Cush drive question.

discussions specific to the 906 Paso
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FasYankee
Posts: 28
Joined: Fri Jun 12, 2015 8:21 pm
model: 906 Paso
year: 1990
Location: USA

Cush drive question.

Post by FasYankee »

I searched "Cush drive" and only 2 posts came up, neither appears to touch on my query.

While I was looking over my recent 906 acquisition, I was checking to see if the engine would turn over, fearing stuck valves, seized rings, etc. as a result of its extended hibernation.

I had the bike on the center stand , notched the tranny into 6th gear and turned the wheel by hand in an attempt to turn the motor over a few revolutions. In that regard everything went fine, nothing was seized or seemed to have sticky spots. :thumbup:

One thing I did notice though was the Allen head cap screws that are in the sprocket appear to be loose? They're not loose in respect to being torqued down, they just jiggle, in unison as I attempt to move the back wheel back and forth (rotate). Any opinions on this? Is that how it's supposed to operate?
jfiore
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Re: Cush drive question.

Post by jfiore »

Try searching for "loose sprocket bolts", there is at least one thread about the issue.

Bottom line - replace them all, use shoulder bolts/screws (preferrably high-tensile steel) with a shoulder that extends into the sprocket carrier, use locking nuts, and Loctite them.

They're loosening because either the bolts have stretched, or the bolts and nuts were re-used and have vibrated loose. Even if you tighten them, they will loosen again (rather quickly, too) and if they back out far enough they will damage the swing-arm.
Mc tool
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Re: Cush drive question.

Post by Mc tool »

There have been a few instances of the sprocket bolts coming loose , and a few theories on how to stop it . This is not peculiar to Paso's .... lots of bikes have rear sprockets. I have never had my sprocket bolts come loose , and I cannot understand how anyone could operate a bike with the rear sprocket bolts chewing into the swingarm AND NOT KNOW :banghead: . I think its a maintenance thing , I spose one could argue that the power pulses of a V twin MAY cause a shock loading that could loosen the bolts but , like I said , it aint peculiar to Paso's , and singles would have to be worse. My sprocket is held on with cap screws ( hi Tensile ) and nuts ( not lock nuts ) and Loctite . The whole idea is that the sprocket is clamped to the carrier by the mounting bolts , and as such shouldered bolts would only be of benefit once the sprocket has come loose and the bolts are in shear, having said that , I do agree with jfiore that shouldered bolts should be used. When mounting sprocket make sure the mating surfaces of both the sprocket and the carrier are clean and smooth, these are the surfaces that clamp together and it stands to reason that if they are not smooth and clean ( like a layer of chain lube and grit ) then they are hardly likely to clamp solidly , bit like putting crap on your brake discs and then expecting a steely grip........ aint gunna happen. It all comes down to basic maintenance/ cleaning. When you clean a bike you ( eventually, for some )get to know the bike and anything out of the ordinary gets to be a bit obvious ( I have a friend that apparently believes basic maintenance should be done in the middle of @#%king nowhere on the side of the road , and I don't ride with him anymore coz Im sick of waiting round ( in the middle of @#%king nowhere)( on the side of the road ) while he bolts back on whatever bit has just fallen off ).The cush drive does have a bit of movement back and forth around the axle , if its wiggly sideways too then a inspection of the sprocket carrier bearings is a must. :)
I wish I was young again............Id be heaps smarter than last time
FasYankee
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Re: Cush drive question.

Post by FasYankee »

Maybe my post was unclear. The bolts aren't loose as in torqued down. Using a hex key they're tight and don't rotate in either direction. They jiggle. As I'm not familiar with the construction of Ducati's I was wondering if it was supposed to be like that...I've owned and ridden literally hundreds and hundreds of bikes since that first leg-over on a Honda mini-trail 50, and I've seen some wacky shit as far as construction methods. I was just wondering if the Italians had some odd way of securing the cush rubber or something.

As it stands right now I'm not getting too serious into examining this bike at all. All I'll probably do this season is drain/rinse the tank and then probably cover it with a sheet. My current project bike on the lift needs to be finished before I delve into another lest my ADD blows off the charts and I end up with a desmo valved Honda.
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JWilliam
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model: 906 Paso
year: 1989
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Re: Cush drive question.

Post by JWilliam »

Speaking as a Paso owner who has ridden literally thousands of miles on his, the sprocket bolts don't 'jiggle'. They are bolted to the carrier, the carrier sits on the cush drive rubber and the cush drive sits in the wheel well. All this tensioned by the axle bolt. Don't ride it - take it apart - there is a good (bad) reason for this play.
FasYankee
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Re: Cush drive question.

Post by FasYankee »

Hahahhaaha......ride it! Bwahahaaahaaaa! Yeah....um, no. The way I do things, by the time this thing has been ridden it will have been completely disassembled, inspected, any suspect parts replaced. I'm positive there will be some things that will be powdercoated, (I have my own 3'x3'x5' PC oven in case anyone needs anything done.....even a frame!) the center stand for instance has some rust on it, the rear grab rail has some normal rubbing of the thin black paint....so yeah, no worries regarding this being one of those sprocket bolts grinding the swingarm/parts falling off scenarios......I'm definitely not that guy. This is probably "rescue" bike #6 I think, not including the supermotos that I've converted. So I've been around that block. I was just curious if Ducati had some funky cush drive apparatus...I literally looked at it for .234 seconds till my wife was screaming something about building a pool house for her or something.....
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paso750
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Re: Cush drive question.

Post by paso750 »

as it was said before the sprocket is bolted to the sprocket carrier (there are nuts on the backside). The sprocket carrier sits with the rubber cush drive behind it in the pan that`s bolted to the rim. What holds them together are the bearings and bearing spacers. In the end the torqued down axle. Below a simple drawing.
Nothing should jiggle or move. If the complete sprocket carrier would tilt a bit I`d check if the rubber cush drive is still ok, has shrunk over the years or whatever.
First I`d remove the wheel and then the sprocket to inspect the holes in the sprocket carrier. I had one with oval holes. Apperently the bolts had come loose at some point in the past and were just retightened. That didn`t work.

G.
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FasYankee
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Re: Cush drive question.

Post by FasYankee »

Out of curiosity, I took a peek at it. I removed one of the sprocket bolts, and 1 of 2 things has happened (possibly both). The bolts are shoulder cap screws. The shoulder portion (the part without the threads) seems to have stretched and/or the holes in the sprocket have elongated/worn to an egg shape. So the shouldered cap screws were tight to the shoulder, but the shoulder portion being too long (stretched) didn't allow for the cap to come in contact with the sprocket itself.....weird. The P/O (my uncle) is very meticulous about his stuff (keeping clean/changing oil/minor stuff) but has mechanics do anything that requires real wrenching. I'd have to assume the mechanic found the bolts to be loose, tightened them in an attempt to remedy the situation, didn't consider the possibility that the bolts had stretched and since they were, it continued to move under load, Worsening the issue. I gues that the best option would be to get a new sprocket, new shoulder cap screws & possibly a new carrier. It's really tough for me to have this bike in the garage right now.....it's distracting me from my current project bike.....I was in the middle of fabricating the 4 into 4 exhaust when it was bugging me to no end to go investigate.
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paso750
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Re: Cush drive question.

Post by paso750 »

The shoulder portion (the part without the threads) seems to have stretched
or the bolts were replaced in the past and some were used that had a too long unthreaded part in which case the nut would have been tight at the end of the thread and the whole bolt would still jiggle.
Now that you know what it is you can carry on with your other bike ;)
FasYankee
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Re: Cush drive question.

Post by FasYankee »

paso750 wrote:
The shoulder portion (the part without the threads) seems to have stretched
or the bolts were replaced in the past and some were used that had a too long unthreaded part in which case the nut would have been tight at the end of the thread and the whole bolt would still jiggle.
Now that you know what it is you can carry on with your other bike ;)
Good point. In either case the sprocket & bolts will be replaced with proper items. The carrier *probably isn't damaged, but when the time comes I'll take a good look for sure. I'll start a new thread when I get her up on the lift.
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ducinthebay
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Re: Cush drive question.

Post by ducinthebay »

When I got my 2nd Sport, the wheel was in sad shape, the the swingarm was nearly gnawed through. One bolt was just missing, another broken, and the remain ones were loose and rattling around. A few more miles and it would have been catastrophic. Needless to say, I replaced a lot of parts on that setup. Make sure the bolts come from the inside of the hub, so that if they do come loose, the free play doesn't chew a big groove in your swingarm.

Not supposed to be loose. Something is definitely wrong there and needs to be addressed.

Cheers, Phil
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.
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JWilliam
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Re: Cush drive question.

Post by JWilliam »

Sprocket bolts and Disc bolts are supposed to be made from high-tensile steel. As such their strength is not from being tightened to a high torque but that the bolt will not bend under load. It doesn't sound as though these bolts are made from the right stuff, as by your description the bolts have deflected under load. I also don't think you will be able to put the bolts in the 'wrong' way, inside the carrier are hexagonal slots to take the hex side of the nut and bolt. However, I have never found this to be a problem with my Paso. The correct metal graded bolt and a nylock hex will last for ever.
Mc tool
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Re: Cush drive question.

Post by Mc tool »

What ? nah, a " high tensile" bolt is just that, high tension , high tensile strength . When a high tensile bolt is tested it is stretched to the limit of its elasticity , which is the point at which it will return to its original dimension , stretched a bit past this point the "stretch" will be permanent , and a little more bolt will snap . Hi tension has nothing to do with a bolts resistance to bending , although it stands to reason that a high tensile bolt being tougher ( not necessarily harder ) may also be more difficult to bend than a mild steel bolt :) and in any event the bolts in our beloved rear sprocket would be under shear stress should they begin to loosen :) :)
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ducinthebay
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Re: Cush drive question.

Post by ducinthebay »

Loctite, Loctite, and more Loctite.
the off road guys use RED Loctite on all sprocket bolts, and plenty of it. Sometimes a sprocket change includes a set of sprocket bolts and nuts. A lot cheaper than a swing arm, or hub.

If the bolts are suspect, change them. Never trust an old nylock nut.

Cheers, Phil
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.
Mc tool
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Re: Cush drive question.

Post by Mc tool »

Mmmm yeah , the thing is that , being a motorcycle owner/rider/abuser for 36 years now I have not ever had a sprocket come loose , well not that I can remember ( and that might be an issue :D ) and it aint because of any rigours maintenance schedule ......or gallons of Loctite ( it will probly happen to every bike I own now :lol: )maybe I just been lucky ........I have chucked a chain thru crankcases 3 times tho :mad: beats me
I wish I was young again............Id be heaps smarter than last time
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