Scooterbum
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Use a little drop of red loctite on the clips.Haven't lost one yet.
Poulan Exhaust Port Advice Needed
- Thread starter Chris-PA
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Use a little drop of red loctite on the clips.Haven't lost one yet.
Chris-PA
Where the Wild Things Are
Well, I took apart the original 46cc engine. This one has very good compression and the bore, ring and piston look really good. The ring, groove and piston top had a fair amount of carbon, probably from running TCW-3 oil for a while in the past, so I cleaned that off.
The piston does not have the cut out on the side to allow better access to the transfers, it's basically a slug with the skirt cut up a bit. The transfers are 1mm lower, I assume for better torque/compression, and without the piston cut out they are effectively longer. They are a little wider though with the smaller bore. The cross section has a similar hook-shaped profile on one side, I assume so that mix pushed ahead of the crankshaft counterweights is captured in the transfer runner groove. I left all that alone.
I did a very mild port, primarily on the exhaust to remove the ridge where the steel insert went:
It's still only at 54% of the piston width. I did a little on the intake as well, but still conservative (the area of the intake port is so much larger than that of the carb already):
Then I sealed the carb adapter plate to the rubber seal in the carb mount with Yamabond - the rubber seal is a little distorted and I never liked how it fit. Plus this will make mounting the carb easier since the metal plate won't keep falling off.:
Last, I used some Ultra Copper RTV to seal the heat shield to the exhaust port since the upper part of the flange has such a narrow sealing surfact:
I'm hoping to put it together tonight. It will be interesting to see how it runs compared to the 49cc engine. The porting is not too different and the ignition timing is the same (advanced about 6deg).
The piston does not have the cut out on the side to allow better access to the transfers, it's basically a slug with the skirt cut up a bit. The transfers are 1mm lower, I assume for better torque/compression, and without the piston cut out they are effectively longer. They are a little wider though with the smaller bore. The cross section has a similar hook-shaped profile on one side, I assume so that mix pushed ahead of the crankshaft counterweights is captured in the transfer runner groove. I left all that alone.
I did a very mild port, primarily on the exhaust to remove the ridge where the steel insert went:
It's still only at 54% of the piston width. I did a little on the intake as well, but still conservative (the area of the intake port is so much larger than that of the carb already):
Then I sealed the carb adapter plate to the rubber seal in the carb mount with Yamabond - the rubber seal is a little distorted and I never liked how it fit. Plus this will make mounting the carb easier since the metal plate won't keep falling off.:
Last, I used some Ultra Copper RTV to seal the heat shield to the exhaust port since the upper part of the flange has such a narrow sealing surfact:
I'm hoping to put it together tonight. It will be interesting to see how it runs compared to the 49cc engine. The porting is not too different and the ignition timing is the same (advanced about 6deg).
Last edited:
Chris-PA
Where the Wild Things Are
I buttoned it up last night and got it started before I quit. I put it together with the original 46cc carb (WT529 IIRC). When I got home tonight I put a bar and chain on it and went over to tune it and noodle some persimmon, just as I was doing when the other engine ate the circlip. I got it sorta tuned, but the needles were out kinda far, and it was inconsistent, and then it quit. So I took it back to the barn and found the fuel line had popped of the carb inlet, but I decided to put the same carb I was running on the 49cc engine on it (WT285). They're the same venturi size, but it seemed to work better - and it did here too.
The saw is running quite well, and I'm hard pressed to tell any difference from the 49cc motor. It probably has better compression, and the porting is about the same, so perhaps that's no surprise. It might not be revving quite as high, but I was conservative on the tuning too - I certainly took some rpms out of it with the H needle. It can certainly pull the full bar (20" minus the spikes) while noodling and not bog.
So I guess that completes this journey, and the 2775 is back to its original engine, but ported and with timing advanced, and running the carb from the PP315.
The saw is running quite well, and I'm hard pressed to tell any difference from the 49cc motor. It probably has better compression, and the porting is about the same, so perhaps that's no surprise. It might not be revving quite as high, but I was conservative on the tuning too - I certainly took some rpms out of it with the H needle. It can certainly pull the full bar (20" minus the spikes) while noodling and not bog.
So I guess that completes this journey, and the 2775 is back to its original engine, but ported and with timing advanced, and running the carb from the PP315.
