It's not fun. I took all my meat off the band to fit the 272 piston and run a base gasket and it's got silly high compression. Like I'm sure it would cut faster with less.
372 Pston swap/mod
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It's not fun. I took all my meat off the band to fit the 272 piston and run a base gasket and it's got silly high compression. Like I'm sure it would cut faster with less.
Good info. Did you try stacking gaskets? Raising exhaust higher? Just curious. I’ve never done a bore cut that deep.
No, with 1 gasket it ended up with the intake right at 80deg and 20 thou of squish. They didn't machine the quench pad of my big bore jug at the factory so it was all wavy, I just took it to it cleaned up. The old super glue sand paper on a junk piston and spin it with the drill trick, didn't take that long with 120 grit.
Yotaismygame
Juiced Saws #GetJuiced
I can cut bands easily so it’s not a big deal. 200psi doesn’t bother me. With the 268 piston and nothing off the exhaust you’ll make about 195psi.
Chainsaw Jim
CJ Saws, LLC
Yotaismygame
Juiced Saws #GetJuiced
Elbowing? Just simple convo going on here
mixxer
Lord of Combustion
Ordered one last night...
Nice to have these readily and inexpensively available...
OEM Husky cylinder is still in perfect shape and I was not excited about having to go to a 52mm aftermarket cylinder of unknown quality... so I'm glad that this 50mm stock bore version is again available
For my own modded 372XP I'm currently at 160psi on the nose with no base gasket... Hoping to run 170~185psi for my own tuning preference...
Anxious to see where this setup ends up
Yotaismygame
Juiced Saws #GetJuiced
I don’t mean to be a **** but the piston you bought and the piston this thread is about are two entirely different things. If you haven’t already go back to the first page and start reading. Personally I would send the piston you bought back and have me send you a 268 pop up piston.
mixxer
Lord of Combustion
Ok...
I'm always ready to learn something new...
Not caring even a little bit where the base piston comes from, I'm ready to hear what difference it makes if you end up with the squish clearance and compression you are looking for .
The topic can simply be about pistons that get you the deck height and compression you are looking to achieve, it doesn't have to be about modifying a piston from another model...
Another thing to consider is thermal stability of a piston as well as the heat load that the top/ comp comp ring is subjected to. It is possible to have too little heat sink path for proper heat transfer from dome to piston skirt. Can't unload the heat until it migrates to the piston skirt and cylinder wall... Thin domes impede heat transfer...
Also , piston rings need a set temp range via their distance from the piston crown in order to keep their tension and shape characteristics .... Lessen that distance and at some point you are also gleefully dancing in a mine field...
For 35Bux it will be interesting to check this piston out.
Ready to hear all the known evils of this piston that as yet is an unknown entity to me...
I'm always ready to learn something new...
Not caring even a little bit where the base piston comes from, I'm ready to hear what difference it makes if you end up with the squish clearance and compression you are looking for .
The topic can simply be about pistons that get you the deck height and compression you are looking to achieve, it doesn't have to be about modifying a piston from another model...
Another thing to consider is thermal stability of a piston as well as the heat load that the top/ comp comp ring is subjected to. It is possible to have too little heat sink path for proper heat transfer from dome to piston skirt. Can't unload the heat until it migrates to the piston skirt and cylinder wall... Thin domes impede heat transfer...
Also , piston rings need a set temp range via their distance from the piston crown in order to keep their tension and shape characteristics .... Lessen that distance and at some point you are also gleefully dancing in a mine field...
For 35Bux it will be interesting to check this piston out.
Ready to hear all the known evils of this piston that as yet is an unknown entity to me...
This thread is about taking a 268 piston and making a high top from it. The one you bought is 372 based. It's a totally different piston design, the 268 is a lot lighter and doesn't shroud the transfers as much.
mixxer
Lord of Combustion
So no deviation allowed under
High top...
Pop up...
High compression piston arrangement??
No one allowed to discuss any alternatives to a machined 268 style piston at all... ?! Just one and only one piston for increased compression...?!
That's a little Nazi like in a tech forum, don't you think??
I'm not talking about Stihl pistons ... Or Echo pistons... Or Homelite pistons...
I'm not even talking about a piston for any other saw except a 372XP...
And for the record... The OEM skirted piston absolutely does NOT block flow to the transfers in any way... To claim that it does would mean a serious lack of understanding of how transfer ports work...
Unless the goal is to either make bank off selling machined 268 pistons... Or to suppress the free speech exchange of ideas and information... I really don't see why anyone would have a problem with merely talking about another piston...
High top...
Pop up...
High compression piston arrangement??
No one allowed to discuss any alternatives to a machined 268 style piston at all... ?! Just one and only one piston for increased compression...?!
That's a little Nazi like in a tech forum, don't you think??
I'm not talking about Stihl pistons ... Or Echo pistons... Or Homelite pistons...
I'm not even talking about a piston for any other saw except a 372XP...
And for the record... The OEM skirted piston absolutely does NOT block flow to the transfers in any way... To claim that it does would mean a serious lack of understanding of how transfer ports work...
Unless the goal is to either make bank off selling machined 268 pistons... Or to suppress the free speech exchange of ideas and information... I really don't see why anyone would have a problem with merely talking about another piston...
Yotaismygame
Juiced Saws #GetJuiced
Your'e getting too heated about this. This specific thread is about the 268 piston swap into a 372. If you want to discuss other pistons or ways of making a 372 stronger either search because its been talked about tons already, or post a new thread in the chainsaw section. It's really annoying when researching a subject and you come across a thread with information you want only for that thread to go off and talk about something else entirely.
This has been stated multiple times in this thread already but ill say it again. The windowed 268 piston allows more transfer flow, its lighter, the intake skirt is shorter giving more intake duration, and because the pin to crown height is greater you have to machine the piston into a pop up. Doing so will net around 195psi if no grinding is done to the cylinder. Anyone can make a pretty strong saw just by dropping this piston in their 372.
The piston you bought is just a "welded" pop up. Which means material was added to the top of the piston. I would assume .020" was added to the top of that piston. which will net you about 15-20 psi more compression. You now have a heavier than stock piston with more compression but no other positive effects. There will be plenty of people who want to talk about your piston if you start your own thread. This thread is for discussion on the 268 piston being used in a 372.....
This has been stated multiple times in this thread already but ill say it again. The windowed 268 piston allows more transfer flow, its lighter, the intake skirt is shorter giving more intake duration, and because the pin to crown height is greater you have to machine the piston into a pop up. Doing so will net around 195psi if no grinding is done to the cylinder. Anyone can make a pretty strong saw just by dropping this piston in their 372.
The piston you bought is just a "welded" pop up. Which means material was added to the top of the piston. I would assume .020" was added to the top of that piston. which will net you about 15-20 psi more compression. You now have a heavier than stock piston with more compression but no other positive effects. There will be plenty of people who want to talk about your piston if you start your own thread. This thread is for discussion on the 268 piston being used in a 372.....
mixxer
Lord of Combustion
Let me get this straight, you are stating that a company has bothered to non porosly weld aluminum and then re machine the piston ?? As opposed to being a company (meteor) that makes all sorts of pistons just deciding to machine a blank casting differently??
Also... I'm calling out anyone who wants to think that you are getting more transfer flow out of a 268 or any style of windowed piston in the 372XP cylinder...
Do you not understand fluid dynamics and that air flow behaves as a compressible fluid?
Air in the crankcase is ALL at the same pressure as the piston descends in the bore... It's not low pressure near the crank throws and high pressure under the piston... That is a physical impossibility ...
The transfers on the 372xp open where the cylinder meets the crankcase , like a dirt bike engine, and unlike the channels that are open to the walls like older or inexpensive chainsaws...
The sides of the OEM piston do not protrude to block any of the transfer port entrance at any time... The flow is not impeded in any fashion... There is not a pocket of high pressure charge trapped under the piston... The entire crankcase sees the same pressure and the flow enters the transfers at the optimal point to straighten and guide flow... Where cylinder meets case...
Airflow can go fast... And it can turn... But it doesn't ever want to do both at the same time... A big part of the voodoo of good porting is making that happen as well as possible, especially in a 4 stroke..
This absolutely is not the case with any pressure differential in a 2 stroke crankcase... But just for the sake of argument, let's assume you do have magic trapped high pressure charge only under the piston.... If it were allowed to shoot sideways through piston windows at 90degrees to the port opening... Or worse yet, through the window, up the cylinder wall, and then turning 180degrees to wrap around the base of the cylinder into the transfer port... All at high airflow speeds .. well... It ain't happening... You would have a disastrously detached and restrictive airflow that would actually impede correct/ laminar flow coming from the crankcase... Thank God none of that is even possible with the laws of physics...
Now... Lighter pistons are great ... If they are lighter and still strong enough, I'm all for less weight and less inertia that the rod has to deal with... And I know the 268 piston windows/ webbing can give it a weight advantage ...
But as far as the $35 pop up goes... I'm betting it isn't welded... and I know for a fact that the style doesn't block transfer flow even the slightest...
And truth be told, if I knew you were offering modded 268 pistons before I ordered this one... I would have preferred to buy one of them from you for the trick style of the lighter / webbed skirt design.... Custom machined definitely has coolness appeal to it.
If this piston comes and it actually is welded, I won't use it.... I wouldn't want the casting to have had the thermal stress of welding ...
And... I don't think the title of the thread says "268 style only" anywhere in it...
Also... I'm calling out anyone who wants to think that you are getting more transfer flow out of a 268 or any style of windowed piston in the 372XP cylinder...
Do you not understand fluid dynamics and that air flow behaves as a compressible fluid?
Air in the crankcase is ALL at the same pressure as the piston descends in the bore... It's not low pressure near the crank throws and high pressure under the piston... That is a physical impossibility ...
The transfers on the 372xp open where the cylinder meets the crankcase , like a dirt bike engine, and unlike the channels that are open to the walls like older or inexpensive chainsaws...
The sides of the OEM piston do not protrude to block any of the transfer port entrance at any time... The flow is not impeded in any fashion... There is not a pocket of high pressure charge trapped under the piston... The entire crankcase sees the same pressure and the flow enters the transfers at the optimal point to straighten and guide flow... Where cylinder meets case...
Airflow can go fast... And it can turn... But it doesn't ever want to do both at the same time... A big part of the voodoo of good porting is making that happen as well as possible, especially in a 4 stroke..
This absolutely is not the case with any pressure differential in a 2 stroke crankcase... But just for the sake of argument, let's assume you do have magic trapped high pressure charge only under the piston.... If it were allowed to shoot sideways through piston windows at 90degrees to the port opening... Or worse yet, through the window, up the cylinder wall, and then turning 180degrees to wrap around the base of the cylinder into the transfer port... All at high airflow speeds .. well... It ain't happening... You would have a disastrously detached and restrictive airflow that would actually impede correct/ laminar flow coming from the crankcase... Thank God none of that is even possible with the laws of physics...
Now... Lighter pistons are great ... If they are lighter and still strong enough, I'm all for less weight and less inertia that the rod has to deal with... And I know the 268 piston windows/ webbing can give it a weight advantage ...
But as far as the $35 pop up goes... I'm betting it isn't welded... and I know for a fact that the style doesn't block transfer flow even the slightest...
And truth be told, if I knew you were offering modded 268 pistons before I ordered this one... I would have preferred to buy one of them from you for the trick style of the lighter / webbed skirt design.... Custom machined definitely has coolness appeal to it.
If this piston comes and it actually is welded, I won't use it.... I wouldn't want the casting to have had the thermal stress of welding ...
And... I don't think the title of the thread says "268 style only" anywhere in it...
mixxer
Lord of Combustion
The thread title actually says :
"372 pston swap/mod"
Where "piston" is spelled wrong ...
If their actually is a "pston", I'm totally in the wrong thread because I don't even know what that is...
But as far as modding the 372 with a piston swap, I would think that an off the shelf stock bore $35 piston with increased compression would be of interest to any 372xp owner looking for an easy compression/ torque bump up...
"372 pston swap/mod"
Where "piston" is spelled wrong ...
If their actually is a "pston", I'm totally in the wrong thread because I don't even know what that is...
But as far as modding the 372 with a piston swap, I would think that an off the shelf stock bore $35 piston with increased compression would be of interest to any 372xp owner looking for an easy compression/ torque bump up...
Yotaismygame
Juiced Saws #GetJuiced
Well after finishing up two 562s on Saturday I was a little bored last night and decided to do some more experimenting. I had a 372 top end laying around that I had previously done some work on and decided to pair it with a slab sided 268 piston. The top end has a widened intake, widened & polished exhaust, lower transfer wall lowered, little material taken out of the lower transfers, and stretched uppers towards the intake.
I took 040 off the squish band instead of doing a pop up which resulted in a 020 squish. 372s have a little lip on the squish band which must be about .005 because normally with 040 pop up 268 you get around 025 squish but once I smoothed the whole band up it ended up at 020. I then took .002 off the base just to clean off all the crap stuck to it. Easier to let the lathe do the work compared to me scraping it off.
Here's the numbers I decided on. 100, 122, 84. (268 piston will give you a 83-84 intake without doing any grinding).
The ring still needs to seat so as of now compression feels stock. Case compression felt very strong, saw ran great. I think I could take the exhaust up another degree to 99 and see some gains. Saw spins up pretty squick, held rpms very well.
Conclusion? I couldn't tell a difference between doing a band cut or pop up. Other than when cutting the band you'll have more grinding to do. The slab sided piston felt like it had more case compression, still felt light but maybe a touch heavier than the windowed piston.
I sharpened the chain pretty aggressive, used the soft setting on my husky raker gauge. Saw seemed to pull it just fine.
I took 040 off the squish band instead of doing a pop up which resulted in a 020 squish. 372s have a little lip on the squish band which must be about .005 because normally with 040 pop up 268 you get around 025 squish but once I smoothed the whole band up it ended up at 020. I then took .002 off the base just to clean off all the crap stuck to it. Easier to let the lathe do the work compared to me scraping it off.
Here's the numbers I decided on. 100, 122, 84. (268 piston will give you a 83-84 intake without doing any grinding).
The ring still needs to seat so as of now compression feels stock. Case compression felt very strong, saw ran great. I think I could take the exhaust up another degree to 99 and see some gains. Saw spins up pretty squick, held rpms very well.
Conclusion? I couldn't tell a difference between doing a band cut or pop up. Other than when cutting the band you'll have more grinding to do. The slab sided piston felt like it had more case compression, still felt light but maybe a touch heavier than the windowed piston.
I sharpened the chain pretty aggressive, used the soft setting on my husky raker gauge. Saw seemed to pull it just fine.
Yotaismygame
Juiced Saws #GetJuiced
Tested comp and it’s about 168psi. Probably will settle around 175 after the ring seats.
Looks to run well.
I like the popup mod because at any time you can put a regular 372 back in with no mods.
Not everyone can cut the base/band.
Yotaismygame
Juiced Saws #GetJuiced
You still could. Ditch the base gasket and put a stock piston back in. You’ll end up having a near stock squish. But why put a stock piston back in? Just slap another 268 piston in..
I didn’t really do it for other people. Just merely for experimentation. Was pretty curious how the non windowed piston would compare.
I didn’t really do it for other people. Just merely for experimentation. Was pretty curious how the non windowed piston would compare.
That's cool, maybe you could put a stock piston back in a see how it performs now with the work you've done, then you'd be making a good comparison of the two to see what you gained with the piston. I thought the compression would have come out a bit higher, but that should be great for a work saw. What elevation are you at, it that a corrected compression #? The reason would be incase you couldn't get another popup to put in right away, sometimes it's nice to be able to grab a stock part and install it.
What happens when someone get the saw that doesn't know/understand what's been done inside. It's not far fetched as we've seen it many times here.
Nice you have the tools to do all that.
Yotaismygame
Juiced Saws #GetJuiced
I’m only at 200ft. Compression ended up there because when cutting the band it lowers the exhaust port. I had to raise it 5 degrees. Machining cylinders is merely to raise compression and lower the intake. But you only raise the compression to gain room to play with the port timing. If I raised the exhaust that much on a stock saw comp would end up pretty low. If I put a stock piston back in squish would end around .040” and I would lose intake duration. End up basically being a woods port with a raised exhaust. Is the 268 piston better than stock once ported? Probably not. But it does turn a stock saw into a much stronger saw by just dropping a piston in.
