Belt Drive Upgrade

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Oct 17, 2007
Howdy ,

I have just picked my 850 up after having a RGM belt drive put in it and am amazed at the difference it has made.

My clutch is much lighter and the noise is greatly reduced.

In fact it feels like my left leg has been numbed as I cannot feel any vibration.

Money really well spent.

Belt Drive

I agree with the difference such a conversion makes. I fitted a RGM belt drive about 8 years ago together with different clutch plates (also from RGM) - when I reassembled it I thought something was wrong as I could pull the clutch with one finger !! but it worked and still does now - no slipping/dragging - I haven't adjusted it for four years. Two other things I did fit was the RGM clutch push rod modification with a ball bearing and short 'slider' to help prevent gearbox oil creeping along the push rod and into the primary chaincase - works well. I also fitted their needle roller thrust bearing behind the clutch - it makes the plates lift 'cleaner'.

I fitted an RGM belt drive conversion to my '74 850 a couple of years ago.
Also really nice clutch action.

But a bit of a fiddle trying to align the gearbox correctly to the crank pulley. I fitted another tensioner from RGM which helps.

Also the belt tension is important, must be very slack on a cold motor (at least an inch and half free play. I made the mistake of over tensioning the belt and could hardly select gears when hot. :)
Thanks for the advice on the tensioning of the belt.

I will be riding this weekend and will check the tension when it is hot.

The belt drive is on my 850 Mk1 and compliments the RGM close ratio and has made the bike a real fun machine up through the hills.

Has anyone done anything about venting the primary drive after fitting a belt drive conversion?

I don't want to cut slots in my primary drive casing on my '74 850.

I thought about cutting two small portions out of the rubber sealing band. One at the front of the casing (to allow air to enter) and one at the lower rear of the casing to allow air and any water etc to escape.

Or maybe it's not that important to vent the primary drive? :idea:
I've had an RGM belt on my Mk3 for twelve years or so unvented without any problems, and still on the same belt.

Hey Guys,

Thanks for raising the cooling question as I was wondering what to do.

I hope I can get the life you are getting out of yours Cash.

Really nice mod you have there Norbsa and most of it probably hidden behind the alloy Z plate.
I don't have the eqiupment to carry out such a mod like that in my workshop.

As Cash seems to have had no problems without venting his, maybe I'll not bother with any mods and just keep an eye on the tension when the motor's at running temp.
Although I'm sure the summers are a lot warmer here than in Cumbria U.K.

RGM instructions indicate more free play required in warmer operating conditions, I've got about an inch and a half free play which seems really slack when cold, but when warmed up there's almost no free play at all. :)

What belt do you have from RGM is it a AT10 and if so is it a red belt or is grey as shown on their homepage.
I am asking because my bike has a Hayward belt drive which uses a Syncroflex AT10 ~30mm wide and 890mm long and I need to get a new one, after I blody fool started my reassembled bike without having tightned the nut on the screw thats activated by the clutch push rod, this resuted in a large hole in my inner primary :( and damage to the belt.
As far as I can see the red belt "gen-III" from syncroflex (mine is a red syncroflex) seems to be the strongest and can be run in oil.

Hello all,
I also use a RGM belt drive for over the last ten years.
I run mine un-vented without any problems but plan to use a vented cover on a project I am building.
I use the aluminium pressure plate which gives a very light action which comes in 'Handy' after suffering a severe break & dislocation on that wrist.
Also Lucky from Denmark the RGM belts are 32mm wide AT10 syncroflex grey/green colour available in 890mm & 920mm length.
They also sell a special kit for MK3's.
Regards Hursty.

Yeeahh Lucky, :lol: I was maybe lucky that no further damage was done to the bike.
Talked to Tony Hayward an hour ago, the belt he uses is the red GenIII syncroflex which can withstand temps up to 100°C the other type goes up to 80°C, the belt he uses is 30mm wide, a standard is 32mm so I ordered one from him.
The red belt can be run in oil, life expectance about 5 year or dry lifeexpectance 11 year.
Venting should not be nessesary, but now I have a nice hole in mineI might go for it :lol:

Belt Drive Upgrade


on my RGM belt reads the following:- 091-synchroflex AT 10/890.

It's a sort of light beige colour.

Hope this helps :)
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