M900 belt tension newbie questions

[Mr Gazza]

Well you've already done the most important things, which is fit the new belts and check all the bearings. Next is to use the correct torque on the tensioner quadrant bolts. I know the torque in my head but I won't put anything in print without checking the book. I personally never use thread lock on those and I'm not alone.

The belt tension is over thought all to often by many I think and the frequency method is often revealed to be confusing, I've never bothered with it.. It's for musical instruments not motorbikes!!
Sounds like you've got the horizontal tension cock on to me. Even when it's right with a 5mm Allen key you can still get a 6mm through with enough will, so I would be happy with that. Over tight is a bad thing, slightly slack won't do any harm. As you say it won't slip.
Remember to use a 6mm key on the vertical belt with a 7mm being very hard to pass.

It's not a bad idea to just run it up with covers off first time and keep an eye on the tracking of the belts over the pullies.. It's fun watching the white patches of paint shooting round anyway..

[Nickj]

Sounds about right to me Spuggy.
A tight fit for a 5 and a bloody hard shove to get a 6 through has worked out fine for me on a few 750 motors and my S2R, probably totalled over 100K on them with this method of tensioning.
I'd be pickier and more precise on the quatro motors, my 748R was done with a tuning method but that was a totally different beast.

[spuggy]

Originally Posted by Mr Gazza

Next is to use the correct torque on the tensioner quadrant bolts. I know the torque in my head but I won't put anything in print without checking the book. I personally never use thread lock on those and I'm not alone.

Job done and buttoned up, ready to tip in some fresh fuel as soon as I can make it into the garage and wheel it out without expiring from heat exhaustion in a puddle... I refused the temptation to fire it up until I confirmed the torque number I used on the tensioner bolts.

Just could not see it for looking in the PDF, but the dead-tree 1999 M900 workshop manual (anyone ever seen a 2000-2001 dead tree version? Been keeping an eye open for years and never seen one in English...) gives 26nm, or a smidge over 20 ft/lbs for the M8x1.25 tensioner bolts. Which was, after rejecting obviously stoopid outliers, what the internet had said. And what I used.

I do note the manual gives exactly the same figure for the M8x1.0 fixed tensioner stud, which later models seem to have revised downwards somewhat,... And also says I can't do the job without the Ducati tension gauge and the special tool to move the idler, LOL...

The fixed stud is spec'd for thread lock in later manuals, apparently. Probably because of the lower torque spec and the coarse thread.

[Brian.]

Originally Posted by Mr Gazza

Sounds like you've got the horizontal tension cock on to me. Even when it's right with a 5mm Allen key you can still get a 6mm through with enough will, so I would be happy with that. Over tight is a bad thing, slightly slack won't do any harm. As you say it won't slip.
Remember to use a 6mm key on the vertical belt with a 7mm being very hard to pass.

Good evening Mr Gazza,

I'm in the process of doing my M750 belts & tensioner bearings (that bit was fun ) and I'd like you to know why you recommend a slightly slacker tension on the vertical belt please?

Thank you!

[Mr Gazza]

It's generally accepted that the vertical cylinder runs a bit hotter than the horizontal as it doesn't benefit from quite so much cooling air.
So the clearance is a bit more to allow for a bit more expansion.

[Brian.]

Thank you very much, I understand now

Brian.