Mag Chain Madness MK2

Could there be a tight link on the chain, perhaps? That could cause the effect you are experiencing. Clutching at straws now really......

This always confuses me. If thetotal distance around the two sprockets is fixed then the chain cannot go tight and slack because the chain only has one length. So if its tension does vary, surely it must follow that the distance around the sprockets varies? In which case, the hole in the middle of one or both of the sprocketsis not the middle of the circle described by its teeth. So sprocket must be wonky. I suppose uneven chain wear could be to blame if it is so bad that the chain won't sit down the same depth into the sprockets at different positions.

If the tight and loose locations occur with the sprockets at opposite 180 degree angles, then the sprocket(s) are to blame. If they occurwhen the same bits of the chain arein the same place, then the chain is at fault. Maybe the relative positions of the sprockets can be changed if it's a sprocket issue? So the offset bulge (if they have one each) always has the same angle to the horizontal.

People often do not compensate with the appropriate back pressure rotation when measuring chain tension. This is profound with the high loading of the camshaft timing chain but still applies to the weaker rotational loading that a magneto creates, Trick is to rotate the DRIVEN sprocket/gear TOWARDS the turning force direction(to oppose it)that the chain is creating at at any time...then measure the slack....Les

Les, doesn't that translate to the other chain run though? This could be the reason George is seeing a variation in tension if he is only testing at one point on one run. Come on George you must have progressed by now or are you on an Easter break

I am currently rectifying what looks like the consequence of an over tight mag chain that created a fracture in the Mag platform when the motor heated up. It had been repaired with a cold stitch weld and a supporting plate back in the 60's. I am grateful for the methods and ability of modern welders.

Cheers

Jon

Hi Jonathan. I know what you're saying. With the cam chain the slack is "hidden" by the chain tensioner and one tests on the top run which can feel bar tight but if you do the correct back rotation you get to feel all the available slack (dummy cover fitted incidentally)

The same mistake can be made on the mag chain but not so profound...It is easy to just feel one run do the the rotation and check the same spot thinking it has tightened or become more loose due to the loading change.

What one also has to remember is that any difference caused by sprocket wobble is amplified by a factor of 4 times!...Eg: a 1mm wobble is + and - 1mm = 2mm..... then there are 2 chain runs (top & bottom) so that makes a 4mm difference in overall length of the chain run between tight and slack so it doesn't need much of a wobble to cause a big variation.....Les