924Board.org

[gegge]

I didn´t want to reuse the 30 year old stock flywheel bolts and expected to pay a lot when buying new ones from Porsche. It wasn´t easy finding short M12 x 1.5 with a shallow head in the hardwarestore either. Especially if you want grade 10.9 or better. Remember that flywheel bolts are different from ordinary bolts and the stress is severe.

Finally I noticed that BMW (E30) M3 with the S14 EVO engine with single mass flywheel used bolts that are very similiar to ours: HEX BOLT M12X1,5X22 11220616143 $2.01

Even better, ARP does provide a kit of 8 pcs in their Pro Series, originally developed for NASCAR competition and has a 200,000 psi rating. #201-2801 for some $50
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[peterld]

Great find Gegge!
_________________
80/81 932/8 ROW

[ideola]

I just installed a set of these on the Club Sport motor and I can confirm that they work perfectly. I also measured the early S2 flywheel (which is what I installed on the club sport), the S1 flywheel, and the NA flywheel with washer, as well as the depth of the blind holes in the end of the crank.

These ARP bolts are 22mm long and have a 8mm unthreaded shank. The heads of these bolts are about 1mm shallower than the stock bolts, so not concern about interfering with the clutch disc either.

All of the flywheels I measured had 9mm or longer depth where the bolt passes through; the blind holes in the crank are ~18mm; so from my measurements and test fitting, it appears that these bolts should work for ALL of the 924 applications. The only one I can't confirm for certain is the late S2 931 flywheel with the rubber damped clutch disc because I don't have one of those flywheels on hand. However, looking in PET, it indicates that those bolts are 18mm long, which is only 4mm shorter than these bolts, and there should be plenty of depth in the crankshaft blind holes to accept the additional length.

I will be adding these to my site later this week
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75 Fiat X1/9 | 80 US 931 '941' | 78 Poli-Form

[gegge]

There seems to be another ref for OEM BMW M12x1,5x25 in 12.9 quality: 244238930

A picture of OEM 10.9, BMW 12.9 and ARP Pro:

I
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[daniel]

Sorry for rehashing an old thread -
Installing a set of these in my race motor and upon reading arp's instruction it says to install without any washers and specifies a torque setting. So:
1. I assume the round disc that goes between the flywheel and bolts is NOT counted as a washer and should be retained?
2. As the kit is originally intended for a BMW I assume I should use the Porsche specified torque settings?

Cheers

Daniel
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[MikeJinCO]

I believe the torque is generally based on the bolt properties as they want a stress of mol 70% of the yield strength. The original bolt probably a 12.9 has a yield of about 170K psi. The ARP 8740 is a min of 185ksi so it would be torqued a bit higher. That doesn't always hold with specific applications like rod and head bolts. JMO.
_________________
Mike
Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
cricketdesigns.com

[MikeJinCO]

I believe the torque is generally based on the bolt properties as they want a stress of mol 70% of the yield strength. The original bolt probably a 12.9 has a yield of about 170K psi. The ARP 8740 is a min of 185ksi so it would be torqued a bit higher. That doesn't always hold with specific applications like rod and head bolts. JMO.
_________________
Mike
Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
cricketdesigns.com

[924RACR]

Yeah, I'd be inclined to use the ARP spec, for exactly this reason...
_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Cedric]

What's the arp spec? I seem to have lost my papers..
_________________
1980 924 Turbo

[Mike9311]

...and let me add, please make sure you use whatever lube ARP specs per stated torque. If they require their lube for a particular value, don't use something else.

For me this matters more for something like rod bolts

I found one link indicating ARP lube or Loctite with identical value but it was seller. ARP talks about this subject too in their tech section.
_________________
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

[daniel]

Hi All
Re torque settings: ARP recommends 105 ft/lbs however haynes recommend 65 ft/lbs. I am not worried about the bolts, I am worried about the thread in the crank shaft!

Re the flat disc/washer. I emailed ARP and they confirmed that the flat disc is fine to use.

I will reply to ARP re the torque settings and see what they say.

Cheers
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[daniel]

This is the reply I got from ARP regarding torque settings:

Hi Daniel,

Unfortunately as you are not using these for their intended purpose/application we would not have installation guidelines. I will say though at such a low torque the bolts could come loose.

Best regards,
Zac Kimball


I am a little worried now due to the large difference between stock torque settings and ARP settings. What did those of you who have used these bolts before use?

Cheers

Daniel
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[gegge]

The crank is made of forged steel compared to the cast iron block.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs