clutch bolts keep snapping

[vestandpants]

evening guys,

been hard at work on my 65 today, thought it be about the right time to re-install the clutch. i bought new clutch plate bolts last month (6mm) as well as a new friction plate.

armed with new and recon parts, manuals in hand and read throughly I gave it a go.

I set the torque wrench to 23nm as per instruction and began the slow process of doing the bolts up, using the method spelled out in the manual (1 bolt 1 turn then its opposite 1 turn and so on). I must admit they were getting incredibly tight when the sound of metal tearing had me dismantling the lot carefully to try again with the old bolts.

I did test the torque wrench to see if was broken but it did 'click' when pushed. then i tried with the old bolts and this time i was even more vilgilant. Each bolt was on the same number of turns, everything was going dandy i got all of them upto 15nm. I then increased it to 18nm and the first went 1/2 turn then 'click'. onto to its opposite and that went a whole turn then snap. more bolts to be put on order!

my question here is did I do anything wrong? is 18-23nm just a little bit too much for a 6mm bolt? do you guys have any suggestions on how to install a clutch from your own experiences?

[montmil]

You sound awfully calm, vestandpants. I'd be doing some serious torque wrench tossing about now! Perhaps a pint or two before posting?  

It doesn't seem likely that the 6mm bolt/s would fail at the suggested 23nm setting. And you are sure of your wrench? Might you be able to borrow another wrench a do a test with some loose shop bolts? Perhaps confirm your wrench's performance.

It has to be frustrating for you. Were you able to extract the broken bolt/s? Was it the bolt head that failed or the shank?

My granddaddy, when asked how to torque bolts and studs properly, told me to, "Pull until it gives, then back off half a turn." Thanks, Grandpa!

Monte

[bobo]

Seems like a dumb questio but are you sure the wrentch is Newton Meters and Not Foot Pounds?  (Foot punds are 1.4X)

[Justin B.]

The various manuals (even factory) are rife with incorrect torque specs.  What does that work out to in lb/ft?  The only clutch I have replaced (1980) had 6 mm bolts on the plate and they won't stand much in the way of torque.  Maybe you are using specs for the later 8mm bolts?

[nhmaf]

That spec sounds like what I used for my '82 model's bolts, which are larger diameter, I think... :-/

[steve hawkins]

I had the same issue with my 1979 R65 some years ago.  

An aircraft engineer mate of mine declared that the torque specified in the haynes manual was far too high - for the 6mm bolts - laughably so.  

So we torqued them up far less - have not had any issue since.  We used aproximatley half that specified - but we really did it by 'feel'.  Clutch has been working fine for 2 or 3 years.

You need two torque wrenches normally - a small torque wrench for a small amount of torque on small bolts and a big one for the big jobs - as you will find that you need to be well inside their ranges for them to be anywhere near accurate.  

But you also need to develope some experience, so that you can spot an obviously wrong torque setting, but also to spot a right torque setting and a weak bolt...tricky.

What we need is for people with various manuals to quote the specified torque for this job.  See if they are different.  Any takers?

[Justin B.]

Relevant information split out and movrd to FAQ section.  Please continue discussion in this thread so as to not clutter up the "FAQ" posting... [link=http://suraklyn.com/yabb/YaBB.pl?num=1223906519]This Thread[/link]