Chain hits swingarm - What would you do?

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dimka pdx

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Hi guys,

I have been building a project off and on for a year now, and getting very close to that first ride. However, just like any project with a fair amount of mods/fabriaction, you are sure to run into something that doesn't fit.

A little background: The bike is a 81 XS 650 Special. The idea was to build a cafe looking street bike. The rear suspension is a Ducati monoshock, and I actually had to redo it a number of times before it worked well. Either way, because of the monoshock and the current ride hight, the chain hits the top of the swingarm. See pictures below (of issue and project in general).

WHAT WOULD YOU DO to fix this dilemma? Keep in mind that everything is already powdercoated, but I can definitely grind and weld on the swingarm.

I have read plenty about sprocket tensioners, but they look like they take a fair amount of space. I could do a skateboard wheel tensioner, which is also a space commitment in already tight confines. I have thought about hard mounting (two tabs...no spring) a small sprocket since I can control the tension with the rear adjusters...what do you think? Also, hard mounting a skateboard wheel?

Most of the tensioners I see are mounted on the bottom...but I need to put it on top to fix the issue. Is this okay? Would love to hear what the gurus on this forum would do.

IMG_0873.jpg

IMG_0874.jpg

IMG_0869.jpg

IMG_0870.jpg

IMG_0875.jpg


And here is a work in progress pic from this summer:
Xs650ingarage.jpg
 
does it still rub when you are sitting on it with proper chain tension? if it clears, you could make a rubbing block for the top of the swingarm. I would use delrin to make one.
 
jamesgs4 said:
does it still rub when you are sitting on it with proper chain tension? if it clears, you could make a rubbing block for the top of the swingarm. I would use delrin to make one.
Click to expand...

When I sit, it does NOT seem to rub. However, I haven't ridden it yet, so I don't know if the rear suspension unloading would cause it to start eating the swingarm heavily.

Thanks for the advice on the delrin. First I ever heard of it, but looks like it is a type of plastic. How would you recommend to mount it to the swingarm?

PS - I know there is a guy on this forum who built a VERY cool cafe racer with a similar delrin chain guide, but cannot for the life of me find the thread.
 
jamesgs4 said:
does it still rub when you are sitting on it with proper chain tension? if it clears, you could make a rubbing block for the top of the swingarm. I would use delrin to make one.
Click to expand...

Also, do you have a sense of what the proper chain tension is? I know that it usually measured by putting a straight edge on top of both sprockets and pushing the chain down on center of the chain between the sprockets...and measuring the distance between the straight edge and the amount of chain flex/droop.
 
First off damn nice looking bike but how did you not notice that before powder coating? It looks like its hitting only up front. I think you could fit a chain slide to the swing arm like a motocross bike would have. They would be flat and your swing arm is round but I think you could make one work. They are delrin as the above poster mentioned.
 
yep, i was going to suggest a bigger sprocket, you could even go for a 19 tooth front and a 38t rear. cheers

Posted via Mobile
 
yamaman said:
yep, i was going to suggest a bigger sprocket, you could even go for a 19 tooth front and a 38t rear. cheers

Posted via Mobile
Click to expand...

I don't know why I didn't even think about the sprockets and a different size. Anyhow, I now have an 18T front and a 38T rear ordered (should come mid-week).

A quick chain questioin:

Can I use two master links in a chain?

I already shortened the chain to size, and with bigger sprockets it will obviously need to be longer. When I bought my chain, I bought a 130 inch knowing I'll need to make a custom size. When I bought it, I received two master links (I didn't know once came with the chain). Can I try and lengethen the chain by using two master links and leveraging some of what was left of the orginal 130 inch chain?
 
On the chain you can but it's not reccomended. I don't think anyone makes a 19 tooth sproket. The 18 tooth almost hits the clutch push rod.
Lots of bikes have the plastic guard on the swingarm.
Leo
 
You could do a hard mount like you had asked on the top, but you will need a longer chain. Two 'master links' is not recommended, only in an emergency situation, like getting out of the desert to a gas station or somewhere. With a new chain, 2 master links usually come with it, a 'clip' type, and a 'rivit' type. I think your still going to have a problem even with the bigger sprockets. The Delrin 'plastic' is a very durable type and wears real well, almost like Kevlar. It is a bit pricey, but for the small amount you need is not going to break you.
 
Leo, your probably right about the 19t front sprocket. I'm sure I've seen it done somewhere though!

Depends on how it turns out with the 18t, but a 19t could be done, unless there is another reason not to?????????

Some have changed the clutch to a "pull" action, the actuator is on the other side of the engine then. Also the shift shaft can be converted to right foot shift. Yeah it's all major work, but if it's what you've gotta do, well it's just what ya gotta do!
 
Nearly all dirt bikes have a plastic swing arm guard. just adapt one till you see how it works in use.
 
That is one cool looking bike! Great job!

The plastic guide from dirt bikes is a good idea but it doesn't address the real problem: the swingarm is too low at the rear. My suggestion is to disassemble the shock and add a spacer to limit the downward travel. It shouldn't take much, maybe 1/4".
 
I had the same issue when I canted the shocks to put more weight on the front of mine. I run an 18T front sprocket (520), nylon chain guide on the top of the swingarm from a dirtbike, and a chain tensioner to keep it all together. Like you're seeing, it really only rubs when the bike is unloaded, but you still need to account for it.
 
dwyatt said:
I had the same issue when I canted the shocks to put more weight on the front of mine. I run an 18T front sprocket (520), nylon chain guide on the top of the swingarm from a dirtbike, and a chain tensioner to keep it all together. Like you're seeing, it really only rubs when the bike is unloaded, but you still need to account for it.
Click to expand...

Thank you!

Is there any reason I couldn't just run a tensioner, or a skateboard wheel, on top of the swingarm? It seems like that would negate the need to run a chain guard.
 
Delrin, certain Nylons, or any other suitable UHMW plastic would be fine. Delrin is a little more expensive, harder, but machines very cleanly. UHMW polyethylene is a little cheaper, and machines nicely enough with standard woodworking tools (but beware of tear-out, similar to any grainy hardwood).
There's a huge range of shapes and materials available at McMaster-Carr. Check out some of the weird ones, like Oil-Filled Cast Nylon (a 12"x1"x2" piece only $15 or so), loads of possibilities.

Chad Going's monoshock cafe has a nice plastic channel block. Is this the thread you're thinking of?
 
Last edited:
osteoderm said:
Chad Going's monoshock cafe has a nice plastic channel block. Is this the thread you're thinking of?
Click to expand...

That's exactly the thread I was seeking! You the man!

I really like his chain guard design...not to mention a hell of a bike build. Even though a few of the welds look so so, I dig the frame tubing work.
 

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