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I think I killed it :-(
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Mon Jan 04, 2021 12:22 pm    Post subject: Reply with quote

US s2 is 8.0 C:R
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2224
Location: MI

PostPosted: Tue Jan 05, 2021 1:41 am    Post subject: Reply with quote

Carrera RSR wrote:
ARP fixings requires ARP grease

It comes with the studs though..

MLS is probably the better way to go, but I haven’t had any problems with my new stock gasket under ARPs.. Yet..

It’s debatable what one needs to do to the finish on the block deck and head surface in order to use an MLS as they require a certain standard of smoothness/finish..

MLS gaskets can also be bought in many different thicknesses, so you can either retain your stock CR, or raise or lower your CR, depending on what thickness gasket you choose..
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Tue Jan 05, 2021 9:25 am    Post subject: Reply with quote

50RA finish on the surfaces for Cometic. Pretty stock finish, nothing special.

Stock HG don’t last too long on 1.0bar + boost.
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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
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: 357
Location: South Florida

PostPosted: Mon Feb 22, 2021 2:19 pm    Post subject: Reply with quote

So I'm finally taking the head to the machine shop. I keep looking for valves or a head, but haven't been able to find much yet, but I realized if someone were to come tell me they had some valves, I don't really know exactly what I need. So I'm going to have them tear it down and tell me exactly what I need. Probably should have done that from the start.

In the meantime, I have the tops of these pistons. A few people have mentioned sanding down the edges where they impacted the valves, so I was wondering how smooth they need to be, and what you guys recommend for this. Would you use some sort of sanding wheel on a dremel, or should this be done by hand, etc?
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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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peterld  



Joined: 10 Dec 2006
Posts: 834
Location: Noosa Heads QLD Australia

PostPosted: Mon Feb 22, 2021 10:12 pm    Post subject: Reply with quote

Either/or........you only need to remove the sharp edges to avoid detonation. It doesn't need to be a work of art......remembering that the more you remove the lower your compression ratio.
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Last edited by peterld on Tue Feb 23, 2021 11:30 pm; edited 1 time in total
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Mon Feb 22, 2021 11:45 pm    Post subject: Reply with quote

Just brake corners and smooth things out. Depending on how bad things are are start with 400 grit sandpaper and move to 600+. You can also use one of those dremel scotch brite wheels but be careful. Hard to control sometimes. Be light handed and have patience


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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: 357
Location: South Florida

PostPosted: Tue Feb 23, 2021 3:04 pm    Post subject: Reply with quote

OK, sounds good, thank you everyone.
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-----------------------------------------
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: 357
Location: South Florida

PostPosted: Thu Mar 18, 2021 2:12 pm    Post subject: Reply with quote

Update: I heard back from the machine shop. I have three bent exhaust and one intake valve (I think that's the way it was, unless I've reversed them), four bad "buckets" and a broken cap that helps hold the cam in place. According to the shop, that last bit is the one thing they didn't think they could source. They said they could possibly weld it, fab something or just put it back as-is, but it wouldn't be right. So I had decided to just try to source the valves, but I think I pretty much have to source a used head now. Which...I think I have. I am just awaiting some photos.

Does it seem weird to have broken that cap? I wasn't expecting that, but maybe it's not so uncommon. The cam itself is OK, apparently.
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-----------------------------------------
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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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1015
Location: Maysville, Colorado

PostPosted: Thu Mar 18, 2021 10:57 pm    Post subject: Reply with quote

Just my opinion. If you have trouble finding a different head. It might be worth trying to save the existing one. A cam cap from almost any head would probably fit. I may have one yet in my recycle metal box from a 1977 NA head. The cam won't work with either a welded cap or different one so all the surfaces would have to be reworked and and then line bored for the cam. It is getting harder to find people to do that, but race motor shops can do it. It is an alternative tho not inexpensive, to finding a new head. If you do go after a new one I'd be happy to take the old one. I have a full set of ok valves from my conversion to 7mm stem valves and buckets also. I would personally get a set of ACM buckets from Sweden(ACM bought out Parner who made them for us) rather than use the stock ones. A full set is about $120 and then just use Alfa($5 ea) 9mm shims for valve clearance.

When we set up the head with a reground smaller diameter cam, we got a piece of about 1/8" steel, mikked it,we then used a feeler gauge to get total thickness, got 7 out of 8 right. We took out the one too tight and shortened the valve by .002. Last and only time I checked valve clearance It took 2 hours total including removing the cam and distributor. I had to buy 4 new shims and swapped 3 others around as I had all the clearances and existing shims recorded. The new buckets weigh about 53gm, vs over 80gm for the old ones it significantly decreases the loading on the cam. Many of the new OHC motors cars use solid shims including Toyota, VW, Audi and almost all motorcycles. So in my opinion the issue of easy valve adjustment is a bit over blown. This was all(we did not need the line boring) done by a good motor machinist in our small town and nothing really special. He actually said it was quite easy compared to the microscopic parts found in many of the new 4 valve motors by VW and Audi.

Again if you end up scrapping the existing head, I'd be glad to take it.
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Thu Mar 18, 2021 11:47 pm    Post subject: Reply with quote

I wouldn't scrap the head either. A fab'd cap would be totally fine but they will have to align ream the cam journals. Who knows what forces where there during the event. They should check your cam for runnout as well. Its why we torque our cams in a certain pattern so we don't bend anything and you have a broken cap

I am working on a Ferrea valved head right now as well like Mike. Two in fact except I am using the 6mm stemmed versions as previously pioneered by Gegge. Obvious hope to have a big specific post/thread about all this in the coming weeks. Doing everything myself
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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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morghen  



Joined: 21 Jan 2005
Posts: 8339
Location: Romania

PostPosted: Fri Mar 19, 2021 12:09 am    Post subject: Reply with quote

How is the cap broken? pictures..?
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1015
Location: Maysville, Colorado

PostPosted: Fri Mar 19, 2021 7:59 am    Post subject: Reply with quote

I checked my scrap pile and the old cam caps are gone. Sorry.
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
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Paul  



Joined: 02 Nov 2002
Posts: 9467
Location: Southeast Wisconsin

PostPosted: Fri Mar 19, 2021 11:18 am    Post subject: Reply with quote

Was the cap broken before you took it to the shop? I've never seen a cap broken by slipped timing. There is a specific procedure in the FSM concerning removing the caps, did the shop follow it?
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bureau13  



Joined: 07 Sep 2017
Posts: 357
Location: South Florida

PostPosted: Fri Mar 19, 2021 12:23 pm    Post subject: Reply with quote

All good questions. I hope they shop followed procedures and isn't blaming my timing event for something they did. I never noticed a broken cap but I haven't seen it since they took it apart to investigate.

My thought was not to scrap the head necessarily, but to get another head and scavenge whatever parts were needed from one head to the other, in whichever direction makes the most sense.
_________________
-----------------------------------------
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: 357
Location: South Florida

PostPosted: Thu Apr 01, 2021 1:51 pm    Post subject: Reply with quote

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"?)
_________________
-----------------------------------------
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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