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Onan 12.5 with Kubota HDKCB Spec B maintenance


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I changed the oil, filter and the air filter on my Onan 12.5kw Spec B generator today.  It has 4400 hrs approximately. My new to me coach is a 2002 Monaco Signature 40.  Unfortunately there were no maintenance records available when I purchased the coach. Since the Onan is a SpecB model I assume it is not the original.  I was wanting to change the fuel filter and belt.  After removing the top panels as well as the side door, I could not find a fuel filter.  Does it have one or is it using a feed from the Cummins ISL 500 fuel filtering system?

I could see the belt and could barley touch it from the top access.  It’s in really bad shape -very cracked.  I’m hoping some of you have done this belt replacement before and can give me advice on how to access the belt to change it out and get the tension adjusted correctly.

Thank you,



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It's a time consuming job as there are somewhere around 2 million screws that have to be removed.  Hopefully your Signature has the generator on a slide out for access.  I bought everything from Cummins and replaced some parts as preventative maintenance.

Here is a list of parts I replaced on my HDKCB Spec B:

Onan HDKCB Spec B Parts

43 Belt, Drive              511-0219                     $16.64

39 Water Pump           132-0448

39 Water Pump Gasket 132-0447

Coolant Pressure Cap 14 PSI   130-4320

39 40 Thermostat       130-6329

39 Thermostat Gasket 185-6004

38 Coolant Hoses        503-2500


40 Water Temp Sender 193-0318

25 Oil Filter Adapter Gasket 122-0886

25 Oil Filter Adapter Plug Gasket 122-0884

40 Pipe, Water Return 503-2553

40 Clamp, Hose           185-6722

40 Clamp, Hose           503-2552

Onan HDKCB Service Manual.pdf Onan HDKCB Spec B Parts Catalog.pdf

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Bill B2 & Jim C,

Much appreciation for the manuals.  I had not been able to locate it.  My generator is on a slide.  This helps out a lot. I sure couldn't see the fuel filter when I did the oil change.  I'm going to have another look today. Getting at the belt will not be fun as it's on the back side of the slide out as you know.  I'll have to get under the coach to get at the back side.  I did have the top off and took off a half million of the screws and then replaced them when I did the other aforementioned maintenance.  Looks like I will have to go for the full million to get the job done!

Thanks for your insight,





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