Belt tension: Am I pushing my luck?

[JonS2R]

My bike is nearing 20k miles. The prior owner had the valves checked and belts changed just shy of 14k. I've maybe put 1k on the bike since buying it so I knew it would be coming due for the valves/belts. I was hoping I could get through summer and do the job once it starts getting colder out. However, I recently changed the spark plugs and pulled the belt covers off just to take a look at things and check the tension and belt condition.

I've done plenty of reading on setting the belt tension and also picked up the Desmo Times manual. Harmonic frequency method aside, it seems the original consensus was to set horizontal tension with a 5mm allen key and vertical with a 6mm allen key. Then Ducai revised the frequency recommendations lower. Thus, the Desmo Times manual suggests setting tension with a 1mm feeler gauge for the horizontal and a 4mm allen key for the vertical (if I remember correctly...I don't have the manual in front of me).

The condition of my belts looks pretty good. There's no obvious cracks in the ribs or wear along the edges. However, they seem to be quite slack.

For the horizontal, I could fit a 6mm allen key between the belt and roller. The fit was somewhat snug. I could squeeze a 7mm key in by rolling it under the roller which was a pretty tight fit. The same goes for the vertical cylinder with 7 and 8mm allen keys. I ran the engine with the covers off and the belts didn't look to be so slack that they were flopping around or anything.

I'm just wondering if they're within an acceptable range to continue riding for another month or so or if they're so slack that they need to be changed immediately.

[Buhgaboo]

My bad...s2r...I was referring to 821...I know the methods don't correlate between years

[chipripper]

It's really easy to use the frequency method, using a guitar tuner app on a smart phone. If the belts look good, I would adjust the belt tension and keep riding till the valve interval. 

[Buhgaboo]

Fwiw mine hum at around 2k rpm if too tight...loose is relative...as long as it can't skip a tooth and the cams still index together in relation to tdc your within tollerance

[Howie]

How many months on the belts>

[JonS2R]

How many months on the belts>

They were changed February 2016

[greenmonster]

"Thus, the Desmo Times manual suggests setting tension with a 1mm feeler gauge for the horizontal and a 4mm allen key for the vertical (if I remember correctly...I don't have the manual)"

My MTS1100 had those clearances when l bought it.
Hz made whining sound, esp when fully warmed up.
Belt showed sign of wear.
Bad recommendation, does LT really say so?!?

Set both to 5mm Allen and ride rest of season.

[koko64]

Just my humble opinion, but the locations of the belt rollers  on each cylinder are not symmetrical. The belt rollers on the H cylinder appear to have similar belt deflection in relation to the pulleys, but on the V cylinder the "idler" roller doesnt deflect the belt very much with nearly all the deflection done by the adjustable tensioner roller. It explains the different gap needed for the manual tension method. In light of advice and discussion with members here, I have settled on 4-5mm on the V and 3-4mm on the H. Note that this is measuring the gap on the idler roller, not the adjuster roller. I then run the bike until hot and check for bearing squeal, belt whine, etc and check tightness. The figures are a little imprecise because it depends on your hand strength with the Allen Keys! The thermal expansion of the cylinders is more than you expect, so the loose settings make sense. You should hear the belts and rollers complain with oem settings during a hot Aussie summer's day! I once tried the 1mm on the H but IMO it was too tight when hot.
Bottom line is, (to quote an older bloke here  ),
"Tight enough not to skip a tooth and loose enough not to strain the bearings and belts."

Belts are replaced every 2 years or 20,000kms/12000 miles.

I trialed and adjusted my practice due to the advice and experiences of others here.  It has been good to compare notes (often via pm). Thanks to you blokes.

[JonS2R]

Bad recommendation, does LT really say so?!?

I'll double-check the manual when I can but yes assuming I'm remembering correctly. However, that only applies to the 1000DS.

[DuciD03]

"Thus, the Desmo Times manual suggests setting tension with a 1mm feeler gauge for the horizontal and a 4mm allen key for the vertical (if I remember correctly...I don't have the manual)"


Set both to 5mm Allen and ride rest of season.

1mm? Really? That's new to me!

"Tight enough not to skip a tooth and loose enough not to strain the bearings and belts."

Belts are replaced every 2 years or 20,000kms/12000 miles.

- my 2 cents -

Ive used the 5 mm on 800 & 1K s2rs for 10 years without a problem; it there too tight (or loose) then you'll do damage, (guess this goes without saying ...); agree with the dudes above quoted.

[koko64]

To be clear I was referring to the 1100 models which have caused me the most concern. I use the 5mm Allen wrench method on both belts for 750's and 900's.

[koko64]

Out of interest I set the H cylinder belt on an MTS1100 on the loose side (4-5mm) within timing specs and ran it for 5-10 minutes on our winter day here (50F) . The dash only showed 52C and the belt was already tight to the tune of a 1mm feeler gauge just fitting between belt and roller when deflecting the belt with thumb pressure. Interesting. I also like to see what the hot setting is. I thought that you wouldn't want it tighter than that on a summers day in city traffic or on a summer ride through the canyons. Glad the belts are stronger nowadays.

[MonsterHPD]

Out of interest I set the H cylinder belt on an MTS1100 on the loose side (4-5mm) within timing specs and ran it for 5-10 minutes on our winter day here (50C) . The dash only showed 52C and the belt was already tight to the tune of a 1mm feeler gauge just fitting between belt and roller when deflecting the belt with thumb pressure. Interesting. I also like to see what the hot setting is. I thought that you wouldn't want it tighter than that on a summers day in city traffic or on a summer ride through the canyons. Glad the belts are stronger nowadays.

Interesting. I have not done any systemtic tests like yours, but I have noted that different methods give rather different results. Some say 6 mm allen key, some say 4 mm allen key, some say differnt keys in H and V.
A friend of mine has a frequence meter witch he uses on his HYM1100 motor. If you use that to the recommended frequencies, the resulting tension is much higher than what I have got when using any of the allen key methods; in fact I doubt that the "allen key" tension would result in any frequency at all since they are pretty loose.  Has anyone tested tested frequency vs "allen key" tension?

There is also a marked difference in tension when newly adjusted, and after some considerable running time. It would seem to me, it is not an exact science ....       

[koko64]

I think its come up in another thread.

[chipripper]

I just finished my belts and haven't ridden yet. New belts at 100hz yield 3mm on the vertical and 2mm on the horizontal. I think I'll run it for a few minutes and see how much they break in, and how they measure hot. It will be a couple weeks since I need to finish my harness cleanup before I can fire it up. It makes sense to me that the Allen key method would be better, since it yields loose, but not too loose. It doesn't make sense why it's different between the two cylinders.