NickC
ArboristSite Member
Reiterating that as the comments from guys that have cut these jugs would have been talking about the old Mahle's.
Bridgeless transfer ports on Stihl 026 / 260 oem
- Thread starter NickC
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I cut the dome off the piston. No pop up. Flat
Agent smith
NJ tornado enthusiast
Do you then cut the band flat or at a slight taper?
Flat
NickC
ArboristSite Member
Had it chucked up ready and got to thinking...... Why?
So got into some reading about squish bands and angles, Stihl must have there reasons for not doing a simple flat band and piston. I guess it's cos of the offset chamber.
The piston crown isn't a true dome, the outer 3/4" follows a 5° angle then it turns into a radius. The cylinder band is 8°, which is a bit slack as angled bands are generally parallel or more often diverge by 1-2°
So, just for kicks I'm thinking try this, skim the piston to get a defined band hopefully a bit wider. Then skim the cylinder band parallel or +1°. Measuring first to ensure I won't be taking too much off the outer band to avoid free porting.
Due to the better shaped stock chamber I'm already 180psi at the same squish as a stock Mahle cylinder at 165psi, so don't really need to squeeze as much compression out as possible? I'm not looking for a balls out 'cookie cutter' I'd be happy if it noticeably out cuts a stock saw.
So got into some reading about squish bands and angles, Stihl must have there reasons for not doing a simple flat band and piston. I guess it's cos of the offset chamber.
The piston crown isn't a true dome, the outer 3/4" follows a 5° angle then it turns into a radius. The cylinder band is 8°, which is a bit slack as angled bands are generally parallel or more often diverge by 1-2°
So, just for kicks I'm thinking try this, skim the piston to get a defined band hopefully a bit wider. Then skim the cylinder band parallel or +1°. Measuring first to ensure I won't be taking too much off the outer band to avoid free porting.
Due to the better shaped stock chamber I'm already 180psi at the same squish as a stock Mahle cylinder at 165psi, so don't really need to squeeze as much compression out as possible? I'm not looking for a balls out 'cookie cutter' I'd be happy if it noticeably out cuts a stock saw.
NickC
ArboristSite Member
So, I've had a chance to do the cutting.
Took around 1.1mm off the band at the outside to get the 5° cut to the dome.
Knocked ½° off the compound and skimmed the piston.
Checked squish at 1.6mm so took a skim to get a bit closer and double check, nice and even all round at 0.82mm. Decided to go for around 0.45mm (0.018) so took another skim at 0.375mm. Ended up with around 0.6mm so I think the 1mm solder is not compressing properly. Left it there.
Exhaust 100° atdc
Transfers 123° atdc
Intake 75° btdc
Compression with wet rings 225psi
Think about the porting now.
Took around 1.1mm off the band at the outside to get the 5° cut to the dome.
Knocked ½° off the compound and skimmed the piston.
Checked squish at 1.6mm so took a skim to get a bit closer and double check, nice and even all round at 0.82mm. Decided to go for around 0.45mm (0.018) so took another skim at 0.375mm. Ended up with around 0.6mm so I think the 1mm solder is not compressing properly. Left it there.
Exhaust 100° atdc
Transfers 123° atdc
Intake 75° btdc
Compression with wet rings 225psi
Think about the porting now.
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Yotaismygame
Juiced Saws #GetJuiced
1mm solder so .040” is a little thick once your squish gets below .025”. I use solder that will only measure up to .028 or so unless the squish is bigger than that. Nice machine work
NickC
ArboristSite Member
Thanks, I've got some .028 solder on order so will double check with that before going any further. I expect it's the solder though I could have under cut the base, seems to have plenty of compression.
As a side note one of the other 026's I have feels a bit low on compression compared to the others, squish was .043"... The other 44mm was .033" and the later decomp 44.7mm 026 is .022" Not news to you guys I don't suppose but surprised me a bit.
Bore was a little marked up, obviously been seized in the past, not badly with only one or two shallow scores. It's making 155psi so can't be that bad so I think I'll cut the base....
As a side note one of the other 026's I have feels a bit low on compression compared to the others, squish was .043"... The other 44mm was .033" and the later decomp 44.7mm 026 is .022" Not news to you guys I don't suppose but surprised me a bit.
Bore was a little marked up, obviously been seized in the past, not badly with only one or two shallow scores. It's making 155psi so can't be that bad so I think I'll cut the base....
NickC
ArboristSite Member
Been having fun and games messing around swapping the two cylinders and cases, found that there can be significant deviation in the crank deck height. And figured if you have to put any effort into rolling the piston over tdc with the solder in place you'll probably get inaccurate readings... Kept taking skims to gain squish after swapping cylinders and not getting the expected gains.
Anyway, ported the old slightly rough Mahle as a trial, went for 100, 122, 80 with .0155 squish (at outer edge, it increases inwards). Just checked comp with wet rings and it's 225psi, that a bit high?
Porting went ok, could have squared them a bit more I suppose but erred on the side of caution.
Anyway, ported the old slightly rough Mahle as a trial, went for 100, 122, 80 with .0155 squish (at outer edge, it increases inwards). Just checked comp with wet rings and it's 225psi, that a bit high?
Porting went ok, could have squared them a bit more I suppose but erred on the side of caution.
Attachments
NickC
ArboristSite Member
So anyway......
Finally got around to testing them both out, not in any real deep way against the clock with the same chain etc. Just picking them up and cutting, both ported closed and open port saws were similar, maybe the closed had the edge.
Both cut way stronger than stock though which was my only goal, remembered to do a little crap vid of open port Vs stock.
Saw 1 - Strong stock saw with very good compression and muffler mod, 16" semi chisel new Oregon chain.
Saw 2 - Ported open port saw with the same muffler mod, ignition advance and 18" full chisel Stihl chain in imperfect condition. Not set to run high rpm, around 13500 - 13800, conservative squish at 0.7mm so hopefully will be a good saw.
https://photos.app.goo.gl/A3PSh6R2wbUQx1vz9
Finally got around to testing them both out, not in any real deep way against the clock with the same chain etc. Just picking them up and cutting, both ported closed and open port saws were similar, maybe the closed had the edge.
Both cut way stronger than stock though which was my only goal, remembered to do a little crap vid of open port Vs stock.
Saw 1 - Strong stock saw with very good compression and muffler mod, 16" semi chisel new Oregon chain.
Saw 2 - Ported open port saw with the same muffler mod, ignition advance and 18" full chisel Stihl chain in imperfect condition. Not set to run high rpm, around 13500 - 13800, conservative squish at 0.7mm so hopefully will be a good saw.
https://photos.app.goo.gl/A3PSh6R2wbUQx1vz9
NickC
ArboristSite Member
The open port cylinder was ported to the usual numbers (can always cut more if it sucked) 100/120/80 Comp around 230 psi
Seems pretty strong to me so I'm happy, ran it next to my stock 034s today and it's within a couple of seconds. WOT was 13440 after clearing the case so quite slow, in the cut it was pulling hard at 9500 and still pulling well when loaded down much lower.
Piston and plug look healthy so I'm calling that done, thanks for the input fellas.
Both saws similar .325 full chisel, 034s has a muffler port job only. Yes I look uncomfortable, that's down a 45° bank...
https://photos.app.goo.gl/cGmQm9u3tX6ECbSj9
Seems pretty strong to me so I'm happy, ran it next to my stock 034s today and it's within a couple of seconds. WOT was 13440 after clearing the case so quite slow, in the cut it was pulling hard at 9500 and still pulling well when loaded down much lower.
Piston and plug look healthy so I'm calling that done, thanks for the input fellas.
Both saws similar .325 full chisel, 034s has a muffler port job only. Yes I look uncomfortable, that's down a 45° bank...
https://photos.app.goo.gl/cGmQm9u3tX6ECbSj9
