What causes a saw to run hot?

[Magnumitis]

YOU GOTS TO RUN RED ARMOR OIL then all problems go away!But ya gotta pull the jug every 1/2 tank to check the piston!!!!

Sawhawgz is up

 

[brushwacker]

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

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.

 

[brushwacker]

Water in the fuel can sometimes do that but looking at the condition of the cylinder I'm thinking stale/bad gas because it looks like there was still some lubricating qualities to it. The cylinder has a lot of carbon which I've seen in engines consistently run on low quality or old gas.

Or an an plugged up air filter that almost never gets serviced or replaced.

 

[junkman]

Could it be broke because its 30 years old ?

 

[MattG]

What causes a saw to run hot?

Personally I'd have looked for air leaks before tearing it down. Then I'd have gone over the air filter/carburettor like a dose of salts....

 

[Al Smith]

It could be seals .Flywheel side is no problem,clutch side is a rare bird to find .Remember it's a Stihl,they control aftermarket parts by design .
I'm still in a quandry as to why the piston snapped?You can see in the head deck area where it teeter tottered and marked the area around the chamber .Unless it somehow sucked a bite of something that the piston hit on the lower transfers ,usually chit gets blown into the uppers .
Cylinder doesn't look that bad,rings are 038 magnum .Finding a piston might be a chore .Seal will be a chore and not cheap if you do get lucky .I've got one clutch side seal left and have one of my 048's that needs seals .

 

[TJ the Chainsaw Mechanic]

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.

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.

 

[Wonkydonkey]

Pictures can tell a story, there's carbon build up in and on the crank.
An intake pic of the piston would show bad air filter on intake side /dust ingested!?. This would then result in a slow degrading of piston and wrist pin., and then lead to premature ageing and lack of lubing .

But me thinks reduced lubrication as said above (bad air filter) resulting in a over heated lean seized piston for the aftermath
That's my thinkins

 

[Wonkydonkey]

YOU GOTS TO RUN RED ARMOR OIL then all problems go away!But ya gotta pull the jug every 1/2 tank to check the piston!!!!

That's a junk sales answer. But if it works for you keep buying the RED ARMOR

 

[mdavlee]

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.

Pretty sure he has it backwards. Never had a saw diesel on 110 or 108. They have on 87 and 93 in 100° weather.

 

[Bluefish]

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 doubt anyone feels they need to do a "test", but anything I have read disagrees with your conjecture.
For you to make a statement like that I am thinking it is you that needs to come up with the "proof" , or perhaps edit your post...........

Russ

 

[Al Smith]

I don't know how you could tell if it runs hotter .Infrared detector,engine exhaust pyrometer ? Probably not too many have those items on their work bench .BTW I don't know anybody who runs a chainsaw on racing gas .Some think they need aviation gasoline or marine non ethanol.I'm not one of them . It's a chainsaw not vintage 1923 Rolls Royce or a classic 1938 Harley EL .

 

[MattG]

FWIW we have very little choice over this side of the pond. Ever since we lost leaded gas we've all been on 95 octane.

If you want to pay more some stations do sell 98 for flash gits.

However, generally, a higher octane will run cooler, but for a engine which doesn't require a high number, this probably also means less efficiently.

Read this for a few urban myths, falsehoods, and half truths....

http://wiki.c2.com/?OctaneIsControlNotPower

 

[drf256]

The case on that saw looks bone dry to me.

As for the cooling and octane argument, I believe high octane fuel burns slower. But it is likely less volatile and evaporates slower than lower octane fuel.

It probably has more to do with the cooling effect of the charge and less with the burn temp.

 

[Al Smith]

High octane gas aside I don't think it caused the failure of that saw .Firstly according to some the reason the 042/048 only had a short production run time was because of case leak problems .
I'm not sure if the 042 or 048 came out first but early models used high head slotted screws .I had one of those and replaced the case bolts with grade 8 socket heads .The damned slotted heads had a tendency to loosen up .
Also according to some the 048 in it's day had the highest HP to weight ratio of any saw at that time but was discontinued due to the previous problem and I think replaced by the 046.As far as I know none of the others of that design had those problems namely 028 and 038 .

 

[Al Smith]

--more --.I have seen a similar carboned up crankcase on a McCulloch caused by burning bar oil due to a faulty impulse pump .Of course the Stihl uses a gear drive and not an impulse pump so I have no idea how bar oil could get in the crankcase --unless .What if somebody by mistake or ignorance had ran that thing using heavy oil with a heavy mix ratio ? You can't burn chain lube as mix oil .30 WT sae yes but not 80-90 gear lube that has a tacking agent added .Might be a laughing matter but somebody posted a damaged saw on another forum and stated he used 50WT at 32 to 1 and it was screwed up mess .Common sense is not common .

I don't think heat had anything to do with the failure of that engine but bad fuel choice and possibly bad air filter perhaps an air leak did .Might be all three ,for that matter .
BTW I did look up 048 parts on flea bay and they do list after market pistons and several sets of seals .So it could be ressurected if the owner wants to do it .If it were me I think I'd take a chance on it .

 

[MS290man]

--more --.I have seen a similar carboned up crankcase on a McCulloch caused by burning bar oil due to a faulty impulse pump .Of course the Stihl uses a gear drive and not an impulse pump so I have no idea how bar oil could get in the crankcase --unless .What if somebody by mistake or ignorance had ran that thing using heavy oil with a heavy mix ratio ? You can't burn chain lube as mix oil .30 WT sae yes but not 80-90 gear lube that has a tacking agent added .Might be a laughing matter but somebody posted a damaged saw on another forum and stated he used 50WT at 32 to 1 and it was screwed up mess .Common sense is not common .

I don't think heat had anything to do with the failure of that engine but bad fuel choice and possibly bad air filter perhaps an air leak did .Might be all three ,for that matter .
BTW I did look up 048 parts on flea bay and they do list after market pistons and several sets of seals .So it could be ressurected if the owner wants to do it .If it were me I think I'd take a chance on it .

Got a piston kit, base gasket and seals all on order. Can't find a wrist pin bearing though. Any suggestions? Don't really want to reuse the old one....

Supposedly the same bearing as an 041, 045?

 

[Lone Wolf]

Got a piston kit, base gasket and seals all on order. Can't find a wrist pin bearing though. Any suggestions? Don't really want to reuse the old one....

Supposedly the same bearing as an 041, 045?

Do you have a vac- pressure tester there?

 

[MS290man]

Do you have a vac- pressure tester there?

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

 

[Lone Wolf]

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

The exhaust you can use a metal plate and drill holes.