Mastermind
Work Saw Specialist
I have been looking at the 268 piston pretty hard of late though.....
Pop ups and windows. Your thoughts.
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I have been looking at the 268 piston pretty hard of late though.....
Is that the type of piston with the flat sides by the wrist pin?
Tree Sling'r
Addicted to ArboristSite
I agree Randy, I like them.
Freakingstang
Doctor Freakinstein
This has been my experience in a stock bore 372 (not a 375).
I works in any engine as a good way to run a lighter piston. Does it help build torque or rpm???? Both???? Discuss.....
I've been out of the loop/world for 4-5 years. The last saw i played with was a 372 with a machine piston with a .040 dome. It was either a 268xp or 266 windowed piston. I can't remember to be honest. It worked well, but I honestly hadn't played and tested it to the extent I wanted to. Meaning, i haven't gone back in and played with opening up the lowers more, changing timing, etc. It definately revs quicker than my 371 with a windowed piston with no dome, but I don't have any side by side comparisons. For a work saw with a 24" bar, it runs good. I've never seen the 372 as a torquey saw compared to a 460 or 7900 if that makes sense? I acutally read this whole thread the other night looking for Piston info. I picked up a dolmar 5100s with a melted piston and was looking for alternative pistons to install in it And got to thinking, since the 5100 and 7900 originally had a windowed piston but the newer replacements are slab sided...
Eric made a comment about a high compression 372/275 running too hot and detonation earlier in the thread. i am wondering if this is where a windowed piston would help with the cooling charge on the bottom side of the piston? I'm just thinking out loud. There was a ton of great info and ideas in this thread.
Freakingstang
Doctor Freakinstein
Yes. Here is a stock 371/372 single single ring oem piston, a 268 and a 266. I just can't remember which of the 266/268 pistons is which. but both are too "tall" to use stock without cutting them down or cutting the squish band. The skirt is also about 1mm shorter, so if you have already lowered intake and transfers....
Notice one is a full skirt, one is a "stihl" type piston. Once you machine them, you don't have to cut the jug. I did not have access to a mill or lathe when I was playing with saws 4-5 years ago, so I had to really do some research and make my choices well. It was easiest for me to machine a piston than it was to cut a cylinder in a lathe... I have not ran the full skirt windowed piston yet, but there is significant weight differences between the three by feel. I don't have a scale to wiegh them though.
Andre and I have run our 71cc 372s back to back many times now. They are so close it's not funny. If one has an edge, it's Andre's. Mine has a windowed piston, his does not. The moral of the story is that a windowed piston is not required. Does it hurt? Not necessarily. But then again, every saw is different and your mileage may vary.
Freakingstang
Doctor Freakinstein
Short bar in small wood or big bar in big wood?
Did you do less lower transfer work to the windowed piston for the case volume/velocity issues?
I only case match the lowers. I do not hog them out. Comparisons were made last weekend in both 10" cants and 20" Oak.
Trx250r180
Saw polisher
Three XPWs and a 461......
your gettin pretty good with that claw hammer and punch :msp_wink:
rms61moparman
Addicted to ArboristSite
PLAYINWOOD
ArboristSite Guru
Any compression number difference?
buck futter
ArboristSite Guru
great thread!
great Thread guys!
JJ I'm glad you remembered when I adjusted the squish on the 460 with emery cloth. I only needed 2 thou though.
so what ended up being the new hot set up for the 372's who won Terry? What did he do to make the difference?
Regards
David
great Thread guys!
JJ I'm glad you remembered when I adjusted the squish on the 460 with emery cloth. I only needed 2 thou though.
so what ended up being the new hot set up for the 372's who won Terry? What did he do to make the difference?
Regards
David
From what I've been told and seen, Randy and Tree monkey are making pretty strong 372's. However Mike's 372 that has a pop up is still competitive. I honestly think cutting the squish band makes a bigger difference than I or anyone originally thought. I've talked to a few very good builders that concur. IMHO pop ups give you more compression, but not always noticeable gains, and in some cases it may be detrimental. On top of that replacing the piston is now an issue, and I would never recommend a pop up in a true work saw.
Everything I said is however subject to change lol.
parrisw
Tree Freak
My tried and true 372 with popup and windows still impresses all that run it. I haven't shaken down the new one enough to know yet if its any better or not.
Mastermind
Work Saw Specialist
The best running 372 I've built yet had the squish band cut just enough to flatten it and a .025 popup. I'm not done with popups completely. The 550 and 562XP are two saws that work well with popups too. Sometimes the transfer height is so far off after cutting the squish that it makes more sense to do the popup.
But everything we are doing today will be obsolete in a couple of years.
Hedgerow
HACK
Not a fan of pop up's... I put them in the category of "What to use when you absolutely, positively, have no other option's and need more compression..."
Sometimes I think a good running saw with a pop up runs well "In spite" of having one...
:msp_rolleyes:
Flame suit is on now...
:after_boom:
Sometimes I think a good running saw with a pop up runs well "In spite" of having one...
:msp_rolleyes:
Flame suit is on now...
:after_boom:
Mastermind
Work Saw Specialist
You don't need one in my mind. The cut squish is great when you want to lower the exhaust and/or transfers. I can make a #### load of compression that way too.....I like compression ya know.
Popups were all the rage a couple of years ago......remember?
Hedgerow
HACK
Yup... And I've used em'... And I've replaced em'... The 372 was an eye opener...
Replace pop up with flat top...
Lose 15lbs of comp...
Gain 7% useable RPM's in the cut...
Still without a machined squish band...
Go figure...
Trx250r180
Saw polisher
cowroy
Addicted to ArboristSite
Yup... And I've used em'... And I've replaced em'... The 372 was an eye opener...
Replace pop up with flat top...
Lose 15lbs of comp...
Gain 7% useable RPM's in the cut...
Still without a machined squish band...
Go figure...
When you say useable rpm's do you mean torque?
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