Qingqi QM200GY (Qlink XF200) drive chain tensioner

[forchetto]

Some time ago I read a post on chinariders.net by poster "frog" concerning a home made chain tensioner that he had fitted to his bike. The results were described by him as:

"The result is astonishing and disproportionate to the effort and expense involved - bike feels entirely different and has picked up an undefinable air of quality about it - smoother / less vibes and gear change improved. No chain slap - transmission is getting an easier time. Feels tons better."

This is the original thread:
http://www.chinariders.net/modules.p...t=6206&start=0

Ever since reading that, I looked for a suitable device to add to my bike, not because I thought the transmission showed any defects, but mainly as a project to get away from the wife and household duties for a bit longer...

I've already posted the results on chinariders, but I thought of repeating it here so I can bore even more people:

I obtained a universal trials bike type of tensioner, costing about $10-15. This had a sort of plastic sliding pad for the chain to rub on. I wasn't keen on that idea and the tensioner would not have fitted and aligned with my bike's chain at all, without a lot of mods, drilling swing arm, attaching brackets, etc.

Some tensioners have a little cog or roller instead of the slider pad, and I hit on the idea of modifying mine in a similar way. This is the result:

This is the standard tensioner as bought:



This is the ball-bearing plastic roller or pulley:



This is the tensioner modified:



Here seen attached to one of the existing bolts that hold the lower chain guard. No modifications were made to the bike at all:



Close-up view:



Yesterday I did a lot of road testing, mainly to see if the chain jumped off the roller or something, but I have to report complete success so far. Gear changing has improved, although it was already brilliant. Less chain noise and slap. The minimum non-snatch speed is now just over 2000 rpm, remarkable for a single cylinder engine. Driving at low speeds seems much more refined, with none of the slack experienced when throttling on and off.

Following the road test I set the bike up on the workshop stand and ran the engine and rear wheel to observe the behaviour of the tensioner. It's surprising how much up and down movement there is in the tensioner pivot, so this has to be kept well greased. The ball elements of the pulley bearing are best lightly lubricated as well to keep down noise and wear. The bearing balls are exposed so a quick spray with the chain lube aerosol is easily done.

The only downside I've observed so far is an increase in friction (and possibly power loss) due to the pressure applied by the tensioner. This was just empirically observed by noting how long it took the back wheel to stop, after removing power, both with the tensioner and without.

[kingmarty45]

I'm impressed. That is very clever Forchetto.

[CrazyCarl]

What are the chances of the spring weakening over time?

CC

[forchetto]

What are the chances of the spring weakening over time?CC

Pretty likely I would have thought. As I've said, there's a surprising amount of up and down movement all the time so it depends on the spring quality.

If it happens it may be better to adopt a tension spring rather than the present torsion spring. A bit like this home made device. Tension springs are easy to obtain, in lots of different grades and theyre sold by the metre: