Topic: Countershaft holder - proper torque setting for 4 6x20 screws?

[Mark K]

In the process of reassembling the engine on my '73 CB750.

Tried to reinstall the countershaft holder, inserted new o-ring. Attempted to torque original 4 screws to 8 lbs/ft and I broke 1 screw. I figured it was because I was using old screws. Went to Ace hardware, bought 4-6x20 flat screws. Fit perfectly, but same thing happened, broke 1 screw when attempting to torque to 8 lbs/ft. I've been watching Dino's videos (Hack-a-week) and that is the tq he used.

Is there a torque table available anywhere for all the various nuts, bolts and screws on the 750? I couldn't find the torque setting for these 4 screws.

Any help would be greatly appreciated.
Thanks

[RAFster122s]

Make sure the hole is dry and clean, a good blast of air in the hole usually will displace any liquids. It doesn’t take much liquid in a hole to cause a machine screw to break, but you are dealing with a tiny fastener, it does not take a lot of force to snap a small screw. You aren’t going to want to use a 8-12 inch ratchet handle on a M6 fastener…

Std torque spec for M6 fastener is 12Nm for class 8.8 and 16Nm for class 10.9

http://www.melco-service.com/docs/AMAYA_OS_v10/AMAYA/Torque_Specifications
Which is more conservative…


https://crafter.fastenal.com/static-assets/pdfs/Torque-Tension_Chart_for_Metric_Fasteners.pdf

[Mark K]

Make sure the hole is dry and clean, a good blast of air in the hole usually will displace any liquids. It doesn’t take much liquid in a hole to cause a machine screw to break, but you are dealing with a tiny fastener, it does not take a lot of force to snap a small screw. You aren’t going to want to use a 8-12 inch ratchet handle on a M6 fastener…

Std torque spec for M6 fastener is 12Nm for class 8.8 and 16Nm for class 10.9

http://www.melco-service.com/docs/AMAYA_OS_v10/AMAYA/Torque_Specifications
Which is more conservative…


https://crafter.fastenal.com/static-assets/pdfs/Torque-Tension_Chart_for_Metric_Fasteners.pdf

Thanks RAFster122s, I cleaned the holes, but used some blue loctite. I used a torque wrench set to 8lb/ft. I'll check out those links you included.

[Don R]

 I like to use an inch pound torque wrench on m6 bolts.

[scottly]

Std torque spec for M6 fastener is 12Nm for class 8.8 and 16Nm for class 10.9

Most of the stock fasteners are not that high of class; 3 ft/lbs (or 36in/lbs) is probably more appropriate.

[PeWe]

I should tighten those with max 9Nm. (6.64 ft lbs)
Std 8.8 class has 9.8Nm as max for M6 (7.2 ft lbs).

I use countersunk allen heads there. I really do not like X-heads.

Then when tightening engine covers and cam holders, the thread is more fragile aluminium, often with pores.

I tighten cam holders max 9 Nm. This when head has Wurth time-serts. 8Nm if not.

I tightened most M6 with 10Nm before, 7.37 ft lbs

https://www.omnicalculator.com/conversion/nm-to-ft-lb

Important with a good torque wrench. I have a Hazet 2.5-25Nm 1/4" socket for the smaller.
Hopefully still correct. I always set it to 0 direct after use.

[scottly]

The stock fasteners aren't 8.8.

[scunny]

look at your ring open end set. very small leverage for 6mm. snug will do.

[Mark K]

Had to remove the screws with a manual impact driver, they were really tight.

I appreciate all the suggestions from everyone here.

[scottly]

Had to remove the screws with a manual impact driver, they were really tight.

That is typical, especially with the flat-head screws. The conical underside of the head tends to get wedged into the countersunk holes, sort of like the way the alternator rotor is locked onto the tapered end of the crankshaft, with no key-way. Even the standard cross-head case cover screws get stuck, so I usually go straight to the impact driver; if I can't turn the driver by hand, then I tap it with the hammer until they break loose. Like Scunny said, the 6mm screws don't have to be that tight.  

[PeWe]

I had to drill the heads so they fell out. Cover off, a plier helped to get them out.