MS880 Cylinder - toast?

[flames]

Started to look at my 880 tonight, as it was intermittently stalling during idle.

 

I figured it was carb probs, but did a compression test 1st, got about 140psi, not too bad I thought. - popped the exhaust off, noticed a few minor score marks on the piston, saw that the rings looked a little odd (not seized though) and could see and feel a small hard bit embedded on top of the piston.

 

After taking the cylinder off it was clear that the upper ring's anti rotation pin had come out and that was the thing embedded on the piston top. The top ring had rotated and worn the chrome away around the exhaust port.

 

Amazingly the saw was still cutting really well, loads of power!

 

This piston was an after market replacement (probably not a meteor though) that has done 4 years of hard work, so I'm not too devastated.

 

But here's the big question - is the cylinder still usable?

[MATTMOSS]

I would certainly start to clean it up with some fine emery cloth and some acid, see how it comes up.

I cant really tell from the photos- has the ring opened out into the port and worn the edges away?

Its amazing how these things come up with a bit of patience and some elbow grease.

[spudulike]

That bore looks bad - it looks like the exhaust port has wear all around it framing the port in bare aliminium plus it looks pretty scored.

 

Difficult to always tell from images but it looks past it to me:thumbdown:

[flames]

I would certainly start to clean it up with some fine emery cloth and some acid, see how it comes up.

I cant really tell from the photos- has the ring opened out into the port and worn the edges away?

Its amazing how these things come up with a bit of patience and some elbow grease.

 

yeah the ring has definately worn the exhaust port

 

That's my gut reaction too spud, do you know how much the exhaust port can be opened up on an 88 cylinder? The rest of the pot is not too bad, scoring is minor - not deep and only below the port.

 

Why is there not an after market pot for 88

[MATTMOSS]

Oh dear, if that is bare aly around the port then I would say it is definitely scrap.

[flames]

For reference, here are some pics of the piston.

 

I don't know how much a Stihl piston would have been, but I think a genuine part wouldn't have failed like this £25.50 one from China.

 

Looks like the materials are inferior, the top ring anti rotation pin appears to have worked it's way through the piston top, the lower one has started to embed as well and the ring can pass over it now. The ring edges have started to peen over. Also one of the gudgeon pin retaing clips has lost an end.

 

Other 88 users: if you (or some else ) seizes your saw and you can salvage the barrel, maybe invest in a genuine stihl piston

 

-called round a few places to see about replating, no one seems to do blind bores. I have one place to call tomorrow. (spoke to Langcourt - don't do chainsaw cylinders, and BDK engineering - very helpful but also don't do blind bores). Has any one had any luck going this route?

[bobh]

As I found out to my cost these cheap pistons can be very expensive indeed.

I know how you feel, at least with mine it was only a 650 cylinder that got wrecked

[flames]

Where was this back in Feb...

 

STIHL LATER VERSIONS MS880 CYLINDER & PISTON ASSEMBLY (60MM) NEW 1124 020 1209 | eBay

 

-anyone used one of these yet?

[flames]

The above reminded me that I took a few re-build & test pictures...

 

For comparison: new Chinese piston compared to genuine Stihl one (on right with rings fitted). I fitted the genuine Stihl cylinder & piston.

Vac./pressure test.

Tach. and temp. sensors & test cut: 50" - 8-9k rpm loaded in cut. (Unloaded 13k rpm, tuned a little rich to run a little cooler for milling.)

After short milling cut: Idle speed 2.5k rpm, temp: 171°C (Max temp after 5min mill cut: 200°C, Idle temp after few mins about 130°C.) Sensor in fins above exhaust port.

 

I can't take any credit for the use of these sensors, I've just copied an Australian chap, - to compare and monitor how my saw runs during milling. FYI this is a cheepo tach no good for tuning, refresh time is far too slow. I used a wireless Fast Tach for that.