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mjg6319

cckb oil filler leak

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mjg6319
Hi everyone, I'm new to the club having recently picked-up an AC 720 with the Onan CCKB engine. Got the tractor, changed oil, cleaned air cleaner, replaced deck belt etc. Mowed the lawn and after about 30min noticed light smoke from under the hood. Opened the hood and oil is all over the left cyl. Coming from the oil filler tube. Took filler off and gasket was cracked, replaced it. Started again and still getting oil from filler. Decided to open filler at idle. Bad idea! Oil puking out at high pressure! Checked the crankcase breather, hose clamp was missing and the hose was brittle. Cleaned breather cap, replaced baffler material and hose. Well, to make a long post longer...still getting crankcase pressure at idle, leaking has slowed, but still seeping at filler. Any ideas? No oil smoke from exhaust, but maybe bad rings? Is this just a cckb thing? -Any help would be appreciated!

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mjg6319
Aaron, I haven't removed the filler tube assembly only the cap w/ dipstick, that's where the oil is coming from and so that's the gasket I replaced. I guess my main concern is with the crankcase pressurization which seems to be the root cause of the leak. I thought by reconnecting the breather hose (which was not connected when this first happened!) it would solve the pressure problem. But, I'm still getting what seems to me is excessive pressure in the crankcase. Does yours do this also? Maybe I just need a more substantial gasket for the filler tube to contain it? -Mike

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eagle5473
my bad I assumed it was the oil filter housing (thats another spot that always leaks) And not the oil fill neck, I would still thread lock as there is lota of vibration also check the crank case to the block I had lots of leak from there as well

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D-17_Dave
Not sure if I'm remembering correctly since I'm not home and can't check, but, I didn't think the oil level came that high. To the bottom of the filler tube that is. I wonder if the dipstick gauge has been changed/modified causeing you to slightly overfill the oil level? I'd still double check to make sure you have air flow out of the crankcase breather so it's not building too much pressure.

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mjg6319
Thanks to everyone for your replies. I've removed and cleaned the breather cap in solvent to loosen the check balls (marbles?) and reinstalled it along with a new hose to the intake (w/ hose clamps this time!). The leak seems to have slowed, but there is still pressure in the crankcase at idle. Is this normal for these engines? I removed the filler cap on a 16hp Briggs twin on another tractor while it was running, and it doesn't seem to be pressurized as this Onan does. The pressure in the Onan is high enough at idle that it's difficult to replace the cap after it's removed.

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JimS
I think the appearance of pressure in the engine when the oil fill cap is off is normal but is not necessarily an indicator of a problem and is really misleading because it is not a normal operating condition. The pistons displace air in the crankcase as they move in the cylinders. On the downstroke the pistons going down in the cylinder will pushed air out of the crankcase. On the upstroke the opposite occurs and air will actually be pulled into the crankcase. It may look like there is only pressure when you try to put the cap on because you can see the cap being blown out. It is harder to see the air being pulled back in because it is not strong enough to pull the cap back in. With the cap on and the crankcase "sealed", however, the breather system works differently. On the piston downstroke, any pressure buildup in the engine will be relieved through the breather check balls. On the upstroke, however, as the pistons try to pull air back into the crankcase, the check balls close and a partial vacuum is actually created in the crankcase. Because of this vacuum condition, very little air is actually actually expelled from the engine when it is running. And assuming the breather is not plugged, there should not be a pressure buildup. I am not sure if I explained this very well but I guess what I am saying is that having the cap off is not a normal engine condition and doesn't really indicate what is happening in the engine.

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mjg6319
JimS, Thanks for your reply, your explanation does make sense. Since there are no other indicators of a problem (i.e. smoke from the exhaust) I'm feeling more confident that the leak stemmed from the inoperable breather rather than bad rings, valves, etc. I used it the other night to pull out some stumps from the flower beds that my wife has been wanting gone for years and they all came out on the first try! So, I think I'll stop worrying and be happy with my purchase!

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GregSch
Do realize that on the onan engine there is no distributor and both plugs fire at the same time. That means both pistons are at TDC at the same time and then they both move to Bottom dead ceter at the same time. Many engines are designed so that when one piston goes up the other goes down. There is alot less turbulence in the crank case that way. My cckb tried to blow oil out the filler tube for 12 years. Keep the vent clean and the dip stick tight and it will probably out live us both.

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gretsch
Try bending up the two tongs that tighten the cap down when you put the cap on. They can become bent down over time which causes the cap/gasket to not be tight against the filler tube.

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mjg6319
Thanks again everyone. I'm finding more and more info every time I logon here. What a great braintrust for these machines! I've mowed twice since I replaced the gasket under the cap and cleaned/reconnected the breather and have had no problems. There is still a little seepage around the cap, but not enough to blow around the engine compartment like before. gretsch - I noticed the tabs and bent them out slightly when I replaced the gasket which did seem to create a tighter seal, thanks for the suggestion.

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