Onan Microlite 4000 shaft locks up on occasion

When Onan went to the aluminum block on the Nhm’s and Bge’s they weighed around 270, the Cck weighed over 300 with the cast iron block and they had 3.5 quarts of oil and oil filters and ran at 1800 rpm’s.
The 4000 microlite weighs around 170, 1.6 quarts of oil no oil filter and runs at 3600 rpm.
I can’t help that they had to stay competitive.
I have a 4000 microlite and I’ve worked on few of each one of the generators.

Tom_M wrote:
My '87 BMW K75 motorcycle has an all aluminum sleeveless block. As far as I know there have been no issues with it. But then there was the Chevy Vega with a sleeveless aluminum block which had major problems mainly because it had a cast iron head. The different metals did not play well together.

Yep. For years engineers have played with high silicone content aluminum alloys for use as cylinder wall materials. (other materials as well, hard chrome, nikasil (air cooled aircraft engines) boron nitride, teflon, etc. to name a few) As you mentioned, in your BMW, they can work fairly well. Unfortunately in the GM engines (Vega) they didn't work out at all but, IMO, not because of the aluminum cylinder walls. The cylinder blocks were easily damaged by overheating which caused the 2 center cylinders to warp away (inline 4 cylinder) from the head/head gasket causing a MASSIVE coolant leak. Game over. The silly design of the water pump (drive shaft too long) would cause most of them to fail at about 50,000 miles dumping the coolant out the driveshaft seal. One trip above the boiling point was all it took.

I've used ridge reamers in American iron (50's, 60's, 70,s) all the time just to get the pistons out of worn cylinders without breaking the rings/ring lands. I've never seen cylinder ridges lock up an engine. I'm not saying it cant happen. Just that in my limited experience, I've never seen it. IMO, if your engine is locked up, (seized internally) . . . . you probably have much more serious issues.

Chum lee

The problem as described by initial poster is caused by starter drive. Onan tech for 35 years+. Have fixed this issue literally dozens of times. have worked on hundreds of Microlite/Microquite gensets, and seen engines lock up due to broken con. rods, crankshafts, balance shafts, camshafts, dropped valves, seized rotor bearings, etc. However, since it can be freed up by jerking on flywheel/blower wheel, and then seems to run ok, would bet the farm on being a starter drive problem.

bounder39zman wrote:
The problem as described by initial poster is caused by starter drive. Onan tech for 35 years+. Have fixed this issue literally dozens of times. have worked on hundreds of Microlite/Microquite gensets, and seen engines lock up due to broken con. rods, crankshafts, balance shafts, camshafts, dropped valves, seized rotor bearings, etc. However, since it can be freed up by jerking on flywheel/blower wheel, and then seems to run ok, would bet the farm on being a starter drive problem.

Thanks. I was leaning toward the starter being the problem also.

I figure I'd keep going with it for a few more weeks until I have the opportunity to drop the generator for repair. And what might be the issue? Starter gear not retracting? Starter gear broken tooth? Can anything REALLY BAD happen by me continuing to use it with questionable starter drive issues?