Post by brucek on Sept 12, 2016 19:30:43 GMT 10
I had some warranty work to be done after a recent road trip (failed tappets and camshaft which stopped me 60 km west of Cobar NSW, see earlier post on Mechanical Questions & Answers).
Before I took the bike up to Uralla for the work to be done I gave it a good clean up and since I was well and truly back on the bitumen I swapped the Heidenau K37 rear back to the spare and put the Duro spare back on the rear. Whilst I had both wheels off I took the opportunity to check the torque of the wheel hub drive spline screws (that was interesting!) All but one of them took up about ¼ of a turn before the torque wrench clicked off at 30 Nm. One screw didn't want to play at all, it got close but wouldn't torque up so I didn't push it any further and thought "no problem I'll just get this added to the warranty job, 'they' can sort it out". I'm thinking a 'Recoil' or 'Helicoil' thread insert would be required. Turned out to be beyond the capabilities of the repairer and not covered under warranty anyway. No problem there, I can fix that, Ive done thread inserts before. The bad news is the dodgy screw in question came back broken off in the hole which left me the nice job of extracting the broken bit. The good news after getting the broken bit out of hole (just to cut to the chase) was that it didn't need an insert. It wasn't the tapped hole which was the problem. It was the crap material the screws are made from.
So, what I did was to run an 8 mm tap down all the holes to clean out any dirt/corrosion/cured thread locker etc. and make sure the thread depth was sufficient to prevent the screws from 'bottoming out' before clamping the spline flange. All good there, we have 20mm of screw protruding from the bottom of the drive flange and 25mm of thread depth. I didn't have to tap the holes any deeper.
Now to test the 'dodgy' hole. I could see the first two or three threads were mashed but thought I'll test this sucker before I go to the expense of buying a Recoil thread insert kit. All good there, the suspect hole tightened up to 30 Nm no problem. BUT ! one of the remaining screws wouldn't torque and just gave an audible 'tic' when trying to torque it up (another 'aw shit' moment, this was now TWO failed screws). Again, I didn't push it any further. I removed all the screws and here is the result (see the piccy).
A trip to the local nut and bolt supplier had me a dozen (proper) 12.9 strength grade, Zn plated, low head, cap screws on order (I'm going to replace the screws on both the rear and spare wheels all at once, not taking any chances).
Moral of the story, don't trust bog std. Ural threaded fasteners in high stress areas (they're made of chalk), check the length of screw/depth of thread engagement, i.e. check that the screws don't bottom out and use a quality torque wrench of trusted accuracy (mine's a Repco Warren & Brown job which I've had for over thirty years).
Before I took the bike up to Uralla for the work to be done I gave it a good clean up and since I was well and truly back on the bitumen I swapped the Heidenau K37 rear back to the spare and put the Duro spare back on the rear. Whilst I had both wheels off I took the opportunity to check the torque of the wheel hub drive spline screws (that was interesting!) All but one of them took up about ¼ of a turn before the torque wrench clicked off at 30 Nm. One screw didn't want to play at all, it got close but wouldn't torque up so I didn't push it any further and thought "no problem I'll just get this added to the warranty job, 'they' can sort it out". I'm thinking a 'Recoil' or 'Helicoil' thread insert would be required. Turned out to be beyond the capabilities of the repairer and not covered under warranty anyway. No problem there, I can fix that, Ive done thread inserts before. The bad news is the dodgy screw in question came back broken off in the hole which left me the nice job of extracting the broken bit. The good news after getting the broken bit out of hole (just to cut to the chase) was that it didn't need an insert. It wasn't the tapped hole which was the problem. It was the crap material the screws are made from.
So, what I did was to run an 8 mm tap down all the holes to clean out any dirt/corrosion/cured thread locker etc. and make sure the thread depth was sufficient to prevent the screws from 'bottoming out' before clamping the spline flange. All good there, we have 20mm of screw protruding from the bottom of the drive flange and 25mm of thread depth. I didn't have to tap the holes any deeper.
Now to test the 'dodgy' hole. I could see the first two or three threads were mashed but thought I'll test this sucker before I go to the expense of buying a Recoil thread insert kit. All good there, the suspect hole tightened up to 30 Nm no problem. BUT ! one of the remaining screws wouldn't torque and just gave an audible 'tic' when trying to torque it up (another 'aw shit' moment, this was now TWO failed screws). Again, I didn't push it any further. I removed all the screws and here is the result (see the piccy).
A trip to the local nut and bolt supplier had me a dozen (proper) 12.9 strength grade, Zn plated, low head, cap screws on order (I'm going to replace the screws on both the rear and spare wheels all at once, not taking any chances).
Moral of the story, don't trust bog std. Ural threaded fasteners in high stress areas (they're made of chalk), check the length of screw/depth of thread engagement, i.e. check that the screws don't bottom out and use a quality torque wrench of trusted accuracy (mine's a Repco Warren & Brown job which I've had for over thirty years).
