Cracked Swingarm!

Last Sunday, while fueling my truck, I was checking out my bike on the way to ride. I noticed an inch-long black squiggly line on my swingarm. Upon further inspection, I realized that the weld was cracked. Not sure how long it had been there, I marked the crack with a sharpie marker before I started the ride. I figured that if the crack doesn't get any bigger, I was OK to ride. I stopped every couple of minutes to check the progress during the ride. About 5 miles into it, I went over a particularly wooped-out section of trail and decided that I should check it real soon. The crack had grown a quarter inch :) . Time to pack it up while it was still fixable. Here's what it looked like:


I took it to welding shop that the local Yamaha dealer recommended and the gut did a fantastic job. He prepped it by grinding the crack then reinforced the weld with a nice, thick bead of aluminum. And he only charged me $35. I got it back together and went for a hard ride yesterday. Everything seems as good as new. It was lucky that I noticed it when I did. A new swingarm is $500!

[ November 24, 2001: Message edited by: Rich in Orlando ]

Rich, Why does it look so flat on top of your swingarm? Like the weld on top was grinded down for some reason. This may have played a role in the cracking of your swingarm. Also whats with the 4 lines of marks on top, whats the cause of that? ~Hitman~

I used foam and a bead of silicone to keep my chain slider from rubbing a hole in my swingarm!

Those lines are where the chain wore through the chain slider and ate up the swingarm. I bought the bike used and I think the guy who had it before me had ground off the weld bead to keep the chain from wearing through. When the guy fixed the crack, I had him fill in those grooves and weld a bead across the top of the swingarm like it's supposed to have.

I think part of the reason the crack formed was due to a very loose chain. I had over 2-1/2 inches of free play in the chain just before the crack formed. I think the chain was hammering the top of the swingarm and contributed to the crack.

I now use double sided tape to secure the chain slider to the swingarm, as suggested on Thumpertalk. A friend of mine with a YZF brought up the idea of glueing a thick piece of rubber (like a truck tire innertube) to the swingarm first, then installing the chain slider. I may try this when I replace the slider again to keep the swingarm from getting damaged.

The TM Designworks chain slider may be a solution to this problem. Just be prepared for the increased chain slap you'll hear with it. My swingarm shows no wear at the trouble spots.

I ground down the top part of my weld just like that about 2.5 years ago because if you don't, it pushes up the chain slider and the chain will keep rubbing a hole through it. I'll check my bike out today and see if there is any sign of a crack like the one pictured above and report back later.


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