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john deere 318 help, i think the Onan is done for good?

22822 Views 103 Replies 28 Participants Last post by  alfieepstein
New to this forum, and i must say it looks fantastic! lots of helpful people, and lots of great tractor stuff. I bought my "new" 318 in the fall. My first real garden tractor. I searched for quite some time for a machine that could bag vast amounts of leafs, and clear alot of sloped, fairly steep, slippery driveway, and decided on this 318. came with power blower/catcher for leaves and the auger snowblower. It did a great job with the leaves. I was so excited to plow the driveway on this first winter storm in chicago. Well, i tried plowing without the chains, (1st mistake) and the driveway was too slippery, so i went to go get the chains and while doing that, the engine started sounding different, almost like it was on choke. Well, the engine then quit, and now won't start. The starter seems to want to crank it over, but can't so i get a grinding noise. I fear the worst, a siezed engine. There was oil in it, my only concern is that it was parked on a hill for a while, could the oil have drained back leaving no lubrication? is there an oil pump on these Onan engines? I am fairly mechanical, but haven't dealt with tractors too much. Usually if instructed well i can find the problem. my question now is, where do i start? What can i look for to figure out if this engine is done? I'm assuming that since it started ok that it is nothing electrical, and the snow thrower wasn't on and it was in neutral so i don't think its anything related to those two issues. I'm just praying someone with a good knowledge of these machines has seen this before. I don't really want to have to start the post of "so what's the best repower engine" :banghead3 although i'm pretty sure that that is coming.
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Does your 318 have a B or a P Onan?
I have a Onan service manual from Gravely for the B series if you are interested.
Onan parts are crazy expensive now here in Canada since Cummins took over.
I ended up scrapping my old faithful Sears GT18 ( it had a B48), when it needed a lot of rejuvenating at 3000hours, because of that.
The fuel pump on my B48 crapped out at 1400hours run-time when the neoprene diaphragm ruptured. It took me a long time to find the problem. I made a new one out of nylon reinforced silicone rubber sheet which lasted until the Onan's BIG END OF LIFE POOF.

By the way, that Onan manual is a PDF but too big (2.5M) to attach here.
OK AMS4LIFE, I'm still assuming that your Onan is a B series and your fuel pump is on the carburetor run by pressure pulses from the crankcase.
Remembering my woes, that pump is not very strong even when new and a bit of icing in the fuel filter (screen) would give grief. As the machine ages and the fuel line rubber dries out little cracks develop and the connections at the fittings is no longer as tight. All this can add up to the pump sucking air instead of gas. Of course, if the diaphragm in the pump is also as old, it can have some unseen pin holes which further diminish its effectiveness. Try a bit of vacuum on the hose when disconnected from the the crankcase and see if you get some fuel coming through the diaphragm.

P.S. That PDF of the Onan "B" manual is still available and waiting only for an email address to go to.
I'm happy to hear that the Onan is running. Good fight!
Old Onans had resistor plugs with copper ignition wires. Sometimes people will go to an auto parts store and buy regular replacement wire by the foot and end up with resistor ignition leads. Resistor plugs on resistor leads = reduced spark. If there are other factors involved, like carbon build-up in heads or on the pistons, which will raise the compression ratio and inhibit the spark, a No-Go is likely. That raised compression can also make cranking harder ( and eats starters)

Don't you just love the "ker-plink, ker-plink, ker-plink" that Onan makes when idling?
Yes, it sounds like that twin is now running mono. Probably that nice "plinka-plinka- plinka" that it used to do at idle has now turned into a "pop-pop-pop". Do you have a compression gauge? Or, pull both plugs and crank with with your finger in the plug holes ( one at a time is OK. Do you have compression? It should be good in the one good cylinder and maybe low or none in the bad one. If no compression, then you might have a valve stuck open. Low compression could show a valve not closing all the way because of carbon buildup on the stem or something worse better left unmentioned for now (like a bad piston ring - oops,I said it) . Pull the valve cover and see if they move properly while cranking (no plugs installed). If compression is good, then put a plug on the wire, ground the plug shell and see if you get a nice fat spark when you crank. If not, a bad ignition lead could be the problem. Check the connection at the coil. Don't have resistor ignition wires with the resistor spark plugs. It reduces the spark.
Good luck and please give us some progress reports when you can.
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I checked the net for info and Champion RS17YX/909 plugs ( or equivalent) are the current correct part number for the P2 Onan engines
Hi there ams4life. If you are considering an "un-pure" 318 and don't want to spend the $1500 on a new Vangard or Kohler, try looking at some of the Chinese engines, even diesels.
For $800 you can get a 20HP Honda GX670 twin photocopy good for 1000 hours with proper maintenance. I have a friend in the tool and equipment rental business and he regularly replaces engines (Onan, Kohler , Briggs etc) with Aisan imports with good results. Its all about " bang for the buck". The main concerns are shaft size and rotation. Your P218has a 1.125" shaft and clockwise (facing the shaft end) rotation. Fitting a tall V-twin in the space of the flat boxer style Onan may involve some work too. I know lots of 318 have been re-powered with current engines but I have no personal experience - Google the subject and I'm sure you'll get more info. Look here -
Hey Onanparts - those look like CCK internals to me. OK, so NOBODY makes them like that anymore. Well maybe Lister-Petter but who wants to pay $200 per horsepower these days?
Yes I agree, real Honda is better at $2000+ but 1000 hours translates to many years in ordinary (i.e. not commercial) use. As I said, it is all about bang for the buck. For example a lawnmower with 1000 hours on the engine would probably have no deck left, just some rusty bits (unless its like my 30 year old Lawnboy Mag).
I re-built a CCK on a generator after it ran over 5000 hours at 1800RPM powering a highway arrow-board sign. That was over 15 years ago and the parts alone cost me close to $900. The engine ran like new after that and then the generator field coil went to lunch. I sold it as is and recouped my costs but I learned that sometimes rebuilding antiques is best left to the connoisseurs with deep pockets.
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