Topic: Primary Chainwheel Damage

[slikwilli420]

As I gather parts for my new VSH engine build, I was starting to pull pieces together and started working on rebuilding the primary chainwheel. I had one that I rebuilt a few years ago with the "heavy duty" rubbers from Europe that turned out to be really nothing more than pieces cut from rubber cord. It had a ton of play in it and and I swapped it for a rebuilt one from Cycle X for the start of the 2020 season. I pulled it apart yesterday to use for my new build and noticed a significant amount of slop between the inner steel portion (holds the needle bearings for the main trans shaft and has splines for the clutch basket) and the outer aluminum piece that is the inner half holding the damping rubbers.

My question is if this is going to be something that I need to look after each race season or if there is a way to fix it? My first thought would be to drill at the seam of the steel and aluminum piece 6 holes that would house hardened steel pins. Im guessing the steel inner has splines in it that grab the aluminum cast around it and that constant race abuse has started loosening that connection. I can move the parts may 0.010" axially and hear oil squishing in the gap. The pic below may help.



If there isn't an real fix, then Im going to take up a collection of late chainwheel hubs and have a healthy stock on hand for my post-season refresh regimen.

[Old Scrambler]

Could you show us a pic of the cap-screws?

[slikwilli420]

Could you show us a pic of the cap-screws?

Cap screws? The only screws were the ones replacing the rivets which were high grade counter sink screws, loctited and price punched. They all came out undamaged.

[Old Scrambler]

Are they threaded to the top?............If so, that could be a factor. Those cavities are filled with flowing oil so some lateral movement should be expected. When tightening, the plate should have mild pressure on the rubbers.......so slowly tighten each screw similar to the pressure-plate routine.

[slikwilli420]

Are they threaded to the top?............If so, that could be a factor. Those cavities are filled with flowing oil so some lateral movement should be expected. When tightening, the plate should have mild pressure on the rubbers.......so slowly tighten each screw similar to the pressure-plate routine.

I think we are talking different things here. The part in the picture has the aluminum cast around the steel center. Those pieces are now loose from one another. I can move the steel piece inside the aluminum one with my hands. I'm trying to determine if there is a way to prevent this in the future.

[Old Scrambler]

gotcha........   That's new to me.

[Don R]

 I'm wondering about drilling 3 or 4 pins radially. 

[slikwilli420]

I'm wondering about drilling 3 or 4 pins radially.

My thoughts too Don. It would take some stout machinery and carbide tooling but would be worth it to not have to deal with this every other year ongoing.

[kmb69]

Part of the reason these are in production in my shop right now.

Focused on the gear drive version first but designed for both chain types also.

[MRieck]

Part of the reason these are in production in my shop right now.

Focused on the gear drive version first but designed for both chain types also.

Show off. 

[Medyo Bastos]

Id show off too if i had mad skills like Keith!


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[slikwilli420]

Part of the reason these are in production in my shop right now.

Focused on the gear drive version first but designed for both chain types also.

Is the gear the and same as the gl1000 gear? I'm converting to hyvo so that's what I'd need. I also need to get with you Keith to have my Morse chain riveted to be endless.

[kmb69]

Show off. 

Maybe? ? ? 
You saw it here F I R S T !
Mainly publishing some of MY stuff from MY "The SOHC, Honda Could've/Should've Built" project so a certain PAIR of narcissistic, paranoid, schizophrenics don't copy it and claim the idea as their own.

Id show off too if i had mad skills like Keith!

Thanks Angelo, I think! 

Is the gear the and same as the gl1000 gear? I'm converting to hyvo so that's what I'd need. I also need to get with you Keith to have my Morse chain riveted to be endless.

Yep. And it will work with an Automatic crank (shown) or a DOHC crank.

[Jerry Rxman Griffin aka MuthaF'er]

Leroy you do good work 

[bwaller]

50 years after the fact, man oh man. Crazy good Keith.

[PeWe]

OK, so a CB750 with around 100whp need a stronger primary chain hub?

Mine got new cush rubbers installed by a shop in Germany that riveted it together.
https://www.fourever-classic-parts.de/index.php?option=com_content&view=article&id=26&Itemid=31

The CCC chains have almost no stretch after 30.000 km.

But if the issue is the hub design itself, not only the rubbers......

My bike is a street bike, mostly cruising mixed with some fun WOT 70-200kmh, mostly up to only 160. Not racing style with very frequent hard decelerations.

If my engine need it, part for sale?

[kmb69]

Leroy you do good work 

Thank you Spanky.

50 years after the fact, man oh man. Crazy good Keith.

Thank you Brent.

If my engine need it, part for sale?

Not sure if they will work yet. Machining the prototypes for my gear drive now.

I'm wondering about drilling 3 or 4 pins radially. 

The attached picture is a stocker I turned down to see if it could be retrofitted for my purpose. The internal steel piece has 4 lugs that the aluminum was cast around. Honda used this method in several components and it usually worked well until we try to go beyond design parameters. You can see a couple of very small pits/voids in this one but it had not let go. Some of them may have had more casting issues than this one. Not so sure that you could effectively pin these.

[kmb69]

This is a modified "stock" version I considered prior to hearing about Larry Hayes snapping off the clutch splines on his dragbike.
The stock inner material is relatively low grade stuff but would probably hold up to what most folks could throw at it.
A 42-40 Mod 1.0 spline is machined on the outside. The new "inner-outer" is machined from titanium and splined for a size on size fit.
Requires a new RH plate machined from steel, also splined and provides the bearing stop step that got machined away on the inner.
Then uses the stock GL1000 sprocket and dampers. This would be a LOT simpler and less expensive than what I decided to do.

[scottly]

I think we are talking different things here. The part in the picture has the aluminum cast around the steel center. Those pieces are now loose from one another. I can move the steel piece inside the aluminum one with my hands. I'm trying to determine if there is a way to prevent this in the future.

Is this that common? I don't think I've heard of this problem before, and it's hard to imagine how it would happen with a functioning cush system. Perhaps the "rebuilt" part was from a failed gear-drive experiment, primary chain failure, or Power Arc ignition induced damage? 

[Don R]

After seeing the cut down part and how it was made, I'd have to say a couple pins won't help much. 

[slikwilli420]

I think we are talking different things here. The part in the picture has the aluminum cast around the steel center. Those pieces are now loose from one another. I can move the steel piece inside the aluminum one with my hands. I'm trying to determine if there is a way to prevent this in the future.

Is this that common? I don't think I've heard of this problem before, and it's hard to imagine how it would happen with a functioning cush system. Perhaps the "rebuilt" part was from a failed gear-drive experiment, primary chain failure, or Power Arc ignition induced damage?

I rebuilt it a few years ago. It was the first one in my sportsman bike. I did use the soft rubbers from Europe so that might be the cause. They were football shaped after just 2 seasons of use. I do not run a cush drive on the wheel so that might be it as well. I suppose there could have been chain failure in its previous life but the other two are very unlikely. It may not be common at all but was pretty alarming when I found it. I have a fresh one going in the new engine build and hope there are no more issues but it will be something I check over with each tear down from now on.

[PeWe]

OK, the primary hub has a harder life without a cush  drive on the wheel.

[kmb69]

OK, the primary hub has a harder life without a cush  drive on the wheel.

Bingo!

[johno]

not easy for a 50hp design to handle 100 hp !
More so it is not a steady state strain either when circuit racing, it can be from abusive riding styles, I remember on this forum Mark McGraw saying he had a rider that regularly popped the chains out the top of the cases on a certain corner at Daytona and it started to happen when he was getting over 90hp. Chains are tricky to control , resonance, change of load direction, inertia all combine. Certainly good quality chains, tensioner and components help but rarely are they all engineered together in most classic racers, as the old saying goes, anything is only as good as the weakest link.
I have enjoyed this thread , Keith modestly comes up with a fix that has been plaguing the ol SOHC Honda since 1969. Speaking of chains Ive been waiting for Matt to thrash the guts out of his bikes and let me know how the new CX cam chain tensioner holds up.

[simon#42]

OK, the primary hub has a harder life without a cush  drive on the wheel.

Bingo!

we had problems with rotax 250 powered gp bikes destroying clutch gears , the advice from the factory was to stop using cush rubbers in the rear wheel . after this we had no more problems . i have never quite worked out why this was the case .