Gearbox Top Bolt - Worn Out

Thought this picture might be of interest.
I used to have a belt primary and at that time fitted a double sided gearbox adjuster bolt. When later fitting an Alton starter i went back to chain primary and the adjuster on the primary side then becomes a pain to access due to the starter motor so i recently went back to a stock single sided adjuster/bolt.
The pic shows the recently removed top bolt from the double adjuster, deeply slotted where it has been bitten into by the mounting plates. I don't know of any time when i was riding without that top bolt tensioned. Nice soft stainless i guess.

Ouch

I don’t understand how this can happen unless you’re using some kind of different adjuster set up? And unless the bolt has been run loose?

Are you sure it’s not some PO ‘modification‘ to allow greater movement of adjustment etc?

That bolt was installed during my ownership so in this case i am the dumb PO . I'm not aware of any machining but the belt drive etc was installed by a paid "expert" when I pulled the bike out of hibernation 15 or 20 years ago - kids big enough and mortgage small enough etc - so you never know. The "expert" died a couple of years back so i can't ask.
The head of the bolt was on the primary side (we had to pull the whole primary off to remove it), and the adjuster on that side to the front , so the slots are also in what was the front face, which did puzzle me too. Normally if things are loose the final drive will pull all to the rear and overtighten the primary but if anything i have been having to retension a loose primary of late. Perhaps time for a good look around under there.
Just before that bolt was replaced i did have a senior moment and forgot to fully tighten the bottom gearbox mount after adjusting the primary chain, and that fell out somewhere along a 2 hour ride - i had loaned the bike out so don't know when. It is hard to imagine that much damage in a hour-ish of gentle use though.

Looks similar (but not identical) to the one RGM offer in their Mk3 kit.... Perhaps: 'inspired by?'

My money is on this being some kind of ‘modification’ instigated my your ‘paid expert’. Possibly the belt was too short and the stud was hard up against the slots and this was his way of gaining clearance ?

I've had a look in my magic folder and August 2005 RGM belt drive kit and double sided tensioner, bought from an NZ reseller.
Interesting on the Mk111 version, that has a square cut by the look of it whereas mine looks more like set off centre and turned in a lathe but "inspired by" is looking likely.
Moving right along then.

ntst8 said:

Thought this picture might be of interest.
I used to have a belt primary and at that time fitted a double sided gearbox adjuster bolt. When later fitting an Alton starter i went back to chain primary and the adjuster on the primary side then becomes a pain to access due to the starter motor so i recently went back to a stock single sided adjuster/bolt.
The pic shows the recently removed top bolt from the double adjuster, deeply slotted where it has been bitten into by the mounting plates. I don't know of any time when i was riding without that top bolt tensioned. Nice soft stainless i guess.

Click to expand...

are the slots regular, like lathe generated, or only on two sides where plates caused them ( highly unlikely, IMHO)?

ntst8 said:

Thought this picture might be of interest.
I used to have a belt primary and at that time fitted a double sided gearbox adjuster bolt. When later fitting an Alton starter i went back to chain primary and the adjuster on the primary side then becomes a pain to access due to the starter motor so i recently went back to a stock single sided adjuster/bolt.
The pic shows the recently removed top bolt from the double adjuster, deeply slotted where it has been bitten into by the mounting plates. I don't know of any time when i was riding without that top bolt tensioned. Nice soft stainless i guess.

Click to expand...

That kind of wear could only occur from inadequate effective tension. Regardless of whether you're using single or double side tensioners, the job of the tensioner is to achieve the correct alignment and tension. Then you tighten the bolt(s) and there should be no wear/fretting against the clamping bolts.
IMHO what you have shown is purely inadequate tension or preparation (cleaning area of friction).
Regardless of "how" you achieve alignment and tension, the friction grip of the upper (mainly) and lower bolt are what maintains that tension.

ntst8 said:

Moving right along then.

Click to expand...

That's only you , suspect this thread has legs for 2 or more pages.

What oil were you using for it to get that bad?

It wouldn't hurt to check all of the mounting holes and bores along with the gearbox case top mounting lug and spacer width in regard to the inner dimension at the cradle.

That looks to be an eccentric adjuster bolt specifically for MKIII belt drive. The MKIII primary is normally at a fixed distance. The adjuster moves the gearbox a tiny amount within the normal feed through seal. A MKIII has a fixed hole in the engine cradle rather than a slot for adjustment like on all pre MKIII
I can't conceive why it is used in that application. Did they loose the original bolt?

I have a spare OEM bolt on the shelf...

EstuaryBoy said:

What oil were you using for it to get that bad?

Click to expand...

I'm not falling for that trick, we all know that this area is self lubricating

dynodave said:

That looks to be an eccentric adjuster bolt specifically for MKIII belt drive. The MKIII primary is normally at a fixed distance. The adjuster moves the gearbox a tiny amount within the normal feed through seal. A MKIII has a fixed hole in the engine cradle rather than a slot for adjustment like on all pre MKIII
I can't conceive why it is used in that application. Did they loose the original bolt?

Click to expand...

No Idea why either but there must have been some parts mixing out of my sight - it didn't have the plain lever for cam adjustment as shown on the RGM pic, but a threaded rod and double nut through an anchor mount. So a real hybrid. Unless RGM used to cheat and use the Mk111 style bolt and just vary the attachments for pre Mk111? I don't have any photos from back then so we will never know.