DIY chain tensioner

[supermanotorious]

loose chains are bad for all of us, I've long considered making a tensioner but now I'm getting down to business, THIS site gave me inspiration, the spring is called a torsion spring and I'm ordering it from HERE

I'll make the "arms" from scrap flat stock laying around my shop and take an old skateboard wheel and bearing set for the contact point.

I'll take lots of pics and share at that time.

 

[fodio]

Great! I started to build a tensioner weeks ago but got stuck in the process. I'm using 22T #35(the only one I had available) but I think it is to big.

If you want I can send details of each part.

 

[qtband]

Where can you get a sprocket with a bearing on it like they use in your first link?

Edit: Nevermind. Found it at McMaster Carr

 

[supermanotorious]

Any chance you can create a "slot" in your flat stock so you can adjust the height of the sprocket? You could drill two holes then use a jig saw to cut the slot. Then you could weld the flat stock to your frame and adjust then adjust the tensioner for your chain.

Great! I started to build a tensioner weeks ago but got stuck in the process. I'm using 22T #35(the only one I had available) but I think it is to big.

If you want I can send details of each part.

THIS is what qt found!

 

[supermanotorious]

I'm looking at getting the return torsion spring from Grainger now, what are your guesses as to the deflection angle of the spring in this set up? 90, 180, 270, or 360?


EDIT: FANTASTIC pictures HERE

 

[supermanotorious]

well I watched their video, in the above picture, the tensioner is at rest and it takes some imagination but I can now tell is a 180 degree deflection angle, if you see the picture when the tensioner is "loaded" or you watch the video you'll get it

 

[machinist@large]

If you decide to run any type of spring loaded tensioner, be aware that you will need to be on top of keeping your chain lubricated. In a standard fixed spacing application, the unloaded side of the system allows lubrication to work into the guts of the chain. That lowers the amount of lube you need.

Under constant tension, you won't nessisarily need more lube for your chain, but you need to monitor what kind of shape your chain and sprockets are in. If you see a red rusty substance building up on the chain and sprockets, then you don't have enough lube.

And while I could start a debate about the best chain lube, a cheap oil can full of clean, new motor oil (the same as what you're pouring into your engine) is a darn good start. And for the record, your chain has proper lubrication when it's bathed in oil: if you're a neat freak that's more worried about looks than function, you're on your own.

 

[fodio]

Where can you get a sprocket with a bearing on it like they use in your first link?

Edit: Nevermind. Found it at McMaster Carr

In Costa Rica I found just regular sprockets and bearings, so some lathe work was required.

 

[fodio]

well I watched their video, in the above picture, the tensioner is at rest and it takes some imagination but I can now tell is a 180 degree deflection angle, if you see the picture when the tensioner is "loaded" or you watch the video you'll get it

Then tensioner should be able to move just a little bit more than 90* (ie 120*). This will depend on the sprocket size. So 90 won't be enough so the next one is 180.

 

[fodio]

Any chance you can create a "slot" in your flat stock so you can adjust the height of the sprocket? You could drill two holes then use a jig saw to cut the slot. Then you could weld the flat stock to your frame and adjust then adjust the tensioner for your chain.




THIS is what qt found!

It is possible, but my original idea is to use a normal extension spring. The tensioner will be connected to the frame with a bolt and will swing in a similar way as your proposal. The spring will be connected between the frame and the flat part of the tensioner.

I'll try to get a torsion spring.

 

[Badot]

I'd like to add a few things to the original post...

One, the article doesn't mention that the chain tensioner needs to be located on the slack side of the chain (when the engine is pulling) or else it won't work properly.

Two, the article doesn't mention that a chain tensioner of that type shouldn't be used on vehicles which exhibit any engine braking unless you want massive driveline slop and thrown chains.

Three, I can't discern any method of which the pictured tensioner stops at the most tensioned point. So as soon as it hits vertical, there's nothing stopping it from continuing on its arc and suddenly releasing all the tension it's previously held.

Also worth noting, once a chain has stretched more than about 2%, the wear on your sprockets start accelerating massively, whether tensioned or not, and the chain should be replaced.

 

[fodio]

Where can you get a sprocket with a bearing on it like they use in your first link?

Edit: Nevermind. Found it at McMaster Carr

Look at this one....they also have #40
http://www.surpluscenter.com/Power-...T-1-2-BORE-35P-IDLER-SPROCKET-1-2408-18-A.axd

 

[Sinbad001]

Why do you think you need a tensioner? Have you ever seen one on a motorcycle? If your chain is loose, adjust it. If your chain is coming off then your sprockets are not lined up properly.

 

[mckutzy]

On custom cycles and other machines, sometimes you can't adjust via the axle(my bike for ex), so a tensioner is needed.
Obviously this is one of many options out there.

 

[OzFab]

Have you ever seen one on a motorcycle?

Umm, the tensioner on my kart uses pit bike parts...

 

[fodio]

Why do you think you need a tensioner? Have you ever seen one on a motorcycle? If your chain is loose, adjust it. If your chain is coming off then your sprockets are not lined up properly.

There are an important number of motorcycles with chain tensioners that touch the chain not just the adjustment of the position of the rear tyre.

Look a this:
https://www.google.com/search?q=mot...PksASD2IKIDA&ved=0CAkQ_AUoAg&biw=1600&bih=805

 

[Badot]

There are an important number of motorcycles with chain tensioners that touch the chain not just the adjustment of the position of the rear tyre.

Look a this:
https://www.google.com/search?q=mot...PksASD2IKIDA&ved=0CAkQ_AUoAg&biw=1600&bih=805

That all looks like a bunch of poorly designed aftermarket garbage.

Here's the thing -- if you're accelerating, the top of the chain is under tension. If you're coasting, nowhere is under significant tension, and if you're engine braking, the bottom is under tension.

When you put a springloaded tensioner on the bottom side of the chain, if engine braking is introduced, the tensioner will pull back to its untensioned position, introducing lots of slack into the top of the chain (very dangerous) and a large amount of play in the driveline (also very dangerous).

So if you add on a ratcheting system (which I don't see in any of those photos by the way) and it won't go slack under engine braking... problem here is that anything with rear suspension NEEDS a little slack or else your chain and sprockets will be massively overloaded from suspension travel (very dangerous). Even if you don't have rear suspension, the uneven stretching of the chain will, again, massively overload the final drive.

Again, I'll mention that none of those devices appear to have a max tension stop meaning as soon as they reach that point, 100% of the tension they've previously held is released (very dangerous)

Yes, you can add modifications (such as backlash on the ratchet system) to make it mechanically feasible and safe. No, it won't be worth the work unless you're doing it to enjoy the project rather than for the end result.

 

[Sinbad001]

^^Agreed^^

Most go karts and ridged mini bikes don't have adjustable rear axles, so the engine mount is slotted for chain adjustment. If you are making a custom machine and don't provide for chain adjustment, it is a poor design.

 

[supermanotorious]

my machines do use slotted engine plates but I find it a pain to slide the engine for the perfect tension, additionally they do not have engine braking since the tranny is a TAV, the spring tensioner/chain combo will be designed to not have enough travel to "flip" over to "no tension"