bikemike
loud pipes save lives
Yeah a pipe did wonders om my saw
Reducing Squish on a Poulan Clamshell
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bikemike
loud pipes save lives
Yeah a pipe did wonders om my saw
smokey7
jack of a lot ace of a few
I am looking at a.pocket pipe forbit to see. I am looking for another 630 or 670 jug also. Can you bridge a open port 625.0or thers like it. What do you do to a open port jug? Does anyone.make flanges for. Piped saws?
Chris-PA
Where the Wild Things Are
Cool! I could draw up a lower pan pretty easily on Inventor, and we now have a plug-in that will basically write the G-codes for the mill. However, I'd have to get time on the machine and get help from the guys in the shop, and everything is set up for production. So I don't think I will go that route.
Thanks, but thankfully the piston and cylinder are OK and I expect they will run fine. It's just the 3D printed plastic pan filler that I added that was destroyed.
I don't even know if it does anything, and I'm sure the engine would run great without it so other than dyno testing I'm skeptical that a comparison test would be conclusive enough to be worth the trouble. Nevertheless I went to considerable effort to modify the crank and I'd like to put the modification back - just not with that material.
bikemike
loud pipes save lives
Well i can say if your going to go with a pocket bike pipe make the header pipe as short as possible it worked wonders on my poulan 46 cc i have a very broad power range now and it sounds good got some vids on you tube mike schlak
Mastermind
Work Saw Specialist
Compression my man.........it makes huge differences.
Chris-PA
Where the Wild Things Are
So I've been thinking about why the first pieces failed, and my suspicion falls on the attachment system which was just epoxy. Given how completely the stuff was cleared off once it failed it might have been better if I had dimpled the surface under the epoxy. I don't know what got it started, but maybe the epoxy let go in a spot.
Given that, I decided that I'd like a positive mechanical means of attachment, and the way I wanted to do that kind of eliminated an aluminum part. I modified the design to add a lip at the edge that would be confined between the cap and the cylinder. Then I added a hole at the bottom for a locating pin. I decided to make them out of ABS this time, as it is harder and has a higher melting point, and it is sandable.
We've had trouble printing ABS, but I spent some time messing with temperature profiles and reducing the print head speed, and I got it to work pretty well.
I had to bevel the lip on the inside of the cap, and I added two locating pins (which are stainless 2-56 screws):
This is how they fit:
I was mostly happy with how it fit, although I wish I had more locating pins to hold the upper ends against the outside. I was all ready to put it back together with a little adhesive to secure the fillers.
BUT.......
There's a little problem. ABS dissolves in gasoline. Which was why I used PETG in the first place! I forgot. I set an extra part in a container of 2-stroke mix and it was getting gooey in 30min. I'll have to wait until Monday to print new ones in PETG, and hope that they won't fail the same as the first ones. I am considering adding additional locating pins if I think I can flex the part onto them.
Given that, I decided that I'd like a positive mechanical means of attachment, and the way I wanted to do that kind of eliminated an aluminum part. I modified the design to add a lip at the edge that would be confined between the cap and the cylinder. Then I added a hole at the bottom for a locating pin. I decided to make them out of ABS this time, as it is harder and has a higher melting point, and it is sandable.
We've had trouble printing ABS, but I spent some time messing with temperature profiles and reducing the print head speed, and I got it to work pretty well.
I had to bevel the lip on the inside of the cap, and I added two locating pins (which are stainless 2-56 screws):
This is how they fit:I was mostly happy with how it fit, although I wish I had more locating pins to hold the upper ends against the outside. I was all ready to put it back together with a little adhesive to secure the fillers.
BUT.......
There's a little problem. ABS dissolves in gasoline. Which was why I used PETG in the first place! I forgot. I set an extra part in a container of 2-stroke mix and it was getting gooey in 30min. I'll have to wait until Monday to print new ones in PETG, and hope that they won't fail the same as the first ones. I am considering adding additional locating pins if I think I can flex the part onto them.
LegDeLimber
Addicted to ArboristSite
A step at the end of the pan radius would do wonders for trapping them.
You know you've gotta be thinking about it already.
That taper will still let them loose.
IF the tips (thin tips = most susceptible/saturate-able area) swell any little bit, it's going to push them out.
Plus I'd toss a set in some E-85 "gas" (if available) to see what it does to them.
I'm thinking of the E-85 as a way to push both any susceptibility and the results time.
[ at least use some of whatever corn-gas that you're tormenting yourself with ]
A warm location for the test container would be preferred also.
The mix oil could even be not getting along with the plastic.
So ditto on immersion testing.
Just 'nother half dozen mason jars of gunk, huh?
Ain't R&D a hoot!
You know you've gotta be thinking about it already.
That taper will still let them loose.
IF the tips (thin tips = most susceptible/saturate-able area) swell any little bit, it's going to push them out.
Plus I'd toss a set in some E-85 "gas" (if available) to see what it does to them.
I'm thinking of the E-85 as a way to push both any susceptibility and the results time.
[ at least use some of whatever corn-gas that you're tormenting yourself with ]
A warm location for the test container would be preferred also.
The mix oil could even be not getting along with the plastic.
So ditto on immersion testing.
Just 'nother half dozen mason jars of gunk, huh?
Ain't R&D a hoot!
Chris-PA
Where the Wild Things Are
Well, I'll think about the step vs. bevel - there's not a lot of meat on the edge of that cap and a step will cut in further. I was worried about breaking through as it is. I think if the part gets flexible enough to be pushed out by the bevel it won't last anyway.
The PETG actually has decent resistance to both gasoline and ethanol.
Not surprisingly the cap is cast with a little be of draft, and so it's a little narrower at the bottom than it is up by the bevels. When I print the replacement parts I'm going to try to accommodate that. It will cause some issues as that was the side I had down on the print bed and now it will no longer be flat.
Chris-PA
Where the Wild Things Are
Today I printed the parts again. I modified the design to accommodate the draft of the metal cap. I added ridges to the bottom of the part where it would be elevated off the print bed. I knew it would be a pain to cut them off but I couldn't come up with anything else.
Here's the drawing:
And here's the printed part:
It took a bunch of cutting, filing and sanding to clean it up but it wasn't too hard to do. Then I added more locating pins:
And here's how they fit:
I glued them in with Seal-All, and bolted the cap to a cylinder until it set. Then I put the engine back together with sealant. Hopefully I'll have the saw back together soon.
Here's the drawing:
And here's the printed part: It took a bunch of cutting, filing and sanding to clean it up but it wasn't too hard to do. Then I added more locating pins:
And here's how they fit:
I glued them in with Seal-All, and bolted the cap to a cylinder until it set. Then I put the engine back together with sealant. Hopefully I'll have the saw back together soon.
drf255
BAD CAD
That's super nice work there Chris.
smokey7
jack of a lot ace of a few
Printers rock!!!!!
bikemike
loud pipes save lives
I'm too computer phucktarded to use those
Chris-PA
Where the Wild Things Are
It's all back together and running - I didn't take any pictures of it assembled as it looks just like it did on all the other threads where I've built this saw! It started and seemed to run just like it did before, but it will have to wait until (hopefully) tomorrow before I can put it in wood. I just so happen to have an ash I dropped on Sunday that needs to be bucked up.
Chris-PA
Where the Wild Things Are
I got a chance to run the saw in that ash before the daily deluge hit. This was a standing dead ash that was really hard. On my first cuts it was not very fast and it made a lot of dust in addition to chips, and I figured maybe the 91VXL was in need of some touch up. So I put on a 16" bar with some sharp Carlton N1. It was faster, but still made quite a bit of fine dust. I measured 10,800 to 11,800rpm in this first cut:
Then I took a look at the 91VXL, and it wasn't dull. So I put it back on and gave it another try (looks like I cut off the very end of the video - not sure how I did that):
It's definitely loaded more, running maybe 9600rpm, and it cuts slower.
That's all I had time for before before the storm. I played with tuning a bit, and had some vapor lock issues - I didn't really feel like I got it running quite right. Then again, this is different wood than I was running it in and it's quite a bit harder.
But the saw stayed together!
Then I took a look at the 91VXL, and it wasn't dull. So I put it back on and gave it another try (looks like I cut off the very end of the video - not sure how I did that):
It's definitely loaded more, running maybe 9600rpm, and it cuts slower.
That's all I had time for before before the storm. I played with tuning a bit, and had some vapor lock issues - I didn't really feel like I got it running quite right. Then again, this is different wood than I was running it in and it's quite a bit harder.
But the saw stayed together!
Chris-PA
Where the Wild Things Are
I put the chain for the longer GB bar on the chain vice this evening, and as usual it's easier to see the condition there than it is on the stump. I won't say it was dull, but it's sharper now! I suspect this is part of the issue I was seeing.
mexicanyella
ArboristSite Operative
This is fascinating stuff; more well-documented experimentation, and in an area that never would have occurred to me. Using a 3D printer to fabricate plastic crankcase inserts! My gray "36cc" Craftsman is a easy-to-start, good-running little saw but yours runs like an animal, and with a 2"longer bar to boot. Really cool.
Hopefully the following digression is okay here since squish-talk seems to have wrapped up...and you may well already know all this but...you made a comment a page or so back about this saw's porting not being ideal for a pipe. I think a two-stroke with any porting, in any state of tune, can benefit from a pipe; it's a matter of sizing and shaping the pipe to work in the engine's operating range...and deciding--as in all things related to the search for more HP--whether you will settle for less power over a broad range of rpm, or more power over a narrow (and probably higher) range of rpm. If you have the ability to weld or braze sheet metal, it would be interesting to see you build a pipe to work with one or more of your saw(s).
You know your port timing, which would give you a starting point in terms of headpipe length and overall length. Headpipe and stinger diameters are pretty much determined by exhaust port area. You could still spend a LOT of time trying to optimize cone angles before finding the ideal configuration--some pipes have compound angles of divergence and convergence, which introduces even more variables--but with the basic diameters and lengths in mind, I'd bet you could whip up something that would be significantly better than a box-shaped muffler with a diffuser and outlet hole in it. Looking at Bikemike's 4620, it seems possible to do it in a way that you could even hold the saw safely and operate it in most positions without burning yourself on it.
My point is, pipes don't exist to make more power at higher rpm; they exist to improve scavenge efficiency and retain fuel in the cylinder at whatever rpm you want. The absolute lack of any two-stroke bike WITHOUT some form of expansion chamber exhaust, even trail bikes, from the 70s on, is evidence that it's worth it even on engines in a fairly mild state of tune, and if it can work over a broad-enough speed range for a trail bike, it can work for a WOT-all-the-time saw engine.
I managed to build pipes that worked on a bike I had without even doing much math, after reading up on how they worked and how the various dimensions affected operating parameters...using info from the early 70s by Gordon Jennings. Using parts of existing pipes saved me having to make my own cones. A .pdf of Jennings' useful "Two-Stroke Tuner's Handbook" and his article "Do You Really Want to Know About Expansion Chambers?" are easy to find on Google. Or I can send them to you if you're interested and haven't seen them already. Clearly, I really wanted to know about expansion chambers.
Hopefully the following digression is okay here since squish-talk seems to have wrapped up...and you may well already know all this but...you made a comment a page or so back about this saw's porting not being ideal for a pipe. I think a two-stroke with any porting, in any state of tune, can benefit from a pipe; it's a matter of sizing and shaping the pipe to work in the engine's operating range...and deciding--as in all things related to the search for more HP--whether you will settle for less power over a broad range of rpm, or more power over a narrow (and probably higher) range of rpm. If you have the ability to weld or braze sheet metal, it would be interesting to see you build a pipe to work with one or more of your saw(s).
You know your port timing, which would give you a starting point in terms of headpipe length and overall length. Headpipe and stinger diameters are pretty much determined by exhaust port area. You could still spend a LOT of time trying to optimize cone angles before finding the ideal configuration--some pipes have compound angles of divergence and convergence, which introduces even more variables--but with the basic diameters and lengths in mind, I'd bet you could whip up something that would be significantly better than a box-shaped muffler with a diffuser and outlet hole in it. Looking at Bikemike's 4620, it seems possible to do it in a way that you could even hold the saw safely and operate it in most positions without burning yourself on it.
My point is, pipes don't exist to make more power at higher rpm; they exist to improve scavenge efficiency and retain fuel in the cylinder at whatever rpm you want. The absolute lack of any two-stroke bike WITHOUT some form of expansion chamber exhaust, even trail bikes, from the 70s on, is evidence that it's worth it even on engines in a fairly mild state of tune, and if it can work over a broad-enough speed range for a trail bike, it can work for a WOT-all-the-time saw engine.
I managed to build pipes that worked on a bike I had without even doing much math, after reading up on how they worked and how the various dimensions affected operating parameters...using info from the early 70s by Gordon Jennings. Using parts of existing pipes saved me having to make my own cones. A .pdf of Jennings' useful "Two-Stroke Tuner's Handbook" and his article "Do You Really Want to Know About Expansion Chambers?" are easy to find on Google. Or I can send them to you if you're interested and haven't seen them already. Clearly, I really wanted to know about expansion chambers.
David Young
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Big Block
WFO or I don't go
Thats a running little bastard
