1975 911s flywheel bolts

[hienz]

Which flywheel bolts should I buy because the prices are all over places.
Also I bought the 12mm torc from Snap-on but still too hard to remove the old bolts;
how do you put those bolts on at very high torque?

[winders]

I like the ARP flywheel bolts....

[mikedsilva]

Originally Posted by hienz

Also I bought the 12mm torc from Snap-on but still too hard to remove the old bolts;
how do you put those bolts on at very high torque?

Lock the flywheel... use a strap of metal (or a crescent wrench) and one of the pressure plate bolts.

[Flat6pac]

Some people use loctite on them.
Use heat and they should come loose.
Lock flywheel across the bell housing bolts.
Bruce

[hienz]

Originally Posted by winders

I like the ARP flywheel bolts....

Do you needed special tools to install ARP flywheel bolts?

[winders]

They are 12-point bolts…see here:

https://lnengineering.com/porsche-late-911-9-pieces-flywheel-bolt-kit.html

[Zuffenwerker]

I’ve been using the “cheap” bolts available from ssf or worldpac for a long time. Never had an issue but neither of those distributors usually carry total crap.

Daniel

[chrismorse]

I just received a set of 6 ARP flywheel bolts. they are not TORX, rather, they are, "TRIPPLE SQUARE" 12 point, just like the stock porsche bolt. That is what the counterman at Napa called them after a brief inspection.
WE had to heat the bolts to get then to break loose.
The correct tool is particularly important, because the head is so shallow and if the tool, (or the incorrect tool). slips and buggers the bolt head - removal has been termed "difficult")
Napa, Carlisle tool: M12 sts3812m

I have heard reports of high reving race engines losing flywheels, so ARP bolts are cheap insurance, stock redline seems to be just fine, (from Pelican posts, not personal experience).

chris

[gled49]

The old Porsche bolts were a very high grade 14. All the new replacements are 12.9. Don’t know what the ARP bolts are and the new Porsche bolts don’t show the grade. The new 12.9 bolt heads will pop off at 130 lbs, the original Porsche bolts would torque past 150 lbs. just some info.

[hienz]

I used the Snap-on torx to remove the flywheel bolts from my 75 911S, the 12 points torch slipped out and the torch damaged but the bolts won’t loosen. I am grinding off the head of those bolts to get the flywheel out and now trying to get those headless bolts out. So far two broken with small pieces inside, one out completely, and three more needed to come out.

[hienz]

Originally Posted by chrismorse

I just received a set of 6 ARP flywheel bolts. they are not TORX, rather, they are, "TRIPPLE SQUARE" 12 point, just like the stock porsche bolt. That is what the counterman at Napa called them after a brief inspection.
WE had to heat the bolts to get then to break loose.
The correct tool is particularly important, because the head is so shallow and if the tool, (or the incorrect tool). slips and buggers the bolt head - removal has been termed "difficult")
Napa, Carlisle tool: M12 sts3812m

I have heard reports of high reving race engines losing flywheels, so ARP bolts are cheap insurance, stock redline seems to be just fine, (from Pelican posts, not personal experience).

chris

Chris,
How do you know the correct length of the bolts when ordering ARP?
As far as I know different year required special length or else too long will destroy the engine.

[Walt Fricke]

AFIK, all the 12mm bolts Porsche used for this application were the same length, at least for the cars with flat flywheel 911 or 915 transmissions with the 6 bolt cranks.

I find using an impact wrench makes short work of removing these bolts, you don't need to hold the flywheel in place. Less likely to damage the bolt's "hex" as well. And I use red Loctite and 150 lbs/ft torque when installing. This is required for race motors reved over 65 or 7000 rpm with a 70.4 crank. At stock torque, even green Loctite sleeve retainer won't keep these bolts from backing out at those RPMs. In fact, even tack welding the bolt head to the flywheel isn't enough, per what a mechanic friend claimed to know. The factory never did figure out how to keep these flywheels on on race motors. They switched from a long stroke to a short stroke when racing a nominal 2.5 liter motors because of this issue. In their 2.8s, supposedly they dealt with the issue by replacing all the bolts (or at least retorquing them) after every race event.

On install, of course you need fix the flywheel using a tranny stud and a pressure plate bolt and either a strap between the two, or - simpler - a small open end or combo wrench in compression (which you can use in the proper orientation for removal with non-impact means as well.

If you keep the revs down below the redline, you should be fine with factory torques.

The 9 bolt later flywheels don't need any special installation beyond the factory torque as far as I have heard. Certainly solid up to constant upshifting on the track at 7,000 RPM.

I didn't realize these were grade 14s. I'll have to be careful of that when next I have to deal with my 70.4 race motor. But, against all advice, I just reuse the old bolts, now that I have learned how to remove them without damaging them. Never had an issue. These don't seem to react like stock flywheel bolts. It is a 4th order harmonic node right on the mating surfaces (so engineers say) which acts to loosen the bolts. I don't think one would find that these bolts elongate with use, the way an overstressed bolt will when subject to reciprocating forces or the like. All the forces here are in shear, and the extra clamping load at 150 pounds/foot seems to prevent rotation of the bolt head.

Having these bolts back out is kind of bad news. Metal to metal transfer occurs between the flywheel and the end of the crank. Leaves the flywheel useful only as a bench holder for putting the rods back on a crank. If lucky, the crank end can be machined flat again. Speaking from experience.

So borrow an impact wrench - the battery operated ones these days will provide all the torque you need, and you don't need an air compressor if you don't have one.

Let us know if this will buzz the remaining bolts off - at least if you haven't buggered their heads too much so the triple square won't hold.

Me, if I had a buggered inhex in this application, I'd weld a 17mm or maybe 15mm nut on the end of the bolt. If the heat didn't break things loose all by itself, the torque you could apply with a socket should. You might consider doing that with the ones whose heads you ground off, once you get the flywheel itself off, if the release of the torque and vice grips aren't enough to get the stubs to turn.

I've tried to get the shortest triple square Allens I could. Not an issue with the impact gun on removal, but for torquing after gentle use of the impact when reconnecting the flywheel it helps to keep things short. With a longer

[Walt Fricke]

I went and measured a bolt: 25mm

The only length issue I can think of has to do with the thickness of that special 6 hole washer plate. Some - maybe early, like for 901 transmissions? - are thinner than others. Or maybe the other way around. I don't have both plates handy, but someone here knows.

[chrismorse]

I just got the same bolt length as Walt.
Both the new ARP and the stock Pelican flywheel bolts 25mm.
The ARP instructions specify 95 ft lbs with loctite 242 on the threads and arp lubricant under the head, (supplied).

I like Walt's method of torquing to 150 and will ask ARP about this and the use of the washer plate between the bolts and the flywheel.
chris

[gled49]

The flywheel bolt are 12 point. There was a 28mm bolt used with a thicker bolt plate, maybe around 69, 999 067 007 02. The new Porsche bolts, 911 102 171 00 have a KAB or no markings on the head. I have not tested the torque to 150 as my race engines are 9 bolt now. I also did as Walt did, 150 ft lbs with red loctite with the 14.0 bolts. We always replaced the bolts with new, and I never threw away the old bolts so now I am reusing them when needed. I also use the short 12 points tools but only the German brands, I’ve found Snap-on’s Are too soft.

[chrismorse]

I no longer have a washer plate, is one advisable? It is out of stock at pelican but they can order from Porsche for $$60, if you are not in a hurry - "Hurry" bumps the cost to $90, or you can wait for 3 weeks.
I really really don't want to lose a FW.

Earlier today, I talked to ARP about torque and washers. Hanes and Patric Motorsports say 105 or 106. ARP says 95, definitely not 150. Their instructions say blue, 242 loctight, (on further questioning, he said blue for ease of removal - the implication was that red would be better - but, you may need to take it apart...). He wouldn't budge from 95.

Any experience with upping the torque, or an ARP, or am i just better going back to a grade 14 factory bolt, if i can find one???????

One thing he was adamant about was NO washer, Split or wavy under the head of the FW bolt, because it promotes loosening.

???
chris

[manbridge 74]

I never use loctite and have yet to have one loosen up observing factory redline and torque spec.

It should be mentioned that getting loctite between flywheel and crank is a sure recipe for loosening. Use a q-tip and apply sparingly to both surfaces would be how I’d do it.

[Walt Fricke]

ARP is correct about no washers as such. I am referring to the round plate with six holes in it, which are in the same asymmetric pattern as the holes in the flywheel and threaded holes in the crank. That you absolutely have to have. The flywheel you took off had one. Washer is a reasonable name for it, as it sits under the bolts and above the flywheel, but doubtless there is a better name for it.

If you don't plan to exceed the factory redline for this motor, follow ARP's recommendation.

If you do plan to rev to wherever the torque curve of your modified motor says you should upshift (there is a sort of formula for this - upshift when the torque delivered to the wheels in the lower gear at shift RPM equals the delivered torque in the new, higher gear), well I'd ask this engineer if he has any experience with 70.4 mm 911 cranks and flywheels. I got the 150 lbs/ft from none other than Bruce Anderson (RIP), who knew what was happening in the Porsche racing world. I can pretty much guarantee you that factory torque values won't keep those bolts tight at 8,000 RPM - I had them back out twice on me. The symptom was an inability to get a complete clutch release, as the bolt heads start rubbing on the center of the clutch disk. At speed you can shift more or less normally, at least for a while. So the second time this happened I quit promptly (unlike the first time). If you need to have the end of the crank machined flat again, that means a full teardown.

A stock SC with a stock transmission should upshift in the 6,000 to 6250 range. I am informed that by adjusting cam timing and distributor timing, and maybe some fussing with the CIS, it works best to shift higher if it is a late Euro. The dyno will show where to shift.

Where did this grade 14 notion come from? My INBUS X7N bolts are stamped 12.9. Looking around, I don't find evidence of a metric 14 point something. 12.9 seems to be the strongest regular metric bolt.

[manbridge 74]

I pulled grade 14 bolts out of my 74, first time clutch had ever been out. I took pictures and posted them here as well. It’s true that they are NLA but we’ve had no issues with the grade 12.9 bolts that Porsche supplies today.

[hienz]

I finally got 4 flywheel bolts out. The first one was very hard because I did not use any heat. The 2nd, 3rd, and 4th are out after I grounded off their heads and then use some heat on those headless bolts. The other two are already broken maybe from too much torque put on by the previous mechanic ( I can see the JB weld in there ). Now I am planning to drill them out. Thank you everyone for valuable info