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Stihl MS 211/C with low compression issue


John Rainford
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Cutting through some logs that were around 12 inches thickness the saw started getting stuck in the cut, ie there was not enough power to allow the chain to cut as it would normally do and it stopped moving. Small logs with less diameter were not a problem. I have a motorcycle repair shop opposite where I live so I asked them if they would do a quick compression test for me. It came back at 70. With what I have learnt from this web site I know that this is far to low for optimum power. So now I need to find out what is causing the problem. I have previously torn the saw write down for another issue which was resolved and the piston, crank arm and cylinder internals look good to me. The piston rings move freely and look fine and I made sure everything was replaced the right way round. Do I need to shell out for a pressure/vacuum test to get to the route cause or are there other things I could check first which don't need specialist tools. Any help would be appreciated.

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1 minute ago, John Rainford said:

Cutting through some logs that were around 12 inches thickness the saw started getting stuck in the cut, ie there was not enough power to allow the chain to cut as it would normally do and it stopped moving. Small logs with less diameter were not a problem. I have a motorcycle repair shop opposite where I live so I asked them if they would do a quick compression test for me. It came back at 70. With what I have learnt from this web site I know that this is far to low for optimum power. So now I need to find out what is causing the problem. I have previously torn the saw write down for another issue which was resolved and the piston, crank arm and cylinder internals look good to me. The piston rings move freely and look fine and I made sure everything was replaced the right way round. Do I need to shell out for a pressure/vacuum test to get to the route cause or are there other things I could check first which don't need specialist tools. Any help would be appreciated.

Might not be the right compression tester for that . Spud will be along @spudulike

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If it was only 70 psi I doubt it would start . 70 psi is not enough to support combustion . I don't think it was the right compression tester .  More likely what the other guys are saying about bar dressing / sharpening / etc etc . 

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As others have said, 70psi isn't enough to support combustion. It is possible that your garage tested the saw with a tester for cars allowing the engine to be continuously cranked. You need something like a gunson hi gauge with the very soft tip mounted Schrader valve.

It may be worth removing the muffler for a look at the piston and the carb may be a possible cause but difficult to tell if the whole machine has been stripped and rebuilt for one reason or another.

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As Spud says, pull the muffler off and check piston for a part seized piston. Piston can seize in a couple of seconds during a single run, so just because it was fine when you last saw it, that's no guarantee its still good. If the saw ran ok (post rebuild) and then started messing about that's the first place to look - no point risking further damage for the time it takes to do a quick check. 

 

Your saw has that easy start contraption on it I think, which is a shame - it means you can't do the quick and dirty compression test where you pick the saw up by the starter cord.

 

bmp01

 

 

 

 

 

 

 

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