Desmoquattro belt tension question

[carlosbarrios]

So, I just finished the valve adjustment on my 04 S4R (996 desmoquattro).  I know that the belts should be tightened to vibrate at 110 Hz between the crank pulley and the tensioner pulley, when the cylinder is at TDC.  I'm assuming that this is with the engine cold (duh).  I went for a ride, and when I came back in, I noticed that with the engine warm, the belts were MUCH tighter (measured at 145Hz).  When it cooled back down, the tension went back to 110Hz.  Is this normal?

I changed the belts 7500 miles ago, and they are still in good shape, so I'm reusing the old belts.  I'm also assuming that the 110Hz tension is the same for new and used belts, right?

The torque setting for the nut holding the eccentric tensioner pulley is supposed to be 25 NM, with some lithium grease.  This seems a bit low, and I'm skeptical about using grease and not red locktite.  What torque do you guys use, and do you use grease or threadlocker?

[mdriver]

So... Are you actually saying that you have a meeter for reading belt frequency. May I ask why?

I can't actually say if 145hz normal. But It would make sense that the belt would be tighter when the engine is hot. Therefore vibrating at a higher frequency.

[clubhousemotorsports]

Your findings are right on the money and that is a good example of why you do not want to over-tension the belts. with the dual spark motors Ducati was spec-ing 140Hz and when hot the tension would be over 200Hz, Geee why are all these tensioners failing?

lower starting tensions are safer for many reasons as long as they are not so loose that you could jump timing. Also as you noted a new belt will loosen just as a chain would take an inital stretch. If you factor this in you are fine but if you are capable of checking your own , why not do so after 1000 miles on new belts.

Just curious what are you using to check your belts?

[johnster]

I know that the belts should be tightened to vibrate at 110 Hz between the crank pulley and the tensioner pulley, when the cylinder is at TDC. 

Hey, that's a second-octave A !!!! 

make sure it's not sharp or flat, or the belts will be out of tune!!!   

-In all seriousness I never realized that cam belts were tensioned this way....That's why I love it here, I learn something new every day!!!!   

[carlosbarrios]

Your findings are right on the money and that is a good example of why you do not want to over-tension the belts. with the dual spark motors Ducati was spec-ing 140Hz and when hot the tension would be over 200Hz, Geee why are all these tensioners failing?

lower starting tensions are safer for many reasons as long as they are not so loose that you could jump timing. Also as you noted a new belt will loosen just as a chain would take an inital stretch. If you factor this in you are fine but if you are capable of checking your own , why not do so after 1000 miles on new belts.

Just curious what are you using to check your belts?

That's what I figured, I just wanted to double check it was normal.  I'm using a computer software with a microphone.  The software is free: Musical Tuner v1.2 by W.A.Steer. http://www.techmind.org/audio/index.html  It displays the frequency, and tells you when it's stable, and also shows the waveform, which is very nice because when you pluck the belt, you'll know when the reading is correct.  I've gotten VERY consistent results with this software and a Labtec computer microphone positioned right below the belt.

What torque do you guys use for the tensioner nuts? 25NM? Do you use locktite? Do you re-use the old flange nuts or replace them?

[Speeddog]

The belts are tighter when the engine is hot due to the expansion of the crankcase, cylinder and head.
The center to center distance of the pulleys is a tiny bit longer, about .015" or so.

My S4 service manual specs 26 Nm and Lock 1, a low-strength threadlocker.
That torque spec is pretty typical for M8 fasteners.
You can use some blue loctite.

I've run with 10mm freeplay (5mm 'up', 5mm 'down') on the belt, between the cam pulleys.
Over 30k miles on my S4 with zero belt issues.

[DrDesmo]

What did you require for tools and such? I have gotten SO many conflicting info about this process ... Ranging from "it takes 20 minutes" to "it's the end of the world, practically the next thing to launching the space shuttle" with all sorts of cam wheel holding tools, castle nut tools, 20 x 22 mm offset box wrenches, etc ... OY VEY 

Where'd you get your instructions too?  DucatiTech / LT Snyder / ?

Thanks!  [moto]  I'm tackling this myself once my belts and etc. come in from Chris.

-Adam

[jerryz]

I concur with speeddog on this but I gine the vertical cylinder 6mm play on the belt as it runs hotter. I reuse my belt locknuts with loctite a few times burt also keep spares .

[Speeddog]

What did you require for tools and such? I have gotten SO many conflicting info about this process ... Ranging from "it takes 20 minutes" to "it's the end of the world, practically the next thing to launching the space shuttle" with all sorts of cam wheel holding tools, castle nut tools, 20 x 22 mm offset box wrenches, etc ... OY VEY 

Where'd you get your instructions too?  DucatiTech / LT Snyder / ?

Thanks!  [moto]  I'm tackling this myself once my belts and etc. come in from Chris.

-Adam

Tools required aren't anything out of the ordinary.
5mm allen wrench to get the covers off.
Getting the middle cover off is a fiddly Zen thing, don't force it.
Rotate the engine till the cam drive pulley dot lines up with the hashmark on the cases.
Note where the cam pulley dots are, taking pictures is good.
13mm(?) box wrench to loosen the eccentric locknuts.
Remove the old belts, and install the new ones.
Make sure the pulleys are lined up, the vertical intake will fight back because of the closer springs.
Orient the eccentrics so they're 'towards' the heads, that way belt tension tries to rotate them in the direction that *tightens* the locknut.
Set the belt tension, this is a bit of a PITA as the hex is big, but access is poor.
Tighten the locknuts.
Check your work.
Reinstall the covers.

I think that's it...

[carlosbarrios]

What did you require for tools and such? I have gotten SO many conflicting info about this process ... Ranging from "it takes 20 minutes" to "it's the end of the world, practically the next thing to launching the space shuttle" with all sorts of cam wheel holding tools, castle nut tools, 20 x 22 mm offset box wrenches, etc ... OY VEY 

Where'd you get your instructions too?  DucatiTech / LT Snyder / ?

Thanks!  [moto]  I'm tackling this myself once my belts and etc. come in from Chris.

-Adam

For the valve adjustment I used a guide from a post in this site:  http://ducatimonsterworldwide.org/index.php?topic=1312.0
I have a document of this post with very good pictures, let me know if you need it, I'll email it to you.

For the belts, they are pretty easy, basically what Speeddog said.  You need a 5mm allen for the covers, a 12mm wrench for the pulley locknuts and a 24mm wrench to turn the pulley to set the tension.  Setting the tension can be done with the 5mm of play between the cam pulleys, or use the software I posted above with a computer microphone.  Obviously make sure the engine is COLD!  Before you start, you might need to take the tank off. I did.

Tools required aren't anything out of the ordinary.
5mm allen wrench to get the covers off.
Getting the middle cover off is a fiddly Zen thing, don't force it.
Rotate the engine till the cam drive pulley dot lines up with the hashmark on the cases.
Note where the cam pulley dots are, taking pictures is good.
13mm(?) box wrench to loosen the eccentric locknuts.
Remove the old belts, and install the new ones.
Make sure the pulleys are lined up, the vertical intake will fight back because of the closer springs.
Orient the eccentrics so they're 'towards' the heads, that way belt tension tries to rotate them in the direction that *tightens* the locknut.
Set the belt tension, this is a bit of a PITA as the hex is big, but access is poor.
Tighten the locknuts.
Check your work.
Reinstall the covers.

I think that's it...

I'm pretty sure you need a 12mm.