924Board.org

[Mclaren924]

Hey all, I recently have found myself knees deep in a beautiful 931's possible open heart surgery. I was put in contact with this gentleman by a good friend at CRE and long story short he has an intercooled 931 with some widebody gts? fenders on it and a 944 turbo front bumper and some sort of nose piece. Has a top mount IC and some AFR and boost gauge to match. I have no doubt this car was owned by somebody that was on this board at one point and hopefully they are still here. The car has been bounced from mechanic to mechanic and has recently showed up with me to do a cs steering wheel, new dash, parking brake, bad exhaust smell, and a few other odds and ends along with a good inspection. Chief original complaints were extreme exhaust smell with windows up and really stiff steering/handling. Car has barely seen a few hours of driving in past year because of bad boost leak that shop before me fixed. Car drives 3 hours down to me without issue so stowed it for the day, next day i come out to test drive it and check oil and its about half so I add a little and then warm it up and drive about 20 min. Drives fast but very stiff and steering is brutal with 16" 205's on R888's and massive sway bars and stiff springs in front, it feels much faster than my other 931 S1. After getting in the air, I start inspecting entire car and notice a pretty good puddle of oil in the valley of all the intake runners. I pretty quickly ascertained its either going to be the valve cover which I deemed unlikely, the pcv valve/aos being blocked, or it was leaking out the throttle body boot. Disconnected pcv line from airbox and started engine and felt pressure escaping as well as a clean airbox and filter told me it wasn't the pcv. Once I pulled the vacuum lines off the intercooler for the boost gauge, I knew it was going to be bad. Entire intercooler is soaked with oil inside and there's a pretty good puddle sitting in throttle body and the attached boot. Inside of intake is thoroughly coated when inspected through throttle body. I work down to both of the cold side portions of the turbo from the top by removing the airbox and fuel lines off the FD and then the FD itself, than finally the rest of the intake track off the turbo intake. Big buddle of oil on the intake seal and in the short little piece connecting the IC to the turbo. Going under the car the turbo has a few visible leaks coming from the housing mating surfaces and some lower bolts on the cases. I at this point gather the turbo is becoming an oil pump and pumping oil leaking from inside itself, up into the intake track and therefore into the engine. I did notice on my drive over it was leaning out almost any time I got into boost past 3500 rpm. I've been told by the gentleman who owns it that its on a strict 91 diet and I have began to wonder if it leaning out was possibly caused by large oil consumption reducing the octane of the fuel. After my 20 min test drive the oil was almost off of the dipstick. I believe the turbo will either need refurbishing or replacing to quell this issue but I would like to hear what everybody thinks.
https://imgur.com/czV65BX

https://imgur.com/j2I3BMP

https://imgur.com/uChQ9uj

https://imgur.com/iXJbnW2

https://imgur.com/OFt2mC1

https://imgur.com/a/0V0B3nD

https://imgur.com/a/IwaznoI

https://imgur.com/a/0V0B3nD
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[Beartooth]

Oh man, this is taking me back a couple years to when I first got my 931 going! As soon as I got it running, I noticed oil seeping from the TB boot, and found it was throwing oil up the charge tube. So I assumed the turbo oil seal was bad and embarked on the turbo R&R adventure. I had the turbo rebuilt by GPOP shop, got it all back together, and I still see evidence of oil up the charge tube. It's not nearly as bad, but that may partly be because I replaced the ratty old boot and hose clamps (that were too small; may not have been original).

Rabbit-trail here, but here's how to fixed the boot issue. I bought a 3.125" D by 3" L reinforced silicone tube and a couple heavy-duty clamps that do the job much better. The hose is just a little big; 3" might work better, but might be a pain to stretch over. The clamps are around 3/4" wide and have a stack of beveled washers under the bolts so it's spring-loaded. I got the parts from Summit Racing; the boot was Vibrant Performance, and the clamps were Mishimoto.

Anyway, what could be really bad news is I think the reason I'm still getting oil up there (and burning a ton of it) is because there's so much blow-by, it's pressurizing the crankcase and interfering with the drain-back from the turbo, which I hear can cause a good seal to blow oil. My leakdown numbers were something like 95/70/70/40, so I have two bad and one very bad cylinder. I haven't quite gathered what motor is in the car you're working on, but it seems broken rings are very common on S1 pistons. I'd do a leakdown check on that car before anything else - there was a thread I found here that talked about similar oil issues caused by blowby, so it's not just me. The irony in my case was that I actually did need a new turbo. Not only had someone completely bodged a turbo install - using hardware store bolts, apparently! - but something had chewed up the turbine wheel. The turbo that came with it was either a new replacement or a rebuild (judging by appearances) that never had a chance because somebody with no clue slapped it on. I suspect somebody threw some money at that, then parked the car shortly after.
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1980 931 diamond in the rough

[Mclaren924]

Thanks for the reply Beartooth! Yes I also weigh the possibility of a blown motor so I'm about to head down to the shop to compression and leak down test it. My customer bought this car heavily modified and apparently the motor is a 2.1 L with forged pistons on stock rods and crank and was done within last 10 years. I believe it was a pretty well known 924 shop in Arizona that did the motor but I can't recall the name. Will report back with what I find in the compression and leak down numbers, I assume it will be fine but a turbo is a very long job and not cheap so it will be good to rule out all possibilities . I talked to a company/gentleman in Germany named Schwabenlander and he does a whole bunch of hybrid/custom 924 bolt on turbos so If the turbo is bad, I think my customer will go with a 6 AR housing with some machining done to fit a taller custom made compressor wheel. Apparently it is good for 1.5 Bar of boost which is more than enough for stock CIS.
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[Cedric]

The engine could of course have gotten damaged regardless if it was rebuilt or not, especially on 91 octane.. But if there is no oil traces in the crank vent it do sound like the turbo is the issue. You could also run the crank vent into a bottle to see if it comes out any significant ammounts.

Yeah, removing the turbo is not a fun job, i rather do it on the bench with the engine out, its tricky to do a good job in situ and try to follow the hot side torque procedure.

The scwabenlader guy makes good stuff, I chatted to him a bit a while ago to know more about his background and what he does with the turbos in detail, it does cost quite a bit of money though, you could possibly do something similar at a local skilled turbo shop, either just a billet wheel upgrade or taking the compressor side from some other car like a 951. But he does some fine tuning of the tolerances aswell to increase performance, that I wouldnt explore without experience

Regarding the oil drain, when i had a smokey turbo a bunch of years ago i ran it without the oil drain connected (just drained into a bucket) to be sure it still smoked and it wasnt any blockage in the hose. Can be done for a short while if you are careful, the flow is not so high
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1980 924 Turbo
www.instagram.com/garagecedric/

[Mclaren924]

Oh man it was going so well until it wasn't

Got solid 150 average across all 4 cylinders for compression and it passed a leak down test on all 4 cylinders with flying colors. Got excited here and began to believe the motor was good, than I drained the oil. The oil was like Frappuccino for first two seconds and then a constant stream of grey/blue colored oil pours out with obvious metal flake. ####. Caught a sample so I can send it off to be tested for it's contents. Pulled the oil filter off and it's laden with metal even on the top rim where the threads sit and the oring mount, will need to cut it open to see how much is really in there. Going to pull the pan off tomorrow and check it out along with a few main bearings and rod bearings. Currently saying a prayer for this motor and my poor customer.

I believe in two theories that cause this situation, more understandable is the turbo seal went bad fast and started pissing oil into the intake and essentially became an oil pump and sucked the sump dry in turn tearing up the bearings in the bottom end. Explanation 2, the motor was ran low on oil and tore up the rotating assembly bearings and the turbo bearings causing the seal to go and the large amount of endplay I found in the turbo wheel.

I believe the turbo going bad couldn't put this much metal into the oil, especially because the turbine spins smoothly and freely and makes no noise. I would like dissenting opinions on this. All of the oil that was leaked into the charge pipe, intercooler, tb, and intake was clean good looking oil. The stuff in the pan was horrible.

I agree Cedric, a rebuilt motor in my experience is more likely to fail than a factory one especially with how little care most people put in. At CRE a transaxle shop in SD, I am basically doing a nut and bolt fix up and complete engine rebuild on a martini 77 car after the previous shop took this gentleman's 5,000 and put a motor in with no pilot bearing, the wrong valves in the head, missing main bolts, list is never ending. Point being that you are right and there's a good chance this motors not healthy despite recent rebuild.

I really am trying to decipher how on gods green earth you take this turbo apart and then get it back together correctly with torque specs on everything. Yes I have the factory manual and while their way obviously works, its easier said or read than done lol. Really debating if this project just became an engine out job with all the factors at play considered. Will add a few hours labor but may be worth the investment as everything can be gone over and done much easier. Thanks for listening to me ramble, Will try linking photos again



Saddest Disco ever


Shaft play (not the sexy type)
https://i.imgur.com/0xkBCOI.mp4
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[Cedric]

Shaft play isnt good but not chaotic, in your most optimistic case the metal is from a worn down axial bearing in the turbo, otherwise its definitely engine out time, that amount of glitter isnt promising. If you drop the front axle and exhaust there will at least be some more space to get the turbo down, the screw on the turbo flange at the back might need a few extensions and angles to get to.

This is the TB I was tinking about with the torque procedure
https://drive.google.com/file/d/0B3GfYntUoi5adlJaREpGU2RtNVU/view?usp=drive_link&resourcekey=0-d8G_OsaFvW0jsmCfp3WXHA
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1980 924 Turbo
www.instagram.com/garagecedric/

[924RACR]

Well, that's far from the worst oil I've ever seen come out of an engine - I was definitely picturing worse. But no, that's not great, and I agree it's not likely that the turbo is the source of that.

So yes it's probably engine out time; dropping the pan and looking at the bearings will probably confirm that. A drag, but that way you can be certain all is done properly, as noted. On the plus side, the more difficult to obtain parts (valvetrain) sound like they're still in good shape, which should make the rebuild more in line with a normal 924 NA rebuild...

I'd expect this is due to low oil pressure, and the turbo excess oil consumption causing a low level etc makes more sense to me.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mclaren924]

Wish I had better news on all fronts on this car. Pulled oil pan off along with all the drain and feed lines for the turbo. The oil pan had a grey film on the bottom a lot like an auto trans pan on a 200k chevy truck with a 4l60 (lots of metal and gritty grey paste). At this point I had very little hope for the engine but still pulled off a main cap and somehow it's worse than I expected.

Crank is marred in multiple spots and the bearing has been worn down to under material (copper?). Safe to say oil starvation amplified by turbo turning into an oil pump was probably the case here.

Just read through his past work invoice's and he just had an oil change done along with 4k worth of various work and they only quoted him 5 qts of oil, normally not a problem in a 5qt car. This car has two 1 qt aftermarket oil coolers mounted in the nose... Really beginning to think if this thing was filled 2 qt low and then was driven 3 hours (180 miles) to me, maybe the turbo went bad due to no oil and then ate the seal? I guess it really doesn't matter now, both the turbo and the motor are due for major surgery.

The picture below was the frontmost main bearing and just the bottom of it, I can't imagine what the top rod bearings look like. Really hoping the block, head, and pistons are at least okay as its an overbore with forged Ross pistons. That being said I saw some unhappy signs in the bottom of the bores that were exposed from below so I hold very little hope. Going to be a complete engine out at this point and will have to tear into it and see what extent of damage is. Cannot believe this motor wasn't knocking at all and still had 1.5 bar at warm idle. Will update what I find when I get motor out in next few days. Thanks for the replies guys! Going to try and keep this thread rolling till the car is running again.





Video of groves
https://imgur.com/UgQ7v2i
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[Cedric]

Thats pretty bad, though mine ran possibly for several decades with deep scores in the bearings i didnt know of due to some contamination some time during the engines life, both on race track and lots of boost, it was quiet and had good oil pressure, so they arent very picky engines, or rather overly beefy. If they have oil of course, which that one probably didnt, or something in the assembly went seriously wrong.

That engine will need a pretty deep clean anyway, so a full teardown,wash, measurment will be needed here i assume. Blocks are dirt cheap, so hopefully the pistons have survived, so you can move them over to a new bored block if necessary.
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1980 924 Turbo
www.instagram.com/garagecedric/

[924RACR]

Oh damn... yeah, time to get out the mikes (micrometers) and measure those journals... though TBH that level might be able to just be polished out... while that bearing is certainly toast, maybe the crank itself survived without too much...

Looks like you've bit off the maximum content there, bud!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mclaren924]

924Racr you could not be more right lol, the last thing I wanted was a car in pieces with motor oil and coolant everywhere while I'm trying to move in to the new shop. Out here in Cali it's practically paying to get brain damage trying to open an auto shop especially in Oceanside where I'm at. Need to get all city and fire inspections by them and to their understanding I'm a fabrication and machine shop which is true, I just didn't fully disclose the nature of what I was fabricating and machining lol.

I just got the motor out and torn down and all I can say is that there's only a few parts worth saving, head, valves, springs, and connecting rods...

I was wrong in my theory about what happened, I will link videos down below that show all. Long story short is the crank walked into the rear of the thrust washer and basically ground it away/friction welded itself to the main cap/ cut a groove in the main cap as well. It also caused the oil pump gear to get a weird wear pattern and the completely chewed up the inner race part that the snout of the crank runs through. The forged ross pistons are probably toast, lots of vertical scratches on skirt of piston that I can catch finger on and there's a good amount of embedded material into the skirts. The bores aren't too chewed up but would def need some cleaning up and coupled with the nuked thrust bearing main cap, I think it's best to just take a block off the shelf and start fresh. The cam has bad pitting on all the lobes I could see without spinning it over, will disassemble the head tonight or tomorrow and see how bad the buckets are and what guides and seats are like. The oil pickup has giant shard/slivers or metal that the screen caught so I'm of the mindset here, both his oil coolers ought to be replaced along with the pickup, the pan can be cleaned, what about all the turbo oiling stuff? Can that be confidently flushed and reused or is it bad news for that stuff too.

Figured out what happened late last night so couldn't spend much time thinking or trying to figure out WHY it happened but I have some theories but would like to see what you old timers think. Also going to go through clutch and flywheel assembly and make sure that's correctly assembled with right parts.

Thanks all

Thrust bearing Carnage
https://imgur.com/a/miYrDyJ

Oil pump Carnage
https://imgur.com/RWcCThb

https://imgur.com/pxOgMT8

Crank walk
https://imgur.com/Z1YVIGE
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[924RACR]

Wow...

I've long wondered if perhaps the damage to the thrust bearing can be caused by bad placement of the torque tube shaft in the torque tube, if maybe it's sticking out too far? Seems worth checking.

Generally I'd think the turbo oil hoses/lines can be OK for reuse if they're thoroughly flushed. Coolers are the big problem due to all the tiny passages perfect for trapping debris...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fifty50Plus]

In the 50 years I've been rebuilding Porsche engines, I continue to be amazed at some of the abuse they suffer by poor mechanics and actually start up and run the first time. Some of them continue to run for some years with significant damage. I have no idea why your crank walked so much but Vaughan might be on the right track or a wrong PP and throw out bearing.
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

[Mclaren924]

Shit, I was so damn tired I linked the same vid twice. Here's the real thrust bearing carnage.

https://imgur.com/a/MNkUXku

Need some advice on these pistons, forged Ross 2nd oversize and they sit almost flat with the deck, maybe .030 recessed. They are pretty beat up on the skirts and I'm of the mindset they are probably toast. Three are in better condition but still can catch a finger on multiple vertical grooves. One piston has 15-20 grooves that catch a nail and the whole lot are slightly worn on both sides so they are no longer a perfect circle. Unfortunately I think these things are smoked but would like your guys input. I have heard of Line2Line doing coatings and possibly being able to fix this if anyone can weigh in on that.

https://imgur.com/IFi7DS4

Yes I agree with both you guys, I think this has to be clutch pack or torque tube placement related. I will note that There was only a little bearing in the flywheel and not the usual pilot bearing that's in the crank that I'm used to seeing on cable clutch toofahs. I would imagine they would all use the same pilot bearing in the end of the crank regardless of clutch setup but somebody correct me If I'm wrong here. IF I'm reading the PET correctly, the turbos should use the same PN pilot bearing as a 77 924.

Will head into the shop and check on the TT length and disassemble clutch pack to see what's going on. Something strange I noticed was I couldn't get the pressure plate out, feels and looks like it's being held in internally by the TOB or something else, It wiggles around and moves back and forth a little but just wont slide out. Do i need to push the shift fork froward to release it or what am I missing here lol.
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[924RACR]

Ah, are you unfamiliar with the clutch fork and pressure plate arrangement for the Turbo? It's identical to the 944; the clutch fork pivot shaft must be pulled out to allow the fork to slide off the pressure plate, otherwise it's captured, yes.

So very different than NA.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype