Doing a freshen on a 125 rev 3 ,bolting up the head to Cly and torquing to 22 newton meters the head bolts seem to stretch and 1 snapped. Any thoughts on this?are they one use type bolts?am I using the wrong specs or maybe my tourque wrench is Faulty .

Hi Sprinter 27

Not owning the 125 I don't know what size thread the Cyl Head bolts are, but I know that 22nm is a lot of torque if the thread size is not an M8 and/or very high spec material.

See this link for suggested Beta torques.. be aware it refers to a 270.

http://www.trialscentral.com/forums/topic/28936-torque-settings/

If you look up fastener torques on google like this:-

http://www.leytonfasteners.co.uk/pdfs/TorqueValueGuide.pdf

be aware there's lots of variables involved.

Dom

The Evo manual shows a 20 - 23 NM that seems to apply to all models.

• If you are using an extension on your torque wrench to reach the bolts, this affects the numbers. The torque reading on the wrench needs to be reduced based on the length of the extension.
  
• Could someone have installed aluminum head bolts? With steel bolts, I would expect the threads in the cylinder to strip long before the bolts break.
  
• It a could be bad wrench. I have found the cheap ratchet type wrenches to be very inconsistent. Beam types are much better.
  

Edited June 8, 201313 yr by mcman56

Well they are m 7 special bolts (shouldered) and appear the same on all model sizes. Guess I'm going to blame my torque wench ,but its odd as its a decent one.

OK, M7, that's the information needed.

M7 metric coarse thread, 10.9 specification bolt (high tensile) = 21.3Nm recommended torque.

Dom

Well they are m 7 special bolts (shouldered) and appear the same on all model sizes. Guess I'm going to blame my torque wench ,but its odd as its a decent one.

Borrow another torque wrench

Torque a nut or bolt

Felt pen the socket and the work

Loosen

Use the other torque wrench and torque to same value and see if the felt pen marks line up

We use this to check cylinder head torque etc, works well

If the marks don't line up then the 2 wrenches are different

Doesn't it depend on the length of the bolt as well since what you're measuring is the stretch of the bolt. The head bolts are mighty short and if he's stretched the others and snapped one and the earlier info is a significantly lower torque then I'd be suspicious of the 21-22Nm number. Here's the numbers from the original post. I did check on the flywheel nut and it is correct.

Call a dealer or your importer.

Tightening torque Rev3:

Shock absorber-Swingarm 45Nm

Shock absorber-Frame 45Nm

Connecting frame rod-frame 23 Nm

Cylinder-Crankcase 20-23 Nm

Primary drive gear 120 Nm

Handlebar 25 Nm

Engine-frame 50 Nm

Swingarm bolt 90 Nm

Front wheel axle 65 Nm

Rear wheel axle 65 Nm

Steering stern bracket 25 Nm

Rear fender bracket 10-15 Nm

Front brake pad 20-23 Nm

Rear brake pad 20-23 Nm

Engine Head-Cylinder nuts 15-16 Nm

Front axle fixing nuts 10 Nm

Flywheel 140 Nm

Edited June 11, 201313 yr by dan williams

Well it's turned into a confusing issue. Sourced new head bolts ,had the torque wrench checked and googled all over .betas service manual specs these bolts at 22 nm for the 125. Bench tested and could see it was " likely " going to break if I continued. So it's going back together at 18 nm.

This also confused me, it seems maybe the translation to english is maybe not the best & the cylinder barrel to crankcase nuts can easily be confused with the cylinder head bolts. I set my torque wrench to 22 nm for the head bolts & one stretched, I've re-worded & grouped the settings to what I think they should be:

Tightening torque Rev3:

Connecting frame rod-frame 23 Nm
Handlebar 25 Nm
12:01 16/10/201412:01 16/10/2014Swingarm bolt 90 Nm
Shock absorber-Swingarm 45Nm
Shock absorber-Frame 45Nm
Rear wheel axle 65 Nm
Rear brake pad 20-23 Nm
Steering stern bracket 25 Nm
Rear fender bracket 10-15 Nm
Front wheel axle 65 Nm
Front brake pad 20-23 Nm
Front axle fixing nuts 10 Nm
Engine-frame 50 Nm

Cylinder Head bolts 15-16 Nm
Cylinder Crankcase Nuts 20-23 Nm
Flywheel 140 Nm
Primary drive gear 120 Nm

1 Nm=0,1 kgm

Just my opinion but based on many years as engineer / mechanic. 21Nm is about the limit for M8 fasteners into aluminium and I would therefore expect M7 to be about 3/4 of this or 15 to 16 Nm.

Torque is a very poor way of setting the clamping force of a fastener because the friction in the threads varies so much. The sps system whereby a small torque is used to take up slack and then the fastener is rotated an additional number of degrees is a far better method.

hand tighten only for those suckers...

Ugh, bolts, nuts... If it holds the head to the cylinder 15-16Nm

This reminds me of the time my local dealer got his Nm/ and Lb/ confused! Yes, if you keep cranking they stretch until they pop!

Hey Cope that's cheaper than NASA getting their units wrong. Fortunately doesn't happen often.