Cam Chain Tensioner....beating a dead horse

cyclon36 · Post by **cyclon36** » Sun Dec 12, 2010 8:11 pm

Found what might be a solution on the big bore site: http://www.bore-tech.com/CB.html

Look down a few products and you'll see a slider version they sell for the adjuster. I wonder if it's adaptable to the CB77.

jensen · Post by **jensen** » Mon Dec 13, 2010 3:47 am

Hi,

The valve train of a standard CB72 / 77 is working very well. It has roller bearings, and not very stiff springs. And on top of that, it has a relative short chain (SOHC). If you replace the worn parts, it will do just fine. The weakness of these bikes is the transmission, not the valve train / crank. Because the rollers are obsolete, you can make a new roller, which is less work then chancing to a whole different way of tension the chain. A blade chain tensioner as used in early fours did have problems too.

Jensen

Snakeoil · Post by **Snakeoil** » Mon Dec 13, 2010 11:43 am

I agree, Jensen. I think the reason these rollers fail is the material is simply aged and like many early plastics dies from old age. A replacement roller made from Delrin or similar material will probably last longer than us.

Cyclon, I think you are trying to fix a design problem that does not exist. The basic design of the roller is sound. It's the roller material that is the problem in my humble, inexperienced opinion.

regards,
Rob

LOUD MOUSE · Post by **LOUD MOUSE** » Mon Dec 13, 2010 11:56 am

How many of ya have figured why they become sprockets?. ............lm

Snakeoil wrote:I agree, Jensen. I think the reason these rollers fail is the material is simply aged and like many early plastics dies from old age. A replacement roller made from Delrin or similar material will probably last longer than us.

Cyclon, I think you are trying to fix a design problem that does not exist. The basic design of the roller is sound. It's the roller material that is the problem in my humble, inexperienced opinion.

regards,
Rob

OldStan · Post by **OldStan** » Mon Dec 13, 2010 10:31 pm

I'll give it a shot. Since all the pressure is applied only by the rollers and only on the center ridge (until you get excessive sprocketing) I would guess that the indents are caused by the loss of elasticity in the surface of the roller material. I'm guess that your resurfacing method removes the stiffer surface material allowing the ridge to once again flex.

Am I close or way off base?

Wilf · Post by **Wilf** » Mon Dec 13, 2010 11:25 pm

Owners not periodically adjusting their cam chain tension, allowing the chain to whip?

Wilf

Snakeoil · Post by **Snakeoil** » Wed Dec 15, 2010 11:42 am

The one engine I had apart had impressions in the rollers from sitting for a long period without moving. The primary roller also had small impressions in one side from probably sitting at well.

What you cannot tell is if that happened from sitting for years, months, weeks or days. My guess is with age and heat, it takes less time for the impressions to form because the material has loses it's resiliency. Once you have impressions in even part of the roller, it will have a greater tendency to follow the chain pitch consistently and therefore end up producing permantent impressions over time.

Now if the roller material cracks at any of those impressions and begins to chunk, then that same process could continue around the roller. As it loses material, the rollers sink deeper into the roller and basically form a sprocket out of the roller.

So my guess is material property loss over time leading to impressions in the roller while at rest for long periods, combined with operation once impressions begin to form turns them into sprockets.

Or maybe they just cook from heat and nothing else.
regards,
Rob