Newbie Observation/Question

Discussion in 'General Questions' started by layboomo, May 29, 2009.

  1. layboomo

    layboomo New Member

    Hi although I'm fairly new(OK very new) to the MB thing, I'm not new to bicycles and it sure looks to me like many people are making use of chain tensioners instead of removing slack in the chain itself! Shorter chain lines are always better....what am I missing? I'm waiting for the parts for my first build but I would never try to take up that much slack with that mickey mouse little tensioner that comes in the kits. If I'm wrong someone please enlighten me.

  2. srdavo

    srdavo Active Member

    In my case, I need to use the tensioner for the chain to clear the chainstay. believe it or not, the tensioner works really well.
  3. s_beaudry

    s_beaudry Member

    Same here with my last build with the 66cc frame mount...

    Would of shortened the chain, but the tensioner kept it off the frame, so I had to use it!
  4. layboomo

    layboomo New Member

    Thanks Dave. I'm trying to gather as much information as I can before my parts arrive,but that kit tensioner just mounted on one side looks weak to me? I'd be afraid that it would be pulled into the spokes. I can see where you would need help on certain bikes to clear the chainstay...but only supported on one side just doesn't sit right with me? :thinking:
  5. HoughMade

    HoughMade Guest

    I need the clearance on the chainstay too, but from a basic standpoint, the chances of both chains being able to be adjusted to the proper tension by wheel movement alone is about 0.5%. It does happen, but not often.

    With the in frame 2 strokes, the engine can be spaced to eliminate the tensioner in some circomstances, but with my 4 stroke, I have no fore-aft adjustment, so a tensioner is a must.

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    Last edited by a moderator: May 29, 2009
  6. ENO

    ENO Member

    Chain tensioner

    Hey Layboomo..ENO (Down Under)..Yeh cheap tensioner (chinese HT)..What I am going to do is use a Skateboard wheel that has ball bearing racers and attach two large steel washers either side to act a rails to ensure the chain doesnt slip or jump off if the chain becomes slack. And yes..if the chain breaks and tangles in the back wheel..goodbye spokes..major problem..I also bought a better quality chain from an outlet that supplies chain for chainsaws and ride on mowers etc..Cost me $15 AU for a ten foot length which is enough for three chains on our Schwinn Stingray chopper..The bike outlet wanted $30 for a replacement chinese one...Links $5 each (bike shop)..33 cents at chain dealer...Welcome to MBc..When I organise the tensioner i will put a pic on the thread or in MY ALBUM..See ya Good luck ENO (Oz)
  7. Layboomo,

    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: 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 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?

  8. duivendyk

    duivendyk Guest

    The problem with chain tensioners is that ,when the bottom part of the chain tightens up due to rapid deceleration (the engine starts to seize up for instance),the tensioner is subjected a large sideways force,which may bend the assembly so that it may get caught in the spokes,with potentially disastrous consequences.The more pronounced the 'kink' at the tensioner is, the larger this force will be (approximately proportional to the kink angle) ,so from 5 to 10 degrees the force will double for instance.Therefore it's not a good idea to use a tensioner to clear something if the angle gets to be substantial.The notion that chains 'stretch' is incorrect,the links don't stretch,what causes the increase in chain slack is wear at the roller pin bearings.It is much safer to have some adjustment at the engine mount or cure the excentricity of the rear sprocket with a better mounting, in order to get rid of them alltogether
    Last edited by a moderator: May 29, 2009
  9. CatonCam

    CatonCam New Member

    :grouphug:That sounds like a fair summation.:banana::banana::whistling::ack2:
    Last edited: May 29, 2009
  10. Junster

    Junster Member

    You can shim the rear mount on a frame mounted engine to adjust the motor drive chain if you don't need the tensioner for frame clearance. I used a tensioner for about 2 days while everything was settling in. My rear dropouts have no adjustment at all. I don't remember who's idea it was originally but it's called a tee shirt shim cause of the shape while it's still flat. This works great on Mt Bike frames. I still think the best tensioner is no tensioner.


  11. layboomo

    layboomo New Member

    Thanks for the replies guys! I'll have to wait and see what my chain stay situation is,but even if I need a tensioner I can't see myself pushing the chain way up and creating a sharp deflection......that just seems wrong to me? Of all the tensioner solutions I've seen here so far I like the ATV tensioner from TSC best. I like the simple clean mount on the down tube away from the rear wheel and spokes. The skateboard wheel is also a great idea Eno. Thanks! Motor shims are also an option,but it really depends on how it all mounts on the bike and I won't know that till next week.
    Last edited: May 30, 2009
  12. layboomo

    layboomo New Member

    So I'm waiting for my parts and kit to trickle in this week and I find this on CL as a donor bike possibility for $50! I already have a nice set of Ritchey Slicks and rims in the garage looking for a home. Seems like it might be a better donor than my Cutter with the 700c wheels......thoughts?

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  13. Junster

    Junster Member

    I think it depends on how tall you are. If you look at how close the top tube is to the down tube on the neck of that bike. It suggests that's a pretty small frame. It's a good brand if it fits you.
  14. layboomo

    layboomo New Member

    Well I'm 6' and I'm planning on using a 5" riser bar on whatever I build so I'm not leaning over the tank. That bike frame is actually larger than it looks and it's 30" from the BB to the top of the seat post. The Specialized frame geometry sith the angled top bar makes it look smaller than it actually is.
  15. Junster

    Junster Member

    Cool, I had a Specialized Rocl Hopper Comp a few years ago. I think it was easily the best bike I ever had.
  16. layboomo

    layboomo New Member

    Thanks I tried mocking up the Cutter and there were far too many fabrication and clearance issues for a HT kit IMHO. I will have the specialized frame tomorrow,but I just mounted the sprocket on the 26" wheel I'll be using and it went together Sooooo much nicer that the Cutter wheel! It fits like your first Build with the 1 rubber spacer on the inside.

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