What causes an engine to score/blow up when using a dull chain?

[banditt007]

A dull chain....

-reduces load on the saw (richer mixture)
-"cuts" at higher rpm (richer mixture)
-clogs up the air filter much faster (richer mixture)
-creates fine dust (blocked cooling)

A user of a dull chain, typically...

-presses harder and reduces bar life.
-presses harder and bogs the engine (leaner mixture/over heating)


So I'm thinking what really causes the problem is the USER pushing way too hard to make it cut, which bogs the engine, which puts you into lean mixture territory, and also reduces the air flow across the engine.

So would you agree this is the true cause of engine failure? Because on the surface, a dull chain seems like its easier on the engine, for the most part...

 

[fearofpavement]

Heat. That's the culprit. And a dull chain creates a lot of that in various ways.

 

[fearofpavement]

Not sure where you came up with your dull chain benefits but I think you need to revisit that list.

 

[gunnusmc03]

Usually when your chain is dull, your natural insticnt is to start to reef on the saw and force it through the cut. You can stress the ever living he** out of the saw.

 

[banditt007]

fearofpavement, What exactly is not true on that list? and why so?

gunnusmc03, this is my take on it also, its the user thats bogging the crap out of the saw trying to make it cut.

 

[Bilge Rat LT 20]

A dull chain
Drags thru the cut loading the saw. The dragging/not cutting and clearing chips causes heat which is carried to the saw. Chain stretches and bar burns the oil, smoke comes off the bar. Smoke = heat/friction

Friction loads the saw reducing RPM. More load means heat and reduced cooling air across motor.

Mixture means little.

Sharp chain cuts cooler/easier less load.

Heat kills the saw, the heat source is friction, load, low RPM.
The operator fails to see/fix the problem allowing heat to kill the saw.

 

[blsnelling]

So would you agree this is the true cause of engine failure? Because on the surface, a dull chain seems like its easier on the engine, for the most part...

No. The cause is heat. The engine is being forced to work harder as the user dawgs it in. Lots of heat comes from the chain as well.

 

[Rockjock]

Brad is spot on it is the heat that kills the saw. When you run a dull chain you are running the saw with less load than you are when you are running it with a sharp chain. I can hear the engine running faster when my chain is dull, I have had several saws come to me that had that exact same problem. Chain dull and the saws over heated because they had less load on them and were still run WOT. It is like getting into your car, take it out of gear and peg he pedal to the ground. It will not be long till the car over heats. Put a chain on backwards and try and cut something really press down on that saw and take a RPM reading. It will be much higher than a saw with a sharp chain buried in the wood. Just keep that chain sharp and when you feel it is not cutting as well as it should stop and resharpen or change that chain.

 

[AKDoug]

Uneducated users will push harder, dog in more, to try and get the saw to cut. It's like standing on the brakes on a car and not letting off the throttle one bit. Eventually the temps exceed the ability of the oil to keep a lubricated barrier between the piston and cylinder.

 

[zogger]

A dull chain causing dust and not chips also plugs the oiler holes easier, meaning less oil carried down the bar. Clean chips and a clean bar will run cooler and expel heat as the oil and chips sling off.

But, I agree with the others, the user will just try and make it cut, stress everything on the saw, plus get personally stressed/angry.

Dull chains ain't worth it....

 

[tree monkey]

 

[tree monkey]

dull chain
dull mind

 

[Moparmyway]

dull chain
dull mind

He wont EVER do that again !

 

[square1]

He wont EVER do that again !

I'm not sure how the blazes he did it the first time

 

[Chris-PA]

I think this is an interesting thread and something I have thought about too. From what I've been able to tell a dull chain by itself reduces the load on the engine and increasees the rpm - which enriches the mixture, and should not hurt an engine one bit. But if you push it, then the energy is not going into severing wood fibers, it's going directly into friction and heat at the bar and chain.

Still, I don't see how it hurts the engine until you've pushed it hard enough to drag the rpms down below normal. The engine is producing power, and what that power is used for doesn't effect the engine. Maybe if the bar and/or clutch gets so hot it starts feeding back heat into the engine through the case?

 

[bcaarms]

Take a digging iron and your favorite saw and a sharp chain on a new bar and go make a flower planter out of a 45" oak stump using plunge cuts. When the bar tip is smoking from oil vaporizing when it hits the tip which is changing color it makes me think that maybe there is a lot of heat building up and if I continue to try to cut without sharpening the chain, the heat will eventually get transferred to the saw. So I say the killer is heat. The issue is the operator if he continues with the abuse.