What is the torque specs for this clutch kit?

[klober23]

What is the ft lbs of torque needed to secure the 9 bolts on this clutch assembly (pressure plate)?It's a 1978 911 SC engine. I am finishing someone else's project on this one. I thought these were set to 14.5ft lbs? It's a Sachs GMFZ 225.

Thanks in advance

[The cap'n]

Socket head bolts generally take a little more torque than hex head fasteners. I'd go 18 ft./lbs.

The Cap'n

[safe]

Whatever ft lbs thats normal for an M8 8.8 grade (24 Nm).

[JFairman]

Do you guys put those 8x1.25mm bolts in dry, with a drop of motor oil on the threads, or with a small drop of low yield blue loctite on the threads?

[safe]

No torque values are ever given for dry threads. I don't think it matter if you use oil or loctite, but the workshop manual doesn't say anything about loctite as far as I can remember, I do't use it on those.

[KTL]

The parts diagrams show a lock washer underneath the head of the bolt, plus the spring pressure of the clutch being clamped onto the flywheel helps to lock the bolts in place. No need for thread locker.

As far as lubing the threads, one could say the zinc plating lubricates them. It definitely affects the torque applied. http://www.metricmcc.com/catalog/Ch10/10-1027.pdf

[Flojo]

the 9 (3x3) clutch bolts torque at 35Nm (spec), dry, springwashers.
allways use new bolts here!

[safe]

Originally Posted by Flojo

the clutch 9-bolts torque at 35Nm (spec), dry, springwashers.
allways use new bolts here!

These are 10.9 bolts?

[KTL]

All the technical information I have shows the clutch bolts for a 915 to be M8x42mm and property class 8.8. The torque spec listed is 20-25Nm = 14-18 lb-ft.

No need to replace the bolts unless the tooling is ruined, which doesn't allow you to get good engagement with your hex bit socket. The split lock washers are typically replaced when the bolts are removed. Split lock washers are cheap and easy to replace. Can get them at your local hardware store. Whereas 8.8 class socket head screws are not a common type you'll find at the hardware store. Most socket head screws we see there are 12.9 class.

[safe]

Thought so!
I never replaced them or the washers and they have always stayed in place. On my 3.6 conversion I used 12.9, because I needed longer bolts to make everything fit and that was what I found available.

[Trackrash]

I have noticed there seems to be some discrepancy or changes over the years as to what bolts Porsche used on their clutches.
From the original work shop manual. 10K bolts torqued to 25 lb-ft.

[chris_seven]

Originally Posted by safe

No torque values are ever given for dry threads.

Sadly, I have to disagree - it is very common for manufacturers to specify 'dry' torque figures for the majority of fasteners as this avoids the responsibility for any variation of the quality of lubrication.

The maximum recommended torque for a Grade 8.8 Plain finish fastener is 24.2Nm and this is the 'dry' figure. It is based on a the assumption that the preload created by the application of this torque is 80% of the bolt's yield strength.

If you oil the fastener you will marginally increase the preload but some care is needed.

I believe that all of the figures in the 911 Workshop Manual assume a 'dry' torque unless otherwise stated.

The assumed coefficient of friction (CoF) for a plain dry fastener is around 0.16 but the scatter can be quite high depending on the quality of manufacture and surface finish of the threads. - Figures as high as 0.23 have been measured.

A light oil can help to reduce this scatter and can reduce CoF to around 0.14 so bolts preload will tend to be more even but slightly greater than the assumed value.

However, the best method to reduce scatter is to 'burnish' the fasteners by carefully torqueing them two- three times prior to final tightening and by cleaning the thread between each torque application.

I believe the more important the fastener the more important it is to ensure that the thread is smooth.

Zinc plating is also interesting and if carried out carefully can reduce CoF but cheaply plated fasteners carry the risk of increased scatter due to poor thickness control and again burnishing this type of fastener will help to achieve consistent results.

If you consider that you can reduce the CoF from 0.16 to 0.10 by using modern thread lubes and it is vital that the applied torque is reduced accordingly or fasteners can be quite badly overloaded.

If you take a Grade 12.9 M10 x 1.25 bolt and apply an Ultralube I believe you could cause the bolt to permanently deform by a significant amount of you applied 90Nm.

Loctite will probably reduce CoF from 0.16 to around 0.14 which should be tolerable and similar to oil. The increase in preload is probably around 5%.

[Flojo]

Originally Posted by KTL

No need to replace the bolts unless the tooling is ruined, which doesn't allow you to get good engagement with your hex bit socket.

it's an argument.
the compromize is up to you.
BUT, do you really want to find out the hard way after all the work (engine drop)?!
the bolts don't cost much.

[KTL]

You said "always use new bolts here" and in my mind that makes it sound like they're going to fail if you don't replace them. That's not true and there's nothing in any technical documentation that says these are a one-time-use-only fastener

I don't know what hard way you're referring to after the engine drop. Are you saying these clutch could fail after reusing them? I've got a bunch of data points from my personal experience and local friends' that indicate these fasteners are not risky to reuse. All of these cars have been driven plenty hard at track lapping days and nobody's had a clutch come off the flywheel, or any clutch problems for that matter.

No argument here that the bolts aren't that expensive. But why replace something just for the sake of doing it? That is, unless new and shiny zinc plating is what you desire.

[Catorce]

Wow this topic is spreading like a disease lately. Here are the bolts I replace 100% regardless of condition in a rebuild:

- con rod bolts
- axle nuts
- flywheel bolts
- clutch pressure plate bolts

The reason I have to replace the PP bolts is because of all the bolts on the car, these hex head ones are the most likely to have been mangled by a PO and have the hex part deformed. They are also so soft that it is easy to deform them ever so slightly upon removal.

Supposed to be 18-24 ft lbs depending on the application, but they really get stuck in there over time.

I doubt they will ever fail upon reuse, but considering the flatness of the pressure plate mounting depends on these bolts being all the way snug, i don't want an old nasty bolt preventing that with it's ovaled hex head.

[KTL]

It sure is spreading. And flojo is one of the people resurrecting some of these old threads and jump starting the discussion all over again.

The flatness of the pressure plate's mounting depends on the actual flatness of the pressure plate seating surface and the matching seating surface of the flywheel.

Flywheel bolts seem like they'll forever be an ongoing debate because years ago someone started spreading the rumor around here that they were stretch bolts, just like the conrod bolts. But there's no technical documentation that these are a one time reuse bolt. That said, totally agree its wise to replace these based on inspection. ESPECIALLY a the 6-bolt 70.4mm cranks. Trying to get a stripped shallow headed flywheel bolt removed can be a real battle.

Which axle nuts do you replace? The castle nuts last forever and the only thing I replace is the cotter pin. The self-locking nuts on the later axles do indeed lose some of their grip (these deformed thread nuts are often said to be one time use only) but i've seen them used over and over again with no signs of loosening on numerous cars. Not saying it's necessarily right. Just saying it's been done and i've yet to see a loose axle on those cars we have in our fleet of friends.

Another fastener that's very very wise to replace are the M8 CV bolts. Those are notorious for being over-stressed and almost always have boogered tooling. They're a common length and readily available and cheap. That's a bolt i'd argue is definitely one of the bolts that are stupid to not replace.