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'12 848evo, '13 Hypermotard SP, '94 CBR600f2 track bike, '06 CBR600rr track bike
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Discussion Starter · #1 ·
Hello, I changed my cam belts tonight (848 EVO) used frequency meter pro to read Hz. Everything went ok. My question for the experienced belt changers is, my belts set to 107.6Hz if I back off a little they would go to 80 something Hz, tighten a little from 107.6 no change. tighten a little more 129Hz, so back off and I get 107.6Hz. It seems as there is a small window in the tighten range of adjustment. And backing off drops it to the 80's, tightening goes to 129. Does this sound right? their set at 107.6Hz, I couldn't get them to set at 110Hz or a little more or less. thanks
 

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If they're new 107 is perfect, don't over think the tension. Better to focus if follower eccentric is rotated correctly and crank is in the right position for tensioning.
 

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Discussion Starter · #3 ·
If they're new 107 is perfect, don't over think the tension. Better to focus if follower eccentric is rotated correctly and crank is in the right position for tensioning.
yes that stuff is correct. And I know that 107 is good, just wondering if what I said is happening is normal ?
 

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You need to check the tension with each cylinder at TDC. The cam's are loose at that point, not pushing down on a valve. I have a feeling the gauge you use, is maybe to blame. When I've had problems using a mic, it's because there is ambient noise which interferes. I always have to close the garage door and sometimes I've had to cover myself and the bike with a blanket because we have so much low-frequencey noise here. The shops use lasers, so they don't care what kind of audio is around.

Another thing to remember; the mobile roller eccentric is turned upwards, or towards the cam's, for tightening. If they're not tightened in that way, the belt could touch and give you erroneous numbers as well, but nothing like your experiencing.
 

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Discussion Starter · #5 ·
You need to check the tension with each cylinder at TDC. The cam's are loose at that point, not pushing down on a valve. I have a feeling the gauge you use, is maybe to blame. When I've had problems using a mic, it's because there is ambient noise which interferes. I always have to close the garage door and sometimes I've had to cover myself and the bike with a blanket because we have so much low-frequencey noise here. The shops use lasers, so they don't care what kind of audio is around.

Another thing to remember; the mobile roller eccentric is turned upwards, or towards the cam's, for tightening. If they're not tightened in that way, the belt could touch and give you erroneous numbers as well, but nothing like your experiencing.
Lights turned off in my shop, and no ambient noise. I am not have trouble setting the tension, at least I don't think I am. Maybe I didn't explain the question well, I'll try again. When I tension the belt at 107.6 if I decrease or increase tension a slight amount no more then 1* of rotation the Hz reading doesn't change. Increasing tension a little at a time it would be like this, 107,107,107,129. It seems like 107.6 is where they want to be, if I try for more or less Hz it will be out of range. I know 107.6Hz if a good setting, it with in spec. Just wondering if this is how the belts usually act? thank you very much for the advice.
 

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Nope, it's absolutely not how belts act. It should be like tuning a single string guitar. If you keep plucking, it will keep slowly increasing in frequency. You should be able to hear that "spike" in frequency by ear if you listen carefully. Since you always get the same numbers, I'm a bit suspicions of your gauge.

Maybe the device your using has some memory function and it's storing/cashing results because it's not loud enough to alter it. It could also be the mobile roller getting stuck and it happens to be at those two frequencies.

Also follow my TDC tip above… that will rule out any issue with the tensioning. Remember when the idler pulley dot/line align, that's horizontal TDC, so you've gotta rotate the ending 90 degree's to get vertical TDC for the other cylinder. I also exercise the pulley a lot to make sure there isn't any friction/binding on the assembly which causes it not to be smooth.
 

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There is one thing that I can see that would create the situation you are encountering... I assume you are checking the belt frequency in the correct location, i.e. between the layshaft and tensioning idler. Are you turning the crank in the right direction? You are checking the slackest portion of the belt when doing it right. If you turn the crank the other way, you are checking the 'tight' side which may explain why more tension will simply equalize the readings until you go 'too far'.
 

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I have a piece of software that shows a spectrum instead of a number. It was created in MATLAB and the compiler I have is 32bit. If you have a 32bit pc send me a pm and I will send it to you. It will require an external mic. I am weary of any app that will output a frequency with a 1/10th accuracy. One thing on a pc is you typically get a 60,120hz sine wave so you will have a peak at that point.
 

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To specifically answer your question cbr6. It can be tricky trying to get the tension exact. The condition you report is called slip-stick, i.e. the torque needed to start rotation on the tension tool is greater than the torque to continue rotating it. This leads to overshooting the desired tension in either direction. This can minimized by lubricating the faces on the eccentric shoulders and/or backing off nut pretension.
 

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Tye isn't going to like this but after losing a belt with the above method I will never do it again.
Yea, I've used the 10mm wrench method a few times. In fact, I made a video of it that was circulating for years.

The old spec for Desmoquattro's was 85hz, so I made a video about that and the tool-less adjusting methods.

http://madducracing.com/ducatiservice/Belt tensioning/Belt Tension Service.wmv

Edit: Yes, I'm aware it says 75hz on the vertical… that was the REALLY old spec…

 

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Geez you people are stress-out merchants.
Look, it's really quite simple. Just tighten the belts just enough so that the tension is perfect.
Not too loose, not too tight.
Juuuuuuuust right ;)
 
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