Anybody want to see inside a 151t?

[Ketchup]

I have another one of these on the bench right now. Thought I’d share.

Everything except that little chainsaw heart on the right is the same as a 150t. Mostly a basket of plastic bits woven together and tacked with t-20 screws. They come apart fine once you’ve done a couple but I can’t help but think what the plastic will be like in ten years.
As far as I can tell, this is the only change from the 150. That’s a 0.050” popup straight from the factory with a cute little dimple for the spark plug. This is a brand new saw. That grey/green sludge is Stihl mix. Awful stuff.
Beside a 150 case and piston for comparison. Note the difference in the fresh air window around the wrist pin.

These new pistons have two major casting bosses under the skirt. That just seems wrong to me.

 

[Lnk]

I have another one of these on the bench right now. Thought I’d share.
View attachment 323096
Everything except that little chainsaw heart on the right is the same as a 150t. Mostly a basket of plastic bits woven together and tacked with t-20 screws. They come apart fine once you’ve done a couple but I can’t help but think what the plastic will be like in ten years.View attachment 323097
As far as I can tell, this is the only change from the 150. That’s a 0.050” popup straight from the factory with a cute little dimple for the spark plug. This is a brand new saw. That grey/green sludge is Stihl mix. Awful stuff. View attachment 323099
Beside a 150 case and piston for comparison. Note the difference in the fresh air window around the wrist pin.
View attachment 323100
These new pistons have two major casting bosses under the skirt. That just seems wrong to me.

Is it just my perception, or is the bore larger on the right?

 

[qurotro]

To my surprise it's not clamshell.

 

[Ketchup]

34mm bore for both 150 and 151. It’s a 1.5mm thick sleeve. I measured the stroke at 26mm.


My after BC exhaust number (116) is in the wrong column in the photo. It should be bumped up one.



The combustion chamber is unremarkable. The 201tc-m V2 has a modified chamber to fit the new piston. The 151 has the same old casting. More Stihl sludge in there.


You can see the sleeve better in this photo. I really like how the gasket registers in that flange notch.

 

[Wonkydonkey]

If one were to port one of these, apart from being small. Would you blend in the lowers like everyone does on a husky.

asking for future reference

cheers

 

[Ketchup]

Well, I’ll let you know.


The blending I did is similar to a 346 or 372, but the case and gasket need a little work as well. I may regret lowering the flange but it seems better this way.

 

[Ketchup]

My strategy for this one was mostly a mix of 346 and 2511. I ramped the transfers, raised and widened the exhaust and squared the bottom of the intake port. There was a lot of blending where the sleeve meets the casting in all the ports. The relationship between transfers and exhaust turned out very nice. The ring is in the same position in both photos. The transfers crack right as the exhaust hits full width.




I haven’t done an all-out port job on one of these before so these numbers are experimental and conservative. I’m very open to feedback.


The stock saw dealt some weird numbers. As you can see, it’s no 346 or 2511. Mainly the exhaust is super low and the blowdown is short. Because it’s a strato the blowdown makes sense. I nudged that a bit because I widened the exhaust. I find that on these tiny saws a super small adjustment can have a big change. I tried to stay close to what the engineers came up with, just with better flow and compression.

 

[Red97]

Clutch drum similar to a 2511?

Be nice to find one thst can sawp.

Curious to see how it turns out.

 

[Ketchup]

Since I’m talking builds…here’s the standard stuff.

Carb delimit. I find the low isn’t a problem, but it’s easy to trim the plastic if you want.

Timing advance 6 degrees. Make sure you tighten these buggers extra tight. They strip the key very easily.

Muffler mod. I take the back half of the flange away. If you take the whole thing it’s a lot
louder.

I bend the deflector open a bit and get rid of the keeper strip.

 

[Ketchup]

Clutch drum similar to a 2511?

Be nice to find one thst can sawp.

Curious to see how it turns out.

Afraid not. The 2511t has a lot beefier setup. I think a 151 drum could be fabricated to fit a 3/8 rim drive though.

 

[Red97]

Afraid not. The 2511t has a lot beefier setup. I think a 151 drum could be fabricated to fit a 3/8 rim drive though.

I'll have to give it a try.

Thank you

 

[Ketchup]

 

[Nutball]

Don't they make a 3/8 sprocket for it? Anyone have a parts diagram to check? Supposedly the 150 had a 3/8 available, but I don't know if it is compatible or still made: 1146 640 2006

 

[Wonkydonkey]

I only have the 150 ipl and 1146 640 2006 is the 3/8 sprocket I guess if you compare the bearing sizes you should be able to workout if it fits.

 

[DND 9000]

You can use the 1146 640 2006 3/8" 6T sprocket on the MS 151, 151 T.

 

[Funky sawman]

So the sleeve can be presumably replaced on this cylinder? Would make it interesting for porting if one was to heat cylinder and pull the sleeve, then port it and the aluminum casting separately.

 

[Nutball]

Are both aluminum? Looks so. I wonder why they put such a thick aluminum (if it is AL) sleeve in there? I'd say the 201t has more complex transfers, but they managed it without a sleeve.

 

[Ketchup]

I like the 151 transfer design better than the 201. FWIW, the 201 has side transfer covers.

 

[Ketchup]

Messing with these again. Here’s piston wash on a 30hr saw.


Some piston measurements: I take a tiny bit away on the air windows. 1-2 degrees advanced.

I also widen the intake 0.050”.

 

[NPKenny]

The transfers crack right as the exhaust hits full width.

This is a comment I have not heard before. Would you please share the thought on this? I think it could be helpful in more intuitively understanding what blowdown strategies work best.

I know this is somewhat hidden in a 151T thread, but it is very interesting.

Thank you!