Topic: chain tension, too slack when hot?

[kajtek]

hi all,

i have a situation that seems fairly odd to me. i set my chain tension at tightest point to 20mm slack (as the service manual says for a cb400f), but once the bike is warmed up the chain is much looser, more like 35mm (guesstimate, im going to measure before and after on my way to work tomorrow). this extra slack makes everything clunkier and less fun to ride when its warmed up.

when cold, rides great. when hot, extra drive lash and have to adapt riding style.

so should i be setting my chain tension when hot? or somewhere in between?

for clarity, bike is a 78 cb400f, with a 520 o-ring chain, steel front, alloy rear sprocket. cleaned with simple green, lubed with motor oil (as ran out of the spray on stuff).


thanks

[Dimitri13]

How old is the chain? I've never heard of a chain expanding when it's hot. Are you sure it's not just stretched/kinked, and when you measure it at one point, it's 20mm, and at another point, it's 35mm? A stretched and kinked chain will make everything clunkier.

[kajtek]

chain is pretty new, about 3 months ~ 1000miles. definately not kinked or stretched, clean and lubed, but at the end of a ride, ive checked at a few points by rolling the bike, that there is definately more slack. come back later and its tighter again. its goofy i know, but its definately happening!

tonight i will measure my chain slack when i get home (hot), leave it a few hours and measure again (cold). will try take protos to prove im not crazy..

chain is a tsubaki omega o-ring 520.

ashley

[trueblue]

It is reasonable to expect the chain to expand and get slacker as it heats up, it is metal after all, and it is surprising how much metal expands as it heats up.  If I had to guess without seeing the bike, I would guess that when you've cleaned the chain it is possible that you could have washed some of the lube out of the links and it is heating up more than usual.  The internal pins on an o-ring chain are lubed for the life of the chain, the amount of chain lube that gets in there is very minimal, the reason for chain lube on an o-ring type chain is to lube the rollers on the sprockets.  My chain on my 650 gets a quick squirt of chain lube every few weeks and that is it, I never wash it and I regularly have short stints on dirt roads, so far I have put 7000km on the chain that is on it and have never had to adjust it. 

[kajtek]

hi true blue, i see your point regarding washing out the lube, but i was very careful when cleaning, and id noticed this happening before id ever cleaned the chained. (lubed from new opbviously).

will measure the difference between hot and cold tonight

[trueblue]

The other thing that can cause a chain to overheat is it being too tight, are you checking it with your bike on the ground with the equivilant of your weight on it or on the centre stand, on my 650 with weight on it, it has about 20 mm slack but if I put it on the centre stand I have about 30mm slack and if it is sitting on the side stand it is about 25mm slack.  If you are adjusting it on the centrestand then when you sit on it, it will pull too tight and cause the chain to overheat and this will cause excess slack, I can't be certain this is your issue though but it is worth looking into.