Sthil ms260 rebuild

[Chade]

Hi all

My sthil ms260 was starting fine but overheating and cutting out. My local garden machinery repair place told me it was because the piston/cylinder was scratched and as this would probably have damaged the rod it was beyond economic repair.

Knowing nothing about engines, but surprised by the cost of new chainsaws, I spent some time on google and youtube. I ordered a new crankshaft, piston, various bearings, gaskets and cylinder assembly. It took me alot longer than I anticipated but the chainsaw is now back together with all the bits replaced. I was happy with everything but now realise that with all the jumping about on youtube I have greased one bearing too many. As well as the bearing I should have greased (in the sprocket) I have also lightly greased the little end bearing with lithium grease. I know really I should take it all apart again to clean it and put it all back together, but if I started and ran the saw as it is and everything else was right would it do much harm?

TIA

[T i m]

Do you know how they knew that?

'Probably'?

Ouch (unless they were Chinese clones)?

They are quite straightforward once you are used to them. Daughter had to demonstrate basic engineering skills on her MS260 as part of one of her chainsaw tickets (CS30?). [1]

Are these 'plain bearings' (metal on metal) or 'open' (presumably) roller or ball bearings?

The only place I can think of where you wouldn't want grease is on the centrifugal clutch shoes and they are fairly easy to get to if you thought there was a chance.

If they did have grease on them some brake cleaner might get it off or when I was a lad I'd boil them in some washing detergent. ;-)

Cheers, T i m

[1] When taking their chainsaw maintenance test (at the Arb College) the group all worked at the same time and were 'tested' on completion of the re-assembly.

One lad presented his saw and the examiner questioned 'if he was finished'. He said he was, so he repeated the question ... 'are you sure you have finished', same reply. So he failed him for having the chain on back to front. ;-(

[newshound]

I'd expect it to be a needle roller.

I wouldn't worry about having greased it, once it gets warm the grease will soften and inertial forces will take care of the rest. As it is a two-stroke any grease residues will rapidly be flushed out through the cylinder.

IME modern linings in CF clutches are fairly insensitive to mineral oils. But I agree with your fixes if that is a problem

[Chade]

They said they had removed the muffler and so looked directly at the piston.

Apart from one bearing they were third party at less than a third the cost.

Pin roller bearings. I guess they would be classed as open.

The clutch shoes are grease free.

[Chade]

Thanks. I was worried about it dissolving in the fuel and gumming up the piston somehow.

[T i m]

Ok. Did they give you it back complete and did you confirm the damage when it was apart OOI?

If you still have the old parts, can you feel any slack in the big end bearing or gudgeon pin? If you hold the crankshaft still and the conrod square to the crank, can you move the rod up and down at all (in the same plane as the rod, not sideways or rock it etc)? If not (and same with the piston to rod), you might not have needed a crank if they don't come as one assembly (with piston etc) and maybe keep it as a spare?

OK, result. ;-)

<snip>

Yes, 'open' in that they didn't have seals and you could get grease on them (even if only when out of the machine etc).

Cool.

As newshound confirmed, the chances are any bearing in a chainsaw is unlikely to suffer with (over/) greasing and if it's say on the big end or crankshaft main bearings, are likely to be washed out with fuel pretty quickly anyway (and why there is oil in the 2/ mix).

Well done for saving another otherwise 'written off' tool (we have saved others similarly by mixing and matching 'broken' kit).

Cheers, T i m

[AJH]

This is standard first call with a saw that has become difficult to start, most often the damage is on the hot exhaust gas side and you can see there the aluminium has smeared on the ring.

[newshound]

Won't happen. You will get a trace of (probably) lithium salts as it burns up on its way through the cylinder. Two stroke oils used to be ordinary mineral oils (like the "oil" part of the grease). Modern ones tend to be synthetics with less tendency to form gums and lacquers, but there's only a tiny amount in the bearing compared to what the engine will use in an hour's running.

[Chade]

I will examine it and see. Thanks.

<snip>

I have two other chainsaws in the shed that are not running right one a bequest and one I was previously told was obsolete with parts unavailable. Yet When I inquired at the place that looked at the MS260 they swore they could still get them by ordering direct from Sthil.

[Chade]

It was ok starting just overheated and cut out after a few minutes work. There were some scratches to be seen on the piston and cylinder but I would not say anything had smeared.

[Chade]

<snip>

Missed this question somehow. There was some scratches on the piston and cylinder. They did not seem terrible though and if I had seen a certain youtube video earlier where light scratches were polished out with fine "wet and dry" I might have been tempted to try that. I still might one day as an Sthil 038av that has slightly different symptoms was taken to them at the same time and they blamed it's problems on scratches and declared it uneconomic to repair too.

[T i m]

<snip>

Just for the S&G's I put a new ring in a blower that had broken it's ring and scratched the bore and whilst it did actually run, it didn't run well (unsurprisingly). ;-)

Cheers, T i m

[Chade]

<snip>

Apologies for replying to myself but despite not being to find the part I needed anywhere on the internet a few years ago I now see a new one listed on ebay. Yay!

Right. What do I need to do to a Sthil 026 that has not run for years to get it ready to go?

[T i m]

<snip>

What you sometimes find is a lull between the manufacturer stocking a part and aftermarket manufacturers stepping in to fill the (then fairly limited) niche.

Might be worth dragging them out and giving them a look over, now you have had success with the MS260. ;-)

You can easily check for spark, compression, see if it's getting fuel etc etc, then if it does start but rattles you have a better idea what you might be in for.

Cheers, T i m

[Chade]

I have another post on this thread about the Sthil 026. The other problem saw is a sthil 038av. It starts okay, sounds okay but only runs about two minutes before cutting out.

[T i m]

<snip>

Seen.

;-)

That could be a thermal thing (depending if you can re-start it after it's run for 2 mins and stops or not).

I had an ignition coil on a generator cause that exact problem [1] (it wouldn't re-start until much cooler again). There was 'a' spark when tested outside the cylinder, but obviously not enough to make the machine actually run.

Obviously if it's been standing for any time with any fuel in it a flush of all the fuel system (inc maybe cleaning the carb but leave the actual strip down till last unless you have a service kit for it) might be a worthwhile exercise.

On any old 2/, crank seals can also harden and cause all sorts of strange issues (so would change them on any rebuild if there was any hint of them not still being fully pliable).

Cheers, T i m

[1] Similar with the car, would start or restart when either cold or hot, but not *re-start* when warm. Turned out to be the ECU.

[T i m]

<snip>

A local agricultural equipment place was 'repairing' new 4-2/ [1] strimmers for £50 a go when it was just a matter of adjusting the valve clearance (that literally takes seconds).

Cheers, T i m

[1] Still 'dry sump' so lubrication via the oil but with valves as per 4/ for better economy / emissions (less over scavenging).

[AJH]

I must have missed this; O26s had a strange problem with wearing the piston skirts wafer thin.

[AJH]

With Nikasil lined cylinders it is unusual for the bore to get scratched from seizing or "nipping up" unless a hard foreign object has been ingested. What normally happens id the aluminium piston overheats and partially melts, not only jamming the ring in the piston lands so it can no longer spring out and make a seal but also the bore picks up some aluminium. Often you can get away with replacing the piston and ring but you must remove the aluminium pick up in the bore, both chemically and followed by a light hone.

[T i m]

<snip>

Agreed. I believe the barrels on both my BMW motorbikes and the Merseschmitt are Nikasil plated.

Yeah. I used to spend quite a bit of time in the local motorcycle shop (I was their voluntary 'IT guy' and they were personal friends <g>) so seem loads of those sorts of things of the 'lads' of-road bikes.

Is there any chance any 'smearing' you / we see is the surface Nickel being worn off till it gets to the Silicone Carbide in non seize cases?

Cheers, T i m