Topic: Cb750 Primary Drive Cush Rubbers

[AshimotoK0]

Hi Guys what an interesting thread I started ! (although it was really a steal from another thread)

I have never really been interested in racing so I can't  comment on race engines. I think Nippon has been very honest and frank with us. As he says, he is just a club member and does not represent them. Looking at it from a non-racing point of view and having worked for a company who used to manufacture rubber and rubber/metal bonded automotive components, rubber technology is a very exacting science and the material itself cannot be underestimated. If Honda designed it and chose to stick with it from 1969 and 1978 then I think I would agree with Nippon and try to reproduce the exact same hardness/compound part as stock. I take Nippon's point about the cost of tooling analysis etc but I do have access to all of the testing and technical advice for free. The mould would be expensive but at least if I have the technical data then I can make enquiries about it with my ex-colleagues. I am an electronics engineer who has spent 20 odd years fixing all of my ex-colleagues electrical stuff! I used to work for a large organisation who had rubber technologists, chemists, physical testing facilities, and most of them owe me a favour, so I may get a better price and definitely technical advice for free. I will try the German club direct to ask them to share  technical information. If they are not prepared to share it then IMHO, they are not 'Team Players' and I would not wish to be associated with them. After all the likes of Hondaman on this site give us heaps of knowledge that they glady pass on for nothing.

[lordmoonpie]

Maybe Nippon has hit the nail on the head in his last post. I can't speak for Mark's engine configuration but I am running a hy-vo primary with a DOHC crank and so the hard cush drive rubbers make perfect sense in this setup because I'm not fighting against two sprockets wanting to rotate slightly differently. With a standard twin sprocket setup, perhaps the extra flex works to the advantage of the complete engine's performance at the high level as Nippon says.

Mark - presumably you're experience is either based on A-cranks and hy-vos or those newer super heavy duty chains in which case, are we comparing apples and oranges after all?

Mike - I don't think anyone's getting at Nippon are they? This is a really interesting discussion imho (and maybe one that should be moved to the HIPO forum?)

[AshimotoK0]

Just had a word with my ex colleagues and they are all up for looking at re-manufacture of the standard item. As a bonus, I have discovered that the owner of the rubber moulding company (he started up his own moulding company) is a Goldwing owner, so will be sympathetic to the cause. The analysis/testing/CAD drawing etc  will all be free as I am calling in old favours on this one 

IF ANYONE HAS A NOS RUBBER FOR US TO ANALYSE/DIMENSION THEN PLEASE COME FORWARD TO HELP OUR CAUSE.

[kos]

Maybe Nippon has hit the nail on the head in his last post. I can't speak for Mark's engine configuration but I am running a hy-vo primary with a DOHC crank and so the hard cush drive rubbers make perfect sense in this setup because I'm not fighting against two sprockets wanting to rotate slightly differently. With a standard twin sprocket setup, perhaps the extra flex works to the advantage of the complete engine's performance at the high level as Nippon says.

Mark - presumably you're experience is either based on A-cranks and hy-vos or those newer super heavy duty chains in which case, are we comparing apples and oranges after all?

Mike - I don't think anyone's getting at Nippon are they? This is a really interesting discussion imho (and maybe one that should be moved to the HIPO forum?)

To answer your question about my experience in regards to the hard vs soft rubbers in cush drive....We only ran the automatic CB750A Hy-Vo cranks a few times. Just about all my experiences with cush drive failures were with NEW Cush drives that would allow the forward or reversing input loads to over power the OEM Soft rubbers and allow the unit to lock up. ie: limiting pins were being contacted by side plates and no cushioning was taking place.

Then chains would break.

And by the way Honda of Japan is continuing to make the primary drive assemblies...these were not some units off the shelf at some old Honda dealer. I dealt directly with American Honda Parts Div.

KOS

Mark@M3Racing

[MRieck]

Maybe Nippon has hit the nail on the head in his last post. I can't speak for Mark's engine configuration but I am running a hy-vo primary with a DOHC crank and so the hard cush drive rubbers make perfect sense in this setup because I'm not fighting against two sprockets wanting to rotate slightly differently. With a standard twin sprocket setup, perhaps the extra flex works to the advantage of the complete engine's performance at the high level as Nippon says.

Mark - presumably you're experience is either based on A-cranks and hy-vos or those newer super heavy duty chains in which case, are we comparing apples and oranges after all?

Mike - I don't think anyone's getting at Nippon are they? This is a really interesting discussion imho (and maybe one that should be moved to the HIPO forum?)

To answer your question about my experience in regards to the hard vs soft rubbers in cush drive....We only ran the automatic CB750A Hy-Vo cranks a few times. Just about all my experiences with cush drive failures were with NEW Cush drives that would allow the forward or reversing input loads to over power the OEM Soft rubbers and allow the unit to lock up. ie: limiting pins were being contacted by side plates and no cushioning was taking place.

Then chains would break.

And by the way Honda of Japan is continuing to make the primary drive assemblies...these were not some units off the shelf at some old Honda dealer. I dealt directly with American Honda Parts Div.

KOS

Mark@M3Racing

Now that is interesting

[MRieck]

Just run 30W oil of wintogreen instead of valvoline, that ought to soften em up a bit.

My God....how could we overlook the wintergreen? Brillant

[kos]

I'm not trying to harp on anyone, hope it doesn't seem that way.

mystic_1

Nippon certainly doesn't need me to make his point and I'm all about questioning approaches to problems. My point is Nippon has his and Mark has his.....that's it. I'll be honest..... I am curious about Marks' choice for rear wheel hub dampers.

Mike

We allways used a rubber dampener as per current m/c standards in our racing wheels. Dirt bikes use no dampeners, as ground offers some amount of slip. Street or road race use dampeners of some kind, as tarmack does not offer much slip.


I found a very unique set up in a CB/CR750 I was taking apart...someone had made and installed a very small rubber cushion dampener in the final drive gear of the gear box. Looked like a smaller version of the primary drive. Looked at rear wheel and found out why...now rubbers dampeners in rear sprocket of Morris Mag wheel!

KOS
Mark@M3Racing

[kos]

Of course, I spent more money for the harder primary rubbers in order to see them in person in comparision with the other rubbers. First, I wanted to use them.
Then I decided not to use them in my engine (please see reasons above).  Please do not misunderstand, it does not matter how much the different rubbers cost.
According to your helmet example. I'd rather like to protect my engine components instead of replacing them several times during a race/street season. It is not about the price. I would not throw away my helmet after every ride, too. (IHMO, the molded primary rubbers are a much more better engineerd  and developed (and a more expensive) part). But the club rubbers are subzidized to the members, so they are cheaper than the the harder ones.
I know, that you didn't have a chance to see them in person w/o being a member.
I measured both types of rubbers, the difference between the harder rubbers and the softer club rubbers is approximate 12% (shore).  It sounds not that much, but it is a huge difference. We do not talk about chewing gum. From my point of view, the soft rubbers are hard enough to do the balancing and damping job very well (see above) , even in tuned engines and they protect the abrasion of the involved primary drive components (chain and crank sprocket). This is an important point for me and all non professional racers, too. I'd rather would like to replace worn primary rubbers instead of a crank (but this is not the case until yet. they are perfect.). I never heard a negeative feedback from my classic race (not GP) buddies about the 'softer' primary rubbers and they use them all for years. Of course, there is big difference. If I would ride my bike only a quarter mile like R.C. did, ...with welded primary sprockets and replacing them after every run, or if I want to ride my bike for a whole race or street season w/o replacing primary chains and cranks.
There is the difference.
Mark, i know, you are a serious racer and your are hunting for the max power w/o any compromises, but how many times do you or your mechanics disassemble your engine during a race season in order to replace the primary chains and crank?  Woud a 'normal' rider do that? Mark, how long will your involved primary drive train components last? Your primary chains and sprockets are worn much more faster with much more harder primary rubbers. You know, if the chains are too long, they want to climb over the crankshaft sprokets, especially during alternation of loads and deceleration. Softer rubbers will almost avoid this or they will delay it under race conditions because they protect the chain and crank sprockets much more better. Until yet, i did not read anything about the durability of your primary drive train components.
It is a logical process, harder rubbers will abrase your primary drive train components much more faster than softer primary rubbers. Why did so many guys try to convert the primary drive train into an automatic crank and Hi-Vo chain? And, i repeat, harder rubbers cannot balance the power between the independent primary chains until they receive the equal power from the crank. E.g., with a Hi-Vo chain and automatic crankshaft, you do not need primary (soft) rubbers to balance the chains, but with two independent and poorly made RK stock chains, there is a need to balance the power of the chains until the two single chains receive the equal power from the crank. This is one of the primary goal of the primary rubbers in my opinion.
In case of the poorly made stock RK chains, one of the independend chains will receive more power during the beginning of acceleration and deceleration. The rubbers will balance them.
Mark, you wrote:
"In actual operating conditions on street or racing conditions you DO NOT want to have the two cush drive sprockets moving independently."
Of course i want to have softer primary rubbers and a little movement of the sprockets in comparison with the harder ones, in case i do not have an automatic Hi-Vo cahin. With the given (two single chains) circumstances, we have to live with, what Honda gave us. In fact, two primary chains and two crankshaft sprockets.
I think, we speak about two different things. I speak about durability and a very good solution according to protect the primary drive train components and to quiten down the primary chain rattle to a like new condition with chains in good shape.
You speak about max. power w/o durability.
A serious question, would you remove the rear wheel rubbers inside the hub, too in order to get more power to the rear wheel from the drive chain?
From my point of view, with all efforts you are going to eleminate the function of the primary rubbers, you will increase
the abrasion of all primary drive train components. It does not matter if you have a stock or a heavily tuned engine.
It is just a question of time. But i understand that this is not important or the primary goal for a serious racer like you and your team are.
You need as much power as you can get.

Back to AshimotoK0, currently, The only chance to get the club made primary rubbers is to join the club.
They are reproducing much more parts like oil pump rubbers and springs, ignition springs and so on.
I think (not sure) the current price for a kit of primary rubbers with rivets is Eur 65.00 - Eur 70.00. Not too bad IHMO.
Then you could have your sample and you could start reproducing them,.......but calculate with a minimum of EUR 2000.00 to make your molds, material analysis and production.
I really do not want o make a club probaganda, that is not my style and my intention, I just want to explain the current situation. And honestly, I wish to have more skills in the english language to be able to write more detailed in order to avoid any misunderstandings.

nippon


Question for Nippon

Why are you and members of your club changing out the rubber cushions in the primary drive assembly? Is it to reduce noise in engine/gear box? Or is it to prevent some perceived future failure?

Secondly, have you ever seen a primary drive failure or had an Honda assembly rack-over and have the side plates touch the pins located in sprockets?

Thank you

KOS
Mark@M3 Racing

[lordmoonpie]

To answer your question about my experience in regards to the hard vs soft rubbers in cush drive....We only ran the automatic CB750A Hy-Vo cranks a few times. Just about all my experiences with cush drive failures were with NEW Cush drives that would allow the forward or reversing input loads to over power the OEM Soft rubbers and allow the unit to lock up. ie: limiting pins were being contacted by side plates and no cushioning was taking place.

Then chains would break.

And by the way Honda of Japan is continuing to make the primary drive assemblies...these were not some units off the shelf at some old Honda dealer. I dealt directly with American Honda Parts Div.

KOS

Mark@M3Racing

Very interesting so Mark - does that follow that you never had cush drive rubber problems with the A crank or did you routinely upgrade then to the HD rubbers? What I'm getting at is this a problem with the standard chain pairings only and less so if you convert to hy-vo?

[MRieck]

I'm not trying to harp on anyone, hope it doesn't seem that way.

mystic_1

Nippon certainly doesn't need me to make his point and I'm all about questioning approaches to problems. My point is Nippon has his and Mark has his.....that's it. I'll be honest..... I am curious about Marks' choice for rear wheel hub dampers.

Mike

We allways used a rubber dampener as per current m/c standards in our racing wheels. Dirt bikes use no dampeners, as ground offers some amount of slip. Street or road race use dampeners of some kind, as tarmack does not offer much slip.


I found a very unique set up in a CB/CR750 I was taking apart...someone had made and installed a very small rubber cushion dampener in the final drive gear of the gear box. Looked like a smaller version of the primary drive. Looked at rear wheel and found out why...now rubbers dampeners in rear sprocket of Morris Mag wheel!

KOS
Mark@M3Racing

Exactly Mark. I have seen quite a few very beat up clutch baskets and transmission shaft bearings secondary to using early PM Chicane wheels. I know there are aftermarket dampers for busa's that hold up better to be turbo numbers.

[AshimotoK0]

IMHO I would think that the German club members are changing rubbers because they harden up. I know for a fact that on the 400/4 they hardened up after 10 years use but they were not in a rivetted assembly and available from Honda as a spare part (or at least they were in 1986) - just checked and 400/4 ones are 1.75GBP each from David Silver (totally different from 750 though)

[kos]

To answer your question about my experience in regards to the hard vs soft rubbers in cush drive....We only ran the automatic CB750A Hy-Vo cranks a few times. Just about all my experiences with cush drive failures were with NEW Cush drives that would allow the forward or reversing input loads to over power the OEM Soft rubbers and allow the unit to lock up. ie: limiting pins were being contacted by side plates and no cushioning was taking place.

Then chains would break.

And by the way Honda of Japan is continuing to make the primary drive assemblies...these were not some units off the shelf at some old Honda dealer. I dealt directly with American Honda Parts Div.

KOS

Mark@M3Racing

Very interesting so Mark - does that follow that you never had cush drive rubber problems with the A crank or did you routinely upgrade then to the HD rubbers? What I'm getting at is this a problem with the standard chain pairings only and less so if you convert to hy-vo?

No we did not have any problems with cush drives as they were uprated to my harder rubbers prior to using.  Also, the only problem we had with Morris Hy-Vo chains was chain breakage, even with a shoe type tensioner these chains are not up to the loads which go up with the square of the RPM.   The Morris engineer could offer us nothing more in stronger HyVo chains. He came to that conclusion, as we "git lucky" and took apart and engine prior to out Silverstone Event and found that some of the links of the Hy-Vo chains were breaking.  The 10,900 RPM that the CR750 engine was producing, is too high for these chains.  Might be the reason that most bikes that use them, have a secondary or countershaft... to change chain speeds and load.

And actually we NEVER had chain failures of even new Honda OEM chains unless the standard tensioner allowed too much movement and the resulting lack of tension on chains allowed them to "climb up" on he crank sprocket and the "skip" That leads to a major failure.

I will soon have for sale a self adjusting primary tensioner that will remedy that probleml. Mechanical, not via oil pressure, as low oil pressure does no supply enough tension upon deceleration...which is where the chains fail. And not some thing derived from Porsche or other exotic source that costs a fortune.




KOS

Mark@M3Racing

[kos]

IMHO I would think that the German club members are changing rubbers because they harden up. I know for a fact that on the 400/4 they hardened up after 10 years use but they were not in a rivetted assembly and available from Honda as a spare part (or at least they were in 1986) - just checked and 400/4 ones are 1.75GBP each from David Silver (totally different from 750 though)

Yes, but my question still stands....have they viewed any failures of rubbers?


KOS

[Jerry Rxman Griffin aka MuthaF'er]

Mark,

What does "soon" mean on the primary tensioner? I'm tearing it down now.

Jerry

[nippon]

Hi,

the reasons for replacing the old rubbers with new soft ones are:

- They became hard, caused by oil and heat during their long life, ...santicizer is gone.
   If they would like them harder, they would not replace them.  
- A few of the rubbers became worn after 40 years. Did you ever notice some small black rubber parts in your oil pan?
- They replace them with new softer rubbers in order to receive a longer life of their new primary chains
   and crankshaft sprockets.
- They replace them in order to quiten down the engine noise drastically.
- They replace them because the 40 year old rubbers have wear of shearing. Not a problem after 40 years.
  (it shows me that they made their designated job)
- They replace them because it is a normal expendable part like many others in your engine.

If the rubbers would not get old and hard after many, many years, the club did not reproduce them.
There would be no need to do that.

I'm looking forward to see your primary chain tensioner system.
@all, stay relaxed.

nippon

[kos]

Hi,

the reasons for replacing the old rubbers with new soft ones are:

- They became hard, caused by oil and heat during their long life, ...santicizer is gone.
   If they would like them harder, they would not replace them.  
- A few of the rubbers became worn after 40 years. Did you ever notice some small black rubber parts in your oil pan?
- They replace them with new softer rubbers in order to receive a longer life of their new primary chains
   and crankshaft sprockets.
- They replace them in order to quiten down the engine noise drastically.
- They replace them because the 40 year old rubbers have wear of shearing. Not a problem after 40 years.
  (it shows me that they made their deisignated job)
- They replace them because it is a normal expendable part like many others in your engine.

If the rubbers would not get old and hard after many, many years, the club did not reproduce them.
There would be no need to do that.

I'm looking forward to see your primary chain tensioner system.
@all, stay relaxed.

nippon

So the answer to my question, have you ever seen or viewed a broken primary drive dampener is NO. Have you ever viewed or seen broken chain(s)?

KOS

Mark@M3Racing

[kos]

Mark,

What does "soon" mean on the primary tensioner? I'm tearing it down now.

Jerry

Sorry, not that soon. Winter up here in north county right now and I do not sell what I have not tested. Race tracks around her do not open until May.


KOS

[nippon]

I never saw a new broken primary rubber in stock and 100hp engines.
Yes, I saw partly broken and soaked old primary rubbers.
Yes, I saw broken stock primary chains, but they broke, because the chains were too long
and the guy did not replace them after they reached the limit.
A chain break caused by the rubbers, i did not see so far.

nippon

[MRieck]

To answer your question about my experience in regards to the hard vs soft rubbers in cush drive....We only ran the automatic CB750A Hy-Vo cranks a few times. Just about all my experiences with cush drive failures were with NEW Cush drives that would allow the forward or reversing input loads to over power the OEM Soft rubbers and allow the unit to lock up. ie: limiting pins were being contacted by side plates and no cushioning was taking place.

Then chains would break.

And by the way Honda of Japan is continuing to make the primary drive assemblies...these were not some units off the shelf at some old Honda dealer. I dealt directly with American Honda Parts Div.

KOS

Mark@M3Racing

Very interesting so Mark - does that follow that you never had cush drive rubber problems with the A crank or did you routinely upgrade then to the HD rubbers? What I'm getting at is this a problem with the standard chain pairings only and less so if you convert to hy-vo?

No we did not have any problems with cush drives as they were uprated to my harder rubbers prior to using.  Also, the only problem we had with Morris Hy-Vo chains was chain breakage, even with a shoe type tensioner these chains are not up to the loads which go up with the square of the RPM.   The Morris engineer could offer us nothing more in stronger HyVo chains. He came to that conclusion, as we "git lucky" and took apart and engine prior to out Silverstone Event and found that some of the links of the Hy-Vo chains were breaking.  The 10,900 RPM that the CR750 engine was producing, is too high for these chains.  Might be the reason that most bikes that use them, have a secondary or countershaft... to change chain speeds and load.

KOS

Mark@M3Racing

I think the sheer weight of that size Hyvo chain begins to work against it at 11,000RPM. I think sudden deceleration would be very, very hard on it.

[kos]

Mike.

Exactly, the chain weighs a lot and plus, the changing of direction adds a huge force.  The engineer at Morris did the calculations prior to me trying this, but in his rechecking after I sent him a partial breaking chain..he said...this is not going to work at the RPM you are planning on running this chain at.


Oh well, we tried. Every one was telling us this was the answer, but no one had ever actually done is my guess. Look what that size chain came off of....a GL1000/1100, but they turn about 6500 at max RPM.


KOS

[mec]

the same chain is working in the cb900 bol d´or, redlinig at 9500, in race engine 10500.
the cb1100r does have a wider and heavier chain, rpms as above.

or is there a misunderstanding?
mec

[MRieck]

the same chain is working in the cb900 bol d´or, redlinig at 9500, in race engine 10500.
the cb1100r does have a wider and heavier chain, rpms as above.

or is there a misunderstanding?
mec

What length is the chain Mec? It is the same, exact chain??

[mec]

you are right.
it is the same type of chain. but in the sohc you have to use a longer chain (assuming you use a gl1000 primary gear).

mec

[kos]

the same chain is working in the cb900 bol d´or, redlinig at 9500, in race engine 10500.
the cb1100r does have a wider and heavier chain, rpms as above.

or is there a misunderstanding?
mec

Yes there is a misunderstanding on this. Your talking oranges...we're talking apples. The DOHC bikes use a secondary or "jack shaft" to take power from crank and drive the clutch outer.  And the chain is 1/2 the length of the one you have to use in the CB750 SOHC!   Not even closet to same loads.


KOS

[MFHP]

Yes, I saw partly broken and soaked old primary rubbers.

nippon

+1, this is exactly the reason, why I changed my primary rubbers: found loads of small rubber bits in my oil pan coming from disintegrating hardened 30 years and 70000 miles old rubbers. Well, the noise reduction and smoother riding afterwards is great but probably mainly related to the new chains and tensioner. Instead of riveting the sprockets together again, I used the same method as Mark described it somewhere above in this thread.

Mike