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Discussion Starter · #1 ·
I'll try to make a long story short here... My dad sold me his Cub rider cheap because it was using a lot of oil. I read that the intake is a known issue on these motors and they pull in a bunch of junk, ruining the rings. I tore the motor down and had the bores mic'd out. They were fine so I replaced the rings and upgraded the intake tube, shroud...etc. I ran fine for about 3-4 mowings before blowing black smoke out of the exhaust again. You could smell the burning oil and I'd use a half quart mowing a 1/4 acre lot.
I tore it down again. The valves were sealing, the guides looked good, the rings looked good, and the crankcase breather looked fine but I replaced anyway. The same thing kept happening.
I bought .020" piston assemblies and had the block bored. The machinist said even though the bores seemed mic ok, he could see that the walls were not cutting evenly. Hopefully this is finally it!

Everything is back together and installed. I charged my battery overnight. When I try to turn the motor over, I'm lucky if it will turn 1-2 revolutions. I flipped my charger to boost and it just won't go. While my battery could be junk (haven't had a chance to test yet, though it's fairly new) my question is, could I need a stronger starter? There just isn't enough power to turn it over. Is a weak starter something typical after a rebuild?
It's not easy to rotate by hand. I know 100% that the pistons/rods are installed correctly and the timing marks are aligned.
 

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Did you make sure that the pushrods were seated correctly in the rocker arms? If one of them slipped out, that would jack up the compression.
 

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Try taking the plugs out to see if the engine still turns over hard. If it does, something is wrong that isn't the valves. I doubt this, but is the pulley and belt installed? Is the belt too tight?
 
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Just another idea I had...are the ignition modules gapped correctly? They may be rubbing on the flywheel but it's unlikely
 

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And yet another thing, I have one of these twins and its not easy if impossible to turn it over by hand with the plugs in.
 

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Discussion Starter · #11 ·
Thanks Vortec. I gapped the ignition modules so I know they are good too. I found the lash to be too tight on the exhaust valve of cylinder #2. Once I set that, it turned much easier with the plugs out. I put them back in and I can still turn it but there seems to be a sticking point in the same spot of each revolution. My battery is dead again so that is another problem. I haven't tried to turn it over yet.
I noticed too that as I turn the motor, I can hear a kazoo sound. I assume this is vacuum; it's just strange that I haven't heard that before.
 

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Does it stick on each revolution or every other. If its every other its just normal compression. Does the noise sound like a metallic rubbing and grinding or does it just sound like air
 

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Discussion Starter · #13 ·
I guess I didn't pay attention to whether it was every other or not. I sure hope. That would at least make sense. The noise sounds like air; nothing grinding.
 

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When you readjusted the exhaust valve on cy#2, you said it then became much easier to turn the engine by hand, with the plugs OUT ! With zero compression, I don't understand how valve adjust effected it..? Could it be a 'tell-tale' of something else.?
 

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If the valve clearance was really too tight, the resistance felt would be the valve bottoming out but the cam still trying to push it open more.
 

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Discussion Starter · #20 ·
I have fuel, spark, and compression but I can't get it to fire. I'm thinking it's because I can't crank it long enough. I don't know what else could possibly be wrong.
 
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