A thermal switch on the cylinder to kill ignition when engine is too hot?

[derekc]

With so many chainsaws dying of overheating, why not install a thermal switch on the cylinder to kill ignition when engine is too hot? It should be easy to find a thermal switch to provide no ohm above certain temp and we can tie it to the kill wire.
Stihl and its dealerships don't want your saw last forever?

 

[Dan_IN_MN]

You know, that's not a bad idea. The only thing I would wonder about is usually the piston is the one that gets over heated faster than the cylinder.

 

[AKDoug]

So, what temp are you going to set it at? Where is the sensor going to be? The difference between excessive exhaust gas temp and an o.k. exhaust gas temp is a thin line. It takes time for this heat to transfer through the cylinder and by the time it does, it's often too late.

 

[derekc]

Clip on to the fin or drill a small hole on a fin? It will be try and error to determine the best temp of the switch. If I was to market such protection upgrade, I will sell a set of, say, five thermal switches. Install the lowest temp one first to see if it interrupts normal daily operation. Use the lowest one that doesn't interrupt. This might save a saw later on.
Of course you might need a "disable switch" too.
This, along with a small tachometer, should have been on every high-end saw Stihl makes.

 

[AKDoug]

Won't work. Too many variables to determine if a saw is in danger by measuring heat at one of the fins. A tach on the saw is a recipe for disaster. You are supposed to pay attention to what you are cutting, not numbers on the tach.

 

[derekc]

What would be the disaster if it doesn't work? If it kicks in when it is not supposed to, then just turn it off (using the disable switch so that it doesn't kill.)
You sell stihl saws?

 

[jtracy1223]

It may happen some day but I doubt it will be a simple thermal safty. More likely a new "app" programmed into the auto tune/m-tronic technology.

 

[RedFir Down]

I think there is some valid points here...
I could see it working IF the cylinders we manufactured with a recessed sending unit that is closer to the cylinder wall to give you a more accurate/ timely reading.

 

[Terry Syd]

I'm a former electronic technician. All I see is one more electrical device to go wrong, some more electrical connections to become corroded from being outside in the elements, more weight and more expense, more stuff to maintain.

These are not high BMEP engines running on the ragged edge. The reason these engines get fried is because someone forgot to add oil to the pre-mix or they leaned it out too far or they allowed the fins to get blocked by bar oil and sawdust. I don't know if there is a fix for those things.

 

[MarkEagleUSA]

I don't know if there is a fix for those things.

Nope, ya can't fix stupid!

 

[JC360]

The last thing i would want when when felling a problem tree, or cutting in a bad spot, would be for the saw to cut out on me. Thats not only irritating but down right dangerous.
If saws came with those things, they would be the first thing to go on mine.IMO

 

[zogger]

Something like that would be nice, but perhaps just to an indicator LED instead of the kill switch. Just a warning, getting hot down here! Give ya time to back off, perhaps lift out of the cut or not lean so hard, etc. Time to sharpen the chain or clean the saw.

 

[NewToStihl]

I'm not saying we need to attach any techy-gadgets to saws, but (feasibility aside) I'd rather see a pressure differential sensor to monitor air filter clogging than a heat sensor to warn of over-heating. As mentioned above, a properly operated and maintained saw won't typically overheat. And, as zogger mentioned above, an LED for any of these ideas is better than a saw just shutting off without warning.

Also, a disable switch would never fly. OSHA would crucify anyone who said a safety interlock on a piece of work equipment was useful or necessary, but then provided an easy bypass to it...

 

[blsnelling]

What you want is an EGT probe.

 

[Adirondackstihl]

What you want is an EGT probe.

Or an O2 sensor

 

[blsnelling]

That

Or an O2 sensor

That controls the carb

 

[LegDeLimber]

Just stirring the mud a bit here is all.
If you're feeling self abusive, I'd try a thermal limit switch from a HVAC supply house.
..thinking to put it on the leeward side of the muffler for reasons of least amount of direct cooling air blast.
I'd want it to be near the outlet too though.
Should give you the closest practical method vs direct ex gas temp reading
with the least thermal inertia due to the fairly thin wall of the muffler.

i'm Guessing You'd want to set up a latching logic that allows cranking the saw when below temp setpoint
and holds it while running
but when over temp is reached, would prevent restart until cooled below reset temp.

The clogged filter device.
hmmm, does anyone know what the pressure range of a washing machine water level switch is?
tie it into that start/no start logic board also.

The reason for start /no start was mentioned above regarding the problems if the saw shut off in mid cut.

Hmm now is it ok to shut off in a milling cut but not a falling cut.
how does the tool know the difference?

I truly do not envy the design staff at times.

 

[AKDoug]

What would be the disaster if it doesn't work? If it kicks in when it is not supposed to, then just turn it off (using the disable switch so that it doesn't kill.)
You sell stihl saws?

I do sell Stihl saws. Not sure why that's important.

I do have a bit of of experience using exhaust gas temperature gauges for tuning snowmobiles. The first I used were simple dial gauges. You still had to do a baseline tune on your machine to determine what exactly was excessive exhaust gas temperature. On a snowmobile, depending on the position of the probe, you could actually have higher exhaust gas temps in the tuned pipe than the combustion temps of the cylinder. Many exhaust gas temps exceeded he melting point of aluminum. When I would set up a sled with EGT's I would tune it using plug readings. Once I got where I wanted, I would note that exhaust gas temp and keep that as my do not exceed temp. Later we started running electronic gauges of various types with a stutter box that would stutter the ignition if you hit the high EGT. There were two reasons why these systems didn't come stock on a sled. They added cost to the machine and every machine had a slightly different temp of when it was tuned right.

A single cylinder chainsaw engine is far easier to tune than a multi cylinder snowmobile. You can hear the proper tune and that is really easy to learn. If you can do that, you don't even need a gauge to protect you. Modern AT/M-tronic machines need it even less since they automatically protect the saw from lean conditions.

I'm not saying that your idea couldn't work with the proper research and development, I'm just saying that it's not needed and could add unreliability and possibly danger to a chainsaw.

 

[zogger]

Just stirring the mud a bit here is all.
If you're feeling self abusive, I'd try a thermal limit switch from a HVAC supply house.
..thinking to put it on the leeward side of the muffler for reasons of least amount of direct cooling air blast.
I'd want it to be near the outlet too though.
Should give you the closest practical method vs direct ex gas temp reading
with the least thermal inertia due to the fairly thin wall of the muffler.

i'm Guessing You'd want to set up a latching logic that allows cranking the saw when below temp setpoint
and holds it while running
but when over temp is reached, would prevent restart until cooled below reset temp.

The clogged filter device.
hmmm, does anyone know what the pressure range of a washing machine water level switch is?
tie it into that start/no start logic board also.

The reason for start /no start was mentioned above regarding the problems if the saw shut off in mid cut.

Hmm now is it ok to shut off in a milling cut but not a falling cut.
how does the tool know the difference?

I truly do not envy the design staff at times.

--yep, felling or a dangerous otherwise cut, do not want a random cutoff switch, just an indicator light. ha! Or maybe three lights, one - running good, two- getting a scosh too hot,three- OMG better shut it off real soon now and fix something!

edit, wanted to add, I already have thermal overload protection on my oregon battery saw, it shuts it down. Works too, it will not let you abuse the saw or battery. I would like at least a warning light to come on first though.

 

[AKDoug]

I think that the manufacturers response is that anything that causes you to look at your powerhead and not what you are cutting is not going to happen because of liability reasons. I happen to agree Now, mount those sensor lights in a heads up display in the screen of your cutting helmet, I might be into that