Need some help with a 260 rebuild

That one ate something it couldn't digest .The cylinder looks like it will clean up but that's just a guess .It wasn't straight gassed .

If the cylinder does clean up use either a Dremel with craytex to smooth the chamfer on the intake port or use some fine sand paper very gentley .

I hate to be the bearer of bad tiddings but with a grenaded piston it's always best to do a case spit and make darn certain all the tramp aluminum is out of the bearing .Just a tiny bit of residue of same will cause a bad day if it gets in a bearing .
 
I thought I replied to this???

This piston looks like result of neglect/dirty air filter or dust going thru to make piston skirt thinner.
As piston is almost round cold and sort of oval hot, almost egg shaped, it expands more on intake and outlet sides than in transfer sides.
If it was straight gas'd it should show something some were. Oil film is usually gone, no oil in crankcase or bearings...
Dry ruff surfaces...
It could also be result of a long term airleak from intake boot, cylinder base or crank seals.
That can leave this scoring too if it is run really hard so it gets hot fast as it is running lean.
 
I tried to clean two scored cylinders from my 066, not with oven cleaner, but with Destop (sink caustic cleaner), same chemical process. The melted aluminum goes away easily with a little patience. But I had no luck with this both trials.
Under the heavy aluminum build-up (very big stress on this points, either mechanical and thermal), the nikasil layer had very small cracks in it. We can't see them, but the caustic cleaner yes. It goes throw them, even in a extremely small amount and reacts with the aluminum body of the cylinder. The result is a production of hydrogen which rises in pressure under the nikasil layer. The small cracks are too tiny to allow the gas escaping quickly, so the pressure rises up and blows out the nikasil layer around the defect. You get a loose area at this point and the layer peels off easily. Not a very big hole, maybe around 2 mm wide and 3 to 5 mm long, but enough to ruin the whole part.
Don't try to reuse it, you'll lost compression and risk to send small bits of nikasil in all the engine (and wreck again the piston, rings, and eventually the bearings)
 
  • Thread Starter Thread Starter
  • #31
Think I found the cause

The interesting thing is everything checked out except for the crankshaft. Most interesting thing is the crank case is spotless ???

IMG_2659.jpg IMG_2658.jpg
 
Can you get a pic if the crankcase sides?
This hit something repetitively. Not just once.
Is there main bearing play? Was there play in case bearings?
Piston top damage?

Piston dust will burn. If parts are crushed they are gone. Sometimes in cracks and edges you find a bit if you look hard.
 
I rebuilt 5-6 of these and a bunch of 026.
Proberbly junked more...

I have seen this damage on a 026 with bad bearings, both main bearing and crank bearings made it hit the edge of the case.
 
Well, this crank bothers me. Bearing seat on clutch side show sings od spun bearing.
Looking at the pic's I think something came way to close to crank case side and made markings.
Hard to tell as it is cleaned if it is old or from this incident.
Strange place for a number isn't it? Make sure you oil gasket before assemble....

In any case if this sw is to be good it will need new top end, bearings, seals, hoses, gaskets.
Why not do it right and put a good crank in, new grommet for carb and renovated carb.

I would not use this crank... Not sure if I would use the crankcase either unless the bearings seated perfectly.

Might be easier to get another and use parts left from this one...
 
1. What is this? JB weld? sealer?
2. Markings of something coming way to close...
3. More markings, could be were damage to rod was made perhaps.. (In top of this circle is were you often see the rod hit)
4. More markings on wall that make me thing the crank moved sideway's rather than having something stuck to it.

IMG_2670.jpg



Left side casing also have marks from crank or something stuck to it.
The dirt and stuff inside this case would help tell the story, but either way i would not use crank or case.
Easy to find good used ti spend the money on, so that would be my way to go.
 
I find it very hard to believe there was no bearing play. There should be looking at these pic's.
But what happened first? What is the cause of it...

My theory:
I believe this swallowed enough crap to damage piston (thin intake side) enough that this alu grit came in to crankcase and worked on the bearings as sandpaper would. As play increase it leaks and run hot, causing more damage to piston, perhaps the bearing on right side locked up and spun a bit...

Bad air filter/neglect would be cause I think. The rest is consequences.

Hard to tell for sure, but entertaining guess game none the less....

Would be more accurate with pic's before cleaning and without it apart we could measure it up and see if there was play.

Some play and leaking is OK provided there is no other problems.
A saw can run a long time with this or a locked up bearing spinning on the crank or in housing.
 
I think the dust is actually what killed it .Surprising though because most times the insides of the crankcase will be blackened because of the fine wood chip dust pyrolizing within the crankcase if that be the case .

It doesn't appear though that the piston got cooked which is also surprising because more times than not a sloppy crank shaft will take out the seals .A real puzzler .

Now here's a question which I ask simpley because I don't know .Is the flywheel side seal a single lip seal or a double lip ? I've never seen an 026 apart but according to my IPL's it takes a 12- 20 -5 seal which is the same size as an 020 or 200 T .Now I speculate the 026 uses a buna-n seal where I think the 020T is a viton seal .
 
  • Thread Starter Thread Starter
  • #40
Well guys I guess I'm in over my head ... when I split the case it was really clean. The seals looked great ( I didn't vac. test as I got the saw with the cylinder off.) I found the bearings spinning but they did have ? dust in them as I washed them in engine cleaner and then they really spun nice. There was some wear no doubt but I would say mild - mod. only. I wouldn't say there was any play other than the slightest bit "maybe". On close examination I'd say that the piston arm (sorry if that is the wrong name) has minor play. It really likes to slide from side to side (between the weight) but that is over the needle bearings and that was more lateral movement. I did note some dark discolouration over the needle bearings but that was it. They cleaned up with abit of wiping. Magnus you obviously have a very keen eye because I'd say the case was spotless. I would have said that even slight rubbing on that aluminum housing and I'd have seen obvious wear marks. You guys are the experts and I maybe need to find someone here close to home to go have a look at it. Sorry to have bothered you all.
 
No need to be sorry, this is what I do and I really like it.

I have a great interest in saws and this makes you learn a bit.
That said you must know that internet diagnostic is a guessing game more than anything as you don't really get the all info you need.
Pic's help, but it is far from reality.

If there is dust in a bearing it came from inside if the seal is there, no matter condition.
If it is Grey it is often aluminum, white = Steel, Black =carbon/burnt oil.....
With a piston like this there is no such thing as clean case. You might not see it clearly, but there is crap everywhere unless it is washed.
Grey and white is hard to see unless you stroke surface with dark cloth or finger.

Side play is good in main bearing of piston rod. It isn't going anywhere...
Up and down play big enough to feel by hand is too much.
Case bearing is about the same, if it is enough to feel by hand on crank it is too much.

Considering it will cost you parts in any case it is not worth the risk putting this crank back IMO.
Letts say you do and it gives a 20sek run, you will be pretty pissed....

Better do it right if you are to. Just as much fun and it will last longer and perform better.
 
Just to add you can't save them all because of the expense involved .Toss the parts in a box and put them on a shelf .Given enough time a donor will come along for next to nothing and you're in business .Just try and remember where you stuck the parts in the first place which is often a challange in itself .
 
I find boxes and saws I did not know I had....
Still have a pain trying to find parts I know is there in the piles...

I have boxes to sort them in to, just lack motivation I guess.
It is a bit of work involved....
 
Don't feel so bad as I only have perhaps 5 percent of what you have and I still can't stuff when I look for it .Just the other day I was looking for a complete Mini Mac 6 ,couldn't find it or the other 4 -5 of those minis' I have .
 
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