Refresh Update on the 129
Last week I pulled the engine on the 129 to refresh it, after 5 hard years of use since I patched it together in 2006. I was having misfire issues after it got warm, and the problem was getting worse, though making running adjustments would relieve the problem temporarily. As I suspected, the points lobe on the camshaft was badly worn.
While this seems to solve the main issue with the engine, I see troubling problems coming up in the future. When I installed the engine originally, it had been bored .030 over already, and looked to be a fairly fresh rebuild, but had been junked for a bad points lobe on the camshaft, but the piston and rod assembly were good, and the crankshaft was less than .001 under, and looked clean and polished. I installed the best used cam I had in my collection at the time, and it served me for 5 years.
Measurements on this latest disassembly showed that the cylinder had worn .003 over, not a real big deal, but the crank was .005 under top to bottom, and nominal to the sides, a troubling find. I'm not sure it is worth investing another $125 or so into a crank regrind and undersize rod, since the engine is on its last rebuild anyway, so I got a new exhaust valve and had the local machine shop grind and seat the valves. I haven't put the motor back together yet, I plan to do so this weekend and reinstall it, so I can run the snowblower.
In the spring, one option is to pull the motor back out and swap it into the 125 and use it as a backup mower, and rebuild the 125 motor, which is still on its first set of rings, but is having some valve problems, and put it into the 129. Even better would be to find a K321 or K341 to rebuild, but they are as scare as hen's teeth in these parts.
Anyway here are a couple of pics comparing the old cam to the new.
Old camshaft points lobe detail
Replacement camshaft points lobe detail
While I had the engine out I powerwashed everything and decided to try my hand at tightening up the front axle. It was less trouble than I thought it would be, and I squeezed an 18 gauge machine bushing between the axle and the crossmember, which took most of the slack out. I also installed a new front drive pin on the front axle, and tightened up and greased the steering box as well. The old drive pin literally fell apart when I removed the drive cup.