Jim Storma and Wayne Shytle,
Thank you; hope it wasn’t too much technical word salad. You mention “neutral balance”?? I don’t understand what this means.
I failed to address your question on the connecting rod bearing insert. These bearings are replaceable, shell-type automotive bearings consisting of a steel shell, with a layer of copper, lead, and tin electroplated in layers to form the bearing surface. The relatively soft layers offer imbedability of particulates in the oil to imbed into the bearing instead of scoring the crankpin. This, plus the fact that you can replace the bearing and reuse a connecting rod is the other advantage. Your existing con rod has to be machined properly for installation of this bearing to get the proper preload “crush” on the shells. It offers nothing with regard to performance or increased bearing life. As long as you maintain your engine properly with consistent oil changes, and your current connecting rod and crankpin are in good condition and clearanced to the proper Kohler spec, there is no need to install an insert bearing. The aluminum alloy used in these con rods is actually an excellent bearing material.
Just a little more on single-cylinder engine balance. I’ve always referred to the 12, 14 and 16 hp K-series engines as the “big block” series as they all use the 3.25 inch stroke crankshaft. The corresponding models are the K301,K321 and K341 with the first two numbers in the model indicating the approximate displacement in cubic inches. The displacement increase is accomplished by increasing the cylinder bore diameter. When this is done, the piston assembly increases in mass. The K301 was the first produced engine in this series, with the K321 and K341 following sometime later. With regard to transmitted vibration, here’s how these engines stack up (my opinion):
K301 – Good
K321 – Acceptable
K341 – Terrible!
The massive recip assembly in the K341 (combined with the same counterweight requirement as in the K321) is the driving force behind making this engine a real shaker. Thus it is of paramount importance that the recip mass be kept as light as possible when doing a rebuild. Use genuine Kohler parts when available – I’ve always found these to be the most consistent in quality and light weight when it comes to piston assemblies. If you are rebuilding using an aftermarket piston assembly, compare its mass with the original Kohler parts – you’ll most likely be surprised at the difference.
The picture below shows wrist pins having the same OD and length, but varying in ID. Pin on the left is from a Stens piston, while one on the right is a Kohler part, both for the same diameter piston. The Stens pin weighs almost exactly double that of the Kohler pin. The Stens piston was heavier too, but I don’t remember the difference. I ended up reusing the Kohler pin in the Stens piston.
The K341 is brutal to begin with and any recip mass increase over the stock weights is going to make a bad vibrator even worse. The counterweight plate that I offer will not make a significant reduction in the high recip forces encountered with these heavy piston assemblies, and neither will balance gears. I don’t have a genuine Kohler K341 piston and wristpin to weigh – this would be valuable info if someone that would have these parts, weigh them and contribute this info to the forum.
I personally like the K301 – it is smooth (relatively) and can be made to perform as well as the K341 with some hot-rod modifications…great fun! The K341 does have good low end torque but this is offset by the butt-numbing vibration it produces. It can be reduced to tolerable levels by close attention to the mass of the piston assembly.
It appears to be in very good condition. Much better than my #2 model 125.
