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xenon172

Blown Crankcase Gasket Need Some Thoughts

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xenon172
Had an interesting engine problem that required attention because of an oil leak. It is an Onan Elite 140, 14hp, single cylinder, OHV. The crankcase gasket was blown and it would spit oil as soon as the engine got warm. It is a pressurized system and uses 1 quart of oil including the filter and has 400 hours on it but the problem dates back much earlier. Fortunately it has a low oil sensor so it has not been damaged at least as far as we looked. The first photo is a frontal view so you can get a basic idea of what it is. The second photo is the location of the leak and where someone had tried to repair it with epoxy or some kind of sealant which didn't work. We were able to pull the crankcase cover without pulling the engine. The third picture is of the internal gearing which is pretty sophisticated for a horizontal single. The last photo is the crankcase cover and the gasket was blown in not out just as it appears in the picture. My question is what could cause this? A factory defect? The only other thing that comes to mind is a breather problem. Any thoughts on this would be greatly appreciated. Other than the leak the engine runs great.








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Brettw
It would seem you would need an awful lot of crankcase vacuum to suck in a gasket like that. Is it possible that a previous opening of the crankcase and reinstallation was improperly done and damaged the gasket? Too lazy to tear it back down so they tried to goop it from the outside?

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xenon172
quote:
Originally posted by Brettw
It would seem you would need an awful lot of crankcase vacuum to suck in a gasket like that. Is it possible that a previous opening of the crankcase and reinstallation was improperly done and damaged the gasket? Too lazy to tear it back down so they tried to goop it from the outside?
I don't know the service history on the tractor but that is a good thought. Thanks

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larry8200
I can't imagine how sufficient vacuum could build to do that. The Oil filler cap appears to be vented, The carberator will have a vent tube to keep blow-by fumes out of the crankcase, and even good piston rings wont hold pressure for more than a few seconds. I'd say that almost has to be someones assembly screwup, either at the factory or later. I can't see any reason not to replace the gaskrt and go. Good Luck.

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xenon172
quote:
Originally posted by larry8200
I can't imagine how sufficient vacuum could build to do that. The Oil filler cap appears to be vented, The carberator will have a vent tube to keep blow-by fumes out of the crankcase, and even good piston rings wont hold pressure for more than a few seconds. I'd say that almost has to be someones assembly screwup, either at the factory or later. I can't see any reason not to replace the gaskrt and go. Good Luck.
That's exactly what we're going to do and as long as it is apart replace the front oil seal as well. This is one of those rare times when Onan parts don't cost an arm and a leg, less than $20 for the gasket set and oil seal

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cp1969
I have had this same problem with my Elite 140 at about the 175 hour mark. It now has ~560 hrs with no problem but I suspect it's coming back. I noticed a clattering noise and since I'd recently adjusted the valves, I thought one may have come loose. That was not the problem. The clattering noise I am hearing is the yellow oil dipstick jumping up and down when the engine runs. That is symptomatic of crankcase pressure building. Why the crankcase is not venting properly is not known but it won't be long before the gasket will be blown out again. The Elite 140 has a reed valve located under the valve cover which is supposed to control this. What I don't know is how this reed valve is supposed to be oriented when the engine is off. Mine is not seated and I don't know if that's the problem or not. Single cylinder engines are about the hardest engines to get to breathe right because their crankcase volume changes so much with each down and up stroke of the piston.

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xenon172
quote:
Originally posted by cp1969
I have had this same problem with my Elite 140 at about the 175 hour mark. It now has ~560 hrs with no problem but I suspect it's coming back. I noticed a clattering noise and since I'd recently adjusted the valves, I thought one may have come loose. That was not the problem. The clattering noise I am hearing is the yellow oil dipstick jumping up and down when the engine runs. That is symptomatic of crankcase pressure building. Why the crankcase is not venting properly is not known but it won't be long before the gasket will be blown out again. The Elite 140 has a reed valve located under the valve cover which is supposed to control this. What I don't know is how this reed valve is supposed to be oriented when the engine is off. Mine is not seated and I don't know if that's the problem or not. Single cylinder engines are about the hardest engines to get to breathe right because their crankcase volume changes so much with each down and up stroke of the piston.
I have seen that problem on an Elite 140 but never got involved with trying to fix it. This gasket was backwards like too much vacuum. I have no idea if the reed valve could be involved with that. We never got to that part of the engine on the one we fixed and I have no idea how that valve works. Something to read up on I guess.

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cp1969
Apparently, this is apparently a common problem with these engines. Not only did my gasket blow out as did the one in the photo above, it blew out in exactly the same spot. I really think it has to do with that reed valve. It would be easy enough just to let the engine breathe through an unrestricted opening but I think they want the crankcase to be under a slight vacuum when the piston is at TDC. Too much is bad and so is too little. I have no idea where a person can contact an expert on these engines. I wish I knew where to read up on them.

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cp1969
I'm going to throw some parts at it. I ordered a new reed valve assembly along with a gasket set, a new dipstick, and a new o-ring for the dipstick tube. When in doubt, throw some parts at it. The parts guy at the Cummins truck engine shop (yes, that's where you get Onan parts where I live) was very helpful but he did not have a reed valve assembly in stock to answer my question as to whether the reed is normally closed or standing open, as mine is right now.

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cp1969
quote:
Originally posted by nateb17010
oh heck the problem is that darn cub cadet oil filter... lol I hope you get it fixed.. the very best of luck..
Baldwin 33 is a nice substitute for the CC filter......

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Dark
Actually this may be a logical cause as the Onan filters are of the bypass valve type. Increased pressure can cause a raise in vacume in the crankcase. Not all oil filters are created equal. In a full flow system, all of the oil passes through the filter to reach the engine. If the filter clogs, an alternative route to the engine must be provided for the oil, or the bearings and other internal parts may fail, due to oil starvation. A relief, or by-pass, valve is used to allow unfiltered oil to lubricate the engine. Unfiltered oil is far better than no oil at all. The relief (by-pass) valve is a component of the oil filter itself. Under normal conditions, the valve remains closed. When there is sufficient contaminant in the oil filter to reach a preset level of pressure differential to oil flow (around 10-12 PSI in most passenger cars), pressure differential on the relief (by-pass) valve causes it to open. This condition can occur when the oil filter has become clogged or when the weather is cold and the oil is thick and flows slowly. A few ifs here. If the valve is missing from the filter excess preasure can be formed from dirty filter up to 12 lbs. If the filter has a valve it may not be working causeing same condition. If the filter has a valve and the filter is not clogged too heavy of oil may have ben used check ANSI numbers for your engine to make sure its proper for the engine. If none of these are the issue then put a vacume guage on the engine after repairs and note the operation of the positive crancase ventalation incorporated into the side cover of most engines. the best place to check vacume of the cc is from an adapter plug fabricated to from an old oil plug. If vacume is normal (0to-3) then vacume in the cc was not the reason for the gasket failure. If vacumme is (-4 to -16)there is a direct link to the intake manifold pulling from the cc so in most cases the PCV is the cause.

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cp1969
Got my box of parts last Friday, put them in yesterday. $68 worth. Just for grins, I replaced the o-ring under the oil dipstick cap first and started it up. No more bouncing cap; $0.81 cost (p/n 509-0304). The breather assy (p/n 0123-2014) reed valve is, well, I wouldn't call it properly seated, but it is a lot closer to that than the reed valve that I took out of mine. So, at $10.30, we'll go with the new one. The new valve cover gasket was definitely needed, as oil was starting to leak out the back. $5.02 for a complete gasket set (p/n 102-1441)for the engine wasn't bad, even though I only needed the valve cover gasket. Fuel filter ($4.43) is next on the list of things to be replaced. The original on the tractor has ~575 hrs on it. Time for a new one. Air filter (p/n 140-3010, $9.86) and wrapper (p/n 140-2748-01, $6.28) aren't quite ready to be replaced but will be soon, and this beats the $30+ I paid for the last one at Cub Cadet. I am probably going to return the replacement oil dipstick (p/n 123-1972-01) because at $27.08 it is the most expensive part and I don't think there is anything wrong with mine.

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cp1969
You can see in the photo, the failure occurs at the same place. This tractor is 17 years old and has 600.4 hours on it. I wonder if I should put rings in it. It does not smoke or use oil. You have to be a paying member to post picture or links to them.

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cp1969
quote:
Originally posted by sovereign72
GM Vehicare gasket sealer #2 has extremely high adhesion properties. It might make the next repair last an acceptable amount of time.
Is that sealer to be used with a gasket or by itself?

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cp1969
It's fixed--again. Wonder how long it will last this time. I have a theory that maybe I'm letting the air filter get too much restriction but it's no more than that--a theory. The engine, at 600 hrs, is spotless inside. It looks new. I've been running 15w-40 diesel oil in it since the last repair; Cub Cadet 30w prior to that.

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