It's true of all the "interesting" things about these kits and their use - the infamous chain tensioner is by far the most likely to be dangerous even if installed "properly". As a result there is much debate and many well-meant suggestions regarding them. However I would very much like to point out that not all of these suggestions are appropriate for all bikes!
One of the ones that's been common of late is "Just get rid of the dang thing altogether" - While this
might work on a few bikes, those with horizontal dropouts, very good chains and/or low mileage I for one simply
can't do this with my bike. Without the roller to reroute my chain it would rub my chainstay and wear it badly. Not to mention that even if upgraded to 41 chain, stretch is still a factor to consider. I'd much rather spend a second with a wrench to take up slack on the side of the road than try to pull a link.
Another very common suggestion is spot welding. This is actually one of the better suggestions but is limited to those with steel bikes, access to welding equipment, and while effective - changing the tensioner's placement allows for far more adjustment than were it fixed in place. I'd also rather not take a grinder to my chainstay should I want to move/remove the tensioner.
It's been frequently suggested that drilling a small hole and adding a self-tapping screw to keep the assembly in place is good enough and it may well be - but I wonder if a screw that is small enough to not compromise the chainstay's strength is strong enough to not sheer if the tensioner is suddenly inclined to take a dive into the spokes... It may well be, but I wouldn't try this technique on aluminum chainstays - there's just not enough there to drill holes willy-nilly.
I believe by far the best suggestion is to make a custom tensioner that bridges the upper and lower bars. There's no way anything else can compete with this design. While some have welded up a permanent custom alteration to their bike - obviously one could do this with a clamping design.
I have also noticed there are two distinctly different tensioners supplied with these kits, one with a single bracket and two bolts, another with two brackets and four bolts. Having used them both I can assure you the one with dual brackets and four bolts is far superior for rather obvious reasons. Regardless of which one you use,
both the stock, kit supplied tensioners need to be put in a vice and bent to align with the chain. The chainstay is not at the same angle as the chain and should the roller guide just be bolted on without this easy modification - it's very likely to hang up and force the tensioner into the spokes or "just" derail your chain and lock up the wheel at speed. This may cause you to crash - at the very least it'll damage yer bike and/or engine.
I am somewhat limited in what I can do with my bike, it's aluminum and everything is a
very tight fit. I just wanted to say that while many suggestions made about these shoddy tensioners are correct and are made with the best of intentions - please be careful about what you may be recommending. Each is heavily dependent on the bike's material, chain clearance, and the skill and understanding of that bike's owner. I would ask a few questions about that specific bike and the relitive abilities of the builder before throwing out your favorite fix.
The best I've seen so far;
A nice option if you don't want to/can't weld;
The worst;
Not a bad idea at all - but depends on the bike;
My four bolt/dual clamp that seems to be good enough;
I will be making a "bridge" style that's a clamp design IF I cant get a jack shaft on this build, a jack shaft is of course the best way of all!
I just wanted to throw this out there because of all the things on these bikes the tensioner is by far the most dangerous, a well meaning but ill thought out modification may in fact endanger the rider more than to simply leave it alone or to make an alteration suitable for that specific bike and builder. Even welding it can be dangerous if the welder hasn't the skill or experience to make proper welds that have good penetration yet aren't undercut.
Then of course there's Retmachinist's solution, custom machined out of 6061 Aluminum, with a skate board wheel and bearings (pic 1) and the CNC machined chain tensioner by Ridley Motorbikes on magicalpancake's FELT MP Morini Build (pic 2) and toker_ace's latest sweet creation (pic 3) as well as sportscarpat's sweet custom job (pic 4);
