch = higher torque value?

I reused the existing nuts & bolts (upper and lower end) with my rebuild and haven't experienced any problems. The caveat is that I've probably only got 1,000 miles on everything since the rebuild, and haven't "pushed" things for any length of time during my back road jaunts.
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'79 Eurospec 931

[Lizard]

CMXXXI I have also reused the 924 head studs many times and have never had that cause a blown head gasket,
but the idea behind it is that everytime you use that bolt it stretches and once it stretches enough they will break.
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3 928s,