crank bolt torque (2021)

[Onder]

I see that RGM wants 20 ft lbs on the crank studs/bolts/nuts for the 5/16th pre MkIII.
Norman White says 25 per book.
What is the general opinion of the list on this?
oh...standard original bolts being reused.

 

[Fast Eddie]

Simple. If in doubt, go with Norman !

Plus, workshop manual says 25 ft lbs.

 

[kommando]

Don't use Haynes !!!!

 

[Onder]

I mostly curious why RGM says 20...anybody know?

 

[Fast Eddie]

Don't use Haynes !!!!

It’s the factory manual I’m referring to...

 

[L.A.B.]

Haynes = "Crankshaft nuts...25 ft. lb."

 

[Onder]

Still wondering why RGM want 20 pounds..it is in bold type in their parts catalogue.

 

[Time Warp]

You would need to ask them if they are supplying the fastener set, but lets state the obvious, 90% of folk probably do not even torque those fasteners.

CRANKSHAFT FIXING KIT COMPLETE TWINS CIRCA 1972 ON

067094

www.rgmnorton.co.uk

 

[robs ss]

I see that RGM wants 20 ft lbs on the crank studs/bolts/nuts for the 5/16th pre MkIII.
Norman White says 25 per book.
What is the general opinion of the list on this?
oh...standard original bolts being reused.

I definitely would not be re-using that hardware.

 

[Time Warp]

Maybe they are the same as the Norvil studs. (I thought the bolts/nuts on the 750 went higher than 25 ft/lbs.

Here is one of my favourite quotes from another thread, this one from Mr Hemmings.

".....I never bother with a torque wrench on these, because unless you've got proper adaptors and things to get at the bottom ones I can't see the point of it. So the trick is just to use two good spanners,-and tighten them up."

I could have lent this to 'Mick.

 

[SteveA]

Maybe they are the same as the Norvil studs. (I thought the bolts/nuts on the 750 went higher than 25 ft/lbs.

Here is one of my favourite quotes from another thread, this one from Mr Hemmings.

".....I never bother with a torque wrench on these, because unless you've got proper adaptors and things to get at the bottom ones I can't see the point of it. So the trick is just to use two good spanners,-and tighten them up."

I could have lent this to 'Mick.

View attachment 21241

I'm with Mick on this one!

 

[Time Warp]

I doubt anyone would choose to torque some of the crankshaft fasteners or none of the fasteners if they were handed a simple tool that allowed them to do so (torque all the fasteners to the NVT recommended torque setting)

There will always be an excuse why you do not need to do something.
Its just surprising coming from more than one 'expert in the field for decades.

Clickety click and done , over crank the !@# out of them until you pass wind. (lol)
#
If the RGM fasteners will only take 20 ft/lbs I would be torqueing them and asking if that is dry.
Perhaps this sort of thing comes down to your day job and the resources available.

I actually in some respect regard torqueing the fasteners (including those hard to get to on the cylinder head) as the easy way to do them due to any guess work being removed.
Click click. (shrug)
#
I ordered my Norman White book this morning ($85.80 from Angus and Robertson / Sydney)
It should be a good read.

 

[Fast Eddie]

I'm with Mick on this one!

It’s not hard to learn to get a feel for that kind of torque. Especially when you’ve done the hundreds, perhaps thousands, that Mick has!

I don’t recall reading lots of horror stories of engines failing due to these fasteners failing...

 

[Onder]

And I can add what I was taught: "even torque is more important than the exact torque" .

 

[kommando]

Haynes = "Crankshaft nuts...25 ft. lb."

Not all Haynes, this is from 1984 reprint of the 1973 first print with an added MK3 supplement over the 73 print.

35 ft/lbs is also in the torque figures in front of engine chapter.

 

[kommando]

As for the two figures of 20ft/lbs and 25ft/lbs this may be due to the change in 72 from cycle to UNF where the TPI goes from 26 to 24.

From RGM in their description of the pre 72 cycle thread stud.

CRANKSHAFT STUD 5/16" BSC X 26TPI.

IN LATE 1972 THE CRANKSHAFT FIXINGS WERE RE DRAWN AND CHANGED TO SIX STUDS AND 12 NUTS UNF THREAD. THESE CAN BE USED ON ALL PRE MK3 TWINS.

When Triumph changed their 5/16" conrod bolts from cycle to unf they dropped the torque by 6 ft/lbs.

Important Note: Triumph changed the rod bolt torque from 28 ft. lbs used with CEI 26 tpi bolts to 22 ft. lbs. when they started using UNF 24 tpi threads.

As the RGM stud and nut kits for pre MK3 are UNF this would make sense.

 

[L.A.B.]

Not all Haynes, this is from 1984 reprint of the 1973 first print with an added MK3 supplement over the 73 print.

35 ft/lbs is also in the torque figures in front of engine chapter.

Ok. Both are "25 ft. lb." in my 1990 copy.

 

[robs ss]

It’s not hard to learn to get a feel for that kind of torque. Especially when you’ve done the hundreds, perhaps thousands, that Mick has!

I don’t recall reading lots of horror stories of engines failing due to these fasteners failing...

For the average "home wrenches" like me, it can be hard to trust your sometimes educated hand.
I believe in using a good torque wrench (or equivalent - say spring balance and drilled spanner) whenever you can.
The result has to be better in the long run.

 

[Onder]

I think the thread change is the answer. Looking at various charts, non motorbike, the torque recommended for 5/16 depends on
all sorts of things: TPI, grade of bolt, lube and non lube and which type of lube. It really does vary widely.
One can only wonder if the change for MkIII to 3/8 studs was not just shear strength but ability to increase the tension safely.

 

[kommando]

I used 20ft/lbs plus blue loctite on my UNF 72 crank. So even if the 20 is incorrect the loctite covers the potential under torque.