What do I have here? An atypical 10mm 044 cylinder.

Over the weekend I picked up another 044 project, used and dirty but not abused. It's an early 10mm, with the metal tags and red switch shaft. When I pulled the shroud off, I was surprised to see the top fins going straight across instead of the usual near-45-degree angle. I initially suspected it was an aftermarket item that somebody threw on there, but it's got the Stihl logo. Compounding the strangeness, there are no other logos or names that I recognize -- no KS stamp, no raised lettering that says Mahle or even Gilardoni.

It's definitely a 10mm wrist-pin saw. The ring-positioning pins line up neatly between the intake and transfers, which I wouldn't expect if it were a 12mm cylinder paired with a 10mm piston. It has the D-shaped combustion chamber. If this is not the original cylinder, which is plausible because it did seem a little cleaner than the rest of the saw, then I'd say the replacement was done years ago. At some point the saw ingested a small screw, which got pinched between the piston and the edge of the combustion chamber a few times before it was expelled. Thankfully it didn't touch the plating or do any other meaningful damage.

So, uh... has anyone seen one of these before?

 

I'm just guessing here but could the cylinder be a 12mm cylinder that ran with a 10mm piston? (i.e. the saw is 10mm and someone swapped in an 044 12mm piston later)

Stihl made the cylinder rather than KS or Mahle.

 

I considered it, but from what I've read that combinstion is problematic because of the relative positions of the ports and ring ends. There doesn't seem to be any such issue here.

 

It was one of the latest cylinders on the 440. If the pins aren't in a transfer then it's no big deal

 

Thanks. Given that the pins aren't in a transfer I feel like I must have misunderstood something about the differences between 10mm and 12mm pistons and cylinders. Are there variances in 12mm cylinder design such that some will work with a 10mm piston and some won't?

 

yep

 

I found a saw that belonged to a logger with a 12mm jug on a 10mm saw... and something snagged enough to bust the base of the jug. The case was junk, too, but I got a nice wrap handle, screw cap tank, and tall clutch cover for basically nothing.

 

FWIW I posed the same question on AS and the only person to venture an answer so far said it looked like one that was made during the transition to 12mm, before they'd added a decomp (this doesn't have one). He said he'd heard others mention the such cylinders existed, that worked on either 10 or 12 mm pistons.

 

I didn't think there were any 044's with a decomp?

 

044 magnums had a comp

 

Ideas as to when? Mine was a late model and it didn't.

 

Not sure, my cousin has two of them and they both have the decomp

 

There's been those stihl cylinders found on saws for years. No real pattern to when they used them. It seems they may have been throwing some on from time to time to seehow they held up

 

Were there any MS440's that didn't have a decomp? The IPL only shows one cylinder. If all 440's had decomps then this cylinder is clearly an 044 (i.e. not a 440) part.

Just to make sure I've got it right, is that the problem with using a 10mm piston with a typical 12mm cylinder, i.e. that parts of the transfers extend so far back towards the intake that ring ends can pop out into them? Because that's definitely not the case here. In this pairing the pins neatly track right down the middle of the space between intake port and transfer. It's not even close to being problematic.

 

I never seen any without but I haven't had many of the older ones. I think that's right and not the other way.

 

Speaking of such problems, how does it work with that cylinder you've got in your avatar, with the finger port that actually overlaps the intake? Is the finger narrow enough that you can get away with that stunt, or did you install the piston backwards?

 

Piston backwards. Thats a 288 so the ring is centered any way

 

Yes.

 

Huh. Less consistency here than I'd expect.