Chain too tight

[DanMan1]

The other day my father thought he recalled someone telling him that if you were to set you chain too tight right after heavy cutting, with the bar and chain still hot, that you could possibly bend the crankshaft to some degree when the chain cooled down and contracted.
Does anyone know if this IS possible, and/or has it happeneed to anyone? :blob5:

 

[Lawn Masters]

Its more likely that you'd damage a crank seal. The proper tension on a saw with most bars is to where you can fit a dime between the chain and bar without having tons of slack.

 

[sedanman]

Yes, you can bend the crank. You could also snap the end of the crank off. A friend of mine had a small block Chevy with a 6-71 blower on it. He liked to hear the belt whine so he ran the belt real tight (the belt is responsible for the noise, not the blower) . He bent the crank. Honda had a recall on Civics a while back to replace the power steering adjuster bolt with a thumb screw. If you ran the power steering belt too tight on a Civic you could snap the end of crank off. The engine would still run because the break occurred between the timing gear and the balancer/drive pulley. I have replaced the crankshaft on a Civic because of this. A saw crank is quite a bit smaller than either a SBC or a Civic.

 

[T_Bone]

Hi Dan,

I bought a new MS361 and Stihl warns of this problem in there owners manual.

I can see how that can be a problem using Stihl chains as the steel quality seams to be better than what I was using. Chain streatch is much less with the Stihl chain so if I were too tighten the chain while the chain was warm to hot, then let the chain cool, I could see some excessive pressures on the crank/bearings/seals.

I once bent several 36" x 40ft I-beam's to a radius for a floor beam around a tank with a Oxy/Acet torch and a air water cooler, so heat and cooling can move a massive amount of metal very easy.

 

[Fish]

I don't buy it. Theoretically, it might happen, but I have not seen it.
If you retensioned a RED hot chain too tight, it might happen, but otherwise
this is an old wive's tale. As far as Stihl chain being magically superior,
I really won't give a comment, as the new posting guidelines would omit most
of my response, and likely get me banned.
Otherwise, this topic is really a non-issue, but hey it is Jan., and we are
all bored!

 

[Crofter]

Whether or not it would break the crank right now may be debatable. Wht is a fact is that it can create a situation where there is much unnecessary strain on everthing involved. It is a lose / lose scenario.

 

[Mange]

If the chain was at max tension when very hot, then yes it could create the tension needed to brake a crank.

 

[Crofter]

Do cranks bend before they break from too much chain tension? Do they snap like an elastic band or is it a progressive break over a period of running and circumferentially inwards?

 

[Mange]

I think they break.

 

[max2cam]

Since my chains are almost always too loose, that's something I'll never have to worry about.

 

[Crofter]

Which design (inboard or outboard clutch) would be more prone to engine damage from the shrinking chain scenario?

 

[Lawn Masters]

Both probably.

 

[tony marks]

i think everybody retensions the chain if its new after a little running.
but not to tite.. id be afraid id break a chain with that kinda tension.
never had that problem ,but i guess titened enuff ,you could cause a problem.jmo

 

[glens]

Which design (inboard or outboard clutch) would be more prone to engine damage from the shrinking chain scenario?

All else being equal, the inboard clutch would provide the greatest leverage against the crankcase, definitely.  Another probable factor would be bar length, where the longer bar/chain combos would provide for more links to shrink, thus generating greater force.

I don't think it would snap a crank the first time it happened; maybe not even the hundredth.  But I don't doubt it's bad for everything from the bearing seat in the case to the clutch drum bearing, inclusive.

I try not to let the chains get so hot that they need to be re-tensioned.  It takes at least one of several factors to cause that; factors which are easily monitored and remedied.

Glen

 

[woodshop]

I try not to let the chains get so hot that they need to be re-tensioned.? It takes at least one of several factors to cause that; factors which are easily monitored and remedied.

Glen

This sounds pretty sensible to me... if the chain is so hot it needs re-tensioning because of the heat, you are doing something wrong to start with. Once my saw/chain has warmed up from cutting a while, and I do need to re-tension it I tend to lean toward not making it very tight anyway. My thinking is its already hot so the metal is not going to stretch a bit from heating up anymore, and I always think if I make it too tight I am causing unnecessary wear on bar and chain. Also... didn't I see in one of the posts how the tooth on a chain has to kind of lift off the bar and "rock" as it cuts into the wood? A very tight chain would not let this happen no?

Dave

 

[Crofter]

Glen that is what I feel. You are doing a whole lot of things wrong if this happens. I would like to examine a few fractures attributed to this before I belive you could hear a snap from a cooling saw and pick it up in two pieces. Mind you I am not sayint that you couldn't put extreme and needless stress on a saw by tightening up a grossly overheated chain, but someone would have to be pretty crudely prepared to do such a thing.

 

[sedanman]

I don't think the tight chain would snap a crank unless the saw was running. The Civics I mentioned all failed while running. The extremely tight belts deflected the end of the crank ever so slightly. Since this was always in the direction of the power steering pump and the crank was rotating, the crank work hardened then broke. This is liek you taking a paper clip and bending it back and forth until it breaks.

 

[woodshop]

I don't think the tight chain would snap a crank unless the saw was running. The Civics I mentioned all failed while running. The extremely tight belts deflected the end of the crank ever so slightly. Since this was always in the direction of the power steering pump and the crank was rotating, the crank work hardened then broke. This is liek you taking a paper clip and bending it back and forth until it breaks.

...so you are saying it is metal fatique then that actually broke the crank?

 

[sedanman]

YES, work hardening is the term.

 

[woodshop]

YES, work hardening is the term.

...interesting, work hardening is the same thing as metal fatigue? I'm not an engineer, never heard of work hardening. I always thought that with metal fatigue, the piece or joint that was bent or stressed got softer. So it gets harder? Is that why it fails then... it is actually more brittle?

I love this place, I'm always learning stuff.

Dave