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ARP Rod Bolts Group buy?
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kondzi  



Joined: 02 Jul 2018
Posts: 107
Location: MZ/Poland/EU

PostPosted: Wed Dec 04, 2019 9:01 pm    Post subject: Reply with quote

I'll check with Polish 924.pl community and a local supplier. I'm in for 1 set.
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Konrad
'89 951 US
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safe  



Joined: 18 Mar 2017
Posts: 171
Location: Sweden

PostPosted: Wed Dec 04, 2019 9:49 pm    Post subject: Reply with quote

I'm sceptical that the rod bolts really are stretch to yield bolts. I bet there a 1000's of engine rebuilds out there when they have been reused. I have a friend who reused his bolts and that engine is taken close to 7000 regularly.

Are there any anecdotal stories of rod bolts letting go that wasn't overreved?

For the 911 it says in the manual that the rod bolts should be replaced, but measurements taken on bolts has proved that they don't get stretched beyond yield when torqued. This is for the 10mm pre 84 engines.

That said, some extra safety is seldom wrong. Lighter pistons would be better... Pistons are NLA to and good used impossible to find. If someone has a set with piston ring groves in spec I'll buy them...
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924-76  



Joined: 05 Jun 2006
Posts: 1413
Location: Ontario, Canada

PostPosted: Wed Dec 04, 2019 10:16 pm    Post subject: Reply with quote

I would be in for a set or two base on price.
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Wed Dec 04, 2019 10:45 pm    Post subject: Reply with quote

I put a set in my turbo (along with head studs) years ago when I rebuilt it.

I failed to get a set for my NA racecar, which has been raced with stock original used bolts for 15-odd years. But it's a mild build (per the rules), wasn't too worried.

Then I rebuilt it, and started snapping and stretching the rod bolts! Turned out to be due to a torque wrench off calibration, very aggravating... but it was only about 10-15 ft-lbs high! So not much of a margin to keep me comfortable.

Ended up still doing the rebuild with stock bolts, but much less of a safety margin - want ARP bolts to not have to worry next time.

Side note - I think we determined that the ARP bolts require a slightly higher torque spec than stock, anyway - maybe 10 ft-lbs higher IIRC - to get proper stretch and clamping/squish. I think Dan, among others, had some rod bearings spin before we figured this out. Note that the ARP bolts are assembled with a specific lube for consistency of torque reading, which can lower the required torque.

I have the recommended ARP rod bolt stretch gauge, could check this on the next batch. ARP actually specs out a stretch measurement, not torque...
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safe  



Joined: 18 Mar 2017
Posts: 171
Location: Sweden

PostPosted: Wed Dec 04, 2019 11:27 pm    Post subject: Reply with quote

924RACR wrote:

Side note - I think we determined that the ARP bolts require a slightly higher torque spec than stock, anyway - maybe 10 ft-lbs higher IIRC - to get proper stretch and clamping/squish. I think Dan, among others, had some rod bearings spin before we figured this out. Note that the ARP bolts are assembled with a specific lube for consistency of torque reading, which can lower the required torque.

I have the recommended ARP rod bolt stretch gauge, could check this on the next batch. ARP actually specs out a stretch measurement, not torque...


Exactly.
I have ARPs in my 964 engine.

The best method is torque to a specific stretch, the torque to achieve that is not that important.
The method is to:
You have to measure the length of the bolt (all individual bolts) before the first torque.
Torque to stretch value.
Release tension.
Remeasure, if they don't return to original length (within some limits), they are faulty and should be sent back to ARP.
Torque to length again, final assembly.

Keep the measurements you written down for the next rebuild.

The alternative method is to use a torque value, but then you need the specific grease and torque and release 3 or 4 times in a row.

These instructions should come with the bolts.
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 926
Location: Maysville, Colorado

PostPosted: Thu Dec 05, 2019 12:25 am    Post subject: Reply with quote

I'm a PE mechanical engineer so I have a little(very) background in this type of thing. I agree with Safe that it is quite doubtful that the bolts are actually stressed beyond the yield point as most materials that go past that point start going bad quickly. But, they are stressed to that the point that creep which is a permanent deformation of the part really does occur. All steel materials will creep if held under stress for a period of time and eventually that creep will lead to failure. But with higher tensile strength it will occurs at a much slower rate. The original bolts are probably no better than a grade 10.9 so 104ksi vs the 220ksi of the ARP bolts.

If any of you folks work at a place that have a Rockwell hardness tester we would know the quality of steel used in the original bolts(I'm old school and there is probably new a method of strength testing).

The classical demonstration of creep is to take a coil of lead solder and hang it from a table. The next morning you will find it measurably longer, merely the weight of the lead wire will induce the creep.

So the bottom line is that for us time is as much factor as the strength of the steel.

Just my opinion.

I have contacted ARP, we'll see what they say.
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morghen  



Joined: 21 Jan 2005
Posts: 8196
Location: Romania

PostPosted: Thu Dec 05, 2019 12:41 am    Post subject: Reply with quote

I doubt that the OEM ones are just 10.9
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Thu Dec 05, 2019 3:55 am    Post subject: Reply with quote

PS - failure mode, both in the ones I wrecked in the NA motor and the original one in the Turbo motor that necessitated the rebuild, was the "head" cap of the bolt popped off the shank...
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2004
Location: Somerset, UK

PostPosted: Thu Dec 05, 2019 5:09 am    Post subject: Reply with quote

Just been told that Porsche now restocked the previously NLA OEM rod bolt. Circa $25 each and circa $10 for the nut. No need to rely on ARP special buys unless they are superior to OEM and you need the extra protection? I guess if the OEM is single use and ARP are reusable, assuming you don't over stretch them, the ARP might be worth the bucks?
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Euro924S2  



Joined: 06 Mar 2008
Posts: 183
Location: UK

PostPosted: Thu Dec 05, 2019 5:57 am    Post subject: Reply with quote

Iíd buy at least one set provided they werenít silly money. Iím building a new engine with Vw flat top pistons so either buying new OEM or ARP if this group buy comes off. I too rebuilt my current motor with the used stock bolts, but with the supercharger it rarely sees 6000rpm and itís the revs that really load these bolts.

Iíve heard of a UK engine which was freshly rebuilt only about 100miles old when it span a big end bearing. Was that assembly error or failed rod bolt I donít know but it ruined his day and it just happened to be the 40th 924 anniversary celebration in the UK!!

Just guessing at the above interest we must be approaching 20 sets already?
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kondzi  



Joined: 02 Jul 2018
Posts: 107
Location: MZ/Poland/EU

PostPosted: Thu Dec 05, 2019 6:16 am    Post subject: Reply with quote

By when we close counting? For the moment 2 additional sets for Poland, so 3 total currently including me.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
'74 Ford Capri 1.3 (factory specs)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2004
Location: Somerset, UK

PostPosted: Thu Dec 05, 2019 6:35 am    Post subject: Reply with quote

Euro924S2 wrote:

Iíve heard of a UK engine which was freshly rebuilt only about 100miles old when it span a big end bearing. Was that assembly error or failed rod bolt I donít know but it ruined his day and it just happened to be the 40th 924 anniversary celebration in the UK!!


My motor???
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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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Euro924S2  



Joined: 06 Mar 2008
Posts: 183
Location: UK

PostPosted: Thu Dec 05, 2019 7:11 am    Post subject: Reply with quote

Yes Steve! Didnít know if youíd publicly shared your bad experience with that rebuild so left it anonymous!
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2004
Location: Somerset, UK

PostPosted: Thu Dec 05, 2019 7:22 am    Post subject: Reply with quote

Euro924S2 wrote:
Yes Steve! Didnít know if youíd publicly shared your bad experience with that rebuild so left it anonymous!


Thankfully not my build. I bought it allegedly rebuilt to spec and less than a few thousand miles on it. Spun a bearing. No idea if it was the rod, the bearing or bolt. Either way it blew cash out my wallet. Still have that block stashed.
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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
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Goldwolf  



Joined: 25 Jun 2017
Posts: 223
Location: Athens,GA

PostPosted: Thu Dec 05, 2019 7:51 am    Post subject: Reply with quote

I am glad Porsche is making the bolts, that's awesome news for the 924!
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