bikemike
loud pipes save lives
Since its not hard to expose ur engine try leaving those out once on vid and in for a vid with the porting you have
Ported Poulan Pro Pole Pruner
- Thread starter Chris-PA
- Start date
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bikemike
loud pipes save lives
If my crapsman saw has those plastic pieces i might try to remove them and se if it changes that pos. I dont care if it blows up. I have tried to roach it from cold start and no luck
Chris-PA
Where the Wild Things Are
I doubt that increasing the transfer volume (and it would be a significant increase) and running as open transfers would improve performance, but you never know.
bikemike
loud pipes save lives
Yeah i have not messed with a strato yet but i think the crapsman is a good start. My poulan pro 46cc is not the pooch it use to be.
Chris-PA
Where the Wild Things Are
Well, this project is not over yet, because I.. um... trashed it. I set it too lean and ran it too hard while setting it up, and scored it. Rookie mistake, but it happens. But I need this tool so I spent the big bucks and bought this for $32:
Hey, it ain't a Stihl!
While I wait I did some disassembly and learned something. It was bugging me that the strato port inlet opens to the air valve long before the passage opens to the transfer runner, so I was trying to figure out why they did that. And I found this when I looked at the piston in the cylinder with my modified transfer inserts:
When the piston is at TDC, those notches I made are now open into the case. This is not a problem in terms of running, as open transfers always do this. But it's a problem for strato where you are trying to keep the air in the transfers separate from the fuel/air mix in the case. Stratos don't work with open transfers.
It turns out that the bore is smaller than the width of the crank counterweights, so they had to cut out the lower edge of the piston to clear. And with the simple straight transfer runner casting they could not reposition the outlet, and so they ran out of piston height. They chose to keep the transfer air separate and reduce the strato intake duration. The stock timing is really like this:
However, I think that with the notches I added I will pull more air into the transfer runners, even if it may mix a little right around TDC. I'm betting it won't mix much.
I plan to widen the exhaust just as I did on the first cylinder, and to run the modified inserts.
Hey, it ain't a Stihl!
While I wait I did some disassembly and learned something. It was bugging me that the strato port inlet opens to the air valve long before the passage opens to the transfer runner, so I was trying to figure out why they did that. And I found this when I looked at the piston in the cylinder with my modified transfer inserts:
When the piston is at TDC, those notches I made are now open into the case. This is not a problem in terms of running, as open transfers always do this. But it's a problem for strato where you are trying to keep the air in the transfers separate from the fuel/air mix in the case. Stratos don't work with open transfers.
It turns out that the bore is smaller than the width of the crank counterweights, so they had to cut out the lower edge of the piston to clear. And with the simple straight transfer runner casting they could not reposition the outlet, and so they ran out of piston height. They chose to keep the transfer air separate and reduce the strato intake duration. The stock timing is really like this:
However, I think that with the notches I added I will pull more air into the transfer runners, even if it may mix a little right around TDC. I'm betting it won't mix much.
I plan to widen the exhaust just as I did on the first cylinder, and to run the modified inserts.
Chris-PA
Where the Wild Things Are
So I got the new cylinder today and found that they have significantly changed the cylinder timing. The have also changed the piston - it now has modified transfer slots and is 1mm taller on the sides, so the strato slots in the piston now open into the transfers closer to when they open into the air valve. But it's still 1mm off. I'll get some pictures later.
The biggest changes are that the exhaust port is now 1mm lower and the fuel intake is 2mm higher! This thing has really conservative timing now and I'll have to decide what I want to do with it. Here is what it looks like with the revised piston and cylinder:
Note that the strato intake now opens before the fuel/air intake, which is like other stratos I have seen.
The biggest changes are that the exhaust port is now 1mm lower and the fuel intake is 2mm higher! This thing has really conservative timing now and I'll have to decide what I want to do with it. Here is what it looks like with the revised piston and cylinder:
Note that the strato intake now opens before the fuel/air intake, which is like other stratos I have seen.
I agree with everything you said except not needing the string trimmer for awhile. I used mine yesterday, around here Spring has sprung..
Chris-PA
Where the Wild Things Are
I had a little time to work on this today. Here are the changes to the piston and to the cylinder - you can see how much higher the lower edge of the fuel/air intake is (new cylinder on left):
The round intake opening actually matches in the carb mount better. On the piston you can see that they raised the slot where it meets the transfers to fix the problem with the earlier design:
The casting is actually not bad, but they've clearly tried to reduce any deburring steps as much as possible. With the small bore engines I've worked on I do not do that much beveling of ports, as most of the factory ports I've seen in Poulan and Zenoah engines are fairly sharp - but this is beyond that. There were sharp, rough edges in the intake ports, and the edges of the transfers are like a knife all the way around. I could not get a good shot of intake port edges, but this gives some idea of the edge of the transfer castings:
Even the piston pockets had edges you can cut with. I smoothed most of them to take at least the knife edge off - the transfers were hard to get to.
With the measurements I took, and using the new transfer inserts, the timing should be this (I'll have to confirm that when it's back together):
I thought about this a lot a decided that while it is conservative, this is a pole saw/string trimmer - it needs to have power at a lower rpm as the string trimmer just will not spin that fast. So I'm resisting the urge to open everything up, and in particular to raise the exhaust. Further, the strato linkage on this is more progressive and has a later opening than on the GZ4000s I've played with. This means that the engine switches intake port timing, going from a 130 duration (where it will run fairly often) to a 154 duration, and that seems like just what you'd want for this use.
So my strategy is only to widen the exhaust (from the 42% it came with to 55% of the bore), and use the new transfer inserts without notches, just beveled 0.5mm at the top to match the timing of the strato opening to the air valve. It will no longer have the problem created by my transfer insert notches on the first cylinder, where these opened the end of the transfers under the piston at TDC.
Here are the intake ports from inside - I have not modified them (there are some water drops on there):
I took the exhaust port to 55% of the bore:
I also had to sand the plastic transfer inserts to get them to fit properly, which was not hard but I should not have had to do that. I hope to get it back together in the next few days.
The round intake opening actually matches in the carb mount better. On the piston you can see that they raised the slot where it meets the transfers to fix the problem with the earlier design:
The casting is actually not bad, but they've clearly tried to reduce any deburring steps as much as possible. With the small bore engines I've worked on I do not do that much beveling of ports, as most of the factory ports I've seen in Poulan and Zenoah engines are fairly sharp - but this is beyond that. There were sharp, rough edges in the intake ports, and the edges of the transfers are like a knife all the way around. I could not get a good shot of intake port edges, but this gives some idea of the edge of the transfer castings:
Even the piston pockets had edges you can cut with. I smoothed most of them to take at least the knife edge off - the transfers were hard to get to.
With the measurements I took, and using the new transfer inserts, the timing should be this (I'll have to confirm that when it's back together):
I thought about this a lot a decided that while it is conservative, this is a pole saw/string trimmer - it needs to have power at a lower rpm as the string trimmer just will not spin that fast. So I'm resisting the urge to open everything up, and in particular to raise the exhaust. Further, the strato linkage on this is more progressive and has a later opening than on the GZ4000s I've played with. This means that the engine switches intake port timing, going from a 130 duration (where it will run fairly often) to a 154 duration, and that seems like just what you'd want for this use.
So my strategy is only to widen the exhaust (from the 42% it came with to 55% of the bore), and use the new transfer inserts without notches, just beveled 0.5mm at the top to match the timing of the strato opening to the air valve. It will no longer have the problem created by my transfer insert notches on the first cylinder, where these opened the end of the transfers under the piston at TDC.
Here are the intake ports from inside - I have not modified them (there are some water drops on there):
I took the exhaust port to 55% of the bore:
I also had to sand the plastic transfer inserts to get them to fit properly, which was not hard but I should not have had to do that. I hope to get it back together in the next few days.
Chris-PA
Where the Wild Things Are
I realize this isn't the most exciting thread given it's just a puny pole saw, but I had fun doing it and learned a few things along the way, so I figure I'll finish it up! After re-reading the section of Jennings' Two-Stroke Tuner's Handbook on port beveling, I went back in and added a bit to the bevel on the top edge of the exhaust port:
Then it was time for reassembly. The piston and crank installed into the cylinder:
Partially built up:
Neat little engine:
Then I tortured it. Just for those of you who really want to see how long it can take to cut a piece of wood, here is a mildly ported 33c pole saw with a 16" bar running full skip lo pro cutting a white oak crotch:
Yes, it takes forever, but it does cut it and the engine doesn't sound too loaded. Here's the chain:
Then it was time for reassembly. The piston and crank installed into the cylinder:
Partially built up:
Neat little engine:
Then I tortured it. Just for those of you who really want to see how long it can take to cut a piece of wood, here is a mildly ported 33c pole saw with a 16" bar running full skip lo pro cutting a white oak crotch:
Yes, it takes forever, but it does cut it and the engine doesn't sound too loaded. Here's the chain:
It's obvious you don't know how to sharpen a chain, way too much dust coming out.
Chris-PA
Where the Wild Things Are
Oh OK, you can tell from a video that I have "no idea" how to sharpen a chain - that's impressive. Naturally it's not possible that maybe it needs a touch up - heck, I'll have to send it out for that I guess, as I don't even know what end of the file to hold.
Or it could be that with full skip lo pro chain and a pole saw that prevents you from putting any pressure down you get finer chips, and then video processing makes that look more like a cloud than it really did.
Focus problems - it's not that dull:
Roll Tide
Trolltide
Ported poulan pole saw ! Gotta love it!
Chris-PA
Where the Wild Things Are
I finally got to run this as a trimmer toady and I'm really happy with how it came out. It's got lots of low end power so I can run it slow and not have it stall out in taller grass. And if I open the air valve it will really take off. The variable port timing with the air valve opened/closed is very apparent, and useful.
ANewSawyer
Addicted to ArboristSite
Sorry, but when you say air valve, are you talking about the strato intake?
That wasn't sharpened with a file was it? Looks like a wheel might have done it. Not criticizing, just wondering. My Stihl pole saw has been used a few times but has never been sharpened..
Chris-PA
Where the Wild Things Are
Yes, sorry I should have been more clear. On this design the air valve does not open until the throttle plate is opened fairly far. At low speed it is mostly closed.
Chris-PA
Where the Wild Things Are
This thing is sweet as a pole pruner now too! The 16" bar with the lo pro skip chain is just the ticket, and I will be leaving that setup on full time. I had some low hanging branches that have been getting in my way on the tractor, including a large tulip branch that was about 10" at the root. It zipped that off quite nicely, and it didn't make me stand there forever doing it either.
