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MS291 questions

Steve Orner

Steve Orner

ArboristSite Lurker
Joined
May 30, 2016
Messages
12
Location
Newville
I picked up a complete MS291 for sale in a box completely disassembled because the piston has a hole in it, for $50 today. I want to put it back together. I was looking around for parts I'll need to order and I saw some posts about upgrading an MS290 to MS390 by replacing the entire short block. I've rebuilt some lawn mower engines, but this would be my first two stroke rebuild so I'm learning something new with this project. Are there any similar "repower" options for the MS291? I don't really see any but I wanted to ask here. I'm like Tim "The Toolman" Taylor, more power! The MS291 would be fine for what I want to do with it, but since it's torn apart and I have to order parts for it and there's an upgrade, I might as well do it.
 
HarleyT

HarleyT

A-Hole!!
Joined
Dec 6, 2014
Messages
18,152
The 291 is the big brother of the ms271, so the parts there are interchangeable.
Here is a teardown of a ms271, so you can see how it comes apart.
Part 2 is waiting for my internet to get fixed.

 
Steve Orner

Steve Orner

ArboristSite Lurker
Joined
May 30, 2016
Messages
12
Location
Newville
I have the manual for it now, and videos... hopefully it doesn't become a hot debate, but the manual calls for Dirko HT red sealant for the clamshell, which I would have to order. Would Permatex Ultra Black work? I have a tube here that I use on lawn mower engines without issue.
 
Steve Orner

Steve Orner

ArboristSite Lurker
Joined
May 30, 2016
Messages
12
Location
Newville
I was waiting for the piston, the final piece. It finally came today, and I put it all back together. I used an OEM piston in it, it wasn't that much more than an aftermarket. I cleaned everything and coated everything internal with engine assembly lube to give it a pre-lube. After I put it almost all together I realized I put the piston in backwards (arrow toward the intake). I knew which way to put a piston in, but somehow still did it backwards. So I had to rip it all back apart and fix that. It wasn't terrible to put back together. I didn't even have to refer to any videos, I just looked at the pieces and everything went back together... and I got to do it twice because of the piston mistake. So I filled it with fuel and put oil in it and after about 10 rips on the string with the choke on, it fired up. I left it idle to warm up, until it stopped blowing smoke out the exhaust from the assembly lube. It idled perfectly and has great throttle response. By the way I did the muffler mod with my air die grinder using a dremel cutting wheel and put a couple slots in the side and bent them open, just like another mod I saw on this site. It feels like a beast.

I'm planning to use this in my alaskan saw mill, with a longer than stock bar. I've already swapped the sprocket to a 3/8" and put a 24" bar on it. It's exactly the size I need. I know the 24" bar is a big more than recommended for this saw, but I'm not going to be ripping huge logs with it. I'm planning to make some posts and beams out of young locust that I have on my property to build a wood shed. They're straight as an arrow and only about 8"-10" thick, so I won't be using all the bar. I was going to use my 025 in it but it's a little too narrow even with a 18" bar.
 
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