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Author Topic: 2V belt tension question (!!)  (Read 25043 times)
BK_856er
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« on: September 15, 2008, 08:05:51 PM »

My M695 is still under warranty, so I'm trying hard to leave the scheduled maintenance to the dealer, in addition to the OCD attention it gets from me.

Recently I had the 7.5k mile service done, and I had my dealer install new belts since the 2yr mark was coming up anyway.

Today I removed the belt covers to rule out some possible sources of a minor oil leak, and gosh those belts felt loose.  Belts are obviously new and the adjuster bolts are tight.  I looked over LTs manual and then watched the Chris K. video.  So a 5mm allen key should get you pretty close to whatever method the dealer would have used, right?  I rotated the motor to align the marks and I can easily fit a 10mm allen between the belt and the (smaller) idler pulley.  Floppy loose all over.

This is WAAAAY too loose, correct?

Seems to run fine.  Bit of a flat spot around 6k since I got it back, but otherwise no running issues.

Comments from the experts??

BK


« Last Edit: September 15, 2008, 08:07:33 PM by BK_856er » Logged
brad black
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« Reply #1 on: September 16, 2008, 02:45:40 AM »

i always retension new belts on my bikes after 1,000km or so.  they go loose, so you retension them.  usually they're fine after being done once.
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« Reply #2 on: September 16, 2008, 08:10:16 AM »

that sounds pretty loose, though im not sure if ducati still goes by the same tension they did many years ago. Go back to your dealer and tell them you were inspectng your belts and ask them to recheck them. They use a audio device to record the frequency of the belt when plucked. it could be a bogus belt, or maybe the new specs are just like that. I have a 06 DS1000 and a 5mm is pretty make the beast with two backsing impossible to get through.
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« Reply #3 on: September 16, 2008, 09:15:34 AM »

That's way too loose.
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BK_856er
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« Reply #4 on: September 16, 2008, 09:50:09 AM »

Thanks for the input!  waytogo

I could bring it back in, but it's a bit of a hassle.  I think I will take it on myself.

My '07 M695 workshop manual specifies 145Hz (H) and 160Hz (V) using the optical DDS tool, with each respective cylinder at TDC compression.  Each belt has a specific location for the optical measurement.  The manual also indicates to adjust tension when the value falls below 70Hz due to normal wear.

Does anyone know if those frequencies have been updated?  I came across much lower numbers scanning some posts, but I'm not sure if they would apply to my M695.  I'm assuming that the optical (DDS) and audio (microphone) will give an equivalent result.

I think I have everything that I need to measure the frequency with the microphone method.  In their present state, there is insufficient belt tension to hear ANY frequency when plucking the belt.  They just flop.  I also read about a "45 degree twist" test and tried that....I can rotate past 90 degrees!

BK
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« Reply #5 on: September 16, 2008, 10:06:38 AM »

IMO, go for the '5mm allen key tension' and call it good.
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« Reply #6 on: September 16, 2008, 10:39:25 AM »

Are they both loose or just one?  I ask because you can use the other one as a gauge.  I think the shop set it loose and then it expanded from use which combined to make it really loose.  Remember the key with belt tensioning is to be in the ball park.  It doesn't have to be very accurate like valve clearance and a lot of other measurements.  Just do your best to get it to the correct tension, retention after 1K miles,  and it'll be fine. 
« Last Edit: September 16, 2008, 10:46:56 AM by uclabiker06 » Logged

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BK_856er
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« Reply #7 on: September 16, 2008, 10:55:13 AM »

Are they both loose or just one?  I ask because you can use the other one as a gauge.  I think the shop set it loose and then it expanded from use which combined to make it really loose.  Remember the key with belt tensioning is to be in the ball park.  It doesn't have to be very accurate like valve clearance and a lot of other measurements.  Just do your best to get it to the correct tension, retention after 1K miles,  and it'll be fine. 

Both belts were similarly loose, but the vertical belt was a tiny bit tighter.  For the quick check I didn't confirm which cylinder was at TDC compression, I just rotated the crank until the marks lined up.

I probably have about 500-600 miles on the bike since the new belts were installed by the dealer at the 7.5k service.

I will definitely do the 5mm allen key thing first, and then see what kind of frequency it gives me.

BK
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« Reply #8 on: September 16, 2008, 06:58:39 PM »

They should both be fairly tight. The 5mm allen wrench trick works really well. They will definitely loosen up when you install a new set. The fact that you may not have been at TDC doesn't matter too much, the tension should be pretty similar the whole way round.
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BK_856er
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« Reply #9 on: September 17, 2008, 12:09:36 AM »

I set the horizontal tension with a shortish 5mm allen key.  Not quite sure how tough it should be be slide through.  I did "reasonable force with just one hand and little wiggling".

Then I setup the microphone and the free Audacity audio analysis program.  I plucked the belt and recorded the signal at the location specified in the workshop manual (between the crank gear and the MOBILE roller on the lower side).  The spectrum analysis in log scale allowed me to quickly get the primary frequency, which in this case was 117Hz.  I tightened the belt a tad more and got 128-130Hz.  The Ducati spec for my motor is 145Hz on the horizontal belt, but I understand that it would be wise to use less than that.

Changing the measuring location for the horizontal cylinder to the section between the mobile roller and the cam gear gave a value of 103Hz, presumably due to the longer length of belt.

I rotated the crank exactly one revolution and set the vertical belt tension with the 5mm allen key, although this time the allen required just a bit less force to get past the idler.  Per the manual, I recorded the frequency at the length of belt (between the crank gear and the FIXED roller) to give a reading of 125Hz.  The Ducati spec is 165Hz for the vertical belt.  Presumably the higher number is because this length of belt is longer by about 10mm compared to the region measured on the horizontal belt.  For kicks I rotated the crank exactly one more revolution and measured 131Hz.

I'm going to play with things a bit more because I'm still not sure that I have the allen key force down just right.

So far the audio method is uber cool if you're looking for a geeky science experiment, and it's comforting to have a backup technique on hand to quantify things.  It really is easy to collect the audio data and work it up.  Just make sure that you are plucking/recording in the right spot.  More later...

BK
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« Reply #10 on: September 17, 2008, 04:01:00 AM »

the horiztonal is always tighter than the vertical.  the 1000 had the same spec for both - 145 from memory.  1000 belts won't let you get anything thru at that tension.  the older 620/750/800 belts were 112/124 from memory.  it often does vary every time you turn it over too.
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« Reply #11 on: September 17, 2008, 09:06:18 AM »

Thanks, Brad.

Below is a screenshot of the audio program to give a feel for the data.  The top three traces are individual "plucks" of the belt at three different tensions with the same basic 5mm allen key method, giving roughly 117, 145 and 130Hz from top to bottom.  Generally I would pluck the belt 5-6 times for a given setting with about two seconds between plucks.  The fourth trace is a 130Hz test tone for comparison.  The window in the lower right is a spectrum analysis identifying the peak (frequency) for the 145Hz tension.  The peak frequency from the spectrum analysis was always essentially the same for all the individual plucks.

BK

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« Reply #12 on: September 18, 2008, 06:21:44 AM »

Thanks, Brad.

Below is a screenshot of the audio program to give a feel for the data.  The top three traces are individual "plucks" of the belt at three different tensions with the same basic 5mm allen key method, giving roughly 117, 145 and 130Hz from top to bottom.  Generally I would pluck the belt 5-6 times for a given setting with about two seconds between plucks.  The fourth trace is a 130Hz test tone for comparison.  The window in the lower right is a spectrum analysis identifying the peak (frequency) for the 145Hz tension.  The peak frequency from the spectrum analysis was always essentially the same for all the individual plucks.

BK


I use audacity for "other things"  Wink  I was wondering if it could do freq analysis, or did you use a different program for that?

I have 'helped' my dealer adjust my belts, and the frequency method is variable at best.  Like you said, 1 pluck, 110Hz, the next one 130Hz, etc.  He sort of takes an average of several plucks and calls it good.

But yes, on a 1000DS when adjusted to the 130Hz range, there is no way a 5mm allen is going through.  Maybe a 2mm.

mitt
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BK_856er
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« Reply #13 on: September 18, 2008, 08:03:45 AM »

I use audacity for "other things"  Wink  I was wondering if it could do freq analysis, or did you use a different program for that?

I have 'helped' my dealer adjust my belts, and the frequency method is variable at best.  Like you said, 1 pluck, 110Hz, the next one 130Hz, etc.  He sort of takes an average of several plucks and calls it good.

But yes, on a 1000DS when adjusted to the 130Hz range, there is no way a 5mm allen is going through.  Maybe a 2mm.

mitt

Yes, you can get Audacity to do frequency analysis.  I'm no expert (downloaded it just for the belts) but after playing around for a few minutes I found some good tricks.  Just select a waveform after zooming in and do a spectrum analysis from the pull down menu.  Adjust the parameters to log scale and one of the other boxes to 4,000 or something like that.  Move the cursor over the peak and it will snap to the maximum and display the frequency.  This method was very repeatable, even if the waveform looked kinda junky.  The beauty of the recording function is that you can pluck away and see the waveforms in real-time, adjusting your technique as you go, then go back and quickly analyze the best looking ones of the bunch.  I tried the other little non-recording program, and it agreed with my method, but it was very difficult to get a good lock on the signal and I wore out my finger from plucking the belt.

I used the audio method as more of a reality check to make sure that my "5mm allen" setting was in the ballpark.  In the end I used 5mm at the idlers and about 125-130Hz (compression TDC) after rotating a few times.  I can send you some belt waveforms if you want to play around them.

BK
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« Reply #14 on: September 18, 2008, 07:34:04 PM »

We need a current Duc dealer tech to chime in.  Ducati has been gradually reducing the frequency spec on the belts, particularly the 2V 1000.  I'm not sure what the present spec is.
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