Flywheel bolts – Loctite?

[Paul W]

Hope someone an point me I the right direction…

Installed a new flywheel following the directions in Wayne’s ‘101 Projects’ (p35), no mention of using Loctite so thinking perhaps it wasn’t appropriate with sort of fastener went ahead and torqued it down in anticipation of an engine install this weekend. Flicking through my newly received version of Wayne’s ‘Engine Rebuild’ book the same procedure (p139) references the use of Loctite.

So the question is do I need to buy a new set of bolts and re-do this? Needless to say I’d really prefer not to, but I’m not interested in cutting corners.

Engine is a 3.2L (930/21) and the flywheel is a Kennedy Engineering 901 with 9 bolt pattern.

Thanks

[Flat6pac]

I continue to point out that loctite is not your friend when you take the crank apart. People always mention the red, wow, then you need inexcess of 500 degrees F to break it loose. You cant get the crank out without removing the flywheel so where do you put the torch?
If you tear up the bolt head without loctite, you can cut the head of the bolt off and when the flywheel removed you can remove the bolt remains with your fingers.
How many people here complain if the flywheel coming loose if properly installed? You can tell if the flywheel loosens but in over 30 years 1 engine I didnt torque the flywheel and it was immediately a problem and resolved.
I occasionally use blue on the rod nuts but have gotten away from that to lubing the threads.
Bruce

[Paul W]

Thanks Bruce

[Steve@Rennsport]

Hi Bruce,

FWIW,....I've been loctiting flywheel bolts on race engines since 1974 to help keep them from coming loose and its not been an issue to get them out.

Red loctite melts around 360 deg F so applying some heat to the head of the bolts makes this easy to deal with.

I've never used loctite on rod bolts as that affects torque readings and stretch and it won't help anyone should something fail.

[Flat6pac]

Steve, thanks for the imput, the thought of red locktite just scares me, not being able to get something undone and having to apply major heat to the engine parts.
Bruce

[Steve@Rennsport]

Originally Posted by Flat6pac

Steve, thanks for the imput, the thought of red locktite just scares me, not being able to get something undone and having to apply major heat to the engine parts.
Bruce

Yessir, I can appreciate your concern,... I do not have any troubles removing the bolts with a careful and precise application of heat to do the job.

After hundreds of engines over the past 30+ years, I've not had a flywheel bolt failure from this practice and some of these motors have gone over 9800 RPM,......

A loose flywheel does FAR FAR more damage.

Since I always change the RMS, that heat applied to the bolts has never generated any unintended consequences.

[Carrerax]

Originally Posted by Steve@Rennsport

Yessir, I can appreciate your concern,...

After hundreds of engines over the past 30+ years, I've not had a flywheel bolt failure from this practice and some of these motors have gone over 9800 RPM,......

.

Ok, I gotta ask Steve. Was the 9800 intentional or unintentional

[PFM]

Steve,

On the early cranks / flywheels what do you torque the bolts to in order to survive 9800 RPM? Getting ready to build my 3.0 Euro and want it to stay put.

Thanks,

PFM

[Steve@Rennsport]

Originally Posted by Carrerax

Ok, I gotta ask Steve. Was the 9800 intentional or unintentional

LOL,...Purely unintentional and I've seen them (accidently) go over 10.5K. People need to do whats necessary to prevent missed shifts since the consequences can be quite expensive.

[Steve@Rennsport]

Originally Posted by PFM

Steve,

On the early cranks / flywheels what do you torque the bolts to in order to survive 9800 RPM? Getting ready to build my 3.0 Euro and want it to stay put.

Thanks,

PFM

JMHO, but the best way to assure survival with the 70.4mm crankshaft is to use a Tilton 5.5" dual or triple plate clutch. Those do not stress the flywheel like the normal 225mm pull clutch does and they stay fastened to the crankshaft.

This is a somewhat complex subject so if you need more detailed info, call me.

[ChrisBennet]

If you use loctite on the flywheel bolts (I do), fasten the flywheel down with a few of the old bolts first (I mark them with crayon) and then install the new loctited bolts replacing the old bolts as you go along. This will keep loctite from getting between the flywheel and the face of the crank. I can't remember who told me this but it sounds like something Steve Weiner would have mentioned.

[Walt Fricke]

Ever since Bruce Anderson told me about it, I have used a little red Loctite on my 70.4mm 6 bolt 2.7 race motor's cranks. I use the new bolts with mild torque (this isn't like resizing rod big ends), then remove one by one and apply the Loctite and torque to 150 lbs/ft. I have yet to snap a bolt or have a bolt fail. But once I started doing this I have not had any bolts back out with an 8,000 rpm shift point.

Before I started doing this I shook two flywheels loose, each before getting through a whole weekend. Just like Porsche did when they first started racing this crank.

Though for a stock motor with stock shift RPMs none of this is necessary.

Bruce A - Removeing these Loctited bolts is no problem at all. I use my impact wrench, and they just come right out. No doubt heat would make them easier to remove, but I can't see why one would do that when the impact works. Faster, too.

Mind you, none of this applies to the 9 bolt cranks. They seem not to have the harmonic issues that the 6 bolters do. Nor does it apply to the 66mm cranks.

[JJ 911SC]

Originally Posted by Paul W

Hope someone an point me I the right direction…

Installed a new flywheel following the directions in Wayne’s ‘101 Projects’ (p35), no mention of using Loctite so thinking perhaps it wasn’t appropriate with sort of fastener went ahead and torqued it down in anticipation of an engine install this weekend. Flicking through my newly received version of Wayne’s ‘Engine Rebuild’ book the same procedure (p139) references the use of Loctite.

So the question is do I need to buy a new set of bolts and re-do this? Needless to say I’d really prefer not to, but I’m not interested in cutting corners.

Engine is a 3.2L (930/21) and the flywheel is a Kennedy Engineering 901 with 9 bolt pattern.

Thanks

Paul/Steve

I'm facing the same dilema (101=no, Engine Rebuild=Yes).

Before I got a Porsche 2 years ago, I had never done any mechanic on anything but in the last few months, I had the engine out, snap a few exhaust stud, did my first tap & insert ever after I drilled a stud out without a jig Installed SSIs and so on.

I'm doing the whole Super Sport Clutch kit and just like Paul, got to figure out which way to go.

Wayne's has it both way and thanks to my advance search on "flywheel bolt" find out that Steve recomended it...

So Paul which way did you go.

Steve, if I remember well from Wayne's rebuilt book, he mentioned that too much of locktite is counter productive, so since I never use the stuff, how much is enough. Is there a patern to use it. The bolds that I removed did not seem to have any trace of it. Some bolts that I removed (can remeber which one) had some of the green strengt in the middle only.

I'm putting all new fastner, is there any other bolts that need it.

Yes my head is spinning but after all the work don't need a bolts failure and restart from scratch.

Thanks

J.J

[Traveller]

What does the Porsche factory manual state if anyone has one?

I've never seen a call for Loctite on flywheel bolts on any of the cars/motorcycles that I've worked on and certainly not permanent-high strength (red) that requires quite a bit of heat to remove them.

Some flywheel bolts are a one-time use or stretch bolt. Those get replaced.

[Henry Schmidt]

Red Loctite on 6 bolt, long stroke cranks only.
All others go au naturel. Clean, dry installation and proper torque.

[Walt Fricke]

Traveler and JJ

1) Henry put it in his usual nutshell - only the 6 bolt 70.4mm crank might need help. That's all you really need to know.

2) Stock motors run at stock RPMs do not need Loctite, doesn't matter what crank. Just follow the factory specifications.

3) If, and only if, you are going to run your 70.4mm 6 bolt crank up to 8,000 rpm or above, see my advice at 2/12 above. It works. But that doesn't apply to anyone else. So stop fretting.

Caveat: I haven't built a race motor using a 9 bolt crank, a 3.8 liter 993 Cup motor set to run at 9,500 rpm, etc. But:

a) the 70.4mm 6 bolt has a 4th harmonic node exactly at the flywheel/crank end interface, which, per the engineers who understand such things and report their findings in Panorama and other believable sources, was the cause of the troubles Porsche had with the 2.8 RSR motors, and the 2.5 long stroke race motors. It appears that the other cranks don't have this unfortunate harmonic coincidence, so they don't have this problem at high RPMs.

b) I have not heard of a stock motor of any sort which is run within stock limits having the flywheel come loose. Neither has Bruce, and I bet those who build motors for a living have not seen that either. Bruce reports one instance, due to not having torqued the bolts, and that's it.

When I rebuilt my 3.0 1982 SC motor in 1998, I torqued the 9 bolts to factory spec. This is a dual purpose car, with a full roll cage but street licensed. I shift at 6,250 - 6,500 on the track, because those are the optimum shift points based on the torque curve from the dyno. No flywheel issues.

In future editions of his wonderful books, Wayne may want to expand a bit on the question of Loctite and flywheel bolts. However, as long as the Loctite is applied carefully so it doesn't get into the mating surface, it doesn't hurt anything.

And I repeat: an impact wrench will buzz flywheel bolts held with red Loctite right back out, no sweat. No heat is required. This isn't a deal like head or exhast studs.

Just as a point of interest for race motor builders, my first 2.7 8,000 rpm motor had its stock torque, no Loctite, bolts back out. So for the second build I used green Loctite sleeve retainer, which is much stronger than red. The bolts still backed out. It was only after Bruce Anderson (the book guy, not our Pelican Bruce) told me to up the torque to 150 lbs/ft, with red Loctite, that this problem went away. The conclusion I drew from this was that Loctite alone is not enough if you have a flywheel bolt issue. It may be that the extra clamping force is what solved the problem, but I have no desire to experiment, because it is easy to ruin the crank as well as the flywheel when the flywheel gets just the smallest bit loose.

[Traveller]

Originally Posted by Walt Fricke

And I repeat: an impact wrench will buzz flywheel bolts held with red Loctite right back out, no sweat. No heat is required.

Having used red Loctite (270 or 272) once on the flywheel bolts of a VW Golf and having the experience of having to remove them a week later, using an impact gun would worry me.

I applied lots of heat and they came out with far more torque than I would have liked to apply. The threads of the flywheels bolts didn't look like the day they went in and they are a high grade (12.9) bolt.

Furthermore, the crank and flywheel act as one giant heatsink; I doubt the bolts get up to 450+ degrees F, the recommended temperature to be applied.

So for everyday use, I certainly would never use Loctite as you've also mentioned.

[Walt Fricke]

All are welcome to their own worries.

All I can say is that my experience (substantial for a DIYer, though not for a professional engine builder) is that an impact wrench works fine for removal of flywheel bolts which have been Loctited in place.

The crank threads certainly are not damaged, because I have reused mine many times after a flywheel removal for whatever reason.

For that matter, despite all the warnings against it, I have taken to reusing the bolts. And have yet to have one of them snap as I apply 150 lbs/ft of torque to them. Nor let the flywheel loose. While I am not sugesting that others ignore the standard advice to use only new bolts, I offer this as evidence toward the case that the impact wrench removal procedure does no harm to anything.

In fact, with an impact wrench you don't have to lock the flywheel against rotation.

And, beyond that, you can get a much better purchase on the shallow 12 point socket, because you can press the gun, and thus the tool, hard against the bolt. Which is very hard to accomplish using just a breaker bar.

Try it - you'll like it.

[JJ 911SC]

Walt

Thanks for your replies.

If I followed you correctly doing it (as per Henry posting) "au naturel, clean, dry installation and proper torque" should be OK for my application (street car).

Spend the week oversea so the job is schedule for next Friday...

[Walt Fricke]

JJ

You got it - street cars do fine in this area with factory procedures/specifications.