Do i really need to use a chain guide?

ACIDBURN · #1 (**permalink**) 05-23-2009, 05:27 AM

Hi guys,

Can anything bad happen if i dont use the chain tensioner on a CIF50?.

Also what if the chain is to tight/ too loose (apart from it falling off etc).

Thanks guys

Info much appreciated

leftywoody · #2 (**permalink**) 05-23-2009, 06:48 AM

loose chain's can result in sprocket prematurely wearing out and shreaded pant legs . Tight chains can add premature wear to sprockets and shaft bearings and prematurely stretch chains .

Dan · #3 (**permalink**) 05-23-2009, 06:53 PM

Howdy AB. On china girls, I had always waited for the chain to stretch out then re broke the chain so as not to use the tensioner. I had thought it was just one more thing to go wrong. The only down side is that chain now only fits that one MB and engine. (I swap stuff around a lot) On new 4 stroke, I am planning to keep it. Not suggesting either, just what I have tried.

What is a CIF50?

**2door** · #4 (**permalink**) 05-23-2009, 07:16 PM

A too loose chain can be downright dangerous. If it bunches up on the engine drive sprocket, or comes off the rear wheel sprocket it will be the best brake you can imagine. Sudden stop, for sure and can result in damage to the engine case, rear spokes/rim etc. I'm a firm believer in chain tensioners for several reasons. Chains, even good quality industrial chain will wear and loosen over time. If your bike does not have adjustable drop outs then you'll be faced with cutting the chain and using half-links to keep the tension right. Another reason I like them is that they help guide the chain onto the rear sprocket, if installed correctly. The kit tensioners have some design problems in that they often do not run true to the chain angle when installed on the chain stay. They all seem to require a slight twist to get the pully wheel exactly parallel to the chain path. In addition the tensioner bracket needs to be secured to the frame of the bike to prevent it from rotating into the spokes under load. I've used a 10/32 screw through a hole drilled completely through the bracket and chainstay and others have had good luck with a self tapping screw. Currently I have stopped using the kit tensioner bracket and have opted for a welded bracket that I know will not/ can not move. Hope this helps and it might interest you to know that Dan and I usually see eye to eye on everthing else.

Dan · #5 (**permalink**) 05-23-2009, 08:17 PM

Makes good sence Tom. Really think you should market your tensioner. Lost very first rear wheel to faulty tensioner install. (my fault entirely) Think it made me leery.

Creative Engineering · #6 (**permalink**) 05-23-2009, 08:55 PM

Acidburn,

I've looked at this too...and I don't see how it is possible. I know several people here on the forum do not use tensioners.

I've set up a few new bikes that, (just by luck), the pedal side chain and engine side chain were perfectly tensioned. The problem is that, as Tom pointed out, it doesn't last for long. A new engine chain will need adjustment almost immediately just like on a motorcycle.

Even with a decent amount of adjustment on the dropout, there's nothing you can do because the pedal side chain must also be tensioned correctly. If the pedal side chain was tensioned properly along with the engine side chain...the pedal side is going to remain correct as the engine side stretches.

The only bikes that I have seen with a decent amount of dropout adjustment have been single speed coaster brake bikes, or bikes with an internal planetary set for multiple speeds. In other words they do not use a chain tensioner...the chain is tensioned by the slot in the dropout so that the wheel can be moved back as the chain stretches.

A multispeed bike that uses a deraileur does not need a frame with a lot of adjustment at the dropouts, (it's for wheel alignment), the Deraileur takes up the chain slack.

The difference between a chain that is tensioned properly to one that is dangerously slack is less than one link.

The chain will not fall off when it gets slack...At the perfect amount of slackness the chain plates will ride on top of the sprocket teeth, and not fall off. The portion of the chain that is still seated in the sprocket will ensure that the chain will continue to ride on top of the teeth. In the first 5 degrees the chain will become TIGHT. In the next 5 degrees of rotation the chain will become REALLY TIGHT. After this the engine will be snatched from the frame, or the spokes will snap! It will happen too quick to prevent. On a motorcycle the rear wheel will lock up! On an engine powered bicycle there will be damage!

I have yet to do it, but I have an Electra here at the shop that has long slots in the dropouts for the rear wheel. I'm going to put a chain tensioner on the pedal side chain so that I can use the slots for keeping the engine side tensioned correctly. Correct chain tension is about 1/2" of up-down travel mid chain with the opposite side tight...just depends on which way you roll the wheel whether you're checking from the top or bottom. I prefer to roll the rear wheel forward and check the top, or drive side, of the chain...no reasoning behind it...just habit from MC days.

Without a great deal of fiddling around, and possibly a bit of expense, (high quality hardened chain), I don't see any way around using a tensioner for most bikes?

Jim

Tinsmith · #7 (**permalink**) 05-23-2009, 10:17 PM

Acidburn,

Just finished my first build, and after reading most of the threads on chain tensioners I opted to replace the plastic roller with a sprocket. I bored it out and pressed in a small bearing and it quieted thing down a great deal and I have ridden nearly every day for the past couple weeks with no chain problems. There are a few posts with pics showing a sprocket tensioner. When I get some photos and figure out how to post them I will show what I came up with. Nothing new, but it seems to work real well. Good Luck

**2door** · #8 (**permalink**) 05-23-2009, 10:45 PM

I've attached a picture showing what I did to eliminate the clamp-on tensioner bracket. Hope this helps. It also shows the skateboard wheel used in place of the kit supplied pulley.
Tom

Creative Engineering · #9 (**permalink**) 05-23-2009, 11:09 PM

Quote:

Originally Posted by 2door

I've attached a picture showing what I did to eliminate the clamp-on tensioner bracket. Hope this helps. It also shows the skateboard wheel used in place of the kit supplied pulley.
Tom

Nice Tom, I missed that in your original build photos.

Jim

trackfodder · #10 (**permalink**) 05-24-2009, 06:01 PM

Timely. I was just about to post a bit of wisdom I picked up from Spooky Tooth. I was asking for a drive chain offset link so I could do away with the tensioner. He suggested using an offset link in the peddle chain instead for a safer alternative. It changes the length of the chain 1/2" either way. DUH!