Posted by bkelley on December 30, 2017 at 10:00:53 from (107.204.86.52):
Hello,
I have a wisconsin VH4D gas motor out of an old 1979 bobcat 630. It was running fine and then all the sudden started blowing smoke out the breather tube and losing power. I'm not an engine builder by any means and know enough to get myself in trouble or end up with more questions than answers. Hense the forum post. The motor was rebuilt about a 100 hours ago by a third party. I checked the timing and valve spacing and everything seemed fine there, did a compression check and it was 80 on two of them, a little lower at around 70 on the other 2. I pulled the motor out of the bobcat to pull it apart to check the pistons and rings thinking maybe two of the rings were lined up or maybe broke allowing blow by. Nothing looked damaged and none of the rings were directly lined up but, a couple were close. I did some measuring and the bore of the cylinders is 3.280" and according to the manual the original bore is 3.250". One of my questions is what size should the piston itself be if the cylinder bore is 3.280"? How much clearance should be between the cylinder and the piston? I'm wondering if the pistons are too small? Thanks.
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