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 > Onan Microlite 4000 shaft locks up on occasion

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MopaRV

Las Vegas

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Posted: 04/08/22 03:02pm Link  |  Quote  |  Print  |  Notify Moderator

I have an Onan Microlite 4000 generator and the shaft locked up when I powered off.

This is a new issue and it runs fine otherwise. Oil level is fine.

I broke the shaft free with a wrench on the shaft end with some hard push/pulls on the wrench, and the generator went back to starting and running fine.

Then about a week later, the shaft locked up again.

This last time, I noticed when I powered off, there was a "bell ringing" sound when the generator came to an abrupt stop, at the end of it winding down.

Jerrybo66

AZ

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Posted: 04/08/22 11:27pm Link  |  Quote  |  Print  |  Notify Moderator

I've had almost the same experience. The generator wouldn't turn over to start. I reached in beside the unit until I could feel the motor cooling fins. I was able to turn it by hand a little and it fired up. It's done this a few other times.. It must have something to do with the position it stops..???


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MopaRV

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Posted: 04/09/22 01:49am Link  |  Quote  |  Print  |  Notify Moderator

Jerrybo66 wrote:

I've had almost the same experience. The generator wouldn't turn over to start. I reached in beside the unit until I could feel the motor cooling fins. I was able to turn it by hand a little and it fired up. It's done this a few other times.. It must have something to do with the position it stops..???


I've had the generator in my RV of 14 yrs as a mostly dry camping fulltimer and it's never happened before, and now twice in 1 week??

I was able to break the shaft free again using a wrench.
(No way I can spin it by hand like you were able to)
It fired up again like nothing happened.

The first time after breaking the shaft free, the shaft with cooling fins spun freely, but this second time, the shaft DID spin, but not freely, as if the starter is dragging it? Don't know.

bounder39zman

SC

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Posted: 04/10/22 11:04am Link  |  Quote  |  Print  |  Notify Moderator

The problem is with the starter drive gear . the gear is made of a plastic/fiber material and the drive parts wear with use, then "bind up" in the flywheel-blower wheel teeth. when you reach in the air intake end and grab the flywheel fins you can usually break it free by turning it in opposite direction of normal rotation. the only fix is to replace the starter, which usually requires pulling the genset from the RV, as the enclosure cover has to be removed to access starter. There are really cheap starters available on-line, but they are really "cheap"! You get what you pay for...I would go with ONAN part; 191-2351, usually available for under $100 from Onan parts dealer.

udidwht

Seattle

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Posted: 04/23/22 11:24pm Link  |  Quote  |  Print  |  Notify Moderator

bounder39zman wrote:

The problem is with the starter drive gear . the gear is made of a plastic/fiber material and the drive parts wear with use, then "bind up" in the flywheel-blower wheel teeth. when you reach in the air intake end and grab the flywheel fins you can usually break it free by turning it in opposite direction of normal rotation. the only fix is to replace the starter, which usually requires pulling the genset from the RV, as the enclosure cover has to be removed to access starter. There are really cheap starters available on-line, but they are really "cheap"! You get what you pay for...I would go with ONAN part; 191-2351, usually available for under $100 from Onan parts dealer.


An important reminder....

Always disconnect the battery to the generator if attempting to turn the fan with hand.


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Kpackpackkelley

Bryan tx

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Posted: 04/26/22 03:37pm Link  |  Quote  |  Print  |  Notify Moderator

How many hours on the generator? They get a ridge at the top of the cylinder and get stuck on it.

MopaRV

Las Vegas

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Posted: 04/26/22 03:52pm Link  |  Quote  |  Print  |  Notify Moderator

Kpackpackkelley wrote:

How many hours on the generator? They get a ridge at the top of the cylinder and get stuck on it.


Interesting. I've never heard that one before.
I have about 1700 hrs on it. (Low compared to others I know. One guy I know has 5000+ hrs on his)

I haven't had any problem since my other post on 4/09/22.
When the generator finally breaks for good, I'll know what the problem was LOL.

I'm about to end my drycamping in a couple weeks and head to a park for the next 5 months, so no genset needed for awhile.

Kpackpackkelley

Bryan tx

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Posted: 04/27/22 05:21am Link  |  Quote  |  Print  |  Notify Moderator

If it has a ridge at the top you’ll have to get it reamed if it still runs good and makes electricity.
You can look on YouTube and see ridge on cylinder wall and how they ream them and it may be in your service manual.

Gdetrailer

PA

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Posted: 04/27/22 11:26am Link  |  Quote  |  Print  |  Notify Moderator

Kpackpackkelley wrote:

How many hours on the generator? They get a ridge at the top of the cylinder and get stuck on it.


I have a 120 yr old engine that has never been bored that says you are wrong (yes, that engine has been in my families possession all of it's life)..

A ridge can form and never stop the piston. Basically a ridge only forms ABOVE where the piston rings stop at the top of travel. That ridge is basically the original cylinder bore diameter and the where ever the rings touch they wear down the cylinder walls. Only the rings touch the cylinder walls, the piston is machined smaller diameter than the inside dimension of the cylinder wall so it will never touch the walls unless the rings break.

The rings are sized to stand proud of the piston grooves and act like springs. The rings can move in the piston grooves also..

As far as the OPs issue goes, any ridge formed in the top of the cylinder is not going to cause the problem they have..

RLS7201

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Posted: 04/27/22 11:32am Link  |  Quote  |  Print  |  Notify Moderator

Kpackpackkelley wrote:

If it has a ridge at the top you’ll have to get it reamed if it still runs good and makes electricity.
You can look on YouTube and see ridge on cylinder wall and how they ream them and it may be in your service manual.


Bad information.........

Richard


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