924Board.org

[Cedric]

I use the ring for both in and out of the exhaust side, works well. As long as you only use one of the two types at the same time
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1980 924 Turbo
www.instagram.com/garagecedric/

[chuck21401]

Made some good progress this weekend.

1. Removed final muffler. That was probably the easiest part. Actually it's suspended from bungee cords under the car, will be easier to reinstall.
2. Removed starter. Was hoping to avoid this step..but needed to access a nut connecting the bypass pipe to the WG.
3. Dropped exhaust between turbo outlet and final muffler. Was able to leave the J-pipe in place.
4. 2/4 of the turbo mount bolts had disappeared. Replaced all hardware. The bolts that were in place were M8 X 20mm (1.25). The spec calls for M8 X 25mm (1.25).
5. Replaced turbo to exhaust manifold bolts. Used 1 Porsche bolt and sleeve ($$$) and used APR bolts for the other two. Would like to see everything stay in place before ordering two more sets of Porsche parts.

The turbo mount bracket is connected to the block with four bolts.
This one is easy to get to. The one above that took some stretching and patience. Once I was able to start the bolt by hand, I was able to reach it with an extension and flex socket.



The bolt on the top right is accessible from above with an extension and swivel socket. Tight squeeze past the charge tube. I was ready to remove it, but was able to install the bolt without doing that.



The bolt on the lower right wasn't easier. It is accessible from the front of the car, but only with a wrench. I couldn't get a socket on it!



I tightened down the manifold to turbo bolts first, then the turbo bracket mount...and ran out of time.

Next up -- installing new studs on the turbo and reconnecting the exhaust.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[Cedric]

It really is the world cup of socket extensions and general use of every tool you have in the garage to get to those bolts. Most other things on the car you might do will be so much easier, thats a positive at least
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1980 924 Turbo
www.instagram.com/garagecedric/

[chuck21401]

A bit more progress today.

The Snap-on stud installer (MSK-M1015N) made installing the new studs easy.



The original Porsche studs (900.081.050.02) are NLA. I ordered these from from this site: https://www.treadstoneperformance.com/product.phtml?p=103702&cat_key=305&prodname=M10+X+1.5+42mm+Stud

I was a bit worried that 42mm would be too long but they worked out fine.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[chuck21401]

Decided to try Stage 8 locking nuts. (#3952 Turbo Nut Kit (10mm-1.50))


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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[chuck21401]

My car is back on the road...but now I have new problems. lol

In terms of the loose/missing bolts....

1. Replaced turbo mount to block bolts.
2. Replaced turbo to manifold bolts.
3. Replaced turbo exhaust studs; used stage 8 locking nuts. Used gasket and left out the "fire ring"
4. Tightened j-pipe nuts (not much)
5. Tightened j-pipe to wastegate nuts (not much)
6. Replaced WG mounting bolts/nuts. They had also disappeared.
7. Remounted exhaust; used fresh hardware as needed.

There is a lot less vibration now.

Previously I had replaced the clutch slave cylinder and bled the system using a motive power bleeder. Was still having trouble with the clutch dropping to the floor. Thought maybe I had an air pocket so I bled it again. After driving around it's clear that didn't fix the problem...I'm thinking that the master cylinder is bad. It is not leaking fluid...just loosing pressure from time to time. So that will be the next project along with the related rubber line that runs from the master to the slave.

But here's the bigger problem....

I drove the car around for probably 30 minutes. Seemed to drive as normal....AFR meter seemed normal as well....14.7 at idle/cruise....low 12s into the boost.

So as I'm idling in the driveway I see the AFR is in the 10s/11s at idle... I drove around at bit and it seemed to be in the 11s, 12s, 13s but never at 14 at idle or cruising. Why would the AFR readings change so dramatically all of the sudden? Could there be a problem with the sensor for the gauge? A problem with the O2 sensor? I'll hook up the dwell meter to see what's going on when I have more time. Just doesn't make a lot of sense. I suppose I could disconnect the O2 sensor and try it...seems like that would cause the car to run leaner?


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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[MOTANUL]

I checked the exhaust system today for the first time more seriously.
I have (many) problems in the following areas:
1. When leaving the turbine, between the pipe and the flanges, I think there is a crack all around
2. At the wastegate body - about 4 places
3. A weld at the entrance to the first drum (I don't have any pictures). It loses very little air
4. A weld at the entrance to the final drum. It loses very little air


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1980 Porsche 924 Turbo (931) diamond silver metallic/helios blue metallic
sold Porsche 924 NA 1979

[MOTANUL]

3. entrance to the first muffler. It loses very little air (there are three small holes at the beging of the first silencer / muffler)

The big problems are at the turbo flange and wastegate - strong air is lost in these areas.


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1980 Porsche 924 Turbo (931) diamond silver metallic/helios blue metallic
sold Porsche 924 NA 1979

[Fasteddie313]

Man I love to pressure test but I’ve never thought to pressure test an exhaust like that!

If you have a crack at the turbo flange that sucks, but should be able to be welded easily..

How good is good enough? (Little leaks)
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80 Turbo - Slightly Modified

[Beartooth]

That is quite a few leaks! Definitely some of them could be leaky gaskets. And like Fasteddie said, the others might be easy to fix with some welding. I'm in the process of refreshing everything connected to the turbo; kind of a pain in the butt, but given how much work it would be to go back in, I think I'll just bite the bullet now. One thing to consider: leaks between the manifold and turbine or wastegate could cause lost boost; leaks from the turbine outlet or wastegate outlet and beyond will probably just make noise. Or it could be that the leaks are insignificant enough that they're not really affecting anything...

Anyway, lots of discussion of bolts in this thread, and since reading through, and especially since I'm reworking mine and replacing some hardware, I'm curious what the best choices for nuts and bolts are. I'd go with the Porsche bolts and spacers, but only the bolts are available (apparently), and it seems like kind of a waste without the correct spacer. I'm thinking on the manifold and turbine outlet, I'll use stage 8 locking nuts. On the manifold to turbine inlet though, the question seems more difficult. Somebody mentioned using studs instead of bolts there, but wouldn't that make removal and install a real PITA? Stage 8 makes locking bolts, but I'm concerned that the length is too short: they're only 25mm long; I figure you'd only have 8mm of engaged thread if you use a washer. It would be nice to have a locking bolt, but it doesn't seem there are many options besides Stage 8. I have to wonder, if I were to go the route of using a plain bolt, if I can and should attempt to emulate Porsche one way or another. I could either buy the Porsche bolt, or an ARP bolt, and use a spacer sourced elsewhere (stainless steel?). I'm guessing the longer bolt made for some elasticity, but hard to say... So, what is the best option? I hate to spend over $100 for the Porsche bolts unless there's a good substitute for the spacers, and at the same time, who's to say the Porsche bolt works better than an ARP bolt? But on the other hand, I've seen how much good using just any bolt does you...
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1980 931 diamond in the rough

[Fasteddie313]

I used those black Allen cap head bolts, mani to turbo, until I acquired enough of the original Porsche ones from parts sales here on the forum..

When someone is parting a car, selling parts, selling turbo parts, etc, they probably won’t specifically list these bolts, but ask if they have any..
That’s how I got mine..

I believe 2 of my 3 originals snapped the first time I removed my turbo, so it’s not like they are some magic indestructible bolts either..

I used stainless from head to mani..
Hardware store studs/nuts in WG..
Forget what I used on the turbine to downpipe so it must not have been anything too special..

The head to manifold connection uses those fire rings that expand with heat, and most turbos use the aluminum rings that do the same..
I don’t know how well these seal when they are not hot..

I personally wouldn’t overthink this too much and let it become a hangup keeping you from progressing..




My biggest concern as I have stated many times, what I believe is most important, is correct turbo clocking, clocking it wild, and then careful and complete cross tightening of the various interfaces..

“ I tightened down the manifold to turbo bolts first, then the turbo bracket mount”
No!
I would not do that..

Unless it is the same turbo that came off the same car, and you didn’t remove the head and/or exhaust manifold, I would heavily consider also Reclocking the turbine..

Manifold to head tight, cross tighten hole head studs..
Bearing housing to turbine barely snug..
Turbine to manifold barely snug..
Bearing housing to block mount barely snug..
Block mount to block barely snug..
Like 3-5 ftlbs while wiggling it to seat it all..
Snug it all a little more..
Snug it all a little more..
Pull it all together as one..
Get it like half-3/4 tight..
Tighten what turbine housing to bearing housing studs you can pretty decent..
Pull the turbo back off and tighten the turbine housing to bearing housing good to finish tighten..
Reinstall it and repeat gradually cross tightening all manifold to turbine housing, bearing housing to block mount, and block mount to block bolts, cross tightening all as a package..

These are all completely stiff cast iron connections and anything even a little bit off, not pulled together gradually as a package, could be huge stress once tightened..

We see a lot of cracked cast parts here, even new from the factory, and I believe this is why..

We see lots of cracked J pipes too..
Make sure you aren’t using your tightening to force anything into position..

These things I believe are very important..


The leaks.. I can’t see them in person to judge their severity..
Anything cracked welds on pipes is obviously an issue, but I’m not sure I would expect absolutely perfect seals..

One way to get better seals would be to face your flanges with a file until they are completely flat.. I do this more often on things like bike carb intakes..

The flanges on your J pipe and dump pipe are likely to be warped slightly out of flat.. Hit them with a file and make sure they aren’t high at the bolt holes.. If anything you want them a little low at the bolt holes and a nice flat high just around the pipe where you want it to seal..
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80 Turbo - Slightly Modified

[Beartooth]

Thanks for all the input, I'm definitely coming back to it when I put it back together. I do have a little time since I'm sending the turbo off, and then I'm going to be gone for a couple weeks anyway. Once I found the damaged turbine wheel, I knew I'd be putting it all back together after I get back. I suspect that a major part of the problem with the turbo as I got it is that the flanges weren't flat to each other. The turbo had definitely been out before, and probably somebody either rushed the job, or tightened things down in the wrong order. The threads on the bolts were rounded, and there were marks on the holes in the manifold from the threads.

I'm not sure how likely my idea that the longer bolt is more elastic is; just seems plausible to me. Either way, I'd agree that pure tensile strength probably isn't what makes them special. Right now I'm leaning toward using ARP chromoly bolts (probably 40mm) with spacers, mimicking what Porsche did. I see several sources that sell stainless steel turbo bolt/stud kits, but I'm finding a lot more complaints from people using stainless bolts than chromoly. I might also look into safety wiring. But maybe I'm just being paranoid based on other people's issues.

Anyway, I'm probably lucky not to have any major cracks, considering that all signs point to mine being poorly assembled. Hopefully some care on assembly will help keep it that way. On the wastegate J-pipe, one idea I had was to get a weld-on flex coupling (like this https://www.summitracing.com/parts/vpe-60404), cut the requisite length of pipe out, and weld it in so I don't have to worry about that cracking again (hopefully). I think I saw something along those lines in the technical section, but a more crude solution: cutting the pipe and using a larger piece of pipe and some clamps to make a slip joint. I'd think stainless bellows would be a more elegant solution; only issue is, I can't find one in the same size. I'd either have to go a bit smaller (1.5", around 38mm) or bigger (1.75, around 44mm). Probably easiest to get the bigger one and get an exhaust shop to expand the ends... My truck came with a leaky slip-joint up-pipe to y-pipe that I converted over to stainless bellows; just seems like a better idea. I can see where the J-pipe would be prone to cracking: it doesn't see much heat until the wastegate opens, and then it's a full slug of max temp exhaust, then right back to ambient as soon as the foot comes off the gas.
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1980 931 diamond in the rough

[Cedric]

I happened to develop some of these kind of turbo joints many years ago at an OEM. To make a successful hot screw connection like this many factors come into play. The screw lengt is very important since it can compensate for settling if the screw joint, and also during expansion an contraction when it gets temperature cycled. All material expands differently, which is also a reason why certain materials are chosen in screws and spacers. Crap screw will also oxidize quickly and will loose their clamping force.

If the screws are to expensive(which they are from porsche) you could always buy them from any other OEM turbo installation if you find anything with the correct length. Pretty much all OEMs use proper quality hardware, and its normally pretty cheap to buy them. I use spacers and screws from Scanias diesel V8, because i know what they are made of and they fit perfectly

For assembly I recommend checking through TB 83-03


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1980 924 Turbo
www.instagram.com/garagecedric/

[Cedric]

Regarding flex pipes, i put mine in the downpipe, after the turbo but before were it meets the WG pipe (ROW car). It made installation much much more easier, and also puts less tension in everything. From an engineering perspective the hot side on these cars are not very clever designed, its way over constrained which creates lots of challenges.
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1980 924 Turbo
www.instagram.com/garagecedric/

[peterld]

Good information in TB 83-03.
On the mounting plate to the block, I relieved all four holes to allow a little extra wriggle room. Fitting the turbo and ancillaries while the engine is on an engine stand is a doddle, however doing so while the motor is insitu is probably an 8.5 degree of difficulty, particularly in a RHD version where the steering shaft snakes through the exhaust.
A flexi pipe after the turbo is well recommended.
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80/81 932/8 ROW