bummer - cush hub buffers - failed and missing - ???

maylar · Mar 16, 2020

Onder said:
How long have they been in service?

Umm... since 1975.

gortnipper · Mar 16, 2020

And that is why all our bikes need every original piece of rubber and plastic replaced by now.

joe czech · Mar 17, 2020

gortnipper said:
And that is why all our bikes need every original piece of rubber and plastic replaced by now.

I agree - replaced just about everything on the bike, guess the last thing was the cush buffers. ordered up a set and ordered up a block of PEEK (Polyetheretherketone). someone on the forum used PEEK, so I thought i'd also give it a try. seems this stuff has excellent thermoplastic properties - read this on one data sheet -- "PEEK melts at a relatively high temperature (343 °C / 649.4 °F). looking at the replacement parts, fabricating a set in the shop shouldn't be an issue. if it doesn't pan out, I can always install the replacement AN parts.

Onder · Mar 17, 2020

My herringbone lines seem just fine....

maylar · Mar 17, 2020

Fast Eddie said:
They age, perish, turn to useless powder over time and use. But during this failure process they can still provide enough Cush to hide the decay. Then one day they don’t any more.

So no, it’s not a sudden failure. It’s a gradual decay, but one that can create a sudden realisation of the symptoms.

I'm amazed at the sudden disappearance of mine. Last time I checked them was when I replaced the rear tire, about 4000 miles and 5 years ago. They looked fine then, though I didn't fondle them and verify their integrity. Now a few years later they're just powder. Just like that.

APRRSV · Mar 17, 2020

Hi Joe,
Where did you source the PEEK? I looked at McMaster Carr and they charge the price of gold.

Ed

joe czech said:
I agree - replaced just about everything on the bike, guess the last thing was the cush buffers. ordered up a set and ordered up a block of PEEK (Polyetheretherketone). someone on the forum used PEEK, so I thought i'd also give it a try. seems this stuff has excellent thermoplastic properties - read this on one data sheet -- "PEEK melts at a relatively high temperature (343 °C / 649.4 °F). looking at the replacement parts, fabricating a set in the shop shouldn't be an issue. if it doesn't pan out, I can always install the replacement AN parts.

gnolan · Mar 17, 2020

PEEK would not be a very suitable material for "CUSH RUBBERS", as it is fairly hard (rockwell R 124, which is about the same as delrin). You wont get much shock absorbing with material that hard. It's probably one of the most expensive plastics that you can get.

ashman · Mar 17, 2020

The original rubbers on mine lasted over 35 years and replace them from RGM I brought 3 sets of them to keep in the spares the first replacement lasted about 6 months and no the brake wasn't adjusted wrong, the second set are still going strong after a few years, seems the original rubber was better quality and the newer ones not so, this is from a hard ridding long mileage Norton that I have owned since new.

Ashley

Blewdy Yaink · Mar 17, 2020

Tornado said:
Madass140 has a modern cush drive hub conversion. Bit pricey, but would solve these issues.

Mine arrived from Don yesterday. I'm doing virus dodging this week so I haven't had a chance to check out the items in the box.

joe czech · Mar 17, 2020

gnolan said:
PEEK would not be a very suitable material for "CUSH RUBBERS", as it is fairly hard (rockwell R 124, which is about the same as delrin). You wont get much shock absorbing with material that hard. It's probably one of the most expensive plastics that you can get.

okay - not trying to be argumentative, but what is the stock material, and what is the hardness number (shore or Rockwell) of the stock material? without knowing that number, there's nothing to compare it to. what about Teflon (D52-D55, temp rating -350°F to 500°F). from some of the feedback on various threads, the OE cush blocks have serious issues.

joe czech · Mar 17, 2020

APRRSV said:
Hi Joe,
Where did you source the PEEK? I looked at McMaster Carr and they charge the price of gold.

Ed

bought a small sample piece from a specialty plastics company on line. just enough to fab one set. if it works, a piece from MMC (enough to fab three complete sets would run about $62. pricey - YES (would be about $25/set after shipping. BTW, paid around $30 for an AN set), but whatever solves the problem. I did see a madass140 assembly on fleabay - nice stuff, but a little out of my price range at present.

batrider · Mar 17, 2020

I'm on my 3rd set of buffers in about 40K miles and 40+ years with no complaints about the stock material. Nothing like the Alps around here though.
We used a lot of white Teflon for high voltage insulators in my old job. So soft it would be like using pieces of cheese!

joe czech · Mar 17, 2020

batrider said:
I'm on my 3rd set of buffers in about 40K miles and 40+ years with no complaints about the stock material. Nothing like the Alps around here though.
We used a lot of white Teflon for high voltage insulators in my old job. So soft it would be like using pieces of cheese!

teflon, too soft, PEEK, too hard - there's got to be a goldilocks material out there. looking at the shore charts, a rubber tire has a shore D number of about 15. so, what would be a be a good number? the three sets in 40K miles is good to know. don't know if mine were originals, so AN replacements most likely will have to suffice. no Alps here - probably 10-20 feet above sea level -

gnolan · Mar 17, 2020

Peek is "off the chart" of the Shore scale. Harder than the Scales will accomodate. There is considerable overlap in the Shore scales, where Shore scale 00 is used for softer stuff like rubber bands, Shore scale A for medium density like pencil erasers or tires, and Shore scale D, which goes all the way to hard rubbers like lawn mower wheels. To get any cushion, I wouldn't use anything harder than Tire rubber or the Conveyor Belt material someone suggested earlier - around Shore A 60.
Plastic and Rubber are entirely different. There is practically no shock absorbing quality in hard plastic, like Peek or Delrin. It will fracture when compressed. Go with stock stuff, which should last several years, or build your own from some medium hard rubber.

Onder · Mar 18, 2020

I wonder how much cush block life is due to use and how much is due to age.

maylar · Mar 18, 2020

Onder said:
I wonder how much cush block life is due to use and how much is due to age.

My bet is that age plays the biggest role. In my case, the last time I looked at them (4000 miles ago) they were intact, and suddenly they disappeared. I haven't been overly aggressive with my riding style that it should have caused them to fail.

ludwig · Mar 18, 2020

joe czech said:
I agree - replaced just about everything on the bike, guess the last thing was the cush buffers. ordered up a set and ordered up a block of PEEK (Polyetheretherketone). someone on the forum used PEEK, so I thought i'd also give it a try. seems this stuff has excellent thermoplastic properties - read this on one data sheet -- "PEEK melts at a relatively high temperature (343 °C / 649.4 °F). looking at the replacement parts, fabricating a set in the shop shouldn't be an issue. if it doesn't pan out, I can always install the replacement AN parts.

Joe:
PEEK is not compressible, and if you want to keep mounting your wheel the traditional way, I'm afraid you'll have some trouble making the blocks the right size.
Too big and the wheel won't fit. Too small will make them rattle.
It's different for me, because I can tap them in from the outside, after installing the wheel.
I tried different materials , even steel springs.
Teflon is too soft, etracetal ( delrin) is ok, but PEEK has better heat resistance.
Neither one is compressible, so it will make the hub effectively solid.
If you do want some cushion, then stick to rubber.
Like I said before, IMO the importance of a (this?) cush drive is overrated.
Better is to make your clutch as light as possible.
It all depends on how and on what type of roads you use the bike.

joe czech · Mar 18, 2020

gave up on replacement material - either too hard or too soft. anyway, job is done -- installed AN service replacement blocks. installation was easy and wheel went back on without too much trouble. FWIW, installed the wheel and axle shaft WITHOUT the spacer. used the axle bolt to help support the wheel assembly while I rocked the wheel assembly back an forth, working the tabs into the blocks. when I got it close, used a nylon prybar, and set the wheel so I could get the spacer in close proximity. removed the axle bolt, and tapped the spacer into position and re-installed the axle bolt. one of the easier jobs I've done on the commando. need to adjust the drive chain, and a final torque on everything - it's 79°F, sun shining, and i'm ready for a ride -

cliffa · Mar 18, 2020

I'm sure most folks on here know this, but slack chains have a dramatic effect on life of cush drive rubbers for all makes of bikes. Commando's tend to hide the snap effect of rolling on and off the throttle with a loose chain as it's absorbed into the the ISO's and you don't feel it so much.

kerinorton · Mar 18, 2020

I ended up cutting the 2 ribs off the main rubbers to enable the wheel to slide on easier. Those rubbers have been on my bike at least 8 years now. They have compressed a bit, with profile marks of the spigots obvious, but I still need to pull the wheel on over them from the right hand side of the bike.
Dereck

As for chain adjustment. After I saw a commando rider ask Nes to adjust his chain to the 5/8" or so clearance, Nes told him it was too tight. The rider didn't agree. After about 2 laps, his chain came off. I am happy to let my chain have up to 1 - 1/2 inch of play. It doesn't cause me any problems.