Tension on a chain / Chain Tensioners

[Kemper]

Hi everybody, long time I don't post here.

I was trying to figure out the need of a chain tensioner, what would be a good design and all but I got stuck with some questions. I will try to expose my line of thought so far.
Looking for "chain tensioner info", I tried google without some meaningful result. Then here on the forum. Somewhere in here (sorry, I forgot to get the link and I'm not in the mood to do the search again =P ) I saw someone proposing the question: is the gain of the chain tensioner worth the power loss?
I believe this statement comes from the usage of "slide chain tensioners" (I don't know the right name, but is the one that looks like a block of nylon and the chain slides over it). The friction might be an issue, not mentioning the wear of the part.
Then I start thinking about a pulley-like thing with a bearing to reduce the friction. Okay, sounds cool, but can the bearing hold the force on it? I tried to look for how much force a chain tensioner does, and the strongest I could find was around 200N. Don't ask me why (I really don't know), but I was imagining something on the 1000N figure because of the high-revs. Not mentioning that small radius pulleys would spin very fast.
Now comes the question: if pulley-like things were THAT good, why would Harley-Davidson motorcycles use the slide type one? Just packaging or the load on motorcycle chains overcomes practical use of bearings?
Anyone in the mood to share some experiences/ideas/information?

Thanks in advance!

Paulo Kemper
(soon pics!)

[Kemper]

Hi everybody, long time I don't post here.

I was trying to figure out the need of a chain tensioner, what would be a good design and all but I got stuck with some questions. I will try to expose my line of thought so far.
Looking for "chain tensioner info", I tried google without some meaningful result. Then here on the forum. Somewhere in here (sorry, I forgot to get the link and I'm not in the mood to do the search again =P ) I saw someone proposing the question: is the gain of the chain tensioner worth the power loss?
I believe this statement comes from the usage of "slide chain tensioners" (I don't know the right name, but is the one that looks like a block of nylon and the chain slides over it). The friction might be an issue, not mentioning the wear of the part.
Then I start thinking about a pulley-like thing with a bearing to reduce the friction. Okay, sounds cool, but can the bearing hold the force on it? I tried to look for how much force a chain tensioner does, and the strongest I could find was around 200N. Don't ask me why (I really don't know), but I was imagining something on the 1000N figure because of the high-revs. Not mentioning that small radius pulleys would spin very fast.
Now comes the question: if pulley-like things were THAT good, why would Harley-Davidson motorcycles use the slide type one? Just packaging or the load on motorcycle chains overcomes practical use of bearings?
Anyone in the mood to share some experiences/ideas/information?

Thanks in advance!

Paulo Kemper
(soon pics!)

[J.R.]

I don't know about other types, but what we used last year was a gear attached to a lever arm, with a spring mounted perpendicular to the lever arm. It worked pretty well, and you could use a screw to adjust the amount of tension.

[Thrainer]

Why do you need a chain tensioner? To reduce slop or to have more teeth in contact?
Not the entire length of the chain is loaded equally. The forces on the pulley depend on the location.

Thomas

[Chris Lane]

IMO the neatest chain tensioner design I've seen is one made of a small block of hard nylon (the HDPE self lubricating stuff) cut into a convex arc shaped block with a channel cut into it to stop the chain sliding off the sides.

This block can be spring loaded or fixed.

Cheap, effective, and easy to make.

[Adambomb]

Yes, I've seen quite a bit of use from the nylon block type (most dirt bikes have around 3 of these to go with their multi-meter long chains). These generally don't create a terrible amount of friction since they're typically on the "slack" side of the chain. Another place to look for ideas on this subject is timing chain tensioners, they also frequently use this design, and spin much faster.

However, in the end, there is still some level of friction involved, and also the inevitable wear that follows friction, so instead most teams go with a tensioner design that moves the diff sprocket relative to the engine sprocket, which can be done with linkages, sliding mounting blocks, or even cam-type setups.

As for the necessity of chain tensioning, I would say it's something you can't do without. During the break-in cycle we end up adjusting tension very frequently. Too much tension gives unnecessary loading, and too little results in the chain "skipping teeth." Not only that, but any slop in the chain adds slop in the drivetrain, which makes part-throttle driving very difficult.

[Kemper]

Honestly, when I first wrote this post I had no idea why would I use one chain tensioner (lol)

But, when we first assembled our diff housing with sprocket (which came waaay too late), I found out that, without a tensioner, the sprockets cannot align perfectly with a given chain length (I believe this is not what is called "slack", or might be a source of). By pushing the chain a little bit where a chain tensioner was supposed to be, however, both sprockets fitted perfectly on the chain, so we decided to use one.

Unfortunately it is too late to change a diff housing, but the idea of moving the differential seems cool (although hard to do on a solid diff housing). We dropped the sliding block idea and adopted a rolling block one. Still having trouble to figure out the spring we will need, but we will buy a couple and test.

Thanks for the replies thou, makes more sense now, and will definitely help me if judges ask me on tech about its purpose =]

[Chris Lane]

For chain tensioning, we shimmed our diff carriers out from their mountings, until we got what we wanted. Got the shims laser cut out of aluminium.

[Wes Burk]

We run a solid rear axle so a chain tensioner is pretty much a given due to the Instant Center of the rear suspension being located so far ahead of the engine side drive sprocket. It is to take up the slack in the chain. Does anyone have any ideas or sources of approximately how much force would need to be applied to the slack side of the chain roughly directly between the sprockets (they are spaced about 18 inches apart) to keep proper tension? I have heard numbers of around 25-45 lbs. It is just easy to adjust it and feel when the chain tension is about correct, don't know if anyone has any suggested numbers.

[Kemper]

@Chris

hey, do you have pics of that? Its too late for us to change, but its good to have some ideas in mind for next projects...

[MalcolmG]

We've used a sliding block type in the past, and found that one of the big issues with it is that under engine braking the slack side becomes the taut side, and suddenly you have huge forces in the block. This is something you need to be careful to consider, because if it's not mounted to something which is capable of taking the load, it wont last long. Spring loading it would seem to help here.

Last year we developed a pivoting type which had a roller on both sides of the chain. Worked quite well but caused us a number of problems, mostly due to underestimating the forces due to rolling friction on the rollers and components getting eaten by angry flapping chains.

[ibanezplayer]

We've had a sliding diff setup for...ever until last year, when we went to a nylon wheel setup.


Makes setting up the drivetrain much easier. The sliding diff setup is a pain depending on your rear-box setup.