Running temp of engine.

[Magnus]

I thought this might be a good place to address this as many here run smaller saws and often go close to limit or above of what they can handle or more correct are designed to handle. I thought we could talk a bit of why they get hot, how to prevent it and what happens as it heat up too much.

There is a couple main things that decide how much heat that is developed.
Fuel/combustion, Handling, airflow, exhaust flow is a couple things that decide how hot the saw gets in operation.
Starting out with out of the shop condition saws. This is what most use and today as fuel is what it is and saws get less fuels to get better emissions the saws run hotter. Other restrictions are somewhat needed, mufflers can sometimes restrict flow and in so do its part in creating excessive heat.

The number one heat creator is over load. Dull chains operated on worn out bars with a operator sitting on them to make it cut. This is first thing that needs to be checked and corrected.

Even if you have a sharp chain, you can still overload it with many heavy cuts under heavy load.
Listening to engine and making sure it is running properly is a good way to prevent this.

Try to not let it go down too far in rpm in the cut. This make airflow around cylinder constant and adequate. After a few cuts, flip the throttle a couple times to let air flow around cylinder and cooling fin's.

Keeping saw as clean as possible help a great deal. Much more than most know.
Air filter, cooling fins and the air guide inside starter must be clean to let air flow freely.

Fuel and particularly the fuel/air mix is also something that kills lots of saws.
Not correct fuel, not correctly mixed or a setting that give less fuel than needed create excessive heat.
I am sure many here know how to set the saws carb and those who don't should learn.
It is needed and often overlooked.

Another very common cause of too much heat is air leaks. Gaskets, membranes, seals or impuls/fuel lines gone bad . This alter the fuel air mix and sometimes the different pressures needed to let the saw run right. It can be tricky to find were problem is and it is often more than one issue caused by one problem. A sequence of events that lead to the result noticed.

 

[Magnus]

Most common problem that heat cause is scoring on piston and cylinder.

As material heat up they expand and different materials expand differently.

If you run a saw hot and shut it of the piston will continue to expand or keep its expansion longer as there is no air flow cooling it.
Same thing with idle, but not as bad as some air flow and cool. A couple flips on throttle will let flow increase and cool better/faster.

I am sure many here know a lot about this, but I thought it was about time it was addressed a little deeper. It is the most important thing to learn as operator and often overlooked.

As saws get smarter and emissions tuffer this is something that is needed to discuss.
Lots of money and grief can be saved from very little actual work if the knowledge is there.

 

[Magnus]

Scoring is the most common problem. Cracks in cylinders, case, intake, exoust. Melted covers and all other plastics you can think of.
Wandering bearings, locked bearings. Gaskets and seals that change shape and form as meterial is changing shape and form...
The list go on for ever...

 

[woodworkingboy]

Keeping saw as clean as possible help a great deal.

That is great to read, Magnus. I've long wanted to give people a good reason to keep their saws clean. Most that get brought to me for repair are filthy. Not the most pleasant thing to work on, and a good cleaning does add time to the job. I have a hard time giving the saw back fixed and dirty.

 

[Magnus]

A guy here has specified on the bill how much time and at what rate he clean on...
After a couple tries, they come with clean (sort of) saws.

That is his way of making a point. But it does not help in them understanding the benefits of cleaning.

 

[sotc]

Good stuff Magnus, I often shut my saws down as soon as the chain stops thinking its air cooled so its fine.

 

[Cobleskill]

One would think keeping an air cooled engine clean is just a no-brainer. Lots of people are no-brainers, I guess.

 

[woodworkingboy]

The fins on the cylinder don't get dirty so much like other areas of the saw, I mean they don't seem to get grunged up like where the oil and crud is moving around. I still like to clean around where a rag and screwdriver can reach in.

 

[Magnus]

It has a lot to do with what bar oil is used. I know it sounds wieard, but some oil create a mist and when this is sucked in along with air a sticky surface attract a lot of crap.

 

[Cobleskill]

My fins usually collect some grunge.

 

[Magnus]

One would think keeping an air cooled engine clean is just a no-brainer. Lots of people are no-brainers, I guess.

You would be amazed if you knew how it looks sometimes.

 

[Magnus]

It is not uncommon and is no problem as long as it cools properly. It is when it gets a surface thick enough to prevent air to get to the fin it starts being risky.

 

[Magnus]

Good stuff Magnus, I often shut my saws down as soon as the chain stops thinking its air cooled so its fine.

There are experiments you can do to test this and show!

I put a busted rod on a piston, inserted it to cylinder and heated from inside it so I just barely could touch the fins.
Shut heat of and wait a couple seconds.
Then try to touch the fin...

 

[Magnus]

In most of the engines the heat development is a factor that is well measured, calibrated and considered.
But for some reason it is not so on saws.

Electronically controlled ignition in one system. On some saws, Fuel system is electronically controlled in an other systems.
Both independent of each other and they have no idea if saw is in operational temp, too hot, hot or cold.
Amount of fuel is regulated by rpm alone.
Nothing that measures exousts content, burn % or temp. No indicator on engine itself that can add info to compensate on the saws systems.

 

[MCW]

How many people have siezed up saws due to a lack of cleaning and not an air leak or lean running scenario?

I'd think there is quite a temperature operating range for an air cooled motor over a water cooled motor. Just think of the hammering an old 2 stroke lawnmower gets and yet they just keep on going

I have posed the question before regarding actual operating temps of saws and the use of infrared thermometers on the muffler/fins yet nobody could give me an answer. I'm sure somebody knows somewhere?

 

[Timberwolf]

Another factor in keeping a clean saw is keeping a sharp chain, sawdust plugs up around the fins much quicker than do chips. Also the saw spends less time sucking up chips than dust to get an equal amount of work done.

Here is a graph of a stock muffler modded 026 3 sets of 3 cuts in an 11 inch log.

Under plug temp sensor in blue, EGT probe in Red and RPM in pink.

Over 3 cuts plug seat temperature was up over 400f, keep at working hard for a few min and the temperature can get up over 500f, on a ported saw 600f.

 

[sotc]

Very interesting how all the temps go down when the throttle goes up. Moving that air through helps. Also magnifys Magnus' point about cooling down a bit before shut down

 

[Cobleskill]

I cut a lot of dead Elm for firewood. It makes saw dust even with a sharp chain. I guess that's why I get a lot of build-up of crud on the fins. I have to scrape it off and then blow it out 2 or 3 times a year. It's not like it is that hard to do.

 

[MCW]

I cut a lot of dead Elm for firewood. It makes saw dust even with a sharp chain. I guess that's why I get a lot of build-up of crud on the fins. I have to scrape it off and then blow it out 2 or 3 times a year. It's not like it is that hard to do.

I hear ya! Our dead hardwoods make sharp chains look blunt with all the dust...

 

[Magnus]

There is study's made here from Husqvarna, Partner, Jonsered, and our government testing division.

Why it is not a feature in saws today I can't figure out. It should be a lot easier to keep emissions and performance if the systems interacted.

Weight can't be a issue, as the saws are heavier with the fresh air engines.
Cost should be less than all that is invested in these new series of saws.
The tech is up for it, should not be a problem to let the temp indicator show both ignition and fuel system...
So why is it not on the saws today?
There is something missing in this equation...

Interest?

 

[MCW]

There is study's made here from Husqvarna, Partner, Jonsered, and our government testing division.

Why it is not a feature in saws today I can't figure out. It should be a lot easier to keep emissions and performance if the systems interacted.

Weight can't be a issue, as the saws are heavier with the fresh air engines.
Cost should be less than all that is invested in these new series of saws.
The tech is up for it, should not be a problem to let the temp indicator show both ignition and fuel system...
So why is it not on the saws today?
There is something missing in this equation...

Interest?

I agree Magnus and think that modern saws are dumbed down a fair bit. A local Stihl dealer said there was a fuel injected Stihl saw doing the rounds about 10-15 years ago so the technology is there, the manufacturers just don't want to use it I suppose. Maybe they don't want people checking temperatures on the LCD readout while they're felling a 200 foot tree?

 

[Al Smith]

On the older horizontal cylindered saws that accumualtion of crud was worse than on todays saws .You can still get it though on saws like the 200T .

It's good idea to dust them off peridically with a blast of compressed air .A clean saw is a happy saw .

 

[Magnus]

Ha! LCD readout..

No, I more thinking of the controlling of them thru the systems.
Example:
Say you are doing some heavy cuts and saw heat up. How many pay attention to this? A lot of saws could be saved from recycling if the temp was regulated. Emissions would be better as the saw would run on optimal temp more and more effectively. Saws would last better, cost of repairs less and more run time for the bucks.
This would perhaps mean less saws sold to... I think that might be were the itch is...

 

[MCW]

Ha! LCD readout..

No, I more thinking of the controlling of them thru the systems.
Example:
Say you are doing some heavy cuts and saw heat up. How many pay attention to this? A lot of saws could be saved from recycling if the temp was regulated. Emissions would be better as the saw would run on optimal temp more and more effectively. Saws would last better, cost of repairs less and more run time for the bucks.
This would perhaps mean less saws sold to... I think that might be were the itch is...

I thought you'd like the LCD readout bit Magnus

I gather what you're saying is that the fuel system needs to automatically "richen" the mixture if it begins to overheat under load? This may not end up as clean as the EPA would like but is the only way to cool an overheating air cooled motor as far as I'm aware.

A properly tuned saw still should operate effectively though no matter how hard the cut or how sustained it is. A 200psi modified Makita 7901 I had was right on the edge of being too hot for a work saw. It had a bit of "run on" after hard sustained cuts in hard wood but richening it up 1/4 turn fixed that.

 

[Magnus]

That is were the trick is I think.
A cool saw and a hot saw need separate settings to get same emission results.
As it is today we get a setting that is good for the work we do. Not optimal for cool or hot saw, rather a compromise.

Lets say you could regulate the operating temp of the saw. With timing and fuel system it should not be too hard if they are electronic.
You could faster get it up in correct temp and keep it there.
Too rich will show in performance as well as too lean. Same as too cold or too hot will.