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I think I killed it :-(
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bureau13  



Joined: 07 Sep 2017
Posts: 352
Location: South Florida

PostPosted: Sat Nov 28, 2020 6:57 am    Post subject: Reply with quote

The head is off! Everything came loose pretty easily, but getting the head up and out of the car was painful. Maybe I'm just old and weak. I ended up using an engine lift bar that I bought a while ago to do motor mounts for my 928, but never got around to actually doing it.

The pictures are here: https://photos.app.goo.gl/FkBSAtodaD4YKSXTA

As this is the first time I've removed a head and seen this stuff with my own eyes, I can't say for sure what is normal and what is not. Some observations:

The debris sitting in the cylinders on the pistons is, I assume, bits of gasket and other crud that fell in while I was removing the head, and will be vacuumed out.

All of the pistons have areas that look like finish or something has come off, but cylinders 3 and 4 look specifically like that was recent. Cylinder 1 and 2 don't look as bad, the "flaked off" area is discolored, as if whatever happened there happened a while ago. Is any of this bad enough to have to trash the piston?

Most of the valves have marks on them. Cylinder 2 appears the least bad, which makes sense because that's the cylinder that still had compression. I'm not sure how to tell which pistons are actually bad, vs which are simply marked, or if there's a meaningful difference. Hopefully some of you can read the tea leaves here better than I can.
_________________
-----------------------------------------
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: 2180
Location: MI

PostPosted: Sat Nov 28, 2020 7:26 am    Post subject: Reply with quote

Pistons look fine, lot of carbon, clean em up with something like acetone/atf mix and a wire brush and show them to us again..
Get the crap off of them and look for cracks..
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80 Turbo - Slightly Modified
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Mike9311  



Joined: 14 Dec 2004
Posts: 1057
Location: Chicago-ish

PostPosted: Sat Nov 28, 2020 8:58 am    Post subject: Reply with quote

Fasteddie313 wrote:
Pistons look fine, lot of carbon, clean em up with something like acetone/atf mix and a wire brush and show them to us again..
Get the crap off of them and look for cracks..


+1 on that suggestion
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
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: 352
Location: South Florida

PostPosted: Sun Dec 06, 2020 9:13 am    Post subject: Reply with quote

I cleaned to tops of the pistons, see:

https://photos.app.goo.gl/FkBSAtodaD4YKSXTA

Cylinder 4 has some areas along the sides which I assume were caused by hitting valves, and cylinder 1 has an odd, very small gouge (with a raised-up area) in the dish part, just to the right of the center. Cylinder 3 has some areas similar to cylinder 4, but not as pronounced, and cylinder 2 looks clean, which is no surprise. Nothing looks cracked.

How much of a problem will be caused by the areas that were impacted? I don't know what matters and what doesn't in this sort of situation.
_________________
-----------------------------------------
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: 2180
Location: MI

PostPosted: Sun Dec 06, 2020 10:17 am    Post subject: Reply with quote

No big deal..

Just sand down or remove any sharp edges left on the pistons, because they could become hotspots and cause preignition if they glow..
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80 Turbo - Slightly Modified
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bureau13  



Joined: 07 Sep 2017
Posts: 352
Location: South Florida

PostPosted: Sun Dec 06, 2020 10:35 am    Post subject: Reply with quote

Fasteddie313 wrote:
No big deal..

Just sand down or remove any sharp edges left on the pistons, because they could become hotspots and cause preignition if they glow..


Interesting...I was just talking to a friend who has a lot of experience with cars in general, but not 924s, and he was concerned that if the piston got hit hard enough to make those marks, it might be compromised. I definitely like your answer better though
_________________
-----------------------------------------
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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931-1979  



Joined: 13 May 2016
Posts: 4
Location: Austria

PostPosted: Mon Dec 07, 2020 10:17 pm    Post subject: Reply with quote

I had an engine with contact between the valves and the pistons. The piston ring land (i hope this is the right word) between the first and second ring was cracked on two pistons.
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931/1 - 1979
924 2,0 - 1982
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bureau13  



Joined: 07 Sep 2017
Posts: 352
Location: South Florida

PostPosted: Tue Dec 08, 2020 3:04 pm    Post subject: Reply with quote

Interesting. You couldn't tell from the top? That's a little disconcerting...

931-1979 wrote:
I had an engine with contact between the valves and the pistons. The piston ring land (i hope this is the right word) between the first and second ring was cracked on two pistons.

_________________
-----------------------------------------
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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Mike9311  



Joined: 14 Dec 2004
Posts: 1057
Location: Chicago-ish

PostPosted: Wed Dec 09, 2020 1:01 am    Post subject: Reply with quote

The contact points on your piston at least, are toward the inside (bowl). This should mean you are safe from structural damage like a ring land breaking. In your case it would surprise me

My '80 had something happen to it on the outer edge of the piston. I only knew about it after years of driving the stuffing out of it. Pulled the head for other reasons when I found out. They didn't even clean it up. Everyone's case is different so here is to hoping its just clean up and go
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
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: 352
Location: South Florida

PostPosted: Wed Dec 09, 2020 1:52 pm    Post subject: Reply with quote

Amen to that!

Mike9311 wrote:
The contact points on your piston at least, are toward the inside (bowl). This should mean you are safe from structural damage like a ring land breaking. In your case it would surprise me

My '80 had something happen to it on the outer edge of the piston. I only knew about it after years of driving the stuffing out of it. Pulled the head for other reasons when I found out. They didn't even clean it up. Everyone's case is different so here is to hoping its just clean up and go

_________________
-----------------------------------------
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: 352
Location: South Florida

PostPosted: Fri Dec 25, 2020 8:59 am    Post subject: Reply with quote

I was looking more closely at the head and noticed something: My exhaust manifold is only really being held on by the innermost studs, top and bottom. The outermost are either missing entirely or there is no nut on them. I always felt the car was a bit louder than it reasonably should be, and not through the exhaust. So I guess that makes more sense now.

In removing the remaining ones so I can take the manifold off, all but one of them are unscrewing the stud. That's fine for the one on the bottom, but the two on the top don't unscrew far enough before the end hits the casting. Is there a non-destructive trick to getting the nut off without turning the stud?

Maybe I should just cut them off and buy all new ones...I was thinking I should maybe do that anyway, assuming they're available.
_________________
-----------------------------------------
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: 2180
Location: MI

PostPosted: Fri Dec 25, 2020 9:21 am    Post subject: Reply with quote

I screw them all at the same time so the manifold can come off with the studs.. Then with the manifold off you can grab the stud with vice grips and take the nuts off em and out of the manifold..

Definitely just buy all new ones, just high grade (black) metric studs from the hardware store, or stainless..
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2163
Location: Somerset, UK

PostPosted: Fri Dec 25, 2020 8:04 pm    Post subject: Reply with quote

Most definitely buy a full set of studs and nuts for all exhaust fixings. Never reuse if over corroded.
_________________
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
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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bureau13  



Joined: 07 Sep 2017
Posts: 352
Location: South Florida

PostPosted: Sat Jan 02, 2021 4:59 am    Post subject: Reply with quote

OK, new exhaust manifold studs and nuts are on the list. They don't seem to be available from places like Pelican anymore, so good to know I can use generic ones if they're the right quality. Should I use antiseize, or just dry?

For head bolts, earlier someone mentioned using ARP studs from a Cosworth application, I bookmarked that link, and will do that. I've read that head bolts/studs should get a light coating of oil before installation, I assume that applies here as well.

Regarding the head gasket, I've seen different advice here. I've seen people recommend the Cometic MLS gasket, and then I've seen others say the Victor Reinz OEM gasket is the one to use. My car is a US S2 so I believe that means 7.5/1 CR, quite a bit lower than the ROW cars (which is weird because it's also lower boost). So it seems that if the CR goes up a bit, that wouldn't be a big problem, however I do plan to run at least at ROW boost levels, maybe a bit more if possible to do so safely. Not sure how much the different head gasket materials matter for this, if at all.
_________________
-----------------------------------------
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
Carrera RSR  



Joined: 08 Jan 2010
Posts: 2163
Location: Somerset, UK

PostPosted: Sat Jan 02, 2021 7:11 am    Post subject: Reply with quote

ARP fixings requires ARP grease
_________________
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
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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