How did this saw die, and what to check when rebuilding?

[tychoseven]

I picked up non-running 024 Super on ebay as a parts saw. Everything looks like it's stock and in decent shape, but it felt "off"when pulled. The piston is scored up pretty badly and there are dings in the top of the piston. All the damage is on the exhaust side, the intake side looks fine.
Rather than cannibalize this for parts (my other 024S runs fine) I'm thinking with a new piston I could have two working saws

Any clues as to what killed the saw? I'll be checking for air leaks but don't have a compression tester. I don't want to toast another piston the first time I start it back up.
[photo=large]4222[/photo]
[photo=large]4220[/photo]

 

[TBS]

Take a look at the needle bearings especially at the rods big end.

 

[grizz55chev]

Take a look at the needle bearings especially at the rods big end.

You'll need more than a compression tester, looks lean scorched.

 

[Ozhoo]

Straight gassed and the operator restarted it multiple times. Probably cussing the saw up one wall and down the other along the way till he chucked it across the lawn.

 

[alexcagle]

That looks like an overheat because somebody leaned on a dull assed chain.

 

[tychoseven]

You'll need more than a compression tester, looks lean scorched.

I'll pull down the entire saw if needed, but never done it before. What other tools should I get?

 

[grizz55chev]

I'll pull down the entire saw if needed, but never done it before. What other tools should I get?

Mighty vac is a good start. You either have an air leak, low compression, or both.

 

[tychoseven]

Ok, I have the Mighty Vac. Low compression would cause it to run lean?

 

[grizz55chev]

Ok, I have the Mighty Vac. Low compression would cause it to run lean?

The other way around, air leak cooks the piston and ring causing low compression.

 

[brandonstc6]

Well, it really helps having a press but you can use blocks or wood to support the saw and a wood block and hammer to drive in new bearings. After you split the case and remove the old ones of course. You may just need seals. Be sure to install the oil pump before the bearing. On my first rebuild on a MS440, I didn't have the pump installed first and I drove the bearing too far. So on many saws the oil pump is the stop for the bearing. Also you can use a socket to drive in crank seals but be sure to put a large washer on top of the seal to keep from denting it.


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[alexcagle]

I would rule out the simple things first.
*
We know it's a "pre 2000" saw, because it's not an "MS×××" model saw.
A 16+ year old saw needs the basic things checked. Seals usually don't leak unless they are ripped by bearing cage failure debris, a loose wobbling crank from bearing wear, deterioration from age, or brittle from thousands of heat cycles.
*
Check your fuel filter for plugged-up-ed-ness with it removed and dried. (blow through it) -it should flow pretty easily.
*
Does the fuel tank smell like rottenass old fuel?
If so, take off the carburetor & take the end covers off. Make sure the diaphragms aren't stiff and crinkly, and the screen isn't clogged with sawdust. If so, that may be the cause of death.
*
Is the intake boot split? Some I've seen only leaked under full throttle vacuum.
*
Check that the fuel line isn't rotten and split outside the tank, and it's not spongy inside the tank. A minor fuel hose air leak or collapsing fuel line can both starve the engine at high speed, or exacerbate overheating, resulting in that "chernobyl" piston.
*
Test the tank vent by emptying the fuel, then tighten the fuel filler cap back up. Then hook up that mighty vac to the fuel hose. It should pull a little vacuum, then within a few seconds bleed down to zero.
*
Check the impulse hose for cracks behind the bulkhead, and that it's not unplugged from the barb.
*
Check what spark plug is in it. Should be a Bosch WSRF6, or equivalent. A hotter plug can cause problems. I've seen those auto parts stores sell a spark plug called an" E-3" split electrode tip that causes chainsaws to run hotter, and easier to scorch pistons.
*
Low octane fuel with alcohol can contribute to a scorched piston. If you use premium fuel, there is usually less than 5% alcohol by law (if any). Midgrade fuel, (which is what Stihl recommends for all their gasoline engine equipment), usually doesn't sell as quickly as premium in most gas stations, hence it is not likely to be as fresh a premium.

 

[mkinslow]

That resembles that 066 piston on the saw I reworked awhile back with the gouging and dents in top of the piston. It had lost its bearings and cage on the crank end. Looks like something got inside to me.

 

[cedarshark]

Alex...that is a great action plan for repairing that saw....

 

[tychoseven]

I would rule out the simple things first.
...etc...

Wish I could send you more than one like. Thanks for this!

 

[cus_deluxe]

That sure looks like it ingested something solid. As said above, check bearings and their cages.

 

[tomdcoker]

If I were to rebuild that saw I would completely disassemble it and replace crank bearings, seals and check the big end bearing on the crank. To check the big end crank you need to do a visual on it for a cracked cage and missing needles. Also move the crank throw to a point of center between the counter balances and with your hand on the small end move it side to side, if it does not touch either side it should be good. when you get it back together, checking or replacing everything as you go, fuel line, fuel filter, impulse line and carb. boot then do a pressure/vacuum test. In my opinion the saw was straight gassed or has a major air leak, but that and fifty cents will get you fifty cents worth of what ever you want. Tom

 

[HarleyT]

Put up a pic of the intake side of the piston.

 

[tychoseven]

Here's the intake side. There was more damage than I remember, but it's on the sides of the intake rather than directly opposite the exhaust. Also there's some wear on the skirt, the bottom 1/4 is worn smooth.
[photo=large]4223[/photo]

 

[HarleyT]

I would lean toward straight gas.
Have you tried to clean up the cylinder yet?
Pics?

 

[brandonstc6]

If I were to rebuild that saw I would completely disassemble it and replace crank bearings, seals and check the big end bearing on the crank. To check the big end crank you need to do a visual on it for a cracked cage and missing needles. Also move the crank throw to a point of center between the counter balances and with your hand on the small end move it side to side, if it does not touch either side it should be good. when you get it back together, checking or replacing everything as you go, fuel line, fuel filter, impulse line and carb. boot then do a pressure/vacuum test. In my opinion the saw was straight gassed or has a major air leak, but that and fifty cents will get you fifty cents worth of what ever you want. Tom

I second this idea. That way you can be sure everything is in good condition. I don't know how much you are looking to put into it. I've used aftermarket bearings from China before but I don't know about cylinders and pistons. I've only used OEM.


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