Mastermind
Work Saw Specialist
Yes Sir. It seems to work well. As for how much to remove....it depends on the amount of squish you want when finished and how much interference you have after the gasket is removed.
Stihl 026 Stock / Ported Comparison Pics
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Yes Sir. It seems to work well. As for how much to remove....it depends on the amount of squish you want when finished and how much interference you have after the gasket is removed.
CWME
ArboristSite Guru
That makes sense, thanks for sharing! The 260 is going under the knife once I figure out how to video some before cuts on my camera. Want to know if any gains were had with my work. Got to clean off the lathe and sharpen a bit.
Mastermind
Work Saw Specialist
The 026/260 has a domed piston. So a conventional popup is out of the question. When you get it apart take a good look at the squish band and then you will see the spot that hits first. After getting a good look it will all make perfect sense.
what is the minimum side overlap of piston skirt beyond the port edge, for intake and exhaust?
I don't know the piston brand, and was not planning on replacing it, but I think the skirts are narrower than would be needed to do the ports in the pictures. With stock ports, I have about 0.100 on each side past the intake port, about .100 on one side of exhaust, and .130 on the other side of exhaust. I can get some on the one side, but have thought that .100 was about minimum overlap to still have good sealing. Not so? or are your skirts wider? Left the paper with skirt dimensions at the garage.
kcj
I don't know the piston brand, and was not planning on replacing it, but I think the skirts are narrower than would be needed to do the ports in the pictures. With stock ports, I have about 0.100 on each side past the intake port, about .100 on one side of exhaust, and .130 on the other side of exhaust. I can get some on the one side, but have thought that .100 was about minimum overlap to still have good sealing. Not so? or are your skirts wider? Left the paper with skirt dimensions at the garage.
kcj
Mastermind
Work Saw Specialist
As little as .030 will seal fine. This saw was built with either a stock piston or a Meteor...I can't remember which.
CWME
ArboristSite Guru
Measured the squish with base gasket at .027-.028 and without base gasket at .016-.017. Getting readings from three points on the squish band.
Compression went from 160 cold to 192 cold with the base gasket being the only change.
Now when I seal it up I should gain a little squish back leaving me at an estimate of .018-.019.
What am I missing?
Compression went from 160 cold to 192 cold with the base gasket being the only change.
Now when I seal it up I should gain a little squish back leaving me at an estimate of .018-.019.
What am I missing?
Mastermind
Work Saw Specialist
Are you sure that you are measuring the squish at the very edge of the bore???
I've not seen a 026 that can be ran without a base gasket. The ms260 may be different but the couple I've built were head slappers without a gasket...
CWME
ArboristSite Guru
Yes Sir. I will run some more samples through and grab a picture of them. The PSI jump says that it has to be pretty tight so I don't doubt you at all.
Brian13
Addicted to ArboristSite
Thanks for sharing the information:msp_thumbup:. The side by side pics really help.
The stock base gasket on an 026 is .5mm, so....
Not sure about only measuring squish at three spots. May want to double that, or at least use even numbered locations at opposite sides of the bore for symmetrical comparison of results.
Just my 2 cents. Good luck with it.
Poge
Not sure about only measuring squish at three spots. May want to double that, or at least use even numbered locations at opposite sides of the bore for symmetrical comparison of results.
Just my 2 cents. Good luck with it.
Poge
CWME
ArboristSite Guru
View attachment 210284View attachment 210285View attachment 210286View attachment 210287
Smallest one I got was parallel with the rist pin which is shown in the calipers at .015. Not sure if you can see it in the shots but the solder has a little fold where it was squeezed down the side of the piston a bit. I should mention that this is a newer MS260, bought it new last Jan.
Smallest one I got was parallel with the rist pin which is shown in the calipers at .015. Not sure if you can see it in the shots but the solder has a little fold where it was squeezed down the side of the piston a bit. I should mention that this is a newer MS260, bought it new last Jan.
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Mastermind
Work Saw Specialist
That little area that is smashed on the solder is the relief cut I make on the piston. Normally that area hits and stops the engine from turning. The newer 260 might be a little different animal.
CWME
ArboristSite Guru
Well, I guess I will seal it up and make some test cuts to see where it is at. Go from there with the porting portion of this build. Thanks for the consult on my specific situation. Hope I didn't derail your thread too far.
parrisw
Tree Freak
.015-.016 Is too tight IMHO for a work saw. Stick with .020, the compression gain from .020 to .016 is not worth it.
Mastermind
Work Saw Specialist
This thread and any other thread I start is hopefully a place to have a discussion about the things we all want to learn about. Please derail.
Mastermind
Work Saw Specialist
I agree. .020 is what I shoot for. If I end up at .018 I don't worry about though. Less than that is spooky to me.
CWME
ArboristSite Guru
I have to pull the piston to clean it up anyway. I can turn the popup when it comes out so it won't stay that tight. Really is suprising how much PSI was gained by removing the base gasket. I was NOT expecting a 32 PSI jump. But I am a newbie
CWME
ArboristSite Guru
Shaved off 3.02 seconds on my test cuts with just the base gasket removed, same log
Shaved off 3.02 seconds on my test cuts with just the base gasket removed, same log
Nice! I wonder if I can do the same with my 024. It needs a little help in the power department. :hmm3grin2orange:
chopperfreak2k1
Addicted to ArboristSite
bump for a really great thread. i love learnin' about this stuff.
