Piston widows.

[StihlEchoingHusky]

I've got two pistons I'm looking at right now. A Meteor and a mahle both are for a 046 I've noticed that the windows on the meteor are smaller. Id expect this would tamper with flow but my question is would it help with velocity? Its not a significant amount so I don't think it will choke the flow too much.

 

[bwalker]

On the 046 flow into the transfer ports must pass through the piston windows, so yes it would tamper with flow. Keep in mind that the volume on either side of the windows is relatively larger so it's not going to in crease velocity in a meaningful way.
That's my thought process on the matter.

 

[StihlEchoingHusky]

On the 046 flow into the transfer ports must pass through the piston windows, so yes it would tamper with flow. Keep in mind that the volume on either side of the windows is relatively larger so it's not going to in crease velocity in a meaningful way.
That's my thought process on the matter.

Ya that does make sense. That's why I asked. Would it be safe to enlarge the windows to match OEM? With a high grit diamond bur? I've removed alot of castings flaws of pistons before but haven't increased window size. The structure around the windows is significantly thicker than oem so it should give me something to work with.

 

[bogieboy]

Ya that does make sense. That's why I asked. Would it be safe to enlarge the windows to match OEM? With a high grit diamond bur? I've removed alot of castings flaws of pistons before but haven't increased window size. The structure around the windows is significantly thicker than oem so it should give me something to work with.

Theres a real fine line in thinning piston windows, and usually you dont find that line without crossing it a time or two...LOL too much material removal and now the lower skirt supports are weakened, and potentially more prone to cracking....

Do you trust that the aftermarket castings have as strong a casting as stock? If so, take it down to stock thickness... i dont think i would go much further though... i know some guys like thinning out as much if thw underside of the piston as they can for reduced mass, which equals quicker revving...at the cost of reduced piston life....

 

[StihlEchoingHusky]

Theres a real fine line in thinning piston windows, and usually you dont find that line without crossing it a time or two...LOL too much material removal and now the lower skirt supports are weakened, and potentially more prone to cracking....

Do you trust that the aftermarket castings have as strong a casting as stock? If so, take it down to stock thickness... i dont think i would go much further though... i know some guys like thinning out as much if thw underside of the piston as they can for reduced mass, which equals quicker revving...at the cost of reduced piston life....

Thanks Kent I'm not a complete idiot...... (Well actually!!!) no I don't think it's as good of casting as OEM but my plan was to get it just shy of oem. I ment just enlarging just the inner part of the window and leaving the rest of it alone. It is meteor so I'd say I trust it every so slightly more than any other aftermarket piston you know of anyone making forged pistons? Lol

 

[Al Smith]

I imagine it's just what you are trying for .I've smoothed out the flash or what the Brits refer to as "swarf" ,the mold marks left unfinished around the windows .If that really made much of a difference I really can't say as the replacement piston was not compaired to the OEM simply because the original was just plain not usable .They all seemed to work okay plus they were not race saws so a fraction of second slower on 3 cuts in a nine inch cant didn't really mean that much .

 

[StihlEchoingHusky]

I imagine it's just what you are trying for .I've smoothed out the flash or what the Brits refer to as "swarf" ,the mold marks left unfinished around the windows .If that really made much of a difference I really can't say as the replacement piston was not compaired to the OEM simply because the original was just plain not usable .They all seemed to work okay plus they were not race saws so a fraction of second slower on 3 cuts in a nine inch cant didn't really mean that much .

Yeah I just didn't know if maybe it would effect overall torque. I don't build race saws. I prefer knowing my work has potentially saved someone life/house from a forest fire or it helped build that said house. I am by no means near professional porter status but I've had quite a few customers in my short 11 months with saws. 1 guy is a return I've done 4 saws for. He also has me repairing a boat and also would like an engine swap done on a car.

 

[Al Smith]

I suppose if you really wanted a high quality piston you might consider Wiseco .However some cost more than the saw in question might be worth .I myself have only used the Wiseco cir clips for one of the two complete rebuilds of Partner P-100's during the Covid lock down .That saw looked like it had spent a long time in Great Salt Lake but I saved it .Somebody at one time had jammed14 MM clips in place of the OEM 13 MM .Why it never flew apart I'll never know .Those clips were $15 for two .
I might further add although I find Meteror pistons to be good I don't trust the circlips because they are soft plus slightly over thick and I use either OEM Stihl or Wiseco clips .I spend a lot of time on these rebuilds only to toss clip and turn them into junk .

 

[drf256]

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.

 

[Mastermind]

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.

This. All of this.

 

[StihlEchoingHusky]

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 ended up using the oem wrist pin and cir clips and just left the rest alone. I noticed a major difference but that's only because I have only ever tried the OEM cylinder with the piston that was in desperate need of new rings. The cylinder looks good enough if ran as a firewood saw. I figure if I can get a season or 2 out of it I'm good with that. It was a free saw.

I might hunt down another oem cylinder. I know I could use a 460 cylinder but I'd rather have the D shaped combustion chamber of the 046

 

[Mastermind]

I'd rather have the D shaped combustion chamber of the 046

Why?

 

[StihlEchoingHusky]

It would have better compression Tighter space for the air and fuel to be compressed in. I mean ya same can be true for the other one if you make a pop up and cut the base but I don't have a lathe currently. I know I could send it to someone but I'd rather do it myself

 

[StihlEchoingHusky]

Or is my assumption wrong?

 

[Mastermind]

Or is my assumption wrong?

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

 

[Stump Shot]

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

Sweet!!!

 

[drf256]

I ended up using the oem wrist pin and cir clips and just left the rest alone. I noticed a major difference but that's only because I have only ever tried the OEM cylinder with the piston that was in desperate need of new rings. The cylinder looks good enough if ran as a firewood saw. I figure if I can get a season or 2 out of it I'm good with that. It was a free saw.

I might hunt down another oem cylinder. I know I could use a 460 cylinder but I'd rather have the D shaped combustion chamber of the 046

The oem pin wasn’t too long?

 

[drf256]

Just make sure your circlip groove was fully exposed and clip fully seated. IIRC, I had to turn the standard OEM 12mm 046 pin shorter in the lathe to fit the meteor. It may only apply to the 272 piston swap.

 

[drf256]

These are, from Left to Right,

OEM 046, OEM 064 and I believe meteor 272. Not sure on the 046 meteor pin, but it does apply to other meteor slugs. The 026 meteor has a shorter pin than the stockers.

 

[bwalker]

This is why I won't use AM parts if at all possible.