Stihl 024 - Sherlock Holmes issue - help needed here

[MartDalb]

Hey everyone

Got a mystery case on my hands this time, and I need some help solving it.

Friend of my family has a an old Stihl 024 - from 1992.
It starts, but when put to wood it "won't rev and stalls or runs poorly". (his words)

Short story.
The saw was given to him for free, way back, he has no idea of its background story, he has had it for a few years, only uses it on rare occasions, but now it won't really run well enough to cut.

I did not want to start it up when I got it, so I just took it apart.
Took off the muffler and saw light scoring, and marks on the intake part as well, piston rings were not stuck.

I also started seeing signs of previous owner(s) not putting back original parts on it, like 8mm nuts replaced with Husky nuts on clutch cover, 5mm carb nuts replaced with "lock nuts", Torx27 screws replaced with whatever fit the need etc.
The carb needed a new kit and cleaning.
The impulse line was very worn as well as the fuel line, no holes yet but very close to it.
The black tank vent part was damaged and the " orange vent" inside the tank was gone.
Fuel filter was original, but old style orange (which as I recall is very old)

I did a pressure and vacuum test, it held fine for several minutes on both.

So nothing left but to take off the cylinder.

See picture.
The piston has damage, clearly! but yet had compression.
The cylinder itself seems more or less fine, it has light scratches, but nothing to worry about.

How in the world, does this piston have this sort of damage to it, and the cylinder is still fine? (piston is original Stihl btw, as is the cylinder)
It will need a little sanding, but that's it.
Piston needs a replacement, crank seals are fine.

What the hell happened here?

 

[SteveSr]

Saw ate something that didn't agree with it... Like part of a bearing.

 

[sand sock]

Was the wrist pin retainer there? Maybe something got in the exhaust and caused the piston to chip and break, then score.

 

[MartDalb]

Saw ate something that didn't agree with it... Like part of a bearing.

I have seen a few cylinders and pistons where a bearing had broken, but they have always left some serious damage inside the engine.
This one has not, and there were no metal parts of any kind inside either.

But, you might actually be right here, see my picture.

I think there is a "ball" bearing missing on the clutch side.
The flywheel side seems fine, and as a side note there is no "play" in the crankshaft of any kind, and it has been run like this for some time surely.


Would this saw run if fitted with a new piston, or do I need to split the case and replace bearings etc?

 

[MartDalb]

Was the wrist pin retainer there? Maybe something got in the exhaust and caused the piston to chip and break, then score.

Thanks, checked both sides and both pins are sitting correctly.

What I don't understand is how there is no leftover metal inside the engine/cylinderen or sign of further damage, other than that on my first picture. Odd.

 

[trains]

I have seen a few cylinders and pistons where a bearing had broken, but they have always left some serious damage inside the engine.
This one has not, and there were no metal parts of any kind inside either.

But, you might actually be right here, see my picture.

I think there is a "ball" bearing missing on the clutch side.
The flywheel side seems fine, and as a side note there is no "play" in the crankshaft of any kind, and it has been run like this for some time surely.


Would this saw run if fitted with a new piston, or do I need to split the case and replace bearings etc?

Looks like the race that holds the balls in place has come apart at some stage.
Yes, time to split the case and replace the bearings.
piston could have been scored from poor fuel quality/ mix, run hard when cold etc from prior owner, or with the balls not running true, some wobble on the crank causing an intermittent air leak.
Either way, its old, needs some new seals and servicable items, and will be a lovely saw when sorted.

 

[MartDalb]

Looks like the race that holds the balls in place has come apart at some stage.
Yes, time to split the case and replace the bearings.
piston could have been scored from poor fuel quality/ mix, run hard when cold etc from prior owner, or with the balls not running true, some wobble on the crank causing an intermittent air leak.
Either way, its old, needs some new seals and servicable items, and will be a lovely saw when sorted.

Yeah, sounds about right.
Will be a future project, takes a while to get the parts.

Thanks a ton for the help and time!

 

[Bob Hedgecutter]

I would be concerned the cage that hold the conrod bottom end bearing needles in place is starting to break up and a part of that has looped around the transfer a couple of times- scored the piston and exited via the exhaust port.
I have been caught by that before- replaced a top end, saw ran all good for a wee while and then more of the bottom end bearing cage let go and took out the new top end. Main case crank bearings passed the inspection tests- bottom end bearing felt okay, but on really close inspection and pushing the rod as far over to each crank lobe as possible, in the correct light and with magnifying glasses- it was then quite evident pieces of cage were missing- my fault for not being thorough and too eager to get a sought after saw running for myself- cost a second top end and a good secondhand crank.

 

[MartDalb]

I would be concerned the cage that hold the conrod bottom end bearing needles in place is starting to break up and a part of that has looped around the transfer a couple of times- scored the piston and exited via the exhaust port.
I have been caught by that before- replaced a top end, saw ran all good for a wee while and then more of the bottom end bearing cage let go and took out the new top end. Main case crank bearings passed the inspection tests- bottom end bearing felt okay, but on really close inspection and pushing the rod as far over to each crank lobe as possible, in the correct light and with magnifying glasses- it was then quite evident pieces of cage were missing- my fault for not being thorough and too eager to get a sought after saw running for myself- cost a second top end and a good secondhand crank.

This is solid advice, thanks a lot! You always show up with some quality advice .
I will make sure to investigate every bit before buying too many parts!

(sorry for the late reply, busy irl)

 

[huskihl]

Being on the intake side, usually means it was straight gassed or it ingested something through the carburetor. Bearing pieces flying around show up on the side and top of the piston where the transfer ports are

 

[Jacob J.]

I agree with @huskihl - something was ingested through the intake tract. 024s aren't known for blowing out bearings because of
two reasons:
1. - They didn't make much power new
2.- The reciprocating assembly is light, so they don't put much of a load on the main bearings

They were known for having a poor air filter on the early saws. The flocking would disintegrate leading to dirt ingestion.

 

[MartDalb]

Being on the intake side, usually means it was straight gassed or it ingested something through the carburetor. Bearing pieces flying around show up on the side and top of the piston where the transfer are

Just seems odd that it only really has damage to the piston, no signs on the cylinder at all.

Bearing is toast though for sure.

 

[huskihl]

Just seems odd that it only really has damage to the piston, no signs on the cylinder at all.

Bearing is toast though for sure.

Do you have better pics of the bearing in question?

 

[MartDalb]

Do you have better pics of the bearing in question?

Yeah it is kinda hard to get a good shot in there.
As mentioned, the saw does not have any play in the crankshaft etc.
But it looks like the bearing itself is missing a "ball" inside the bearing, when comparing to the flywheel side.

 

[huskihl]

Yeah it is kinda hard to get a good shot in there.
As mentioned, the saw does not have any play in the crankshaft etc.
But it looks like the bearing itself is missing a "ball" inside the bearing, when comparing to the flywheel side.

Spin the crank a few times and compare as it moves around. There may be a plastic retainer on one side and metal on the other and they may look different. Or remove the pto side seal and inspect from the outside

 

[trains]

inner ball race has come apart, balls are now chasing each other and not being held equally around, at times, there will be play, other times, it will be snug, bits from that have contributed to some of the damage you have already assessed.

 

[Bob95065]

Remove the seals and you'll get to see the outboard bearing cages. You won't see the inboard cages but it's unlikely but not impossible that the outboard side looks good and the inboard side has chunks missing.

I rebuilt several 029s that had bearing cages fail. IMHO plastic cages were a very bad idea but saved Stilh a little money per unit that meant significant cash over the production run. The plastic cages eventually failed and prices of plastic went through the engine. The PO kept on cutting and the crankshaft went eccentric which caused the seal to suck in air. Lean running scored the pistons. I was surprised they ran with the bearings like ghat but they did.

Keep in mind those bearings and seals have been in there for 30 years.