Two Stroke Motocross
Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: cnrcpla on April 23, 2013, 10:28:32 PM
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What's the best tension for a chain? I was doing 3 fingers between chain and swing arm on my old chain, but since I got a new, different one, it's fallen off twice now and more recently has caused me to wreck. I'd like to be able to trust it again, but I don't want to over tighten it... Two fingers maybe?
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try calling the service department at a dealer that sells the brand that you have. they should be able to give you an actual spec distance for your bike.
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i do the old three finger trick, from the back of the slider. where are you checking it at?
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At the back of the slider as well. It was holding up fine up until my last woods ride, it slipped off, jammed up in the swing arm, and locked my rear tire. Wiped out and had a fantastic time getting the thing off. My sprockets are literally brand new too. I don't think chain brand should have anything to do with tension, but I'll try and see what I can find about the specific brand. It's a D.I.D X ring.
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Maybe covering something's you already know but here we go. First the wheel must be aligned directly with the counter sprocket by on a crate with the bike in gear put reverse tension on the chain. Eyesight from the rear sprocket looking up to the counter should have the chain looking like a straight line. Once this is correct when adjusting tension turn each adjuster bolt counting 1/6 turns and turning the other side by the same number of 1/6 turns to maintain the original alignment. As for the actual slack the best way to figure for any bike is to remove the shock and lift the rear wheel to the point where the most slack is needed to avoid over tension. Adjust to "not tight ,not loose". Install the shock back on and now find a 2 or 3 finger spot to gauge things by as a baseline and use this going forward. repeat for each bike you own as the are all close but slightly different (modern bikes). Occasionally check the alignment from the rear to the countershaft (and after any crash) and you should be good. I have never thrown a chain since my 78 RM100 so I think my methods (which is just chains 101) works.
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I'll double check the alignment, I've wiped out a few times since. I'll also do that shock trick. Thanks guys
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Where is it derailing ?
from front or rear sprocket?
Tension or alignment will usually cause a front sprocket derailment, chain guide problems usually cause rear sprocket derailments.
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Its been derailing from the rear. Maybe the chain guide is bent?
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Good place to start looking, as most derailments occur when chain enters the sprocket, and the system runs counterclockwise (at least in the southern hemisphere) a front derailment would happen on the top of front sprocket and bottom of rear (chain guide area).
Also check chain and sprocket have the same pitch..
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At the back of the slider as well. It was holding up fine up until my last woods ride, it slipped off, jammed up in the swing arm, and locked my rear tire. Wiped out and had a fantastic time getting the thing off. My sprockets are literally brand new too. I don't think chain brand should have anything to do with tension, but I'll try and see what I can find about the specific brand. It's a D.I.D X ring.
I meant brand of bike. If you call the dealer and tell the service department what model bike you have they can look in the service manual for you. All service manuals have a chain slack measurement that can be checked with a ruler.
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As your rear suspension travels thru. it's arc the tightest point will be when the countershaft sprocket,swingarm pivot and rear axle are all in a straight line. You want to adjust your chain tension for this position. Are your swingarm pivot bearings getting loose?
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SachsGS I agree, most incorrectly check chain tension while the bike is on the stand... The correct way is to remove the rear shock, cycle the tire up to find the point where the chain is the tightest. Set the chain / wheel adjusters correctly and then re-install the shock.
That's what I've always done, but I've then taken it one step farther. Once its set correctly I'll make a measuring block. I'll put the bike on the stand, letting the tire droop on the stand. I'll take a block of wood and use it to create a tool that I can use to quickly check the chain slack.
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Last time I had a derailment issue it ws due to the swingarm pivot bearings being smoked. Just a little play in those bearings translates to a LOT of play at the back wheel.
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Nope the swing arm bearings all got replaces recently. Linkage, pivots, and even wheel bearings were all done along with new sprockets and the chain this winter. I'll be doing the shock trick and making a tool to measure the slack once I have it dialed in, thanks for the ideas guys
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Rear chain guide was bent
Got it all straightened out now, so hopefully no more derailment. I feel stupid not to have noticed that 
Also set it to the right tension with the swing arm in the correct place. Its about two fingers from the top of the chain guide on top.
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SachsGS I agree, most incorrectly check chain tension while the bike is on the stand... The correct way is to remove the rear shock, cycle the tire up to find the point where the chain is the tightest. Set the chain / wheel adjusters correctly and then re-install the shock.
That's what I've always done, but I've then taken it one step farther. Once its set correctly I'll make a measuring block. I'll put the bike on the stand, letting the tire droop on the stand. I'll take a block of wood and use it to create a tool that I can use to quickly check the chain slack.
I agree with eprovenzano, Great way to keep your chain tension the same every time. That is what I do as well. I use a small piece of plywood that I cut out when I do the measurement the first time when the shock is still off. Once everything is buttoned back up you can use the piece of wood to reset it back the same every time. For more than one bike write on the wood with a sharpie so you can know which piece to use for each bike. Takes a while the first time but after that is is much easier and true to specs.
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I will do that for my bikes from now on make up a template and presto good to go. Q is it better to do this with a new chain and sprokets or is wear and stretch negligable because slack is slack whether it is new or old.
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As for me, (others may feel different or have another opinion) but I do it one time for the bike and use the same template from then on. Only time I have rechecked is when I have done something like had the rear suspension redone or put in new swingarm bearings but it is only because I have everything already off and I am basically just rechecking. I have never had to make a new template for a bike after I made the first one. But that is just me.........