Cam Chain Tensioner....beating a dead horse

jensen · Post by **jensen** » Fri Dec 10, 2010 4:04 am

Hi,

The chain is NOT running constantly in oil.

Jensen

Dana01 · Post by **Dana01** » Fri Dec 10, 2010 2:37 pm

My 1985 Suzuki GS 450-S Salt Flats racer's tensioner is a runner ... it's a flat 8-ish inch bar with shallow side walls

l______l (cross-section not to scale :)

... and is a hard plastic-y material. It doesn't run in oil but was plenty wet on disassembly ... probably getting lubed from the cam chain as it runs along it.

I like the design over a roller because the tensioning force is spread out over a larger area vs a roller.

The issue I see is that on my GS, the roller sits snugly inside a 3-sided channel in the casting, preventing side-to-side, and back travel.

Interesting idea though.

nc_rider · Post by **nc_rider** » Fri Dec 10, 2010 3:05 pm

Snakeoil wrote:....There is a similar material called Turcite that is perfect for bearing applications. Only drawback is a 2 inch diameter rod is $86/foot.

A whole bunch of them could be sliced out of a one foot piece though.. probably be less than $8 each in materials. I'll have access to a lathe soon and could make some if somebody else doesn't do it before I get around to it..

Would they need a bushing pressed in the middle of them, or would the entire wheel be made of the plastic? (it's been a long time since I looked at one of the 305 tensioner wheels...)

Snakeoil · Post by **Snakeoil** » Fri Dec 10, 2010 7:58 pm

The Turcite specs say it is perfect for bearing applications. So my guess, without doing more research, is as long as you have a polished spindle, you are good to go.

I too was wondering about a slipper shoe versus a roller. My guess is there is more than enough oil on the chain to lube a nylon shoe. I think you could saw one out on a band saw using the radius of the original roller as the max dimension for the deepest part of the shoe. You might be able to rig up one of those profile gauges used to copy molding shapes (a bunch of pins in a clamping holder) to get the proper radius for the face of the shoe. Or you could make something to measure that radius. Anything less than the radius of the roller would put less force in individual links and spread it out over more. You could accomplish the same with a larger roller.

I guess the question is, do you need to do that? Is the roller a weak link driven by material, shape, or a function of age? My guess is rollers are the right way to tension a chain and over time they learned that a shoe works as well with little or no impact to life and are cheaper to make.

I love these kinds of discussions. Dontchya wish we all lived within a few miles of each other and could meet at some local watering hole or bike shop to chew on all this stuff every Friday night? I do.

regards.
Rob

cyclon36 · Post by **cyclon36** » Fri Dec 10, 2010 8:20 pm

Snakeoil wrote:The Turcite specs say it is perfect for bearing applications. So my guess, without doing more research, is as long as you have a polished spindle, you are good to go.

I too was wondering about a slipper shoe versus a roller. My guess is there is more than enough oil on the chain to lube a nylon shoe. I think you could saw one out on a band saw using the radius of the original roller as the max dimension for the deepest part of the shoe. You might be able to rig up one of those profile gauges used to copy molding shapes (a bunch of pins in a clamping holder) to get the proper radius for the face of the shoe. Or you could make something to measure that radius. Anything less than the radius of the roller would put less force in individual links and spread it out over more. You could accomplish the same with a larger roller.

I guess the question is, do you need to do that? Is the roller a weak link driven by material, shape, or a function of age? My guess is rollers are the right way to tension a chain and over time they learned that a shoe works as well with little or no impact to life and are cheaper to make.

I love these kinds of discussions. Dontchya wish we all lived within a few miles of each other and could meet at some local watering hole or bike shop to chew on all this stuff every Friday night? I do.

regards.
Rob

The problem is that anything larger than the current roller will not fit into the hole on the side of the head during assembly.

Most modern applications have a "shoe" or some sort of slider piece that pushes against the chain. I think a sprocket would be the best solution though as you could probably find one that's the proper size, and you would have to rig any special mount for it. I wonder why it's not used though. There has to be some reason why manufacturers don't use one though which is why I started this thread in a way. Is it cost prohibitive or is there something else that keeps it from working properly?

Snakeoil · Post by **Snakeoil** » Fri Dec 10, 2010 8:51 pm

I'm think that early 650 Yamaha twins used a sprocket as a tensioner. But there really is no point to using a sprocket. A sprocket is like a gear, in that it is intended to transmit power. There is no transmission of power here. You are only taking up slack in the chain to maintain timing accuracy and prevent the chain from whipping. So to use a sprocket where a roller will work is wasted cost.

As a modern comparison, take a look at the toothed belts used as final drives on Buell motorcycles and the cams on most modern auto engines. The belt tensioner in both cases is a smooth roller, not a toothed roller for the same reason. There is no power being transmitted by that tensioner. And in the case of a toothed belt, there are only teeth on the ID of the belt. So you could not run a toothed tension sprocket on the outside if you wanted to. You would have to run it on the ID of the belt, which is just a plain bad design.

Hope this helps,
Regards,
Rob

cyclon36 · Post by **cyclon36** » Fri Dec 10, 2010 8:59 pm

Snakeoil wrote:I'm think that early 650 Yamaha twins used a sprocket as a tensioner. But there really is no point to using a sprocket. A sprocket is like a gear, in that it is intended to transmit power. There is no transmission of power here. You are only taking up slack in the chain to maintain timing accuracy and prevent the chain from whipping. So to use a sprocket where a roller will work is wasted cost.

As a modern comparison, take a look at the toothed belts used as final drives on Buell motorcycles and the cams on most modern auto engines. The belt tensioner in both cases is a smooth roller, not a toothed roller for the same reason. There is no power being transmitted by that tensioner. And in the case of a toothed belt, there are only teeth on the ID of the belt. So you could not run a toothed tension sprocket on the outside if you wanted to. You would have to run it on the ID of the belt, which is just a plain bad design.

Hope this helps,
Regards,
Rob

Point taken.

How about this though. Instead of having a tensioner wheel with a rib in the middle that breaks up over time, how about putting the ribs on the side. You still have a guide for the chain to keep it from moving left and right, plus the chain is only pressing against a flat area that won't chip.