Weak compression

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Old 03-28-2019, 01:10 PM
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Default Weak compression

When i got my used 1/8 nitro buggy it was hard to turn mootor over(good compression) but after taking a part, cleaning and oiling .. motor turning became very easy?
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Old 03-28-2019, 02:52 PM
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No compression could indicate:


Is it possible you tightened down the head bolts improperly and now have a gap at the head button for air to escape from. Undo the head bolts, tighten each screw just a little bit going in a cross pattern until tight.

Is the glow plug seated properly?

Is the sleeve seated back down in the case properly?

Also when old/used motors are sold, they often are sold full of oil to give the impression that the piston and sleeve still has life left, but once the oil is cleaned out the air pressure blows past the piston exposing the motor as worn out or loss of pinch.


I would take the top end apart again, re-seat everything, be sure to check the alignment of sleeve and case pin to ensure its sitting all the way down in the case. Sometimes the sleeves collar will sit on top of the case pin and not drop down all the way in the case. Hope that helps. Also note, its way easier to turn a motor over by hand when the motor is out of the car, did you check compression while in the car with one finger, and now you are using your entire hand to turn it over much easier out of the car?
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Old 03-28-2019, 03:41 PM
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Is it a pull starter engine?? And you feel no compression at the pull starter?
In that case you probably lost the pin that belongs in the crank pin of the crankshaft or you have mounted the oneway bearing in the wrong way.
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Old 03-28-2019, 05:22 PM
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Originally Posted by Roelof View Post
Is it a pull starter engine?? And you feel no compression at the pull starter?
In that case you probably lost the pin that belongs in the crank pin of the crankshaft or you have mounted the oneway bearing in the wrong way.
Good point, I didn't even think of that! lol. That could be it!
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Old 03-28-2019, 11:36 PM
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I did not take out piston sleeve and piston and krank shaft i just cleand it and oiled... i will check everything you told me...
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Old 03-28-2019, 11:37 PM
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It is not pullstarter engine... and the name is kanai evo2
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Old 04-03-2019, 07:58 PM
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Maybe the compression you felt was old dried up oil from fuel, did it use to be really free feeling with a pop when u turned it over? Obviously a lot of compression in the pop... or was it rigid and firm turning the flywheel with no pop?

If it indeed went from having a smooth rotation with a compression pop to having absolutely nothing then the only thing I can think is your glow plug isn’t in it, or the very top of the block has cracked (which would be the first time that’s ever happened that I know) there’s a good chance somethings not right or your engine is really old. If u have the time just tear down the engine, they are very basic to understand u do not have to put them together with timing measurements or anything, I could tear a new engine down and back together from running to torn down and back running in probably 25 minutes and 3-4 tools.
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