Modifying an AM MS381 Cylinder to fit on a Stihl 440.

[Rich Fife]

This will probably be a waste of time... but, I got bored and figured, I might as well actively waste my time doing something stupid before I hit the weights.

Lower Fin removal And rough blending... is in-progress.
Still have to open the 4 bolt holes in the flange...
Still have to open the intake to make it symmetrical-ish.

Check squish and get numbers.

 

[Rich Fife]

"Stock" numbers... with a 460 piston.

Exhaust 98*
X-fers 118*
Intake 70*
Squish .010"

I like where the starting numbers are.
I especially like the fact that the crown of the piston is below the floor of the exhaust. Now I have the option to taper the piston as well as to match the exhaust roof and floor to the piston chamfer.
Tomorrow, I'll remove .050" from the base and .060" from the squish.

 

[Rich Fife]

.060" from the squishband and added another chamfer... double cut squish... I have a 272 piston in the box... so this one might have a little extra thump to it.

 

[Rich Fife]

Cut the base .020", trimmed the crown of the 272 piston a decent amount... opened the piston windows and raised the x-fers...
final numbers before assembly...
100/118/75
.020" squish

 

[Rich Fife]

Fin removal and blending... good enough for testing purposes... Time to cut the exhaust flange at approximately 15* I might have to clearance a fin or two.

 

[Rich Fife]

Exhaust flange cut... I should have it fired tonight... providing I'm able to get into the garage at a decent hour.

 

[NateSaw]

This is awesome. Post vids!

 

[Rich Fife]

Muffler has interference as well as the sparkplug... lol

 

[NateSaw]

I wonder if hitting that housing with a heat gun, and using a scrench to mold in the clearance for the plug wire would work?

 

[Rich Fife]

I wonder if hitting that housing with a heat gun, and using a scrench to mold in the clearance for the plug wire would work?

It probably should've... I'll have to try that next time!

 

[NateSaw]

My bad! Did you machine it?

 

[Rich Fife]

My bad! Did you machine it?

I clearanced it with a bit.

 

[Ronie]

Looking good, can't wait to see how it runs. I put an after market 381 cylinder on a Poulan 330 and it runs very good.

 

[srcarr52]

Why a 381 cylinder instead of a 460 cylinder? Both are 52mm?

 

[Rich Fife]

Why a 381 cylinder instead of a 460 cylinder? Both are 52mm?

I feel as if Everybody does the 460 cylinder swap... I thought about going that route, as I have an extra OEM 460 cylinder in the parts bin... But, I like taking the path that many don't travel... aka, the hard way.
It wasn't a bad build, but, it Definitely took longer than I had expected due to the fact of having to remove the cooling fins. I still have to make a muffler/pipe for it.

Yes, the 381 is 52mm.

 

[Rich Fife]

Looking good, can't wait to see how it runs.

Once I fab up an exhaust, I'll toss it in some wood post it.

I put an after market 381 cylinder on a Poulan 330 and it runs very good.

Nice! I'm not familiar with Poulans. How many cc's?
I wish I could find an OEM 381 cylinder... in "stock" form they leave A LOT of room for changes...
This one I have at 100/118/76 with .022" Squish... with that said, I'm not impressed with it so far... currently it's set fat without an exhaust... I need to see what the cylinder pressure is... it feels a little soft.

 

[srcarr52]

I feel as if Everybody does the 460 cylinder swap... I thought about going that route, as I have an extra OEM 460 cylinder in the parts bin... But, I like taking the path that many don't travel... aka, the hard way.
It wasn't a bad build, but, it Definitely took longer than I had expected due to the fact of having to remove the cooling fins. I still have to make a muffler/pipe for it.

Yes, the 381 is 52mm.

So you didn't see any advantage to the 381 cylinder besides you could say you did it first?

 

[Rich Fife]

So you didn't see any advantage to the 381 cylinder besides you could say you did it first?

No not really, in my opinion, it would be wise for others just to do the 460 swap.
As for being the first to do it... idk if i am... regardless if I was or wasn't that stuff doesn't matter to me. I just enjoy tinkering and finding different ways to make these things run relatively better than stock. I ordered good used 038 magnum cylinder. I'm curious to see the differences between the two. If they're relatively close I'll do up the OEM and slap it on.

 

[Ronie]

Nice! I'm not familiar with Poulans. How many cc's?

Stock it's 50cc and I think with the 381 cylinder it's arond 68cc. @Maintenance Chief started a thread on Poulan hybrids, https://opeforum.com/threads/poulan-hybrids.27979/, and the 330 is at the end of page four. It's not professional quality work but it runs good. I've also started on a 50cc Craftsman, same as a Poulan 3000 I think, it will be the same cc as the 330 but about a pound lighter. Pics are of the 381 cylinder that's going on the Craftsman.

 

[Rich Fife]

Stock it's 50cc and I think with the 381 cylinder it's arond 68cc. @Maintenance Chief started a thread on Poulan hybrids, https://opeforum.com/threads/poulan-hybrids.27979/, and the 330 is at the end of page four. It's not professional quality work but it runs good. I've also started on a 50cc Craftsman, same as a Poulan 3000 I think, it will be the same cc as the 330 but about a pound lighter. Pics are of the 381 cylinder that's going on the Craftsman.

That's badass man... my old man has an older craftsman and that little sucker screams... I should snag it from him and modify it... then wait for the phone call.

Thanks for the link... I'll check it out.