The ideal ms260 timing numbers.

[thompsoncustom]

Did you heat the head from outside the top until your braze flowed, or did you go right in the bore with your torch?

The possibility of warping is why I never tried an exhaust roof. No choice but to have the heat right by the plating.

Both actually, had someone running a normal propane torch on the outside while I used a mapp/oxy brazing torch on the inside right in the area where I brazed. Piston doesn't make it all the way up to the band so ya it's wrapped, also checked it with just the rings.

What is this? It’s at same location on various pics of your chamber.

I have no idea I'll see what it looks like it person when I get home. Almost looks like a pit on my phone or something got smashed into the band but I don't remember seeing any damage on the top of the piston.

 

[thompsoncustom]

No idea what the little piece was but it's not there now.

 

[drf256]

Well,that stinks. At least you tried.

If you wanna go oem, I may have a jug. I find myself fighting to lower more than raise compression these days, especially on the 1121 model. The machining that’s needed makes them too high in comp.

Hey, it’s not how many times you get knocked down in life that counts, it’s how many times you stand back up.

 

[thompsoncustom]

Well,that stinks. At least you tried.

If you wanna go oem, I may have a jug. I find myself fighting to lower more than raise compression these days, especially on the 1121 model. The machining that’s needed makes them too high in comp.

Hey, it’s not how many times you get knocked down in life that counts, it’s how many times you stand back up.

Thanks.

I'm not gonna give up on this completely and will try to come back around to it at some point just to many projects at the moment to keep playing. china cylinders are cheap enough to keep playing with and throwing away till I get things figured out, wouldn't want to mess up a OEM jug.

A couple of thoughts:

I had the cylinder in the vise with just enough pressure to hold it but that seems to be where the cylinder wrapped on the inside so maybe the vise is the problem not the brazing alone.

I like the idea of a really small combustion chamber as the fuel should burn more completely but like you said at what point does compression become more of a problem then it's worth. It also makes me wonder if compression is all the same say 200psi would the saw be happier at 100, 105, 110 exhaust. I'm sure theres a bunch of variables I don't understand as playing with my saws is new to me.

If I can't get this cylinder running I'm gonna cut the head off of it and use it as mold for brazing the side of the piston. That way if a 110 exhaust roof was great I can atleast widen the exhaust port for more area.

 

[NateSaw]

@drf256 builds a mean one.

I'll second that.

 

[thompsoncustom]

Well played with this a little more, so the cylinder was warped bad enough that I couldn't get the piston to TDC and seemed to be rubbing about a 1/2in lower. I ended up reheating the cylinder and bolting it on the case and running the piston up to TDC and letting it cool. It did help reshape the cylinder to the point it would rotate by hand but was still rubbing. Ended up taking a little off the sides of the piston opposite of the intake and exhaust ports and it turned over freely.

I ran it enough that it got warm but didn't cut any wood with it as it sounded like a diesel which I assumed was from piston slap (it was). Before I pulled the cylinder back off I got compression (170psi) which is about 30psi less than I was thinking it would end up using a compression ratio calculator.

I didn't take any pictures but with the cylinder being ovaled the piston was twisting in there and wearing the exhaust side pretty good and the intake some also but the sides opposite of that had some bad scaring from where the piston grew and rubbing the wall, surprised it still had 170psi.

So that cylinder is dead but I will probably use the old piston and cylinder to see if the piston can be brazed and widened without warping.

Overall I don't fell like trying to braze a cylinder is a good idea just to much risk in warping it.