F: Frame UFM to twin engine, bolt torque?

[Bobv07662]

I haven't been able to find a torque specification table for the fasteners on my C Rapide. The UFM to engine bolts are what I'm looking for specifically. I've read the warning to back the rear nut off 1/6 a turn, but what should the front and rear bolt initial tightening torque spec be?

 

[vibrac]

I do love these intermittent requests for torque figures on Vincents
Please Nobody as far as we can tell ever had a torque spanner on the assembly line bench at Vincent
There is just one I have ever heard (Naturally its an Imperial measure ) and that's disputed a ft/lb either way as it was only established over years of leaking heads and my take is 32ft/lb for the head nuts otherwise for everything else its "tight is tight, too tights busted"
NB in my dim memory of my engineering apprentice days wasn't lbs/ft another animal?

 

[Pushrod Twin]

Correct Vibrac, the unit is lbs/ft, pounds force per foot length. The Rolls Royce folklore. as I recall, is that when a fitter uses a standard length spanner and applies the correct "average", trained and practiced force to that spanner, then the torque is correct. Hence the expression 'Fitters Grunt"
BobV, there are tables of "standard" torques based on thread diameter & pitch, dig around on the interweb.

 

[TouringGodet]

Torque is lb-ft, while a measurement of work is ft-lb.

 

[greg brillus]

Using a torque wrench is a great idea for those who have had a limited mechanical background.........even those who do are a bit suspect.........for one who has worked on diesel engines, trucks or heavy machinery will almost certainly strip most threads on a Vincent........whereas those who spent their life as an aircraft fitter, will probably under torque everything, so things will fall off.......... The front bolt/stud in question should be done up tight, and then backed up with the two 3/8 BSF locking nuts........BSF threads are a medium fine thread, look at torque figures for similar sized unified bolts between the UNF and UNC thread forms and this will give you some idea of where to aim for.

 

[Bobv07662]

Thanks for all your insight on the torque specs gentlemen. My engineering background sometimes has difficulty coming to terms with my British bike enthusiasm.

 

[BigEd]

I have two torque wrenches, I rarely use them on my Rapide except for the cylinder head bolts.
The two bolts you are talking about here, as Greg has pointed out, have lock nuts anyway. How often have you heard of an engine falling out of a Vincent twin? ....... Me neither.

 

[brian gains]

follow German method of torque values; good an' tight.

 

[Bobv07662]

Never seen a Vincent engine fall out, but it happens all the time to light aircraft.
Seriously, I checked mine today and all is well, thanks to everyone who helped me on this.