M900 belt tension newbie questions

spuggy · 11-07-2022, 04:20 PM

So, at the risk of boring the cr@p out of everyone, I need some advice with my first belt tension on a M900 (sitting for 2+ years due to lockdown). The Ducati Suite link in the FAQ no worky for me, so I watched the Brad (the Bike Boy) and ExactFit/CA Cycleworks videos a few times instead.

Belts were not new when left, they'd last been done by the PO's shop. This being the guy who was riding the bike with wrong length chain fitted, and 100+mm of slack in it...

When I removed the belt covers, I was surprised/concerned how slack they were. Not to mention ticked at how tight the tensioner bolts were.

Old belts were ExactFit; they looked pristine. But I had a new set, so off they came regardless. Tensioner bearings all rotated smoothly and seem fine with no play, so the new "just in case" set can sit and wait until they're needed.

My question relates to the belt tension...

I can readily squeeze the tensioner with one hand, nip the slider allen up with the other - and get belt tension high enough that the 5mm allen is a good sliding "feeler gauge" fit on the idler bearing at TDC.

However, despite trying multiple times, I just can't seem to get it tight enough that the 6mm is a no-go. It's tighter/takes more effort, but will still go through.

Yeh, belts are very much tighter than they were before. Much happier with that. Inclined to call it good in fact.

Enter the nagging doubts stage right...

The ExactFit packaging says "90 - 110 Hz" for the 2V belts - the Gates phone app seems to show 70Hz at TDC when the driven section by the crank pulley is plucked. And Brad (who says he never uses the Hertz method for 2V belts) gets 135-140Hz when he double-checks the 5/6mm method with the phone.

It's entirely possible I don't have enough grip strength to squeeze the tensioner tight enough. On the vertical cylinder, I can use a wrench as a lever between the tensioner and the belt cover casting for more tension. On the horizontal cylinder, looks like I'd have to lever against a cooling fin. Which is pretty obviously leads to "duh, no, don't do that".

Am I over-thinking this/second guessing myself? I'm kind of leaning towards "good stiff sliding fit on the 5mm - button it up". Especially as they are obviously a lot tighter than they were before - and they never jumped a tooth...

11-07-2022, 04:20 PM	#1
spuggy Registered User Join Date: Apr 2016 Location: Farnborough Bike: M900sie Posts: 171	M900 belt tension newbie questions So, at the risk of boring the cr@p out of everyone, I need some advice with my first belt tension on a M900 (sitting for 2+ years due to lockdown). The Ducati Suite link in the FAQ no worky for me, so I watched the Brad (the Bike Boy) and ExactFit/CA Cycleworks videos a few times instead. Belts were not new when left, they'd last been done by the PO's shop. This being the guy who was riding the bike with wrong length chain fitted, and 100+mm of slack in it... When I removed the belt covers, I was surprised/concerned how slack they were. Not to mention ticked at how tight the tensioner bolts were. Old belts were ExactFit; they looked pristine. But I had a new set, so off they came regardless. Tensioner bearings all rotated smoothly and seem fine with no play, so the new "just in case" set can sit and wait until they're needed. My question relates to the belt tension... I can readily squeeze the tensioner with one hand, nip the slider allen up with the other - and get belt tension high enough that the 5mm allen is a good sliding "feeler gauge" fit on the idler bearing at TDC. However, despite trying multiple times, I just can't seem to get it tight enough that the 6mm is a no-go. It's tighter/takes more effort, but will still go through. Yeh, belts are very much tighter than they were before. Much happier with that. Inclined to call it good in fact. Enter the nagging doubts stage right... The ExactFit packaging says "90 - 110 Hz" for the 2V belts - the Gates phone app seems to show 70Hz at TDC when the driven section by the crank pulley is plucked. And Brad (who says he never uses the Hertz method for 2V belts) gets 135-140Hz when he double-checks the 5/6mm method with the phone. It's entirely possible I don't have enough grip strength to squeeze the tensioner tight enough. On the vertical cylinder, I can use a wrench as a lever between the tensioner and the belt cover casting for more tension. On the horizontal cylinder, looks like I'd have to lever against a cooling fin. Which is pretty obviously leads to "duh, no, don't do that". Am I over-thinking this/second guessing myself? I'm kind of leaning towards "good stiff sliding fit on the 5mm - button it up". Especially as they are obviously a lot tighter than they were before - and they never jumped a tooth...