Chain guard gap

Aug 14, 2019
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I'm about to make a chainguard, but don't have anything to compare and get measurements. I plan to make a full wrap guard and am curious to know how much gap should there be between the outer edge of the chain to the inside surface of the guard?
 
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Jun 13, 2015
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I've never made a chain guard from scratch, but fitted a bunch and removed almost as many in anger, so take my advice for whatever that's worth. I assume you're talking about a single rear cog, so there shouldn't be much lateral movement of the chain at all. Every bike is different, though, and a bike that's flexible will need more clearance. On a stiff bike, I'd probably go with 1/4", but down to 1/8" if it's a really solid frame. On a floppy bike (like the step-through Spaceliner Interrobang is based on), a 1/4" might not be enough. Also, I don't know how big you are, so YMMV as far as how much the floppy flops (I'm 5'11", ~175 with long legs requiring a tall seat post that can put a lot more torque on the frame than it was ever intended for). Of course, the other thing to consider is how much space you have between the chain line and the plane of the crank's rotation, so make sure there's enough clearance there, as well.
 
Sep 7, 2014
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curious to know how much gap should there be between the outer edge of the chain to the inside surface of the guard?
You don't need much of a gap.

bench.jpg


Will depend a little bit on the straightness and size of the chain ring, bottom bracket flex and mounting point of the guard.

That's a Schwinn which is fairly stiff and has the guard mount on the bottom bracket and it's a fairly small chain ring.

Something with a more flexible frame, larger chainring and guard mounted to the seat tube will probably need more of a gap.
 
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Jul 16, 2019
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I roll on a Worksman trike at my job. Thing gets abused and neglected pretty badly. Sometimes, when I'm riding, I can hear the chain grating on the guard. I stop, stand on the non-drive side, and kick the guard until it doesn't seem to hit anymore. How much gap? Probably two or three kicks worth. I seriously love that trike, have told my manager that it belongs to me if ever we get rid of it.
 
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Here is what I do. I attach the rear of the chain guard on one of the stays or weld a mount to the rear chain stay that I have removed from another big box frame. Then make an "L" out of mild steel and on the part of the "L" that goes next to the bottom bracket make a slotted hole. Bolt the long end of the "L" to the chain guard. Hold the "L" next to the bottom bracket so you have an idea of where to drill a hole in the bottom bracket so that the chain clears. Drill the hole and tap it using vice grips to turn the tap. mount it using a bolt in the bottom bracket and slide the chain guard back and forward until it clears the chain. Tighten the bolt, check for clearance again and then put very small tack welds in the bottom bracket along the "L". Try it again. Don't be surprised if you have to remove the tack weld as it may not be quite right, try again. Once it is good put a complete weld between the bottom bracket and the "L". This has always worked well for me but involves a lot of fussing around. Use an old chainwheel when welding because splatter, flux burn and heat will ruin a nice chainwheel. I could take a picture, if interested, of the 1940s Columbia frame I'm working on after I dig us out from the blizzard.
 
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Aug 14, 2019
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While I appreciate everyone's responses, I obviously misspoke when asking my question. I was wondering how much clearance is usually used from the top of the chain to the inside of the guard.

I plan to make my mounts adjustable.

Here is a cardboard mock up of what I plan to make.

PC020787.jpg
 
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While I appreciate everyone's responses, I obviously misspoke when asking my question. I was wondering how much clearance is usually used from the top of the chain to the inside of the guard.

I plan to make my mounts adjustable.

Here is a cardboard mock up of what I plan to make.

View attachment 109722
Put on the chainwheel you are going to use and center it so chainwheel opening is in the center of the chainwheel. See if it wobbles as they often have a tight spot in the chain. Then make your mock up so that you have enough room to get upper fingers or tools in to put on and take off the chain. With full chain guards you might have to take off the guard to get the chain back on if you aren't careful with your design. My Ganna bicycle has an enclosed chain guard and you have to take the cottered chainwheel off to get a thrown chain back on or even to change the tire. I would say that centering of the chainwheel and chain access is the most important consideration for your design.
 
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Here is what I do. I attach the rear of the chain guard on one of the stays or weld a mount to the rear chain stay that I have removed from another big box frame. Then make an "L" out of mild steel and on the part of the "L" that goes next to the bottom bracket make a slotted hole. Bolt the long end of the "L" to the chain guard. Hold the "L" next to the bottom bracket so you have an idea of where to drill a hole in the bottom bracket so that the chain clears. Drill the hole and tap it using vice grips to turn the tap. mount it using a bolt in the bottom bracket and slide the chain guard back and forward until it clears the chain. Tighten the bolt, check for clearance again and then put very small tack welds in the bottom bracket along the "L". Try it again. Don't be surprised if you have to remove the tack weld as it may not be quite right, try again. Once it is good put a complete weld between the bottom bracket and the "L". This has always worked well for me but involves a lot of fussing around. Use an old chainwheel when welding because splatter, flux burn and heat will ruin a nice chainwheel. I could take a picture, if interested, of the 1940s Columbia frame I'm working on after I dig us out from the blizzard.
IMG_1727.JPG
 
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