Making a Cushier Cush Drive

[dlaing]

So, Rubber as hard as chrome-moly steel is the ideal material as long as it is swiss cheesed.

And I am the one who is off base for suggesting a more durable and absorbing elastomer for the job.

Good grief.

I have never seen inside the cush drive of my V11, but my V65 cush rubbers got torn up pretty good after maybe 20 or 30 thousand miles.

Glad to see nobody here but me has ever seen cush drive rubbers become hard, not like Chromoly, but like plastic.

Maybe it was just the small blocks that used crap rubber, although when new, at least they were soft and compliant.

I do agree a LITTLE swiss cheesing and silicone is better than nothing, but if one has to go to the trouble of removing these button screws, it would be nice to have some better shock absorbers to replace it with.

 

But as usual I am wrong and chrome-moly hard rubber is the superior choice.

 

So for the third time, which spline is it that gets damaged if you don't swiss cheese your rubber?

[Pierre]

So, Rubber as hard as chrome-moly steel is the ideal material as long as it is swiss cheesed.

And I am the one who is off base for suggesting a more durable and absorbing elastomer for the job.

Good grief.

Custom Cast Urethane! David, if you're up for the task, this looks like the "go to" place. They claim they'll let you design your own and specify hardness. Rancho Cucamonga. Give 'em a call - they claim "custom work" and "no job too small."

http://tinyurl.com/2rvhve

[dlaing]

Thanks Pierre, I was looking for something like that.

I really have to pull the cush assembly to get a clear idea.

These guys could be perfect for a run of maybe a hundred cast pieces.

No job too small sounds expensive.

If I am the only customer, given the feedback and PIA factor, I think I could either cast it myself with the metal parts functioning as the mold, or buy stock urethane (available at San Diego Plastics) and cut it to fit. A search by google showed some promising casting urethanes, but few prices were available for the either the stock or the liquid.

If cut to fit is easy, than I could post how-to instructions for making your cush drive as cushy as a young supermodel's assets, rather than as cushy as swiss cheese that has been in the refrigerator for four years.

But I am sure some will argue, "cheese gets better with age"

[mike wilson]

I have never seen inside the cush drive of my V11, but my V65 cush rubbers got torn up pretty good after maybe 20 or 30 thousand miles.

Glad to see nobody here but me has ever seen cush drive rubbers become hard, not like Chromoly, but like plastic.

Maybe it was just the small blocks that used crap rubber, although when new, at least they were soft and compliant.

So for the third time, which spline is it that gets damaged if you don't swiss cheese your rubber?

 

My V65 has just shy of 90,000 on the originals. I changed the ones on my V50 at about 50,000 just because I could. The small blocks are better designed than others, as there are no splines (the ones that interface between the wheel and drive box) to wear. The crownwheel is bolted onto a carrier (which also holds the disc) that has fingers on the other end to fit in between the rubbers housed in the wheel. Those (substantial, cast steel) fingers provide the drive, not some poxy little splines.

 

It seems to me that the splines in the big blocks are the design flaw. If you wished to remove engine braking from the riding equation, you would have to declutch every time you closed the throttle. As you can't, the small amount of play in the spline/socket assembly is hammered every time you transition between power on and off, even when changing gear. Given the vagaries of production assembly, there will be pairs that have greater clearance from new than others. These will be able to produce a better hammering action than closer fitting parts and, presumably, will deform faster. Lack of lubrication will exacerbate the problem.

 

If you want to design/produce something to allieviate this problem, I would suggest that a new form of the splines would be a better option than the cush drive. Ideally, something along the lines of the small block design.

[tikkanen]

I fear for your eyesight Soren:

how many fingers am I holding up?

 

I know 2002 Scuras are almost flawless, but surely there must be something slightly amiss, somewhere?

 

Anyway, just wanted to say that my 2002 Scura showed the same signs as Greg reports, when I did this disassembly at fairly low mileage. The good thing was that I was able to get it apart, but when I tried more recently, in order to inspect the greasy situation, It was stuck tight. That was despite the prior anti-seizing. Must try heat next time, as suggested. For that reason, be cautious when you give it to your mechanic because the job could be more prolonged than expected.

 

As for rubber, while it pains me greatly to agree with Ratchet , it seems to me to be the flexible and shock absorbant and relatively cheap stuff for this basic job. More expensive urethanes may put up with more extreme stresses but that's not called for. The design of the wedges could have been beter tuned, but as with other Guzzi parts, fine tuning is left to the end-customer (and his box of mallets).

 

Oh, a terrible headache has just come on: where's my tub of Ratchet-salve?

 

Allright, BFG

 

I had the standard warthog engine paint coming off and the tranny sprawl thingie which left me bikeless for quite a while. Bar that I've been quite happy with my Scura.

 

My wife just got a major payraise, so I'm tryng to convince her that I desperately need a new pair of rims, i.e. Dymag, PVM, OZ or what have you. If I succeed I'll have the spline checked and greased like Greg suggests.

 

Cheers

Søren

[mike wilson]

the tranny sprawl thingie

 

That conjurs up mental images that I wish would go away forever......

[pete roper]

That conjurs up mental images that I wish would go away forever......

 

Why? Just use more custard and curry paste. Sago and a wetsuit help!

 

pete

[Greg Field]

For all but the Scuras and others with the single-plate clutch, the major hammering takes place on the splines of the i.d. of the flywheel and the o.d. of the clutch hub.

[mike wilson]

Why? Just use more custard and curry paste. Sago and a wetsuit help!

 

pete

 

I love the smell of swarfega in the morning.

[Guest ratchethack]

So, Rubber as hard as chrome-moly steel is the ideal material as long as it is swiss cheesed.

And I am the one who is off base for suggesting a more durable and absorbing elastomer for the job.

Good grief.

I have never seen inside the cush drive of my V11

Good Grief indeed. But what about BAD Grief?!

 

Dave. Do you have a need for grief? I well b'lieve some do. . . You seem to go well out of your way to bring it upon yourself. Do you understand that in lots of cases (as in the case of vampires) if you don't actually invite certain kinds of grief in, it can't actually sink its teeth into your neck and suck your life-blood?!

 

Now you're evidently entertaining the idea of designing a custom urethane cush drive. . .

. . .I think I could either cast it myself with the metal parts functioning as the mold, or buy stock urethane (available at San Diego Plastics) and cut it to fit. A search by google showed some promising casting urethanes, but few prices were available for the either the stock or the liquid.

If cut to fit is easy, than I could post how-to instructions for making your cush drive as cushy as a young supermodel's assets, rather than as cushy as swiss cheese that has been in the refrigerator for four years.

I'm not against trying to improve things. Quite the contrary. But for cryin' out loud Dave, shall we be rational about wot we're doing -- if not practical???

 

You seem to prefer horrifically complicated and expensive science projects without end over simple, proven, and easy procedures that are well documented and well proven. Why not simply bypass the kind of grief you've evidently been going through non-stop for years with your suspension setup (for example).

 

Your down-time must be off the charts. I don't know how you get any miles on your Guzzi at all?

 

Greg provided a clear-cut procedure in the opening post of this thread, complete with explanation and photo's of a method that has been well-proven for decades. It costs nothing and takes relatively little time. Is there something -- anything at all -- wrong with this in your view? If you don't have a drill, Pete has suggested a similar solution, also well-proven for decades, that doesn't involve drilling.

 

Do you really want to open up another Pandora's box and venture into entirely uncharted territory whilst your fork springs and shock spring still (according to your own posts) are the wrong rates -- after you've replaced both once already?? Don't you get very very tired of not riding your Guzzi and/or tired of riding it with wot you know very well (again according to your posts) is a substandard setup year after year , without evidently ever getting close to a point where you're satisfied with it?!

 

Is there some heretofore unexplained reason that you don't just follow Greg's simple procedure? When I drilled my cush drive blocks three years ago, I reckon the drilling part took no more than a few minutes with a drill press. I used the press mostly for convenience, but a hand drill would easily suffice. If you don't have one, could you borrow one?

 

I suggest that if you're bound and determined to experiment with custom urethane blocks in your cush drive, that you're highly unlikely to hit the correct combination of critically important properties for a better solution than drilled stock rubber blocks (spring rate, load tolerance, compressibility, durability, heat tolerance, chemical tolerance, etc.) on the first try. More than likely, such a venture would require many many tries over many many months, if not many many years of road testing, and for the most part, put you in perpetual disassembly and re-assembly mode. Now if you were to accomplish wot apparently no one else in the entire Guzzi universe has been able to accomplish yet, and eventually come up with something superior to wot Greg, myself, Pete, and so many others already have accomplished, and actually achieve this after only a year or so -- you could look forward to exploring more of the unknown in discovery WRT the longer-range durability of your custom urethane cush drive for the next several years. . .

 

Meanwhile, the rest of us will be riding without much thought about cush drives, and NONE of this kinda grief!

 

It's been 3 years since I drilled my cush drive and over 20K miles. It works LOTS better, and shows no signs wotsoever of breaking down -- or any other kind of problem. I reckon others have lots more miles and years on theirs than I do.

 

It would seem that you may've missed Pete's comment entirely:

Rubber is a perfectly acceptable medium for such a part. Why in the name of all that's holy would you want to swap something that's simple, is cheap and works for something that is complicated, failure prone and expensive???? The type of rubber used for the original 'Pie Slices' could certainly be better chosen or, simply drilled as Greg has at the factory! But that would involve cost and labour so it ain't gunna happen so we're stuck with what we got!

You seem to be unusually focused on shaving off grams of unsprung weight in the center of a ~40 lb. wheel and hub assembly by replacing stock parts with custom parts made of titanium, ceramic, etc. If you have to think of your cush drive this way, why not start by comparing the weight of running half the number of drilled stock cush drive blocks against the weight of a custom urethane cush drive. As noted previously, I reckon the weight savings alone at ZERO MATERIAL COST could be HUNDREDS of grams -- maybe even ounces! -- over that of urethane, not to mention the horriffically complicated and expensive alternatives you've suggested of titanium and ceramic parts for spacers and bearings -- let alone a designed-from-scratch titanium spring cush drive!

 

May I suggest simply drilling your cush drive, and get back to your suspension setup, Dave. This is a much more important thing to spend your time on, don't you think -- if not only for enjoyment of actually riding your Guzzi -- but from a safety perspective. I reckon you could be done with your latest science project without end before you start!

[dlaing]

Thanks for the concern Ratchet.

If you read the sag thread, you will realize that my suspension is very well sprung, and that I am only trying to extract a small improvement out of it.

I think the swiss cheese modification would be fine if not over-done, and if the rubbers are not already worn out and hardened, especially because getting some silicone grease in there early in the life of the rubber could help soften them and extend their life.

But replacing the rubber with polyurethane should be a no brainer and better than swiss cheesed steel hard rubber.

All I have to do is find something a little softer than stock, make sure it is rated for durability, and figure out how to mold it. FWIW this looks like about the easiest thing to mold that I can imagine....just seal up the bottom, add mold release(possibly optional)and pour in the mixed urethane.

Child's play really, but maybe a little swiss cheesing to give it room to extrude.

This ain't brain surgery or rocket science.

Urethane is superior to rubber for this purpose in just about every way.

The only situation where it might be worse is in high heat situations.

For example I don't think I would use it to replace the crappy rubber intake manifolds.

Perhaps reinforced silicone would be ideal at the manifolds

But the heat that the cush rubbers will be exposed to is completely tolerable.

The good grief is for the vampires that try to suck the life out of a perfectly good idea.

Yes, your technique would probably ONLY take me 8 hours of cursing and swearing as the bolt heads become unworkable while mine would take that 8 hours plus 6 hours of shopping and 2 hours of molding. BAA, YMMV.

Greg provided a clear-cut procedure in the opening post of this thread, complete with explanation and photo's of a method that has been well-proven for decades. It costs nothing and takes relatively little time. Is there something -- anything at all -- wrong with this in your view? If you don't have a drill, Pete has suggested a similar solution, also well-proven for decades, that doesn't involve drilling.

"takes relatively little time"? what? to open pandora's box to out-engineer Guzzi's engineers?

If I am going through the process that "takes relatively little time" risking bolt head strippage, to out engineer Guzzi, should I really use 7 year old cush rubbers that may now be even harder than chrome-moly steel?

I know, your answer is yes.

Good grief, Charlie Brown!

[Guest ratchethack]

Yes, your technique would probably ONLY take me 8 hours of cursing and swearing as the bolt heads become unworkable while mine would take that 8 hours plus 6 hours of shopping and 2 hours of molding. BAA, YMMV.

Ah yes.

 

Pushing back the frontiers of ignorance with 8 hours of rank amateur shopping and molding experiments on the BLEEDING EDGE of scientific and industrial achievement!

 

You're sure to do far better with your 6 hours of shopping and 2 hours of molding than the entire extended Guzzi Universe has done with cush drives since the first Guzzi cush drives were introduced -- wot, 40 years ago -- in '67?

 

Most sincere best wishes on your next science project without end, Dave.

 

By all means, do keep us posted on your progress.

 

And be sure to let us know how much harder your rubber blocks are than chrome moly -- once you've actually seen and handled them for the first time. . .

 

Now I dearly hate to be the pessimistic curmudgeon here (again, [sigh]). On second thought, scratch that -- I must really ENJOY being the pessimistic curmudgeon here! In any case, my prediction:

 

Working from ZERO frame of reference wotsoever here WRT even the existence of entire fields of advanced engineering study that are more'n likely pretty hard prerequisites for even remote expectations for success with this kind of a project, (let alone any actual experience therewith), you might make it as far as halfway through the first page of the first chapter of Materials Science 101 before dropping the entire course in favor of taking Suspension 101 over again. . .

 

Let's face it -- you'll be taking one wild-a$$ shot in the dark. In other words, it already has all the earmarks of "junk science" at its stereotypical, classic finest. . .

 

 

I seriously doubt that your M is gonna V -- but by all means, please step up your utmost efforts to prove me wrong.

[orangeokie]

 

Would the new Alpina spoked rear wheel come with new rubber in the cush drive, or would one need to take the original rubber parts and use them in the new rear Alpina hub?

 

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[guzzijack]

This is 'thinking out loud' mode, so I'm not stating facts only opening this up for a bit more discussion

 

The basic Guzzi cushdrive with its 6 pairs of rock 'ard biscuits, (hardtack?) have been fitted to big twins since when? V7Sport or even earlier?

 

Those bikes made what - low 50s bhp at the rear wheel? If correct, I can see the need to drill all the cheese triangles and even remove 50% of them for the lower powered bikes. As RWHP has in some cases doubled since then maybe there is a need to think about how much you need to aerate the blocks and even the posibility of keeping them all in there.

 

On the advice of Phil A on my V10 I've done the drill thing, although I think Greg has gone a bit overboard with the bit - I used a 6mm hollow tile drill and made one hole in each corner of the wider end and two holes on the centre line above it. Then flipped the wedge over on its side and put one further hole through the thickest (apex of the triangle) section. I left all the rubbers in and it gives a noticibly smoother ride but I think I'd counsel against going as radical as Grag has done on any V10, V11S or Daytona RS etc.

 

GJ

[luhbo]

How much experience does Greg or others have with so heavily drilled cushions? How many miles?

 

I can see a big risk that all these holes will totaly destroy the cushions in very short time. The reason is that making them "cushier" does directly result in very large elongations for this stiff and hard material. I can imagine that these cheap rubber parts can't stand these elongations and the herefrom resulting stress for a remarkable time.

 

I'm with Jack, few but carefully positioned holes are probably better. Or a lot of holes but then only in combination with a high quality material as Dave has mentioned.

 

Hubert