038 Question

[wildwes]

Could someone tell me what the diameter of the cylinder hole in the crankcase is in an 038 Mag? Or how much clearance I need to insure the piston doesn't hit? I am working on a 038AV to 038 Mag conversion, and I am about to mill the crankcase this afternoon to clear the piston, as it won't clear right now, and I would prefer to know either the diameter, or how much clearance the piston skirt needs, rather than winging it.
Thanks in advance for any help!

 

[Mad Professor]

I think I was the first to do the conversion (2007?).

Without removing anything the piston clears fine using OEM parts.

What parts are you using?

First one I did was an 038S to 038M, OEM NOS stihl P/C kit it is posted here no pcs. OLD NOS Italian Tecomc suff works well too.

Stay away from Ci-Com CRAP!!!

 

[Mad Professor]

PS early/old 038 cases need material on clutch side of case,for 038 early or038S or 38M to fit

This a warnig, from sihl fitting 038S to 038 is P/C ma sevice maual

Not inside case, surface

 

[Mad Professor]

here you go.....

 

[wildwes]

I am using an early 038 case, and the piston won't clear as-is. The clutch side of the hole is smaller as-is, which would explain the bulletin from Stihl.
The P/C I am using is one of the Nikasil kits that Duke Thiesen sells. I don't know where he sources them from, but I was not able to find a good OEM or Tecomec P/C at a price within my budget.

My problem right now is that the existing hole in the case measures 2.025 across the largest part of it's diamter. The piston is 2.0465, so the hole is too small. I don't know how far I need to open it up to provide enough clearance- would 2.125" give enough clearance for a 2.0465" piston? I would assume that since the skirt is only dropping a little bit below the jug that it shouldn't need a ton of clearance, but I don't want to make an incorrect assumption and grenade my saw.

EDIT- I forgot to mention, the 2.125" number I was going with is based off of the fact that the Mag gasket I am using for a template has a hole in it ranging from 2.125" to 2.130" which is why I assume that the piston would have adequate clearance at that diameter- if not, I assume the gasket would create problems already.

 

[wildwes]

And thanks for the manual, I greatly appreciate having access to the information in it, as I did not have a manual for it.

 

[a. palmer jr.]

I think the last conversion I did only required the bolt holes in the cylinder to be enlarged a bit..

 

[wildwes]

I think the last conversion I did only required the bolt holes in the cylinder to be enlarged a bit..

The problem on mine was that the piston would not physically fit into the hole in the case at the bottom of the stroke. Maybe your case was a little newer than mine with the case the same as a super?

I ended up opening it up with an end mill yesterday to 2.128" which makes the hole in the case identical to the hole in the gasket. I will try to get some pictures and post them. When I am completely done I figured I'd make a thread on the process of the conversion.

 

[ballisticdoughnut]

The problem on mine was that the piston would not physically fit into the hole in the case at the bottom of the stroke. Maybe your case was a little newer than mine with the case the same as a super?

I ended up opening it up with an end mill yesterday to 2.128" which makes the hole in the case identical to the hole in the gasket. I will try to get some pictures and post them. When I am completely done I figured I'd make a thread on the process of the conversion.

I’d like to see those pictures. I have two 038 mags, I know converting a 038/038S to a mag isn’t a bolt on swap.

 

[wildwes]

I’d like to see those pictures. I have two 038 mags, I know converting a 038/038S to a mag isn’t a bolt on swap.

I'll get them up- it might be next week one day when I am at my work computer, but I will get them up. I still need to open the cylinder bolt holes, turn down the bolt heads, and open up the holes in the cylinder fins for the torx driver.

Once I get it together the plan is to have it ported if it runs good and doesn't show any issues after a little run time.

 

[a. palmer jr.]

The problem on mine was that the piston would not physically fit into the hole in the case at the bottom of the stroke. Maybe your case was a little newer than mine with the case the same as a super?

I ended up opening it up with an end mill yesterday to 2.128" which makes the hole in the case identical to the hole in the gasket. I will try to get some pictures and post them. When I am completely done I figured I'd make a thread on the process of the conversion.

All I remember was the saw was an 038 AV. I put a magnum cylinder and piston on it and it fit well except the bolt holes weren't far enough out. Instead of elongating them I just drilled them out slightly. The piston fit fine on the down stroke.

 

[wildwes]

All I remember was the saw was an 038 AV. I put a magnum cylinder and piston on it and it fit well except the bolt holes weren't far enough out. Instead of elongating them I just drilled them out slightly. The piston fit fine on the down stroke.

Did you notice a significant power difference going from the 48mm cylinder to a 52mm?

 

[ballisticdoughnut]

Did you notice a significant power difference going from the 48mm cylinder to a 52mm?

It’s like a 10cc jump from a 038 to 038 mag. You’ll definitely notice a difference. Make sure you either do a muffler mod or run the dual port muffler though. Need to let that thing breathe.

 

[huskihl]

I'll get them up- it might be next week one day when I am at my work computer, but I will get them up. I still need to open the cylinder bolt holes, turn down the bolt heads, and open up the holes in the cylinder fins for the torx driver.

Once I get it together the plan is to have it ported if it runs good and doesn't show any issues after a little run time.

Sounds like you’re on the right path. Make certain you slot your cylinder base holes perfectly so the piston is centered in your case opening at bdc.

 

[Mad Professor]

You'll also need to grind the cylinder where the screw heads seat. They won't to tread into the cases properly. That is the screw heads will make the screws canted and if you try to screw them in they will cross thread. I also opened up the access holes in the cylinder for the T27 torx driver.

You can slot the holes in the cylinder using a chain file. I used a 038S base gasket as a template. Be sure to keep the bore centered when you slot the holes.

This was with a OEM 038M cylinder and 038S case.

Here are my notes from 2008:

I just got finished getting an OEM 038M cyl to fit on a 038S case.

The base of the cyl has enough room on the case so no grinding of either was needed to clear the case. I was concerned about this because Stihl mentioned that grinding the case was sometimes necessary when fitting a 038S cylinder on a 038 case (NOT what I’m doing here but similar). This is the first one of these I’ve done so keep it in mind.

The bolt pattern is a little tighter on the 038S than the 038M, more so front to back than side to side. Thus you need to grind (slot) the holes at an angle as the hole differences are greater apart front to back than side to side (e.g. not 45o}. I ground the slots for each hole by ca. 0.040” (front to back) and ca. 0.020” (side to side). There are still plenty of surfaces between the slotted holes and the bore (0.20”) for the base gasket to get a good seal (stock for a 038M was ca. 0.25”).

The area just above where the bolts seat also needed to be ground back to allow the bolt heads to clear the cyl when being screwed in. I did this grinding, and the slotting of the bolt holes, with a Dremel tool and carbide bits.

In one of the four holes it was difficult to get the T27 torx driver through the cylinder fins and into the bolt head. I opened up all the holes through the fins slightly with a 7/32 file (readily available! you can speed this up by chucking it in a drill or just drill them out if you have a drill press).

I did not do this work, at work, so a Bridgeport to slot the bolt holes/drill, would have been nicer, but is not needed. You really just need a Dremel and proper bits to take back the cyl surface (vertical surface that interferes with bolts screwing in) so the bolts can seat against the cyl base and to slot the holes themselves, a 7/32 file will fix the T27 torx clearance.


In fact you need the Dremel to get the bolt heads to fit. One more thing, a dial caliper (0.01”) to compare/measure original cyl holes to where you grind the slots. It’s about a 2:1 ratio length (front to back) to width (side to side) that you take in grinding the slots. No rocket science here! The cylinder now bolts right on!!

 

[wildwes]

Sounds like you’re on the right path. Make certain you slot your cylinder base holes perfectly so the piston is centered in your case opening at bdc.

Will do- that is the next item on the agenda while my students are gone home for Christmas. It's a lot easier to do precise work in a shop without having to keep 20 teenage boys from destroying something in a welding shop

Mad Professor- thank you for all of the notes and tips. It helps a lot to have some guidance on a project like this, as I have never done a modification quite like this.

I am still waiting on one of the crank bearings to get here, hopefully it will come in this week and I can get the bottom end back together.

 

[Mad Professor]

Will do- that is the next item on the agenda while my students are gone home for Christmas. It's a lot easier to do precise work in a shop without having to keep 20 teenage boys from destroying something in a welding shop

Mad Professor- thank you for all of the notes and tips. It helps a lot to have some guidance on a project like this, as I have never done a modification quite like this.

I am still waiting on one of the crank bearings to get here, hopefully it will come in this week and I can get the bottom end back together.

You want to open the muffler up to match the width of ex port, The cans on the 038/038S are quite a bit narrower.

I also open up the baffle on the inner case by drilling a series of holes in it . For the outlet I opened up a dual port as much as possible and still retained the spark screens.

The carb on the 038 is smaller than the 038S or 038M which appear to have same size venturis. The 038S Tillotson or the 038M Bing both work well, rebuild parts are less expensive for the former.

I never got pictures when I did my conversions. If you could post some of your work it will help others doing the same project. I used a NOS OEM Stihl P/C kit on the first one and a Tecomec on the 2nd when they were still made in Italy.

P.S. I had a wonderful metal shop teacher in high school. He would let us bring in our own projects to work on. I'm using the skills he taught me, power mechanics, machine work, gas and electric welding, forging.
My classmates drove him crazy too.

 

[wildwes]

You want to open the muffler up to match the width of ex port, The cans on the 038/038S are quite a bit narrower.

I also open up the baffle on the inner case by drilling a series of holes in it . For the outlet I opened up a dual port as much as possible and still retained the spark screens.

The carb on the 038 is smaller than the 038S or 038M which appear to have same size venturis. The 038S Tillotson or the 038M Bing both work well, rebuild parts are less expensive for the former.

I never got pictures when I did my conversions. If you could post some of your work it will help others doing the same project. I used a NOS OEM Stihl P/C kit on the first one and a Tecomec on the 2nd when they were still made in Italy.

P.S. I had a wonderful metal shop teacher in high school. He would let us bring in our own projects to work on. I'm using the skills he taught me, power mechanics, machine work, gas and electric welding, forging.
My classmates drove him crazy too.

I will probable just replace the muffler with a dual port version, as it is missing the outer half of the muffler anyway. If I do end up reusing the old muffler I will definitely open it up a lot, it looks fairly restrictive.
I figure I'll go with whichever carb I can find easiest, Bing or Tillotson. Do you know why the Bings seem to be so desirable? From what I have read there is pretty much no difference in performance in the two.

I wish I had gotten some pictures of the case while it was actually clamped on the mill. I had the machine shop teacher help me with the machining, as I am no machinist.

I had a teacher much like you are describing too, who made a big impact on me, and is a big part of the reason why I decided to teach. I don't know that any of my students would describe me as wonderful, but I hope that I am able to teach them some skills that they can use. This is my tenth year in the classroom, and the base knowledge that incoming students already have has dropped off a lot since I started along with the maturity level. Cell phones are doing them no favors. Some of them still come in with a genuine desire to learn though, and will bring in their own projects.

 

[VincentFR]

Tillotson still made news carbs for the 038 if you can source one : https://tillotson.ie/shop/he19a-carburetor/

 

[wildwes]

My apologies for the picture quality- I am even less of a photographer than I am a machinist.



The holes have been slotted. It doesn't show well in the picture, but I filed a little and checked the fit, over and over until I got it right. It took me a few hours, I ended up having the time to do it with one of my classes. I also drilled the holes in the fins out for the T27 driver to clear.



I turned the heads on the bolts down to clear the cylinder. These were done with a drill and a grinder just to fit everything up, so they are not pretty. I have another set that will be turned down in a lathe for the final assembly.



The hole in the crankcase after being milled out to match the gasket dimensions.






Cylinder bolted up to the case