zeeway

I have a seven year old Trek, aluminum frame, that I bought used about five years ago. I have converted it to single speed, keeping the front chain ring (50 tooth) and pairing it with a 16 tooth rear sprocket. I also installed a new single speed chain with a chain tensioner, and it works reasonably well on my daily 8 mile +/- ride on nearly flat terrain. The chain has come off a couple of times, so I added a make shift "chain guide" made out of a tubular plastic part of an old light which I attached around the chain and it is held on with tie wraps attached to the chain stay. This has helped, but my chain now makes a slight noise as it goes through the chain guide. And the chain has come off twice in the last two weeks.

I am now considering adding bolt-on horizontal chain stays, so I could delete the chain tensioner and guide. I understand it also changes the bike geometry a bit by changing the attachment point of the rear wheel. So I am wondering of this is a good idea, or a setup for disaster. Your thoughts, please.

nomadmax 

Never meet trouble halfway. There's plenty to go around.

Bat56

say what?

zeeway

My bad....horizontal....dropouts...

Dylansbob 

I've heard of such a contraption, never seen one in use.

If you're having chain derailment issues, it would be much cheaper and simpler to look over your chainline. It's possible your chainring has shifting ramps that are also contributing, but if your chainline is straight it shouldn't matter.

Are you using a freehub with a cog and spacers or is it a threaded freewheel? Is that 50t on the inside or outside of the spider?

zeeway

I am using the original chain ring- so it does have shifting ramps, but the chain line front to back is good. On the rear, I have the 16 tooth sprocket and spacers on a freewheel Shimano hub.

Dylansbob 

Does the chain typically throw to the inside or outside?

If it's to the inside, it's probably the chainring ramps. I'd still consider adjusting a spacer on the freehub and move the cog in whatever way the chain typically falls. All else fails, I'd look at the tensioner. The spring might need to be tweaked to give a bit more tension.

Scrodzilla

People do the craziest things. Just get a new frame.

dabac

I’ve seen frames with replaceable dropouts, allowing a rider to switch between track ends or verticals incl derailer hanger. Have no idea if OP has one of those.

IAmSam

Have you tried adjusting the tension on your chain tensioner?

REDMASTA

remove all parts and re-install...on a new frame.

natloz

Can you post a picture of your chain line from the back of the bike showing both cog and tensioner alignment? May help the discussion.

zeeway

Well, I think I have fixed my chain-flying-off problem...this may be akin to discovering fire, or the wheel, etc. I was looking at my bike on the repair stand and pedaling away, when it struck me that the chain was way wider than the thickness of the chain ring or the cog. The chain ring was original to my 2x11 drive, and so was the appropriate width for an 11-speed chain, and the cog was about the same thickness. In my zeal to be have a cool single-speed bike, I had replaced the chain was a single speed chain...which was much wider between the plates, and thus had room to flop around and occasionally cause mischief.

So...I replaced the chain with my 11-speed (much narrower) chain, took off my home brew chain guide, but kept the tensioner. Of course, I had to trim the length of the chain and put on one of (*#!!&**) master links. I took the bike for a trial ride, and all appears to be well. Maybe I won't use those bolt-on horizontal dropouts after all.

Thanks for your comments and ideas.