372 chain tension problem

[Mattyo]

365/372 and oe and xtorq have same crank, yes

interesting idea of a chunk of wood suddenly taking up space on the sprocket, never thought of that. i can believe that that might bend a crank....

metal shrinks when it cools, so how does a chain get looser when it cools?

i'm not a faller, just a guy that rebuilds junk saws

The chain fits considerably looser on the bar as they cool. Its most importent to check tension after a short break for this reason or a high
percentage of throws will accure within rhe first few minutes of start up.
You may be on the right track. If say it was on the tight side, it does get tighter with the heat. Two factors that may create friction,, One being centripital force that's greater as RPM increases and the other when the cutters go into 'attack mode'
Both tighten the chain against the bar, one as an inward force and the other as the cutters rocks back on the heal shortening the chain with a pull and release. The greater the hook and the lower the rakers then the greater the disturbance. So you have a constant pull and release on a tightening chain.

That's one theory yes.

Commonly with new bars and chains on a chain throw the drivers will mushroom over. So you loosen the chain and sometimes
to 2" belly sag. When you throttle up, so then where does the slack go? It would concave between the the bar and sprocket.
So that's the buffer on a properly adjusted chain, it will has a concave slack to take the disturbance from the bottom end.

Another theory that could be related.
The greatest pressure is at the drive end as it's the smallest sprocket. The least at the middle.
Also you only have max three drivers at play on a 7T at any time and if you ran a hard chunk through the back of it then it may lift the previous pulling driver and that would be of the worst kind of pull to the crank

Some Fallers think when a big cut closes?No that's also what's hard on bottom ends though.

I've had it happen once in 30,000 saw hours.
and I don't run tight chains.

A couple of questions for you: Do you see this much ?
Also this was a new 2010,, 2165 BB ported.
Saw seemed lite compared to all my 372.
Is the crank the same as 365/372?
20 yrs with 371/375/372 and never a problem.
A short time with one Jonsered and I get a bent
crank.

[/QUOTE]

 

[Ted Jenkins]

The chain fits considerably looser on the bar as they cool. Its most importent to check tension after a short break for this reason or a high
percentage of throws will accure within rhe first few minutes of start up.
You may be on the right track. If say it was on the tight side, it does get tighter with the heat. Two factors that may create friction,, One being centripital force that's greater as RPM increases and the other when the cutters go into 'attack mode'
Both tighten the chain against the bar, one as an inward force and the other as the cutters rocks back on the heal shortening the chain with a pull and release. The greater the hook and the lower the rakers then the greater the disturbance. So you have a constant pull and release on a tightening chain.

I am surprised nobody mentioned what the cause for a chain to be loose after a saw cools down. The reason is if every thing is good the chain should be loose after the saw cools. When in operation the bar warms up, but the chain does not so much because it is rotating with plenty of air to keep it cool. The chain stays more of a constant temperature, but the bar gets warmed up and thus expands. When the bar cools down it shrinks and thus the chain has more slack. Only a experienced OP would know exactly how much tension is just right. For the beginner they would need a little trial and error time. This is not to say that when the chain gets a little loose every thing is perfect. The oiler must be properly oiling, sprocket must not be worn past service, bar must not be causing too much drag and so on. Thanks

 

[Westboastfaller]

.

365/372 and oe and xtorq have same crank, yes

interesting idea of a chunk of wood suddenly taking up space on the sprocket, never thought of that. i can believe that that might bend a crank....

metal shrinks when it cools, so how does a chain get looser when it cools?

i'm not a faller, just a guy that rebuilds junk saws

Yeah I was sceptical specifically about the J- red 2165 crank being the same as the 365/372? Tithe one I bent the crank in one.month use.

I was careful in my wordings. I am not saying the chain does or doesn't expand.

Ted explains it well above (although the quote didn't work...expand the quote.)
That's what I came up with also.
After the chain initially stretches out then expansion and contraction is not recognized on the chain.
My slashing saw was a ported 357. filed very aggressively. When it had to to cut two three rounds and It wasn't adjusted perfectly then I would have to shut down and loosen it just a slight. Bigger saws are more forgiving.

There is guys on line saying kind of what what you offered
th as a guess as to a bent crank. They are talking like its word and if you tighten a hot chain you can damage the bottom end with contraction. That's absolute BS.

 

[Mattyo]

Interesting. ...tx!