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Pistion Swapping - Bad Idea?


BlakFyre's Avatar
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07-29-07, 05:00 PM   #1  
Pistion Swapping - Bad Idea?

I had two 2-cycle weed eater/line trimmer engines laying around (OK, so I have about four of them... six including old chainsaws) I figured I may as well try to get one of them working again. I picked the two most promising and started tearing parts off. Different brands, but appear to have the same size engine... i cant remember if it was them, or one of the chainsaws was 39cc, anyways... pistons are the same size as far as I can tell. Same width, number of rings, skirt length... little connecting rod thingy length (correct terminology would be appreciated), cutouts on the skirt seem to be the same. My question is, is it possible to swap them out? The reason for this is the one piston in the trimmer that actually ran somewhat had burn marks along the sides, so I would imagine it wasn't getting good compression.

 
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07-29-07, 06:08 PM   #2  
If the piston is exactly the same size as the one in the engine your restoring,Same number of rings,same length connecting rod.And the piston skirt doesn't hit the crankshaft.and the head of the piston dosen't come up and hit the spark plug I dont for see any problems at all.I've cross bead engines like this also from time to time with out problems.

 
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07-29-07, 06:46 PM   #3  
As far as I could tell, the only difference between the two pistons was that one was slightly more beveled at the top. Actually, I have already swapped them and turned the engine a few times, nothing hits or locks up, the magneto still works. With the spark plug in I have decent compression (not sure if its more or less then before). All I have to do is put the others carb on it and see if it runs. Hanging on to it is probably going to be a pain...(I hop not literally) and I dont think I remember which lines go where on the carb...

 
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07-29-07, 07:29 PM   #4  
Well, once I got the carb squared away, started on 3 pulls... and that was after I flooded it! Works better than either of the two when they were new. Thank you repair_guy for the valuable information.

 
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07-29-07, 08:57 PM   #5  
Glad that you got it running.And FYI the bevel on the top of that piston that you was talking about is to force the intake gases up to the top of the cylinder while the exhoust gases is going out.

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07-30-07, 06:47 PM   #6  
Posted By: repair_guy Glad that you got it running.And FYI the bevel on the top of that piston that you was talking about is to force the intake gases up to the top of the cylinder while the exhoust gases is going out.

put us in your favorates just in case you need us in the future
Yeah, I'm working on all sorts of projects at the moment. Computer case mod, gas powered bike, portable gas powered water cannon =P. I would imagine somewhere in there I'll be back, meanwhile I'll just browse, see if I can help anyone and work on my furnace so I can cast some special brackets and parts. That will be something new!

 
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