Making a Cushier Cush Drive

[Guest ratchethack]

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

Hubert, as mentioned previously, I have over 20K miles and 3 years on this modification. In my case, I used 3 (or was it 4? Can't recall now) larger, strategically placed holes of 10 mm in each block. IMHO the large hole vs. small hole argument is merely splitting hairs. I b'lieve that either would work as well and as effectively as mine has over the years.

 

While this ain't brain surgery, IMHO, it does take a base level requirement of common sense to understand where to put the holes, and perhaps a little shop-level experience and knowledge of the way the materials work and interact -- nothing much more than that.

 

BAA, TJM, & YMMV

[guzzijack]

Hubert, as mentioned previously, I have over 20K miles and 3 years on this modification. In my case, I used 3 larger strategically place holes of 10 mm in each block. IMHO the large hole vs. small hole argument is only splitting hairs. I b'lieve that either would work as well and as effectively as mine has over the years.

 

While this ain't brain surgery, IMHO, it does take a base level requirement of common sense to understand, and perhaps a little shop-level experience and knowledge of the way the materials work and interact -- nothing more.

 

BAA, TJM, & YMMV

 

Okay Ratch you have 3 x 10mm holes drilled, (how many pairs of blocks left in?), I have 5 x 6mm holes with all pairs left in. I see in Gregs first photo of a drilled rubber that 17 holes are in there and he has only left 3 pairs in the drive.

 

I get the feeling, and it's no more than that, that there should be at least all 6 pairs left in on the big twins with higher RWHP. If the 3 pairs of swiss cheeses that are coping with up to 100bhp or thereabouts split or compress themselves to buggery and then fragment you are going to have an enormous amount of slop running up the driveline when both going on and off the power. I'm not going to risk it. The amount and positioning of holes and leaving them all in place as I described earlier gives a noticeable improvement in driveability and I feel secure about not having problems further down the line.

 

GJ

 

EDIT: I have a reason for being cautious in this respect. Back in the early '70s I had an early Honda CB750KO series with big bore 900 kit, yoshi cams etc. etc. to which I fitted a pair of the first available mag wheels which I bought from a european racer. We had to make up a custom cush drive for the rear wheel/sprocket carrier and first used an adapted automobile cush drive assembly from a mini cooper. Lasted about 2 hours before all the rubber split and the carrier started to spin. Ended up making a custom assembly out of machined billet with captive rubber inserts which were about as hard as the stuff Guzzi use but in a different format. There are enormous forces being transmitted in there.

[luhbo]

I'd be carefull with this. I know, Greg has written it down and you Ratchet have given your Amen, but that wouldn't bring me spares when I had spoiled my cushions.

 

Hubert

[Guest ratchethack]

Okay Ratch you have 3 x 10mm holes drilled, (how many pairs of blocks left in?), I have 5 x 6mm holes with all pairs left in. I see in Gregs first photo of a drilled rubber that 17 holes are in there and he has only left 3 pairs in the drive.

 

I get the feeling, and it's no more than that, that there should be at least all 6 pairs left in on the big twins with higher RWHP. If the 3 pairs of swiss cheeses that are coping with up to 100bhp or thereabouts split or compress themselves to buggery and then fragment you are going to have an enormous amount of slop running up the driveline when both going on and off the power. I'm not going to risk it. The amount and positioning of holes and leaving them all in place as I described earlier gives a noticeable improvement in driveability and I feel secure about not having problems further down the line.

 

GJ

Jack, I mostly agree exactly with your take. I edited my post above, recalling that I may well have used 4 holes per block rather than 3. A remembery is a terrible thing to lose. Frankly, I don't think it much matters how many holes you use or how large, if they're well placed.

 

I was so pleased with the driveline smoothness using the full complement of blocks that I haven't tried going to 3 pairs, though this is of course always an option. Incidentally, I have found that the holes serve to retain a little grease and this lets it get distributed naturally by centrifugal force over time. I check it every other tire change and it hasn't needed much of any attention in 3 yrs.

 

I'd be carefull with this. I know, Greg has written it down and you Ratchet have given your Amen, but that wouldn't bring me spares when I had spoiled my cushions.

 

Hubert

Sorry Hubert -- there ain't no guarantees here. We're all just comparing notes on wot we've done. Again, this is old ground here. I've read of Guys drilling Guzzi cush drives for decades, and haven't ever heard of any problems as a result. I think you're in very low-risk territory here myself, but then again:

 

TJM & YMMV

[guzzijack]

Jack, I mostly agree exactly with your take. I edited my post above, recalling that I may well have used 4 holes per block rather than 3. A remembery is a terrible thing to lose. Frankly, I don't think it much matters how many holes you use or how large, if they're well placed.

 

I was so pleased with the driveline smoothness using the full complement of blocks that I haven't tried going to 3 pairs, though this is of course always an option.

 

Agreed

 

See my edited post above for the reason I'm exercising caution on this subject.

 

Incidentally, I would bet a penny to a pound that the majority of guzzis out there are running around with totally rock soild seized cush drives anyway. Even without modifying the rubbers, the simple expediant of stripping, inspecting and lubing the unit at major service intervals would make a major improvement to driveability and length of life of drivetrain and clutches.

 

GJ

[Guest ratchethack]

. . .We had to make up a custom cush drive for the rear wheel/sprocket carrier and first used an adapted automobile cush drive assembly from a mini cooper. Lasted about 2 hours before all the rubber split and the carrier started to spin. Ended up making a custom assembly out of machined billet with captive rubber inserts which were about as hard as the stuff Guzzi use but in a different format. There are enormous forces being transmitted in there.

Gotta admire the ingenuity, Jack, and I would only add that this is the kind of "non-trivial" project that I wouldn't want to take on myself. As you make very clear, it's nothing to trifle with, even with a great deal of know-how and experience on tap. My approach would be best stick with "state o' the shelf" knowledge and experience here than even consider, at the opposite extreme, a "from scratch" shade-tree garage design based on not much more than a wing and a prayer -- as it looks like Dave may soon be discovering (the hard way?).

[belfastguzzi]

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.

Well, quite. So what I did was knock out every other spline. That gives enough clearance to then build a cush-surface on the remaining splines in order to eliminate the dreadful damage caused by the stupid design of metallic spline-on-spline hammer action.

 

I took one of the surplus (craazee Italianos) cush rubber wedges and cut it into slivers of chromified rubber (dremel with diamond disc). I then glued (Araldite Original) these slivers onto the remaining spline faces. The ride is now unbelievably comfy and I engine brake with fearless impunity. I notice a healthy secondary benefit in the form of reduced unsprung weight. Marvellous. Try it.

 

Any ideas for what I can do with the surplus splines now? ebay?

[Dan M]

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.

 

 

That's it in a nutshell. Why does a small problem with a clear solution need to be turned into some major project?

Makes me crazy. Life is too short to make easy jobs harder.

[Guest ratchethack]

Well, quite. So what I did was knock out every other spline. That gives enough clearance to then build a cush-surface on the remaining splines in order to eliminate the dreadful damage caused by the stupid design of metallic spline-on-spline hammer action.

 

I took one of the surplus (craazee Italianos) cush rubber wedges and cut it into slivers of chromified rubber (dremel with diamond disc). I then glued (Araldite Original) these slivers onto the remaining spline faces. The ride is now unbelievably comfy and I engine brake with fearless impunity. I notice a healthy secondary benefit in the form of reduced unsprung weight. Marvellous. Try it.

 

Any ideas for what I can do with the surplus splines now? ebay?

BFG, I'm either slightly confused, or it's merely a semantic thing. For clarity, have you removed every other web (or vane, as Greg calls it) of the forged steel cush drive plate (photo #2 in Greg's opening post)?? When I think of splines, the only splines in the rear wheel hub I know of are the ones in Greg's photo #1. If you cut out every other vane, web, or "spline" as you call it, you must've used a cutting torch or plasma cutter. So wot you've done then, is to glue half-sections of half of the rubber blocks to the remaining vanes with Araldite, effectively doubling the thickness of the rubber blocks?!

 

Innovative, and without question, courageous! Is there some reason you chose to do this rather than the usual drilling/removal of blocks as Greg and Pete have suggested??

 

Enquiring minds (well, you know)

 

 

 

. . . Why does a small problem with a clear solution need to be turned into some major project?

Makes me crazy. Life is too short to make easy jobs harder.

My theory, Dan, to pick up on an earlier comment, is that there are many people who simply aren't happy when the current overall level of grief, antagonism, and anxiety in their lives falls below a certain "pre-programmed" level. When this happens, they quickly act by whatever means is most convenient and close at hand -- consciously or sub-consciously -- to bring their grief level back up to wot they're most comfortable with. I think of it as the Grief Level Optimum. Some seem to have their GLO settings much higher than others. . .

 

That's my theory, as forced upon my attention years ago (repeatedly) by "The EX" , and I'm stickin' to it here. . .

[richard100t]

After having just been into my cush drive & cleaning & lubing it, I'm really surprised that such a small simple thing has generated 53 responses in just a few days. I have to admit it is fascinating to watch some of you peel this onion until theres nothing left to discuss about it. However the way its looking theres at least another hundred or so posts left before at least one of you get tired of it

[Greg Field]

There's no extra drivetrain lash after the modification. It feels like less lash adn far smother in operation. WHat'll it be like in a year? We'll see. The ones in my ELdo have been thusly modified for many years and haven't broken down at all.

[dlaing]

There's no extra drivetrain lash after the modification. It feels like less lash adn far smother in operation. WHat'll it be like in a year? We'll see. The ones in my ELdo have been thusly modified for many years and haven't broken down at all.

Cool, just when I thought the conversation was dead, a argument of semantics rears its pretty/ugly head;

"no, extra drivetrain lash" ???

I guess that boils down to how you define drivetrain lash.

Is lash the rider's perception of freeplay, or is it actual freeplay?

I define it as freeplay between engine and traction and use the term 'noticeable drivetrain lash' to denote rider perceived freeplay.

Because the rubber is now more compressible, there is more freeplay or drivetrain lash, but it feels like less lash because it is cushier and the noticeable jarring of the lash has been reduced.

 

 

 

Well, quite. So what I did was knock out every other spline. That gives enough clearance to then build a cush-surface on the remaining splines in order to eliminate the dreadful damage caused by the stupid design of metallic spline-on-spline hammer action.

 

I took one of the surplus (craazee Italianos) cush rubber wedges and cut it into slivers of chromified rubber (dremel with diamond disc). I then glued (Araldite Original) these slivers onto the remaining spline faces. The ride is now unbelievably comfy and I engine brake with fearless impunity. I notice a healthy secondary benefit in the form of reduced unsprung weight. Marvellous. Try it.

 

Any ideas for what I can do with the surplus splines now? ebay?

Are you a comedian by night?

[dlaing]

That's it in a nutshell. Why does a small problem with a clear solution need to be turned into some major project?

Makes me crazy. Life is too short to make easy jobs harder.

I'd sooner go through the trouble of molding urethane than go after the major project of removing the bolts. Once you have gone that far, why not order the superior part if it existed, or make it yourself if it is easy to do.

I have had some limited experience with plaster, polyester, alginex, and silicone casting, but never urethane. I am certainly more frightened of taking on removing the buttonhead screws in my bike that is more than twice the age of Greg's 2004, than I am frightened of replacing the simple rubber cush with urethane.

Makes me crazy to think that such a clear simple solution is viewed as a major and risky endeavor.

 

Greg is a professional wrench+++ and his experience was,

"The first step was to take it apart. I used my usual technique for buttonheads (which stip easily): 1) heat on the head of the screw for one minute with a MAPP gas torch; 2) insert the appropriate sized allen socket into the screw and give it a wallop with a hammer to shock it loose; and 3) turn out the screw with a ratchet wrench. Two of the screws were loose already. Two others cam right out. The final two took 45 minutes of heating and pounding and cursing. I finally had to drive them out by chiseling a shoulder into the buttonhead and driving them around with a punch. Both fought every turn of the way. It wasn't loctite; it was corrosion between the threads. This on a 2004-model bike that has been in service just 26 months."

I guess my clear solution may be to let it be, although I am curious as to just how hard these chrome-moly steel hard rubbers really are.

[guzzijack]

After having just been into my cush drive & cleaning & lubing it, I'm really surprised that such a small simple thing has generated 53 responses in just a few days. I have to admit it is fascinating to watch some of you peel this onion until theres nothing left to discuss about it. However the way its looking theres at least another hundred or so posts left before at least one of you get tired of it

 

Richard, I think this could make at least another 4 pages before it runs out of steam.

 

By stripping, cleaning and lubing your drive I suspect you've already achieved 100% more than the majority of owners will have done and it will no doubt help with drivetrain longevity! Modifying the cush by drilling and/or removing rubber wedges can be 'the icing on the cake' but I think you/we have to take a common sense approach to the bike it's being applied to.

 

Doing the full Monty on a '72 era bike might be spot on if you consider that the cush drive is, in typical Guzzi fashion, massively over engineered right from the start. I'm just advocating caution in undertaking such radical hole surgery and removal of 50% of the components and effective bearing surfaces on bikes that are throwing out double the RWHP.

 

Each to their own but as I said in my post above, I've seen what happens in this area even when we thought the component specified was beyond actual requirement - and on a bike with less RWHP than the sport Guzzis produced since the mid '90s.

 

BTW, I can't see an emoticon for 'tongue in cheek' but I think BFG might have a use for one to avoid the usual Transatlantic confusion

 

GJ

[mike wilson]

Well, quite. So what I did was knock out every other spline. That gives enough clearance to then build a cush-surface on the remaining splines in order to eliminate the dreadful damage caused by the stupid design of metallic spline-on-spline hammer action.

 

I took one of the surplus (craazee Italianos) cush rubber wedges and cut it into slivers of chromified rubber (dremel with diamond disc). I then glued (Araldite Original) these slivers onto the remaining spline faces. The ride is now unbelievably comfy and I engine brake with fearless impunity. I notice a healthy secondary benefit in the form of reduced unsprung weight. Marvellous. Try it.

 

Any ideas for what I can do with the surplus splines now? ebay?

 

Magnifique!!!

 

Rowland Emmett and Heath Robinson rolled into one.

 

I suggest you offer the cut off splines on Ebay for those unfortunates who have worked their own into an imitation of their grandparents' gums.

 

Because the rubber is now more compressible, there is more freeplay or drivetrain lash, but it feels like less lash because it is cushier and the noticeable jarring of the lash has been reduced.

 

No. Just because you can move it more after contact is made, it does not follow that there is more free play. Free play is exactly that: an amount of non-contact. Softening the cush drive only blurs the boundary.

 

 

Are you a comedian by night?

 

My impression is: 24/7/365/alloted span. I may be wrong.