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I think I killed it :-(
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Thu Apr 01, 2021 6:28 pm    Post subject: Reply with quote

Layers on MLS is thickness dependant. Cannot remember the layers for 0.050. Mine is still wrapped up and unopened. I have 0.080 installed and that was 5 layers

Cometic not really needed on stock or motors running way less than 1bar. Recommended if the boost will be turned up and driven hard. I blew two stock HG's after my engine rebuild and boosting over 1bar. That was partly due to head build issues too. Since the latest rebuilt head and the Cometic was installed its been working fine for 6yrs......and its been driven real hard .....
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Thu Apr 01, 2021 11:01 pm    Post subject: Reply with quote

bureau13 wrote:
UPDATE: Used head from running car acquired and taken to the shop. They showed me my old head, it's so clean now I wanted to lick it.

I see the Cometic site has the 924 head gasket from the Ideola group buy a few years back. I believe 0.050" is the correct compressed thickness, right? One thing that's odd, their web site says that is a 5-layer gasket, but discussion on that old group buy thread was that that was 3 layers. Anyone know the story there? I do want to make sure I'm getting the correct thickness (I am guessing I should stick to stock? Or should I find out how much if any was taken off the head mating surface, and add that to the 0.050"?)


That is the simple most straight forward way or else you will have higher compression. Also Cometic adds layers as the thickness increases. The layers are 'active' and adjust to subtle head to block movement.

You could 'cc the chamber to know your chamber size exactly which should be 19.5 to 20'ish cc or play it safe. Asking the shop is also a great idea and never hurts

.050 is slightly less that stock compressed.
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Thu Apr 01, 2021 11:36 pm    Post subject: Reply with quote

Also finally found my pic of my 1980 cylinder 1 piston. Keep in mind this engine still ran when I tore it half down. Only reason I dug into it was that the turbo was falling off. Screws would keep it tight and I was tired...

I bought the car this way and ran it in anger with boost as high as 15psi. Regularly between 10-13psi with HKS EVC1 (still the best in my opinion since its so easy to go up or down in boost with preset buttons)... I'm holding back as to how hard I ran this car

Piston was always like this because I simply had no idea. No signs of det anywhere. It always ran nice and strong. The dust bunnies you see is because the car is in storage with head off all these years. Longer than this forum's existence


_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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bureau13  



Joined: 07 Sep 2017
Posts: 480
Location: South Florida

PostPosted: Fri Apr 02, 2021 3:03 pm    Post subject: Reply with quote

Thanks guys. I will ask the shop and go from there.

Mike, what do you think caused that piston damage, detonation that you didn't hear? Mine showed nothing like this, just the pretty obvious marks from valve contact.

Piston: "You should see the other guy."
Valve: Breaks in half when I remove it...

Steve, any reason NOT to go with the Cometic? I'm not likely to be running the car super hard, it's just a street car. I was trying to run around 10psi, but of course more is better It's not really that much more expensive than the Victor Reinz, the most annoying thing is that the head seal kits all seem to come with the VR so I'm either buying everything piecemeal if I go with the Cometic head gasket, or I'm getting an extra one that I don't need. Still, not a huge price to pay. I'm planning on using those ARP head studs too. Do I need 'em? Probably not, but you never know...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Fri Apr 02, 2021 4:14 pm    Post subject: Reply with quote

You pay your money and you take your choice....

If you have no intention of wanting to push the boundary of the motor, stick with OEM.....it all works. Swapping to ARP, Cometic etc will cost more and add nothing to a stock motors performance or reliability. Assuming the rebuild is done correctly and all other elements of the motor are to spec and in good order.

If you have future aspirations on performance, then now is a good time to future proof
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Fri Apr 02, 2021 11:10 pm    Post subject: Reply with quote



I always thought it had something to do with the valves in that cylinder. The PO had the head pulled and rebuilt. They might have actually replaced it though now that I think about it

Needless to say I was more than a bit surprised. Just shows these motors are tough little beasts
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11723
Location: PacNW

PostPosted: Sat Apr 03, 2021 12:37 am    Post subject: Reply with quote

Are there marks on the head? That almost looks mechanical, like something was bouncing around in there.
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Toofah King Bad
  • WeiBe (1987 924S 2.5t) - 931 S3
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Mon Apr 05, 2021 11:18 pm    Post subject: Reply with quote

I'll dig around my shelf and see. I don't remember any and the head was pulled an awful long time ago. Its mechanical for sure

Just trying to show these cars can take a beating at times and keep going just fine
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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bureau13  



Joined: 07 Sep 2017
Posts: 480
Location: South Florida

PostPosted: Tue Jun 08, 2021 1:58 pm    Post subject: Reply with quote

Update (not really): Still waiting to get my head back. This is taking forever, but someone told me that all the shops around here are backed up. Must be a lot of engine rebuild Covid projects.

Starting to think about other things that I should consider. What do you all think about the injectors? They all work of course, but they weren't exactly clean when I pulled them. I'd prefer not to buy new ones if I don't need to, but if they're not easily cleanable, I will consider that. Then again, it's not like I need the head off to access them. Should I just soak them in gasoline or something?
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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bureau13  



Joined: 07 Sep 2017
Posts: 480
Location: South Florida

PostPosted: Mon Jul 19, 2021 3:05 pm    Post subject: Reply with quote

Allegedly, the head will be ready this week. We'll see.

I saw a post somewhere where someone cleaned this type of injector with carb cleaner while pulling the little plunger to open it up a bit, so I tried to do that. Not sure how much good it did, but I guess it can't hurt.

Still not sure what to do with the turbo and exhaust manifold bolts/studs. I have something completely non-factory for the turbo-to-manifold, and I really don't think I want to pay the crazy prices Porsche wants for those screws and collars if there's a decent alternative. The crap that was in there seemed to stay there just fine (well one was missing its nut, so maybe not). And the exhaust manifold studs were not good either.

I'm going to get those ARP head studs for the Ford Cosworth that were recommended to me in another thread, I think. Might as well.
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Mon Jul 19, 2021 9:16 pm    Post subject: Reply with quote

Usually hardware stores have those high grade black Allen headed metric bolts. I’ve ran those, turbo to manifold, before for quite a while, and they worked fine..
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chuck21401  



Joined: 20 Feb 2005
Posts: 525
Location: Annapolis, MD

PostPosted: Tue Jul 20, 2021 1:06 pm    Post subject: Reply with quote

For the turbo to manifold, I’m running two of these
https://arp-bolts.com/kits/arpkit-detail-b.php?RecordID=3529 And one of the fancy Porsche shouldered bolts.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler
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bureau13  



Joined: 07 Sep 2017
Posts: 480
Location: South Florida

PostPosted: Thu Jul 22, 2021 2:44 pm    Post subject: Reply with quote

Interesting...I'll look into both of those options.

Any reason why you only used two of the ARP bolts rather than all three?
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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chuck21401  



Joined: 20 Feb 2005
Posts: 525
Location: Annapolis, MD

PostPosted: Thu Jul 22, 2021 11:57 pm    Post subject: Reply with quote

bureau13 wrote:
Interesting...I'll look into both of those options.

Any reason why you only used two of the ARP bolts rather than all three?


With help from the Board I figured out that my wastegate wasn't working properly. When I installed a boost gauge I found that I was running 15psi with no modifications. So I rebuilt the wastegate again including replacing the valve guide. Then I reassambled everything.

It turns out that much of the hardware was was tired...nuts and bolts holding everything together were disappearing. At first it appeared that it was just one of the exhaust manifold to turbo bolts. Later I found that the studs from the turbo to exhaust had backed out...and that I was missing bolts on the mount from the turbo mount to the block.

It's a long story: https://www.924board.org/viewtopic.php?t=44305

I bought the ARP set and one of the Porsche bolts/collar. At $85 a pop I didn't want to replace all three more than once. Plus the Porsche parts took a month to arrive from Germany.

So I replaced the bolts...and one of the ARP bolts backed out. Upon futher investigation, I had to replace other hardware as describe in the thread above. Since I did that, the exhaust to turbo bolts have stayed put. At some point (maybe when Bitcoin goes back to $60K) I'll replace the other two bolts. One is easy to get to....the other one is way up in there.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler
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bureau13  



Joined: 07 Sep 2017
Posts: 480
Location: South Florida

PostPosted: Sat Aug 28, 2021 1:33 pm    Post subject: Reply with quote

I get my head back next week! It's been a while. Is there a way to rename thread titles? I want to have an ongoing thread as I put it all back together again, but the current title is less than descriptive...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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View user's profile Send private message
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