I have developed a large oil leak on my 6K Onan.
I have removed the side cover (around the oil filter) and I don't see any leakage from the low oil pressure switch nor the gaskets on each side of the plate behind the oil filter.

It seems to be coming from behind the flywheel. Is there a common leakage area there? I assume that there is a shaft seal and it is probably the cause.
In the Onan parts listing it is 509-0040.

Can this be replaced from the outside of the cover once the flywheel is removed or it is pressed in from the inside of the cover?

Thanks.

Emery Stora\77 Kingsley
Frederick, CO
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Emery, Jim, & Stick:

I didn't know about that crankcase ventilation problem. But it probably
explains a problem I had early on with my old 4kW: The oil pan cracked
along one of the stiffening creases, certainly due to crankcase pressure
fluctuations, and probably aggravated by that ventilation problem.

Stick, that sounds like something you need to check -- could very well be
causing your problem.

Emery, what is the basis for your belief that the other end of the
crankshaft uses the same seal?

Jim, what's your opinion of that?

Stick, if that's true, it may simplify your repair (if still needed after
ventilation is good).

Ken H.

On Sat, Aug 2, 2014 at 5:11 PM, James Hupy wrote:

> ​...
> This brings me to another issue with
> these horizontally opposed engines on our onan. It has to do with
> crankcase
> venting. When the rings, pistons, and valve guides are tight and new, the
> single valve cover crankcase vent is sufficient to handle the pulses from
> this layout. When stuff wears a bit, these engine vents are not enough to
> prevent pressure in the cases. This will lead to oil leaks on normally
> good
> seals and gaskets. It pays to carefully disassemble the valve cover with
> the hose on it and check the condition of that hose and the gaskets and
> spring loaded disc valve in the cover. On some later engines like the BF,
> they have an integral valve built into the cover. They also contain a
> gauze
> pad that will get plugged up with carbon gunky stuff and prevent a good
> venting. They can be disassembled by bending a couple of crimped tabs. The
> very fine springs can rust and fatigue as well. They are all 40 years old
> and live in a very harsh environment.
> Jim Hupy
> ​
>
>
​
> On Aug 2, 2014 1:47 PM, "Emery Stora" wrote:
> ​...
>
>
> I had ordered an Onan 509-0040 seal on the Internet. It was fairly
>> expensive for a small seal. The package it came in said "Genuine Onan
>> Parts".
>> Much to my surprise when I opened the package I found that inside was a
>> seal with the markings "National USA 470162R.
>>
>> So I probably could have bought it at about any auto parts store and
> saved
>> money on the cost and the $6.95 shipping.
>>
>> I believe the rear seal is the same but it is not leaking on mine.
>>
>
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I wish to give a huge thanks to everyone who has posted on this thread. I have been having all kind of problems with my 6K unit since obtaining my coach several years ago, but something else always came up that pushed it to the back burner until this past week.

It would be hard to start and after it started it would not carry a load. I cleaned the plugs, checked the gap and reinstalled them, still ran crappy. Checked the points, they were set at .019 reset to .016 and it would crank but not fire. Set them to .025" and it cranked easily and ran great even with both AC units on, for about 2 hours with heavy load and then it just shut down. Oil level was OK, points still set at .025", both plugs were fouled out with black soot, cleaned them and it ran again..............BUT

Oil was dripping from behind the flywheel. I cleaned it up as much as I could and restarted it. Oil was bubbling thru the low pressure switch (not from the threads). I then cleaned it again, replaced the switch, put in 4 new qts of 30W, filter, and a pint of main oil seal leak stop after assuming by the amount of oil coming out that it had to be the front seal leaking. I replaced the spark plugs with a hotter plug and leaned out the Carb a little. With a piece of plywood underneath (to catch drips) I started it and ran it for 4 hrs under load while observing the drip patterns. I figured 4 hrs run time would be equal to driving 200 miles required for the leak stop to work. It slowed the leak down but it didn't stop...........SO

A seal replacement is next. Emery, I'm sorry you had the same problem, but your question and the answers received have given me a leg up on what all is needed and the parts required to do the job. I don't post that often but I read here every day and use the archives for questions I usually have. Hopefully after replacing the seal and installing a modified Pertronix ignition, at least maybe I can move on to other things on this coach.

Jerry

PS: My other money pit is air cooled VW bugs. My grandson years ago mispronounced Volkswagen as folkswaffen. I substituted my nickname to his waffen and sitzwaffen became my "handle". It doesn't mean a force to sit, I don't think.