This was copied from another site. I thought you engine mechanics might like to test your skills at diagnosing the problem. There is a statement in about the middle of a sentence that gives a clue as to why this engine that ran so well at first and failed so soon. Being a one lunger, a V8 chevy, ford or a V12 Rolls makes no difference.
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Copied:I have a JD 312 with a Kohler K301. After 1700 hours, it finally broke the connecting rod, which oddly enough isn't the part I need help with. I've grown rather partial to this tractor, so rebuilding was a no brainer, but decided to tinker a little bit with it. Machine shop ended up going .030 over in the cylinder and had them deck the head by .040 to boost compression a little, new rod, piston, rings, reground cam, large base lifters, carb spacer, chevy points, msd blaster coil (with ballast resistor) and home grown valve job, porting and polishing. majority of the information for build found at
www.gardentractorpullingtips.com and midwestsupercub.net.
So I get everything together, and it's running like a champ. Set timing statically with feeler gauge, then with timing light once running. Dialed in the carb, and everything just keeps sounding better and better. Let it run for a good 45 minutes at varying throttle positions (throttle changes VERY responsive), and it's running strong. Drive it around the house to put it in the shed for the night. Next day, choke, throttle, bump the key and fires right up. Driving around the house, the engine starts to race. I look up and see the governor shaft walking out the side of the block. Before I had time to get the throttle or key off, engine shut off. Stood up and reached forward to push governor shaft back in, bump key and starts right away. No noises, sounds normal. Maybe I got lucky? Idle around to the driveway where I have been working on it to fix the governor, which I forgot to put in the spacer sleeve on the shaft which was the cause of all this. Continued to do my last few things, install PTO, service deck, put sheet metal back on tractor etc. By this time it was getting late, and I didn't want to upset the neighbors by starting it up, so I covered with a tarp and left for the next day....
Next day, crank no start. Thats odd. Check connections, grounds, etc, end up finding no spark. Narrow that down to the coil. I knew the voltage regulator needed to be replaced, had one in my truck to put on, just hadn't yet. Over-rev maybe put too much to the coil and fried? Stranger things have happened I guess. New coil, check all connections, components, spark at spark plug. Try again. Crank no start, but one good backfire out the exhaust. Hmmmm. Double check timing, check. Pull plug and it's dark but cleaned up with a wire brush. No strange noises when cranking other then the starter getting unhappy about working so hard. Don't know what else to check, so I grab a compression tester from a friend, only reads 30-35psi. Seems awfully low, but don't know what the "before" reading was, and also with the compression relief on the cam? I don't know. Took the head off, expecting to find something bent or broken, almost disappointed that I didn't at this point. Piston and valves appear to be moving as they should, with no scoring on the cylinder walls, no marks/dings on the valves or seats and no evidence of anything impacting cylinder head. Reinstalled head and torqued. I knew I didn't really fix anything, but had to try anyway. Crank, no start. Double checked, getting spark and fuel. Both good. Pull valve cover and check valve movement and lash to make sure a valve isn't stuck open just a hair. No problem. At this point, I don't even know what else to check. I pull the motor back out of the tractor and drain the oil. Oil does have some very very fine metal flake in it, don't know if that's normal or not on a fresh rebuild as this is my first attempt at a small engine.
Pull off the oil pan, no debris or chunks in the pan. Visual inspection with a drop light, don't see anything odd with the cam or crank. Spin the motor over to find the cam and crank timing marks are still in line. When coming up on the compression stroke, I can hear the motor hissing compression into the crank case. Sounds like it's coming from the valve area. But here's where I wonder, is that normal due to the compression release on the cam, or have I found a problem that I didn't see from the valve cover or with the head off?
At this point, I'm so frustrated I really don't know what to do next and find I am second guessing everything I do or try to do. I don't want to just throw parts at this thing and hope I hit the problem, but short of replacing rings, valves and guides, I'm stuck. Anyone have any suggestions or words of wisdom for me? Any help is GREATLY appreciated.
