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ARP flywheel bolts

 
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gegge  



Joined: 27 Jul 2007
Posts: 1117
Location: Sweden

PostPosted: Fri Oct 05, 2012 10:17 pm    Post subject: ARP flywheel bolts Reply with quote

I didnīt want to reuse the 30 year old stock flywheel bolts and expected to pay a lot when buying new ones from Porsche. It wasnīt 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
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peterld  



Joined: 10 Dec 2006
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Location: Noosa Heads QLD Australia

PostPosted: Sat Oct 06, 2012 9:33 pm    Post subject: Reply with quote

Great find Gegge!
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ideola  



Joined: 01 Oct 2004
Posts: 15542
Location: Woodstock IL

PostPosted: Tue Feb 12, 2013 1:10 am    Post subject: Reply with quote

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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gegge  



Joined: 27 Jul 2007
Posts: 1117
Location: Sweden

PostPosted: Wed Oct 16, 2013 5:24 pm    Post subject: Reply with quote

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
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Carl Fredrik Torkildsen

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daniel  



Joined: 18 Jun 2009
Posts: 636
Location: Sydney, Australia

PostPosted: Mon May 09, 2022 3:48 pm    Post subject: Reply with quote

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
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1170
Location: Maysville, Colorado

PostPosted: Mon May 09, 2022 10:10 pm    Post subject: Reply with quote

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.
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MikeJinCO  



Joined: 08 Jun 2010
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Location: Maysville, Colorado

PostPosted: Mon May 09, 2022 10:11 pm    Post subject: Reply with quote

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.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Mon May 09, 2022 10:58 pm    Post subject: Reply with quote

Yeah, I'd be inclined to use the ARP spec, for exactly this reason...
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Cedric  



Joined: 27 Aug 2004
Posts: 2354
Location: Sweden

PostPosted: Mon May 09, 2022 11:08 pm    Post subject: Reply with quote

What's the arp spec? I seem to have lost my papers..
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Mike9311  



Joined: 14 Dec 2004
Posts: 1291
Location: Chicago-ish

PostPosted: Mon May 09, 2022 11:45 pm    Post subject: Reply with quote

...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.
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daniel  



Joined: 18 Jun 2009
Posts: 636
Location: Sydney, Australia

PostPosted: Tue May 10, 2022 2:34 pm    Post subject: Reply with quote

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
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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
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daniel  



Joined: 18 Jun 2009
Posts: 636
Location: Sydney, Australia

PostPosted: Wed May 11, 2022 8:52 am    Post subject: Reply with quote

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
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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
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gegge  



Joined: 27 Jul 2007
Posts: 1117
Location: Sweden

PostPosted: Wed May 11, 2022 7:46 pm    Post subject: Reply with quote

The crank is made of forged steel compared to the cast iron block.
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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
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