Saw building 101?

[LAWN BOY]

I'm getting a Stihl ms250 from my uncle for free, needs a new piston and maybe cylinder. I was leaning towards using aftermarket parts... Any recommendations on pistons and cylinders on a budget? I'm tossing around the idea of doing an all out build and learning some more stuff while I have it apart. It'll be my first rebuild. What's involved in porting? What tools would I need to do it myself? What about dying the plastics? I'd like to dye them black, what materials would I need for that? This will probably be a project for this summer, but we shall see.

 

[GMB74]

Dying the plastics is simple. Clean them up well, get some Rit dye and a big pot of water, follow the directions on the package.
Aftermarket parts are always a gamble. I have used the cheap no-name pistons and cylinders off ebay and they have worked. But maybe I have just been lucky. Using name brand parts like Hyway may increase your odds, or maybe not. Check the return policy on whatever you buy. If you are going to port the cylinder, you can get by with a lesser quality item because you are going to grind out the defects anyway.
Someone should be along shortly with more specific information regarding porting.

Get the shop repair manual to have handy in case you run into a snag when rebuilding.

 

[Woodwackr]

I wouldn’t spend much on it. That is a $200 saw when completely fixed up.

 

[GMB74]

It's not worth a lot of money, that is true. On the other hand he doesn't have to invest a lot of money. Aftermarket parts are cheap and generally of decent quality for this model saw. If it doesn't work out or blows up, he hasn't lost a lot. Just the cost of tuition for his learning experience.
Here's a thread with some good cheap and easy upgrades, once you get the engine repaired:

Thread 'Bernie’s MS250 Upgrade'

Oct 21, 2023

My good friend Bernie has a nice MS 250 that he’d like me to improve. Usage is for dead tree cleanup on his property and firewood cutting. Runs great, he takes care of his stuff.


After reading a bit more about this model, looks like a muffler mod is in order, but not much else. I hesitate to open it up and adjust intake and exhaust port widths.

Any suggestions on the muffler mod recommended for one of these?

• Paul Fithian
• Replies: 73
• Forum: Chainsaws

 

[hacskaroly]

I'm tossing around the idea of doing an all out build and learning some more stuff while I have it apart. It'll be my first rebuild. What's involved in porting? What tools would I need to do it myself?

Here is a video of a guy porting a clamshell Poulan (similar to the MS250), should give you a good idea of what you might need and how to tackle a porting project.

 

[lehman live edge slab]

Odds are the cylinder will be ok and he could get by with some aftermarket crank seals and a meteor piston kit and only have 60$ or so into it. If it needs bearings I bought 6202 skf for 6-7$ each.

 

[S&S_Work_Saws]

If you need any parts I've got one under my work bench I'll send ya. Just pay for the ride.

 

[92TRX300FW]

I'm getting a Stihl ms250 from my uncle for free, needs a new piston and maybe cylinder. I was leaning towards using aftermarket parts... Any recommendations on pistons and cylinders on a budget? I'm tossing around the idea of doing an all out build and learning some more stuff while I have it apart. It'll be my first rebuild. What's involved in porting? What tools would I need to do it myself? What about dying the plastics? I'd like to dye them black, what materials would I need for that? This will probably be a project for this summer, but we shall see.

i won't reccomand porting an aftermarket cylinder and what i would reccomend you is repairing that ms 250 and sell it then buy a pro built saw and put your time and effort on that saw because an ms 250 is not a fun saw to work on just my opinion

 

[LAWN BOY]

I've heard from others that the 250 is not fun to work on. The thing is tho I'm kinda of expected to at least rebuild it and then maybe keep it since my uncle is giving it to me as a "birthday gift" and so on. So I may as well learn on it and make it cool so it's worth keeping.

 

[hacskaroly]

I've heard from others that the 250 is not fun to work on. The thing is tho I'm kinda of expected to at least rebuild it and then maybe keep it since my uncle is giving it to me as a "birthday gift" and so on. So I may as well learn on it and make it cool so it's worth keeping.

The not fun part I have found is the clamshell cylinder set up (same with the 271, 291, 311 and 391), you have to get the right amount of sealant in just the right places to prevent an air leak between the cylinder, base and around the bearings (no gasket). I just swapped everything from one 271 crank case to another and ended up with an air-leak on the flywheel side - so I have to tear it all down again and clean off the gasket sealer and try it again. I had to do it four times on a Poulan, just could not get it. With these, you can't split the case, they are glued/melted together, so if something gets jacked up on the crank case (in my case with the 271, the plastic on the clutch side melted), you need to get another crank case and swap all the other parts over. After I get this 271 fixed, I have another one with the exact same problem - so I will probably get another $40 used crankcase off of eBay.

You never know, you may end up with the knack for it and it might not be a big deal to you.

 

[lehman live edge slab]

The not fun part I have found is the clamshell cylinder set up (same with the 271, 291, 311 and 391), you have to get the right amount of sealant in just the right places to prevent an air leak between the cylinder, base and around the bearings (no gasket). I just swapped everything from one 271 crank case to another and ended up with an air-leak on the flywheel side - so I have to tear it all down again and clean off the gasket sealer and try it again. I had to do it four times on a Poulan, just could not get it. With these, you can't split the case, they are glued/melted together, so if something gets jacked up on the crank case (in my case with the 271, the plastic on the clutch side melted), you need to get another crank case and swap all the other parts over. After I get this 271 fixed, I have another one with the exact same problem - so I will probably get another $40 used crankcase off of eBay.

You never know, you may end up with the knack for it and it might not be a big deal to you.

I personally don’t think they’re a big deal only one I’ve had issues with so far is one ms250 and it turned out to have a warped bottom pan. From now on I’ll make sure the pan is flat on a piece of glass before assembling. This particular 250 had issues since new and I had apart 3-4 times before i switched the pan.

 

[GMB74]

Working on clammys is a state of mind. Yes, you have to disassemble a lot of stuff to get the engine out of the frame, but once you have done that, the whole engine is there in your hands.
I have found 2 main problems when sealing the crankcase:
1) Check the base plate/crankcase cover/bottom pan for flatness. Over time they warp. Place the cover on a sheet of glass and check it with feeler gauges. If warped, get a sheet of fine wet or dry sandpaper and some oil. Place the sandpaper on the glass and polish the cover until flat.
2) Clean clean clean. No oil, water or dirt in the joint you are trying to seal. Final cleaning with acetone and a clean rag.
Assemble the engine with the cylinder facing down. Get it in the frame, tighten the bolts and leave it upside down overnight to let the sealer cure and not get contaminated with oil running down into the joint. ( you did oil the piston, cylinder and bearings when you installed them, right?)
I have had the best luck using Dirko as a sealant. It will fill in minor gaps and imperfections, Threebond/motoseal/hondabond/yamabond, etc. is thin, meant for zero-clearance applications and may not work unless everything is perfectly flat. Other sealants like Hylomar and Loctite/Permatex anaerobic sealers have been suggested here on this forum, I have not tried them so can't comment.

 

[hacskaroly]

Assemble the engine with the cylinder facing down. Get it in the frame, tighten the bolts and leave it upside down overnight to let the sealer cure and not get contaminated with oil running down into the joint. ( you did oil the piston, cylinder and bearings when you installed them, right?)

I will give this a try, I did not think about the WD-40 on the cylinder and piston/rings running down into the sealer, I can see how that could be an issue.

I personally don’t think they’re a big deal

I have only worked on a few so far and I am sure it will take more practice on my part. Like I said, the Poulan I tried was a pain, of course it was the first one I tried. The 391 and 291 I did went together flawlessly, the 271, minor issue compared to the Poulan. It could also be with bigger fingers, the smaller saws will be more of a challenge!