Exactly! I've got to give it to Scootr though. He nailed it right in the beginning.
Guess this piston
- Thread starter blsnelling
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Exactly! I've got to give it to Scootr though. He nailed it right in the beginning.
bitzer
******** Timber Expert
It'll be interesting to see that thing run and what you do with the transfers. I'm not really familiar with the pro husky jugs but it seems the transfers open and close closer to the crank then Stihls. Just wondering how the big windows fit into the picture. You gunna post pics of the cylinder?
stihlboy
Guess who's back
that thing is gonna scream!
The piston windows are just one piece of the puzzle though. My 372BB has never been as strong as my 460 or 440. I know it can be. So I went back in yesterday to see what I could do about that.
I started by raising the cylinder wall at the transfer opening at the base of the cylinder. I raised it by nearly 1/4". I wanted to open up the area where the transfers take in from the crank case. If the cases were split, I would have case matched those as well.
This opened up and created a dead space on the side of the piston.
So I got to thinking. Other saws have ports that are setup similiarly and have windowed pistons. Not only would that open up that dead space and allow it to be pushed into the transfers, but it would also aid in cooling the underside of the crown, and significantly reduce piston weight. What's to loose? So I threw caution to the wind and decided to try it.
But why the need for all the extra intake area? Well this is the main thing I was after here. I need more transfer area and timing. I raised the transfers a huge 8° and significantly widened them. I didn't not go all the way to the vertical lines, but you get the idea.
Here's the end result.
I started by raising the cylinder wall at the transfer opening at the base of the cylinder. I raised it by nearly 1/4". I wanted to open up the area where the transfers take in from the crank case. If the cases were split, I would have case matched those as well.
This opened up and created a dead space on the side of the piston.
So I got to thinking. Other saws have ports that are setup similiarly and have windowed pistons. Not only would that open up that dead space and allow it to be pushed into the transfers, but it would also aid in cooling the underside of the crown, and significantly reduce piston weight. What's to loose? So I threw caution to the wind and decided to try it.
But why the need for all the extra intake area? Well this is the main thing I was after here. I need more transfer area and timing. I raised the transfers a huge 8° and significantly widened them. I didn't not go all the way to the vertical lines, but you get the idea.
Here's the end result.
I was able to make a few cuts with it last night. At least it still runs
Interestingly enough, max RPMs at WOT did not increase at all. But it's holding RPMs in the wood very well, and that's what I was after. I'll try to get a video up later, but I don't have any before times to compare it too.
Interestingly enough, max RPMs at WOT did not increase at all. But it's holding RPMs in the wood very well, and that's what I was after. I'll try to get a video up later, but I don't have any before times to compare it too.
olyeller
ArboristSite Guru
Baseline?
Did you do some timed cuts with the stock BB setup so you could measure gains? Can't wait to hear how that thing runs! Cutting windows that big in the piston make my hands sweat; you weren't worried about weakening the piston?
Did you do some timed cuts with the stock BB setup so you could measure gains? Can't wait to hear how that thing runs! Cutting windows that big in the piston make my hands sweat; you weren't worried about weakening the piston?
This cylinder was already ported. The intake and exhaust were exactly where I wanted them.
I'm not worried about the piston at all. It's not really any different than any piston I put in any other saw that already has windowed pistons.
I'll have to compare it to my 440 and Andyshine77's 372 to see what I did for it. Which brings something to mind. Andy, you better have a sharp chain ready! I'm coming after you BOY!!!:greenchainsaw:
Farley9n
ArboristSite Guru
Used 372XP BB. Why did you cut the windows??? OOOOOOOPPPPPSSSSSS......Way too late.......Bob
I've had this P&C on my saw for a while. I ported it before I ever installed it. I just went back in for more. I also installed a set of Caber rings while I was at it. It also has a popup piston. BTW, everything looked perfect. Both the P&C were really nice.
Farley9n
ArboristSite Guru
Guess I was too excited when the teacher asked the question and just got my hand up and blurted out the answer before I even turned the page! ......
Now.....I have the same cylinder and piston here on my desk waiting for the grinder. Plan was to leave the transfers at the same opening but slightly wider towards the intake side, square up the bottom of the intake, widen exhaust, do the bottom of the transfers just as you have, then use an 064 piston ( Meteor - also here on the desk) with a pop up that equals the gasket thickness plus a decent squish. The 064 piston is windowed, the rings are pinned in the wrong places and the inside rod opening is too small. So now it's back to the BB piston without windows and I will take what I need for squish from the gasket surface and use that for a popup......Plans Change....Thanks for your willingness to share......
......Bob
Now.....I have the same cylinder and piston here on my desk waiting for the grinder. Plan was to leave the transfers at the same opening but slightly wider towards the intake side, square up the bottom of the intake, widen exhaust, do the bottom of the transfers just as you have, then use an 064 piston ( Meteor - also here on the desk) with a pop up that equals the gasket thickness plus a decent squish. The 064 piston is windowed, the rings are pinned in the wrong places and the inside rod opening is too small. So now it's back to the BB piston without windows and I will take what I need for squish from the gasket surface and use that for a popup......Plans Change....Thanks for your willingness to share......
......Bob
Uh oh. The Stihls are in some serious trouble! No, this is not a scientific test, but the results are clear. I was not able to run the same chain on both bars, but the differences are too significant not to point out a clear winner. Looks like I might have to go back inside the 440 This 372 is haulin' the mail!
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Brad- Looks like you're getting the 372 design fine-tuned...
One of the best running 372BBs I ever had used an 038 Magnum piston...
One of the best running 372BBs I ever had used an 038 Magnum piston...
I don't know whether to be glad or sad, lol. Now I have to go back in the 440
heres a comparison
044 meteor on the left and stock 372xp on the right
so how much is the factory port opend .
ive been going back and forth wether or not i think my 372 is faster dual port or single 1" but i havent timed it to know for sure
044 meteor on the left and stock 372xp on the right
so how much is the factory port opend .
ive been going back and forth wether or not i think my 372 is faster dual port or single 1" but i havent timed it to know for sure
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This 440 has a 460 topend. I open those pistons up a lot too. My 372 really woke up when I added two 3/4" pipes.
this is my top factory port i run it with the sparkscreen installed along with 1" ID tube comeing off the front on my 372. i have block off sheet i can put over the factory port.
ive been running both ports open.
ive been running both ports open.
bitzer
******** Timber Expert
I did a similar job on my 455. Though not in the same class and a strato I was not satified with just opening up the exhaust and intake. It would not hold rpm in the wood well and go figure the transfers are like 6" long at the shortest point. I knew I had to advance timing a little and get as much fuel out of the transfers before the strato ports opened. I raised the bottom of the tranfer about 5 or 6 mm and raised and extended the top of transfer about 2mm up and 4 mm over toward the intake. I also aimed them upwards a little and it is holding rpms a lot better now. There was also no increase in WOT rpms, but thats not what I'm after anyway. Now after seeing this I may have to open up the windows. I thought about it and structural integrity, but was hesitant. Quit giving me ideas man! That saw is really rippin! I'm glad your out there to take the chances and do the experimenting for us! Ha!Ha!
troutfisher
Addicted to ArboristSite
Good thinkin' Brad.
Are other guys windowing 372 pistons?
