GERRY - Yes, all the K-series Kohlers have plain rod bearings. No inserts, just probably a mix of tin & lead coated onto the bearing surface some how. Now my B48G Onan in the 982 has inserts on at least the main bearings, have to check the manual to see if it has rod bearing inserts. The camshaft even rides on inserts.
I've mic'd several K-series crankshafts, and what I've seen is they wear "HOLES" in the rod journal. I'll measure three places along the length of the journal at 45 degrees around the journal and they will be round and no taper within spec then there will be a "hole" over .001" deep in one spot. Which some people could probably run for many hours without an issue but I'll have the journal ground .010" U/S and get a new U/S rod. As we've discussed here many times, aluminum has a finite fatigue life so any time the engine gets run enough to need rings it gets a new rod and exh. valve. I use the same machine shop Dave Kirk uses. The shop's owner rebuilt the K241 in his off-topic tractor a couple years ago and Dave posted a picture of the exh. valve from that engine. The valve stem under the valve head was eroded away and barely 1/8" diameter.
Like I said in my last post, the splash lube system was used in the old Blue Flame Chevy 6's on the rod bearings. And a 235 or 261 CID 6 fed by a little one bbl carb was NOT over-powering a loaded 2-ton truck back in those days so you know they were getting lugged to death on a frequent basis and still running for years without needing shims removed from the rod caps to tighten them up. I'm not really worried about running my engines at 1800-2000-2400 RPM under partial load.
Ohhh and as for ball & roller bearings "Rolling" in oil... you do know what would happen if a Kohler roller main bearing was rolling in oil at 3600 RPM with eleven balls between the races? With 660 balls passing by a point every second, there wouldn't be much liquid oil there to lube them. And if there was, the liquid oil would act as a wheel chock and stop them spinning and they'd start skidding, get hot and fail. That's what was happening to Gordon Jenning's road race Kawi that he was writing about in Cycle magazine. But I think his engine speeds were more in the 9000-12,000 RPM range.
Interesting fact, the turbo in my diesel pickup spins at roughly 100,000 RPM under full boost, which is about 15-16 PSI. It has a plain bearing insert in it, and the insert is also supported by liquid oil, mostly for cooling. Some turbo's run up to 150,000 RPM, but typically those are all smaller turbo's.
DON T. - I had a Clevite 77 insert installed in the forged Alcoa rod I put in my K321 when I built it 7-8 years ago. It was THE hardest part to find, in fact was the reason why it took me over THREE years to build that engine. I know people have machined stock diecast K-series rods to accept inserts but you have to machine the bore on the big end larger to accept the insert by almost 3/16ths of an inch. I would not be comfortable machining that much material away on a stock diecast Kohler rod. The forged rod doesn't really have any more material on the big end, but the mechanical properties of a forged aluminum alloy are so much better than the standard diecast rod that from what I've read, the RPM limit of the forged rod is around 6000-6500 RPM verses 4000 RPM for the stock rod. Only thing better than the Alcoa fprged rod is the machined billet rod like MWSC sells which has an 8000+ RPM limit. But REMEMBER... the flywheel is still the weak link here... the stock cast iron flywheel should not be spun over 4000 RPM in spite of what rod you have in the engine.
I still need to put another THOUSAND hours of run time on the K321 to see if the bearing insert allows the rod journal to run without wearing as much as it would with the stock rod & bearing. I'm not near as paranoid about the fatigue life of the forged rod either. If the stock diecast rod runs 1400 hrs without failure the forged rod should last 2000-3000 hrs, maybe more.
