Piston widows.

[bwalker]

One thing that really gets guys tied in knots is fixating on bulk flow, when timing is alot more important.

 

[Al Smith]

They both make about the same on compression. The hemi design has a better burn though.

If I'm not mistaken it has somthing to do with flame propigation as does a cut dome design commonly called a " pop up " .The Stihl 038 AV used a hemi dome but has an off set cylinder to lessen or prevent a short circuit during the transfer blowing part of the charge directly out the exhaust port .

 

[StihlEchoingHusky]

One thing that really gets guys tied in knots is fixating on bulk flow, when timing is alot more important.

I'm not interested in bulk flow. I'm interested in velocity+timing vs flow. I just didn't know if the smaller windows would have caused a choking point. I've seen those cylinders that people just hog out everything and when reinstalled they wonder where all the power went.

 

[Mad Professor]

You’re thinking correctly. The meteor piston probably takes up more case volume. It’s certainly heavier than the oem, around 6-7g IIRC. And I believe that’s without the heavier pin (the 046 tapered pin is a good/light pin).

I’ve had zero issues with meteor pistons. I like them in an 046, but avoid them in hybrids because of the smaller 044 crank and the increased weight on the meteor.

You won’t notice much difference in performance between the 2 IMHO. Taking the casting flash off is fine, but I’ve personally not seen much gains with piston mods in a side fed lower transfer.

I always wondered about differences in piston assys and mass.

When I did my first 038S---> 038M conversion I had NOS: 038S, 038M, and Italian Tecomec 038M assys. Never worked on an early 48mm 038, or had parts to compare.

All the 038 series seem to use the same cranks. The masses of the piston assys were 94.48, 106.67, and 104.27 g, respectively.

I guess 10-12g does not effect balance much? and/or how critical is balance on a single cyl 2S?

Here is what I checked before I started the conversion(s). I forgot to record if the assys were marked A or B size P/C. I still have the saws so can check that.

Note that the OEM and Tecomec 038M pistons swapped, would be tight (0.001") or loose (0.0035") clearances. The former might be a problem....

Take note of that when mixing parts. I make it a point to always check P/C clearance and ring gaps. I believe Meteor sizes their P/C assys like Stihl. Stihl went to A/B replacement pistons that were a compromise fit for A or B cylinders. I forget if A or B is bigger?

I had good machinist tools to do the measuring and a chemistry balance.

Piston Assy Mass (g)	Piston dia. Skirt (in.)	Piston dia. Top (in.)	Cyl bore dia. (in.)	Cyl clearance (in.)	Piston pin. Dia. (in.)	Piston pin Bore (in)	Piston pin Clearance (in.)
O38S
94.48	1.967	1.962 (0.005 taper)	1.969	0.002	0.4725	0.4735	0.001
038M OEM
106.67	2.045	2.039 (0.006 taper)	2.047	0.002	0.4725	0.4735	0.001
038M Tecomec
104.27	2.046	2.041 (0.005 taper)	2.0485	0.0025	0.4725	0.4735	0.001

To OP, @StihlEchoingHusky , I just clean up the windows never tried making them bigger. Sometimes there is casting flash underneath too.

@Mastermind, you did a 038M conversion back at the "other site", how did that one turn out at the end? I remember you were looking for a Bing carb cause you had the smaller 038 Tillotson.

 

[Mastermind]

@Mastermind, you did a 038M conversion back at the "other site", how did that one turn out at the end? I remember you were looking for a Bing carb cause you had the smaller 038 Tillotson.

I don't even remember the saw.

 

[Mad Professor]

I don't even remember the saw.

Long time and many saws ago at AS. (2012).....You did a 038M conversion starting with a 48mm 038 I think. You had finished building it/got running but you only had the small carb. I was following/posting on the thread. I couldn't find anything in the thread with the Bing carb

From an AS search it used a Tecomec P/C assy, and went to @Dwane(Pa).

Found the thread https://www.arboristsite.com/threads/turning-a-stihl-038-into-a-ported-038-magnum.207165/page-6

And a boobtube video

I still have my first conversion using a NOS 038M P/C, it pulls a 8 pin w/25" bar great.

 

[Mastermind]

Long time and many saws ago at AS. (2012).....You did a 038M conversion starting with a 48mm 038 I think. You had finished building it/got running but you only had the small carb. I was following/posting on the thread. I couldn't find anything in the thread with the Bing carb

From an AS search it used a Tecomec P/C assy, and went to @Dwane(Pa).

Found the thread https://www.arboristsite.com/threads/turning-a-stihl-038-into-a-ported-038-magnum.207165/page-6

And a boobtube video

I still have my first conversion using a NOS 038M P/C, it pulls a 8 pin w/25" bar great.

They banned me from AS....

 

[Mad Professor]

They banned me from AS....

I know that sucked! I've been in ban camp before.

I found this place as AS some members took refuge here, and mention "the other site/place".

Glad you are still monkeying around with saws.

 

[Mastermind]

I know that sucked! I've been in ban camp before.

I found this place as AS some members took refuge here, and mention "the other site/place".

Glad you are still monkeying around with saws.

About 15 years of it. My grandson works with me now.

 

[StihlEchoingHusky]

About 15 years of it. My grandson works with me now.

I have no clue what age he is but has he put burr to metal yet?? I hope to someday experience the something similar. By that I mean Having my own blood working on saws with me.

Back to the post. just something I wanted to point out. It seems hyway is improving Apon their pop ups. Both of these are hyway. I did at one point have a hyway xtorq piston and it was taller overall as well as a few other pistons. As if they added a pop up dish to their pre existing mold. I know this way youd need to lower the jug to get any real benefits. but from my experience it seems like a step in the right direction of making them lighter rather than heavier.

 

[drf256]

Every single Hyway slug I have had in my possession weighed more than the OEM counterpart. Almost all have weighed more than the Meteor equivalent also.

Been at saws for 10-15 years and motors in general for over 40. If one is to skimp and try to be economical on any build, the rotating assemble is NOT the place to take money from. Put the best quality you can inside that case, because a failure there would be the most costly and consequential. That’s my $.02.

 

[Mastermind]

I have no clue what age he is but has he put burr to metal yet?? I hope to someday experience the something similar. By that I mean Having my own blood working on saws with me.

He is 21....and yes. He does all the muffler work. Silver solder, braze, etc. He also port matches the muffler and cylinder if needed.