one more problem that your gonna run into is that the piston will not go all the way down. the bigger piston will go below the deck, so you are gonna have to grind out the hole in the case a little bigger. i just did this to a plain jane 038 and upgraded it to the 52 mm piston. not hard just time consuming.
None of the super to mag conversions I've done have had any issues with the piston interfering with the case, the regular 038 case may be a different story. I've used NOS 038M cylinders with NOS pistons , or Tecomec 038M P/C assys. Never tried this with a Meteor piston.
When slotting the cyl holes you don't just grind towards the bore, you need to use a 038S gasket as a template, or lay things out using machinist bluing. The slots are longer front to back than side to side by about 2:1, ca. 0.040 X 0.020 "
The Stihl shop manual mentions problems with the ridge on the case for 038 to 038 super conversions, they recommend grinding down the case. Again I've had no problems here using a 038 super case assy and Mag cyls.
There
IS an issue with getting the cyl bolt heads to seat. You can: 1) grind out the cyl using a dremel to give enough space for the bolt head to seat, or 2) turn down the outside of the t27 torx bolts. You can chuck them in a drill and run them against a file or grinding wheel.
Could this above be part of your problem?
There
IS also an issue with getting the T27 wrench through the cyl fins to tighten the bolts. Open up the access holes using a chain file. This may not be an issue for all four bolts.
Here are some notes comments from my first conversion:
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!!!
P.S.
If you are using a base gasket, slip it over the piston,
before putting the rings on the piston, otherwise you will tear it and more cursing will be heard........
