Question about overheating.

[Magic_Man]

I often hear about overheating in discussions about compression, squish, timing advance, etc. When is a saw considered to be "overheating"? Is it at a certain temperature ? If so what temp and where is it measured ? Or are there other tell tale signs of overheating with a chain saw ? Just curious and trying to learn here, thanks again fellas.

 

[blackop555]

Same

 

[Frogfarmer]

 

[mdavlee]

When they diesel after a cut is a good sign.

 

[Simondo]

This could be a tricky one to give a definitive description or "Fact" based answer so I won't try as others may have figures.
Il speak from some things i personally have seen and look for.
If using a big saw for milling then there is a risk of over cooking things and unfortunately that can be when its to late....cooling efficiency gets less if crud builds on the motor and in the fan case or the fuel mix is inappropriate (its a coolent to some degree)... The classic "nip up" can take place . The exhaust on the outside can show the amount of heat the saw is pumping out and the cylinder looking in from the plug hole can take on a greyness along with the plug.
The baked on brown black that sometimes shows on the cylinder fins with a saw that is worked hard without cleaning properly to allow for good air flow is another thing I believe is a sign. Iv ofter found a scored up piston with a saw like this on closer inspection.
Had a Husq 254 xp come in to me as a non runner after being told it was almost imposable to start in the last month after it was hot. No Sh@@ !! Filthy baked cylinder and choked up with crud. Cleaned "Properly" and a check through it was a bit down on comp but it was a perfect starter when hot again.
I kept the saw and freshened it up for myself..strong running saw and never any bother.
I have no technical readings and measurements that should be observed ...just common sense that a air cooled engine needs air ! plus if you run it hotter than it was expected to be run at in practice then you could be getting close to its limit of "NO" damage to moving parts.

 

[pro94lt]

Having the fuel boil is one sign... For me if they still start and run and are in tune I'll continue to run them. But if the fuel is boiling it's hot out, I've been running them hard and I'm usually in need of a break lol.

 

[Gunn]

Gas can boil around 100 degrees so that's not always a good indicator.

 

[pro94lt]

Gas can boil around 100 degrees so that's not always a good indicator.

That's true but if the fuel around here boiled at 100 we'd be in some trouble from July-September lol

 

[mdavlee]

I've seen bar oil boil in the tank when milling. That's one of the few times I've had a saw diesel on me as well. Milling with it 100° outside isn't the smartest thing to do but I like it rough

 

[Chainsaw Jim]

You'll know when it overheats because it'll start losing power. Once that happens the rings have likely been weakened.
Advancing the timing or using other methods of gaining rpm without increasing the air flow will cause the saw to run hotter during longer cuts.

 

[Wilhelm]

Having the fuel boil is one sign... For me if they still start and run and are in tune I'll continue to run them. But if the fuel is boiling it's hot out, I've been running them hard and I'm usually in need of a break lol.

A Sachs-Dolmar 103/105/108 will boil the fuel in her belly as the fuel tank is part of the main PH case.
Also, the muffler is underneath the cylinder and fully encased in the PH's case halves.

My Sachs-Dolmar 105 had to endure numerous boiling session's, partially due to my lack of knowledge, but also because she was underpowered for the tasks I threw at her.
She seems to have taken the beating quite well, she's one tough little saw!

When my Sachs-Dolmar 105 would get extremely hot she'd stay at a higher rpm for a few moments after releasing the throttle lever, wouldn't idle and would require throttle lock to be restarted.
And yes, she'd boil the fuel in her belly.

 

[T.Roller]

Simple answer for me is after a cut, if the saw idles down slowly, is a good indicator.

 

[T.Roller]

But could also be an air leak lol

 

[exSW]

I had/have a Remington SL-55 that forever and always boiled the fuel. Winter,spring,summer or fall it mattered not. Fuel tank to close to the engine and if you looked at the cylinder compared to a modern 80cc saw it's much smaller overall. The bores big but the fins are smaller and more closely spaced. That saw was a one tank saw and it lived a relatively short life. Peeled the chrome right off the cylinder.

 

[Magic_Man]

All good info so far , thanks guys. My reason for asking is I like to push the envelope when it comes to performance and engines. Looking for indicators that I've gone too far and my limbing saw is no longer and has now become a 3 cut get together saw.

 

[angelo c]

I often hear about overheating in discussions about compression, squish, timing advance, etc. When is a saw considered to be "overheating"? Is it at a certain temperature ? If so what temp and where is it measured ? Or are there other tell tale signs of overheating with a chain saw ? Just curious and trying to learn here, thanks again fellas.

The easiest way for me to ID "overheating" is when I have to google "mastermind cylinder cleaning"...

 

[Magic_Man]

That's what I'm trying to avoid lol, but yes, that's a good indicator too.

 

[Chainsaw Jim]

I'm not an expert on all reasons that can cause fuel to boil in the tank, but I figured out why my 075 does it. When I shut it off the other day the piston was at tdc sealing off the exhaust port. This allowed the heat from the engine blow pressure back through the intake, carb and fuel line into the gas tank causing bubbling. My fuel in the tank was not hot or warm since I only ran three cuts. Check valves in carbs will prevent this, but the old 075/076 and the like all run tillotson HS which weren't made with one.

 

[smokey7]

My jonny 630 vapor locked on me today.... it was the first time for that saw. I guess 93* heat and a tight tune with e10 is more then it can handle.

 

[Nitroman]

If your saw is properly tuned you shouldn't worry.