Time to Contribute! RD350 Cafe Build

[andrewlk]

Maybe I am still missing the point. What I was trying to say was there is plenty of room to slacken the chain (slide the rear axle forward), such that the chain does not bind or pull as the swingarm travels through its arc or contact the frame/swingarm. If the appropriate tension per the diagram (A and C at max) leaves a bit of slack at top and bottom of suspension travel, then a chain tensioner should resolve this. The only issue with chain clearance would be the location of the left pipe.

 

[jpmobius]

Nice explanation. The key point is that the actual best operating chain tension be adjusted at the max distance between sprockets which as was noted is when the three centers are aligned along a straight line. What the ideal tension is I can't say, but expect it should be slightly looser than what would be ideal for a rigid assembly given the dynamic nature of the suspension and accelerations of the various elements involved. Such assemblies invariably need a bit of slack to absorb "shock" loads brought on by adding the accelerations of independent parts under different conditions. In other words, you slam on the brake reverse loading the chain, and at the same time you hit a big bump pushing the chain to its max tightness. You might like a bit of extra play to help absorb that sort of combination of loads that a rigid assembly would never see and would allow for the chain to be a bit tighter. As to what and how sever damage you might expect, I think the likely event is that you would see elastic deformation of components (they would bend or deflect when the too tight condition occurs and spring back to normal when it loosens up) and serious wear of the chain and sprockets. I'd expect the rollers in the chain to show serious damage before breaking bearings or axles or other major components, although eventually this would seem likely. Certainly that or the chain actually breaking (which does happen) could cause obvious catastrophic problems for the bike and rider, but I think you would see signs of it coming if you payed attention (obviously lots of people are not good at this (paying attention) so big problems do happen more frequently than they should!). But you never know. Lots of horsepower, a handful of throttle with a big bump on an assembly that requires bending just might come apart all at once. In any regard, just a simple adjustment keeps it from ever being an issue.

 

[adventurco]

Maybe I am still missing the point. What I was trying to say was there is plenty of room to slacken the chain (slide the rear axle forward), such that the chain does not bind or pull as the swingarm travels through its arc or contact the frame/swingarm. If the appropriate tension per the diagram (A and C at max) leaves a bit of slack at top and bottom of suspension travel, then a chain tensioner should resolve this. The only issue with chain clearance would be the location of the left pipe.

We're not really talking about chain clearance here. What everyone is saying is that you need to make sure that your chain slack is set at that point, where A B and C are all in line. When setting your chain tension with shocks installed, that line is not a straight line, it is askew and therefore the chain is much looser at that point than it is when A B and C are in a line.

If you were to set your chain to factory specs (with shocks installed) after changing the travel of the swingarm and/or ride height, it will cause the chain to be far tighter than it should be when A B and C are aligned, which is what is being discussed as potential to damage parts.

Judging by the steep swingarm angle and my guess to your rear wheel travel, the point where it is a straight line will probably be right around where your tire would "hit" the frame (looking straight across at it -if you had a pan under there, idk whats really there), so you may never be able to quite get the 3 points in a straight line if it in fact bottoms out before you reach that point.

 

[andrewlk]

Thanks JP

For reference the rear axle travels 2 7/8in before shocks hit their bump stops. At that point there is still 1/2in frame/tire clearance. They are 14.5in overall.

 

[andrewlk]

Been riding a few months now - all is well! Still want to mess with brakes this winter, but just enjoying it for now.