Debate of the Day: Experimental Chain Tensioner

[Stevo]

I designed this chain tensioner to push down on the chain in order to remove the chain slack. When I viewed the video, as expected, the chain tightens on acceleration, slackens on deceleration. Now I'm debating on whether or not the tensioner should be pushing upwards from underneath the chain instead of downward from above. The logic being that the chain slack will still be removed while the chain stays in the acceleration position, preventing cogging and also reducing wear at the swingarm pivot/slider. I'm interested in opinions.

[Electro Flyers]

Whenever possible, the tensioner should be on the slack side(unloaded side) of the chain during acceleration. The one drawback is during regenerative braking, the tensioner will act like the tensioner in the video, and the chain will get looser. If looseness is a problem, I guess a second tensioner could be used opposite the first one.

[Ted Dillard]

ummm... Explain to me why a chain tensioner is necessary? I just woke up and this isn't a fully-formed thought, but it seems to me that you want constant tension on a drive chain so it rides on a consistent radius on the sprockets. That is, you don't want it riding up and down, which, even with a chain tensioner it's going to do... You're essentially running a loose chain and hoping the tensioner is going to keep it where it should be?

Lemmee get some more coffee and wake up a little more, but I'm wondering why you can't just adjust the chain to where you want it and call it a day.

[Richard230]

I like the concept. It reminds me of how Buell tensioned their final belt drive, but I believe their tensioner was located below the belt run. However, you do have to ask yourself why such a tensioner hasn't been installed on other chain drive motorcycles in the past. After all, motorcycles have had chain final drives for around 110 years, yet automatic chain tensioners have never managed to make it to the market. Do motorcycle manufacturers know something that we don't?

My favorite chain tensioning system is the one that Zero uses. Placing their drive belt drive sprocket in line with the swing arm pivot.

[Ted Dillard]

Wait, Richard, are you talking both chain and belt drives? I thought I remembered the Buell being a belt, and the Zero as well. A belt is a different animal, and pretty much needs some sort of tensioning system AFAIK.

...now that I've had my coffee, to speak to the original question, I think the best advice is to position the tensioner so it pushed into the chain oval, which would maximize the contact with your teeth on both sprockets. But re-reading now, I see it is, and would go with Electro Flyers' sage advice. But you know, us trolls (and band members) like to hang together.

[Electro Flyers]

ummm... Explain to me why a chain tensioner is necessary? I just woke up and this isn't a fully-formed thought, but it seems to me that you want constant tension on a drive chain so it rides on a consistent radius on the sprockets. That is, you don't want it riding up and down, which, even with a chain tensioner it's going to do... You're essentially running a loose chain and hoping the tensioner is going to keep it where it should be?

Lemmee get some more coffee and wake up a little more, but I'm wondering why you can't just adjust the chain to where you want it and call it a day.

Because the axis of the drive sprocket is forward of the swing arm pivot axis, the chain tension moves through a slack-tight-slack action as the swing arm moves through its travel. On ICE bikes, normally this action is not excessive because the drive sprocket axis is close to the swing arm. Look at the position of the drive sprocket on this bike. It's much further forward, increasing the slack-tight-slack action and increasing the need for a tensioner.

Slack-tight-slack action. I think I just found a name for our next album, Ted.

[Ted Dillard]

Gotcha.

Slack-tight-slack action. I think I just found a name for our next album, Ted.

Thinkin' a Reggae groove?

[Michael Moore]

There are plenty of automatic chain tensioners on motorcycles, but most of them are on cam and primary chains. However, chain tensioners on drive chains are not uncommon on dirt bikes, especially long travel dirt bikes that have more problem with the "slack" at the ends of the travel. Spring-loaded drive chain tensioners were OEM fitment on Bultaco trials bikes starting about 1969.

A front sprocket/pulley concentric with the swing arm pivot gives constant chain/belt tension, but it may not give the chain squat/anti-squat effects the chassis designer desires. The designer has to decide which feature is more important to them.

cheers,
Michael

[Stevo]

Gotcha.



Thinkin' a Reggae groove?

LOL... I was thinking New Wave genre, maybe Alternative, but Reggae works too!!

Michael hit the nail on the head. Because of chassis constraints, the drive sprocket is at it's location as close as possible to the swingarm pivot as I could get it. I do have a smaller chain tensioner on the bottom run also. I could try to run it without the top tensioner and video it again to see how much difference the slop in the chain makes. I was inspired by the ATK chain tensioners of the past, not Bulltaco. I may also try to flip the spring around and try it from under just to see what happens.

[Michael Moore]

With a rear suspension set up like a modern dirt bike (or even many modern street bikes) there is no slack-tight-slack because the axle/pivot/counter shaft are never in line. Instead, the high pivot means the chain is always tightening as it goes from droop to bump. In this case you can often find a point for a stationary roller on the lower run that will take up the slack at full droop and as the suspension compresses and the chain gets tighter the lower run lifts away from the roller. If you can arrange that then you don't need to have a spring-loaded tensioner.

The ATK system was designed to have an effect on squat characteristics which the spring loaded tensioner won't have. Here's Leitner's patent:

https://patentimages.storage.googlea.../US4299582.pdf

cheers,
Michael