chain tension

Lukesky36

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Oct 3, 2018
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Did you ever think of motorcycle chains like dirt bikes they all have minor slack in them and they do not derail its not a design for them to come off ever. same concept here on these bikes
 


FurryOnTheInside

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Sep 23, 2013
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in general in industry there is no protection against that event when chain goes in high tension, so it will lead to damage of equipment (tearig engine, axle apart)?
on a motocycle chain is adjusted the same way as on a single speed bike, so right alignment is fixed firmly; but if something gets stuck into chain and makes it in high tension it will break engine and other parts?
Usually denim, lol. People get their baggy jeans chewed in the chain ring of their BMX just before they hit a jump and crash hilariously.. Never happened to me, honest. :X3:
I haven't damaged any bikes that way. Though all my single speed bikes have been heavily built BMX bikes.
Pants ended up with a few patches though. :LOL:
 

FurryOnTheInside

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Would this one work better than basic one sold with kit?
A spring tensioner can be used in addition to a fixed tensioner on most bikes (which require the chain to be lifted up to clear the chain stay).
If your bike does not require the chain to be lifted above the chain stay (the frame) then you can use a spring tensioner on its own.

In your attached picture the spring tensioner is doing too much of the work. We can see in the picture the angle of the chain wrapping around tensioner pulley.. It is lifting the chain up to clear the frame, which is a job suitable for a fixed tensioner and not a spring tensioner.
Because..
The spring, even if it's a heavy spring will be defeated every time you bump start your engine, every time you engine brake, and every time you go over a bump/pothole. Over a bump/pothole the chain won't just be straightened (as with bump starts) it will be able to sag downwards. Looking at the picture I can see that the chain will swing up and down a long way and will hit the frame frequently.
Then lets think about the top run of chain. When you bump start and the bottom run of chain is pulled straight, all the slack transfers to the top. The slack chain is feeding onto your 10T engine sprocket.. You know, the notorious 10T engine sprocket? We really need to have minimal slack in the top run of chain during the bump start.
(personally, even with minimal slack I have added a chain tube (aka slider) to help feed the chain on straight, and modified the case to absolutely prevent derailment from the 10T)


It is possible to make a spring tensioner that has limited downward travel! I don't know why companies are selling spring tensioners without this function)
If the tensioner cannot move downward beyond the point where the chain is close to hitting the frame then it may work.
I say "may" because there are a few nuts and bolts to figure out in these situations, and you have to see if you have the space. You also need to know this rear tensioner has very little flex so that it always feeds the chain straight onto the rear sprocket.
A fixed tensioner is very easy to make with sufficient rigidity because it has no arm moving on a pivot, it's just a pulley on a hardened alloy plate attached to the frame at both ends (with preferably four P clips or U bolts), without rubber.

Spring tensioners are fine for quietening the rattle and throb of a normally tensioned chain.
The acceptable and optimal, normal amount of slack (that we all need to have to prevent excessive wear and drag) can just be a bit noisy and can sometimes be felt through the bike. The spring tensioner can help to calm things.
(I just use a far lighter chain than the kit #415, so don't feel it's necessary but with the mass of the #415 it is a good idea.)

The albums of @gary55 show well thought out bikes with #415 chains which are lifted by a fixed tensioner and "quietened" by a spring tensioner mounted to the engine.
 
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