M12 Engine Rebuild

[eo1bart 45]

I have a running12 hp engine that came with a 312-8 parts tractor that I bought. The hour meter on the tractor had approx. 2000 hours on it .

I'd like to freshen up the engine and use it to replace the K301 that is currently in my daily driver. I've removed the head and it is still in spec. but glazed over and wet.

At the very least I'll hone it and replace the rings. Looking for recommendation on how far to go with it. Replace the piston also? buy the whole rebuild kit

for $150 that includes the conrod and valves? Replace crank bearings? Thanks

Edited 5 hours ago by eo1bart

[ri702bill 12,347]

A lot is determined by the size of the both the block and the crank. This is best determined with the engine disassembled.

 

The bore  needs to be measured for diameter, roundness and taper. Three sets of two measurements - at the top near the end of ring travel, midway down, and the bottom of ring travel, taken 90 degrees apart. This will determine if just honing the bore is sufficient (most likely not at 2000 plus hours), or if boring to the next oversize is in order. The tools required are a telescoping bore gage and the correct size micrometer. A dial caliper can be used, but is more difficult to get accurate readings.

Note - if the top of the piston already says .030, reboring may not be possible.

 

It is easier to measure the crank journal. Same idea, three sets of measurements 90 degrees apart.

Again, if the crank has already been cut .010 undersize, it may need to be replaced.

If you have a local trusted Machine Shop nearby, let them do the measurements if you do not possess the proper tools.....

 

One more area - valves, seats, & valve guides. Those need to be inspected for conformity to Kohler specs and are replaceable if needed.

 

IF you go the rebore and recut route, get the oversize piston and undersize connecting rod BEFORE any machine work is done to allow the machinist to remove material for optimum clearances on both.

[953 nut 67,083]

If you do the swap from K Series with battery powered ignition to a Magnum the wiring can be easily modified using the information this thread.

 

[WHX?? 57,200]

3 hours ago, eo1bart said:

how far to go with it.

Other than the bore & big end shape I go by other things as well such as the condition of the rest of the block. Did it see regular  oil changes/ kept full? Big end shape will tell you that. Lots of sludge? Has it been apart before? Did it smoke a little/a lot? Were the fins kept clean? 

In other words what kind of life did it lead in those 2000 hours? 

If it's going to be a daily driver I am already leaning towards full blown. A parade queen maybe just a re-ring. 

Edited 1 hour ago by WHX??