Your task young paddle-on is to find a inexpensive mod, a cost effective bearing that will fit in the alloted area.

too bad you're on the other side of the mountain.

emailing you some pic's

The number of blowups is really small. Its just made a lot of when it happens. Avoiding a problem is easy. These things arent "maintenance free" but they are generally dependable & easy to keep on the road. The cam chain adjuster doesnt just explode for no reason. It requires being ignored & allowed to go past a limit. That can be avoided without much effort & there are mods available to make it dang near impossible.

ok, if lower gear is 60mm, and turning at 6500 rpm, the proposed bearing is doing 26k.... well within spec.... i think we have our bearing locations at opposite ends in our visions... the most efficient method of taking up slack in a chain is extending the distance between gears, but short of stacking stainless shim stock head gaskets, that's impossible in this situation.... next comes wrapping the chain further around the larger gear on the slack slde(this is what the forward shoulder of the rear tensioner does when new, though only enough to pilot the chain down the tunnel)... it has the added benefit of decreasing the per-tooth load on the driven gear (in theory, but with as little actual slack as these chains have, it probably wont be a factor in this example)... about the least efficient method is what happens when the plastic wears, wrapping the slack side of the smaller gear... this is what the vershlagy does.... i checked how the dr650 handles slack adjustment, and it's basically the same grenade adjuster, just designed to go through the back wall of the chain tunnel in the jug...this puts the adjuster in a place where it only ratchets out 1/2 as far to do the same amount of adjustment, gives it less leverage advantage to bend the tensioner, and moves the "wrap" to a midpoint between both gears... that's why no reports of the same problem.... my idea is to use the bearing to tuck the TOP end of the chain, on the slack side, closer to the centerline of the 2 gears... either by using a modification of the original tensioner form (and retaining auto adjusting), or, if that proves too daunting a task, by using the existing pivot bolt for the tensioner( in the head, not the adjuster in the case), as a pivot point for a dog-legged lever, with the bearing at the tip..... manual adjustment done by a bolt/jamnut combo drilled and tapped through the rear wall of the head.... at this location, the bearing will be awash in the bearing splash of the center and right cam bearings, so im fairly certain an adequate supply will be available to it.... as to the mounting to the adjuster/tensioner, as the ground sleeve already requires a press step in the assembly, it would be easiest to to just make the 5mm pin an interference fit to the holes in the bracket, and press it through the 3 at once, ensuring it can never unscrew, un dove tail, etc.... i agree a ball bearing is a much more ideal form for the idea, but the available space constraints kind of demand a needle bearing..... still not happy with 18 bucks for the bearing sleeve combo, though it will be the most expensive component by far....

I think the intent of the current system is to wrap the driver sprocket with as much chain as possible.  Since it's greater than 180° wrap, the likelyhood of the chain disengaging is minimised.

I've seen almost no wear on the leading edge of the tensioner guide and I don't think it's designed to wrap the chain around the driven sprocket.  And being that this gear is twice the size of the driving gear, don't think chain wrap is important here.

I was thinking of a manual adjuster when we were discussing this long ago.  There is a spot on the lower rear cylinder where a fin or two could be faced off and a threaded hole created.  

I also looked at what it would take for the chain to be disengaged.  Manually, very difficult.  But this is why some chains are broken I'm sure.  As when the chain climbs the sprocket enough to disengage, it's about to hit the case.