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jdfrye's avatar
jdfrye
Explorer
Sep 23, 2017

Onan 4000 Microquiet crankcase oil leak

i made a video of my generator leaking oil from crankcase gasket and was wondering before i replace it that anyone has done this and anything I need to be concerned about.

https://youtu.be/cO_Jm8Nqz7w

7 Replies

  • jdfrye wrote:
    here is the update and how I fixed the leak
    https://youtu.be/hCclRkP-PiM

    This is from an old hand on engines: You found out a ratchet isn't a hammer, try to keep that in mind. ;)

    Hopefully, you have the balancing gear indexed correctly. The video shows some paint on the gear but indexing marks are typically forged into the gear.

    Did you adjust the valve lash when you connected the rocker back into place? This is done with feeler gauges and a service manual will usually have the whole process. Most small engines, the valve lash is adjusted while engine cold. YMMV.

    Those reed assemblies use a piece of spring steel for the operating reed. They can and do lose tension from being worked. It is typically about the metallurgy and not about debris interference. There should be no significant debris inside the engine and the video showing a spotless timing gear space (where you replaced the front cover gasket) shows exactly that.

    I have a lot of respect for Onan, Onan/Cummins and even larger Cummins diesels. I've worked on them all and even with some of their quirky design features, they seem to have great durability.

    If you want long engine life and good operation, I'd suggest to follow the manual's service descriptions, religiously. Onan/Cummins seems to shine in engineering and manual service description.

    If I had to diagnose the cause of your oil leak, it would be the reed valve and someone torquing on one bolt that holds the cover plate. Next time (hoping there is no next time), apply some light silicone to the mating surfaces and use the correct torque wrench to tighten the case bolts.

    Good work on stopping the oil leak!
  • here is the update and how I fixed the leak
    https://youtu.be/hCclRkP-PiM
  • Thanks for your replies. I have taken off the crankcase cover and replaced the breather valve, OHV gasket and crankcase gasket. I might have been able to re-torque the bolts but never thought of doing other than trying to hand tighten which didn't help. I'm working on another video on the steps I took on replacing the gaskets and breather valve. The old gasket did look a little crimped. I will be testing it tomorrow.
  • See:

    http://b190.com/files/Onan-Cummins%20RV%20Gen.%20service%20manual.pdf

    Onan Factory Service Manual Page 8-10. Crankcase ventilation/breather service. Then look at the engine schematic drawings in section 10-1.

    That is where I would start but I'm not saying that is the problem without seeing it.

    Chum lee
  • That's way more than a casual gravity fed oil leak and it appears to be coming (pulsing) from higher up on the crankcase above where the normal oil level would be. Is your crankcase breather plugged? That engine is splash lubricated.

    Chum lee
  • Looks like you have a failed front cover gasket. The good news is that it is an easy fix.
  • First step would be to use a torque wrench and re-tighten all bolts to specs. Stuff loosens up over time. That may well stop your leak.