What causes a saw to run hot?

[angelo c]

Yes but no adapter to block off the intake and exhaust. Plus the cylinder and piston are off the saw awaiting the replacements.

Duct tape

And the stock muffler and carby as plates

 

[MS290man]

Duct tape

And the stock muffler and carby as plates

I didn't think of that; thanks!

 

[Ron660]

If you run an engine on 87 and then run it on 110 octane you will see a heat difference. Maybe 87 to 94 you won't see much, but I'm talking High octane...105 to 110 fuel. It'll add heat. Do a test and prove me wrong if you don't believe me.

I'll test that one for you when I have time. I have access to a temp gun at work. I'll check the temps in my 660 and 372 using 93 & 110 octanes. Not sure "how long" it will take to reach a max temp in each octane though. Also, what's the optimum or best operating temps of a saw?

 

[Adirondackstihl]

Saw runs hot if:
mixture is to lean(low or high side)
high octane fuel
dirt built up in the cooling fins on the flywheel or cylinder
dull chain
dirt build up on the starter cover
dirt build up on the air filter
air leak
probably more things

Explain the high octane fuel comment.
Higher octane fuel typically burns slower and cooler than say.....87 pump gas

 

[Adirondackstihl]

I think your wrong on the high octane fuel, my understanding is high octane fuel burns cooler. Pinging is pre ignition caused by heat igniting fuel before the spark,and octane reduces it.
I believe if the timing is retarded will cause overheating also.
In the case of that piston my not so professional assumption it looks like foreign ingestion ( dirt, carbon, etc.) wore out the piston skirt until it was sloppy and weak and then it did what it did.

Advancing the timing will generate more heat

 

[TJ the Chainsaw Mechanic]

Explain the high octane fuel comment.
Higher octane fuel typically burns slower and cooler than say.....87 pump gas

The higher the octane the more combustion you have generating more power(to an extent) and Heat to an extent. Now with 87 you have less octane which means less combustion.....therefore less power produced and not as much internal heat. But I am talking strictly on Bone stock engines. I'm well aware that high compression engines need more octane to run efficiently and not detonate. My 572 with 10.5.1 compression is barely happy with 92 e10.

 

[TJ the Chainsaw Mechanic]

I'll test that one for you when I have time. I have access to a temp gun at work. I'll check the temps in my 660 and 372 using 93 & 110 octanes. Not sure "how long" it will take to reach a max temp in each octane though. Also, what's the optimum or best operating temps of a saw?

That would be awesome, heck I'd just run them both at the same time and see if there's a difference.

 

[Al Smith]

I'm not so certain auto ignition IE diesel conditions would exist in any thing except a super high comp engine .Then if it did the thing would be running on some type of race gas--rocket fuel and would not apply to most people .I know in my case while I normally use high test gas I've never had any type of pre ignition problems even on higher comp modified engines using regular gasoline and only see a very slight improvement using higher octane rating gas .
Tetraethyl lead does very little if anything for a 2 cycle engine .While it is an octane booster other methods are used these days which are actually better than lead .Gasoline at the refinery is tested using a device called a knock engine which uses an electric motor to spin over a cylinder firing on the fuel in question .I've worked installing them some years ago .

 

[mdavlee]

I'm not so certain auto ignition IE diesel conditions would exist in any thing except a super high comp engine .Then if it did the thing would be running on some type of race gas--rocket fuel and would not apply to most people .I know in my case while I normally use high test gas I've never had any type of pre ignition problems even on higher comp modified engines using regular gasoline and only see a very slight improvement using higher octane rating gas .
Tetraethyl lead does very little if anything for a 2 cycle engine .While it is an octane booster other methods are used these days which are actually better than lead .Gasoline at the refinery is tested using a device called a knock engine which uses an electric motor to spin over a cylinder firing on the fuel in question .I've worked installing them some years ago .

I've had a few try to run away on Methanol/nitro. One 395 on pump gas milling when it was 100° outside in the sun.

 

[CR888]

Without getting into a pizing match, I noticed increased heat running high octane fuel. Regular unleaded ran much better. I won't run high octane fuel in saws. I don't know exactly what 'should' happen to engine temps with higher/lower octane but that was my experience the few times I ran it.

 

[rogue60]

Looks like it was run on engine oil (4T) to me or a crappy 2T oil but it's definitely had a hard life worked hard and been hot for most of it.
The outside appearance of a saw doesn't tell you much if say the owner has run it with dull chains its hole life and it finally just gave up from the abuse that's what it looks like to me.

 

[Jeffbecky1]

The higher the octane the more combustion you have generating more power(to an extent) and Heat to an extent. Now with 87 you have less octane which means less combustion.....therefore less power produced and not as much internal heat. But I am talking strictly on Bone stock engines. I'm well aware that high compression engines need more octane to run efficiently and not detonate. My 572 with 10.5.1 compression is barely happy with 92 e10.

Higher octane = less premature detonation in high compression engines = LESS heat
With 87 octane you actually have MORE combustion not less.
Octane is not a power indicator at all. It is anti-knock (pre-ignition) prevention indicator.

 

[Adirondackstihl]

Higher octane = less premature detonation in high compression engines = LESS heat
With 87 octane you actually have MORE combustion not less.
Octane is not a power indicator at all. It is anti-knock (pre-ignition) prevention indicator.

^this

Octane is the fuels ability to resist ignition/detonation.
Higher the number....higher the resistance to ignition.

 

[Lone Wolf]

Flame Speed, Octane Number & Horsepower
Faster Flame Speed Is Always Better For Maximizing Horsepower



There is a lot of misunderstanding about the relationship between flame speed, octane number, and horsepower. There are some connections between these items, but not as many as some people think.

FLAME (burn) SPEED:

THe speed at which the air fuel mixture in a combustion chamber is consumed becomes critical in a racing engine. At 6000 RPM, each spark plug fires 50 times per second. That's a lot of combustion processes happening in a very short time in the same combustion chamber. This is why racing gasoline need to be capable of burning fast. In your daily driver that may not see the top side of 3000 RPM, flame speed is not as critical. In a racing engine, everything is happening much faster, and in a bigger way because the throttle is wide open. The gasoline must burn as completely as possible to make the most possible horsepower. If the gasoline does not get burned in the time allowed, there will be unburned hydrocarbons coming out the exhaust pipe. Besides not making any horsepower for you, the unburned product contributed to air pollution. Flame speed is determined by the hydrocarbon components in the gasoline. It is critical to making max power, but not related to octane quality.

OCTANE NUMBER:

The octane number of a gasoline has little to do with how fast it burns or how much power the engine will make. Octane number is the resistance to detonation. If the octane number is high enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame speeds and some with slow flame speeds. It depends on how they are put together. We prefer fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline than one that has a slower flame speed.

POWER:

The ultimate goal in the racing gasoline business is to convert chemical energy from the gasoline hydrocarbons into mechanical energy or horsepower. The most efficient way to convert the gasoline into horsepower is to have the correct air-fuel ratio and the correct spark timing. A mixture that is too rich or too lean will not make maximum horsepower. The same is true of spark timing: to much or too little will compromise engine output.

OVERVIEW:

As indicated above, flame speed and octane number both impact the amount of power that an engine will develop, but they are independent of each other. To get maximum power from an engine, one must have a gasoline with adequate flame speed (faster is always better), and adequate octane quality to support the combustion process. Tied in with the optimized air-fuel ratio and the spark timing, we have a winner.

 

[qurotro]

I don't know what cause the crank/piston/cylinder to stain black.
But I replace the piston and polish the cylinder with 1000 grid sand paper and this saw still runs good.

 

[danimal]

high octane gas wont make a saw run hot because 93 burns cooler than 87.

EXACTLY...

 

[redlight066]

Yes but no adapter to block off the intake and exhaust. Plus the cylinder and piston are off the saw awaiting the replacements.

Lowes carries the rubber “tiles” in the plumbing section. They are like a dollar a piece.

 

[danimal]

Higher octane = less premature detonation in high compression engines = LESS heat
With 87 octane you actually have MORE combustion not less.
Octane is not a power indicator at all. It is anti-knock (pre-ignition) prevention indicator.

Another exactly,,higher octane burns cooler, takes longer to combust.
High compression takes advantage of this.