924Board.org

[fiat22turbo]

So wait, the grade 5 bolts I bought from Home Depot won't work? Damn.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[Ian89C4]

Not to try and draw out the thread, but I think that you will find there are very few rod bolt failure threads on here or Rennlist. However, when there is one the results are not just - 'oh I heard a rattling in the case." - they are tales of destruction and either complete write of the engine, or at least very serious machining job.
Porsche, Audi and VW engineers are pretty smart and have, I'm sure, a good idea of what they are doing.
I agree that there are ways around some of the procedures in the FSM - but I think that there is no getting around replacing what they tell you to, or what particular torque value to use.

Thank you for all the input gents!!

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Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

[RC]

[daniel]

My understanding is that failures of rod bolts, or any fastners for that matter, has a lot to do with how many times the fastner has been retorqued and if the load is increased beyond what the fastner can handle. Mainly rod bolt failures are due to motor that do significantly more revs than stock.

That been said my new motor will use stock bolts.

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

[peterld]

Aaah Rod Bolt Failure!!!

Yes I can put my hand up to claim to being the 'victim' of this dreaded scourge.

Result: Junked block,rods,pistons,crank,head,cam,turbo,oil pump and speedo cable!
Probable reason: suspected stretch/weakness in 500k old Porsche rod bolt which had been undone and retightened during motor overhaul (due to an unrelated reason)
Now this was a RACE motor, and race motors spend 95% of their lives between 4000-6000RPM, even when decelerating, etc.

Granted, there is a huge difference between a road motor and a race motor, but if you are going to investigate the upper realms of your motor's RPM, you better make sure you've built a goodun'.
That's why motor racing is so expensive - it's not the horrendous cost of entry fees, accomodation, racing suit, helmet, licence, new seat belts every coule of years, etc, etc. It's the cost of the meticulous mechanical work before and after the meetings. That's if you are serious.
Yes I've heard the stories of people stapping junk yard dogs in and blitzing the field, but somehow it never worked for me.

When I was but a callow youth, I worked for a time at a national engine reconditioner (Repco - for those in OZ) where every engine brought in was micc'ed up and the pistons, etc, went into bins dependent on size and basically one engine's now worn (and consequently undersize) parts went into a block with smaller bores, etc, after a quick hone of the bore, some linishing of parts and new rings and bearings.
A quick spray of the outside and good to go! And six months warranty. Did these motors ever fail? Never heard of one in my nearly two years there. Why? These were mostly Mums and Dads cars, or Taxis or travellers. NO big RPMs!!!! No real stress!

So back to our Toofahs. 30+ year old cars with 30+ year old parts with questionable usage and care. Like any old car, a ticking time bomb if you are going to give it the message. Drive it sedately and it will go on almost forever!
Race it, then be prepared to put your hand in your pocket! Lots!
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80/81 932/8 ROW

[Fifty50Plus]

Of all the ugly 4 cylinder post mortems I've performed, I've never seen a broken rod bolt that also didn't have some blue and melted rod bearings -read oil cavitation.
I'm not advocating reusing rod bolts but would in a pinch - on a 4 cylinder. On all the 911s I've built, I ALWAYS use new bolts and nuts on street cars and ARP for the race motors. 911 rod bolts were notorious for breakage above a certain RPM while the rod bearings were perfect. We used to X-ray scores of bolts and use the darkest.
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

[ideola]

I am self-funding a new round of production on these bolts. See details here: http://www.924board.org/viewtopic.php?t=41557
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erstwhile owner of just about every 924 variant ever made