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

Your course of action sort of depends on your budget,and how much you want to do yourself.

The engine needs to come out, that's for sure.

The options I see are these:

replace with a good running used engine.

Tear it down and measure the cylinders and crankshaft. If useable, replace the piston and rod with your used parts. I'd install new rings on both sides after lightly honing.

At the other end of the repair scale is crank turning and/or boring if needed along with the necessary new parts. Starts to get pricy.

You can really tell much until it's laying on your bench in pieces and you have mics or calipers in hand.

ok, well things have gone from bad to worse. I'm pretty sure im looking at a repower here. Essentially this is what i found.

When i pulled the oil pan i found out it was definantly the rod. The rod was shattered. Essentially what was left of the rod then pushed up and lodged inside the piston head. I managed to get the rod part out of the inside of the piston. I got the piston out and from what i can tell the cylinder looks good. I placed one of the extra piston heads i had in there and it seems to slide in and out OK.

The crankshaft has some slight damage however, i took a picture but i needed to use a flashlight and that led to a poor picture, i hope to take one in the sunlight so its easier to see because that's definantly one thing i want you all to look at. There seems to be some extra metal on the part where the rod connects that is almost fused on. I would obviously need to get that off if i were to put a new rod on. but it looks like there is pretty significant wear. So i guess my other question is how "pristine" does crankshaft need to be where it connects to the rod?

when comparing the old piston head with the extra i have, i noticed that they seem to be the same size, however the ring pattern is different. The spare pistons i have use smaller piston rings. Could these be from a B series? The rods on the spares say Onan, so they are Onan pistons, but i know that the old rings wouldn't fit on there, you can visually tell. I took a picture of that as well. So my question is could i use these pistons if they are the same size and the rod is the same size?

here is the link to the new pics

http://www5.snapfish.com/snapfish/t...otsc=SHR/otsi=SALBlink/COBRAND_NAME=snapfish/

Hey AMS:
Are you committed to a rebuild? Certainly educational, but definitely time consuming. I decided against a rebuild because I didn't want to spend what would probably turn into a couple of weeks working on my engine, what with the trips to the machine shop and store to buy/rent tools I don't have, etc. Also I figured I'd end up with a rebuilt version of what is an '86 engine: good but 26 years old just the same....
I bit the bullet and spent the extra $$ on a Briggs Vanguard 18hp engine from SEW: $1640 delivered to my door. Installation took some time, but the electronics really are plug and play plus you get a new PTO clutch and a new muffler. The engine uses a lot less gas, burns cleaner, and starts every time.
Of course, your decision depends on your finances, and your mechanical know-how. Certainly, a rebuilt Onan is a very capable engine and I have to give 'props' to everyone who follows through and rebuilds one. I personally would rather spend my time working 'with' my 318 than working 'on' it. Now I just have to do something with my Onan!
Good Luck!

ok, i will start breaking the entire engine down. I will try and get pictures up of everything and start asking on how to check for damage once it's all apart. Now for a couple more questions.

1. If it was lack of oil was it because it was sitting for 10 minutes or so running on a slight incline? it was on the driveway which has a slant, but not an outrageously big slant. Also there are some hills on the property so it does spend some time on hills. When i checked the oil it seemed fine, and the oil light never came on. (maybe a bad sensor or burnt bulb?) Or is it possible this damage was caused by the previous owner and it just reared its ugly head now?

2. I found a guy selling 2 pistons and a crankshaft for a P218 engine. Said he repowered and is parting out the Onan. (first off how big of a risk is it buying it?) 2nd, If I am replacing all 3 components will it be compatible with my P218? If there is a possibility it won't be, what information do i need to get to make sure it would be compatible?

3. finally after posting 1 and 2. I read the link about rebuilding from Onan parts, and its amazing. Makes me feel like i can do it. I think at the very least i will break it down and see what damage is in there. Finally, after reading that it looks like if that setup measures out ok it would work since all the parts are the same style. Now my question is if i have to machine the cylinders, does that mean i would need larger pistons? or do i just need larger rings?

Well i have taken some time trying to get the engine apart. I think I am going to just repower. Here's the update.

1. I got the PTO off ok, but im having trouble getting the flywheel off. Is it pressed on? do i need some type of puller or am i just being too kind to it?

2. I'm having trouble getting the good piston out. It's catching on the first ring. I didn't want to start banging on stuff in there. What's the best way to get that out?

3. The crankshaft doesn't look good. seems like significant wear on the side with the bad rod compared to the other side. Also there are some gouges and marks on various parts of it presumably from parts hitting it while moving. But to me that journal on the blown side looks pretty bad.

4. I don't think that i have the expertise necessary to rebuild myself. I'm having more trouble than i thought taking it apart. (appearantly this engine isn't as easy as the 3.5 hp briggs and stratton i took apart and rebuilt in shop class 10 years ago )And putting together is a much tougher deal. I worry about damaging parts and making a bigger mess as i go along. I think I am just going to bite the bullet and have a nice new engine. I however, might try to rebuild this one just for the expierience and entertainment in the mean time. If not it will just be parted out to the best of my ability with the stuff i know is good.

4. Thank you all so much for your help. You might see continuing posts as i try to rebuild anyway ( will depend upon how bores and other parts are mostly. Don't mind taking the time but i won't want to spend a ton of money on an engine i probably won't use)

5. Finally, my last questions are on the repowers. I read some other posts on repowers, but am looking for a bit of fresh insight. I've done some research and I am 95% sure im going with the Vanguard. Probably the 23 hp. Figure if im putting in a new engine, what's a few hundred more bucks for a bigger one? My question is this.....

Anybody have any experience with the Vanguards? like them? hate them? Any recommendations on the big 3 replacement engines?

Also, what is in the adapter kits? How much does it take to get the Vanguard (or other engines) in place correctly? Are they parts i could fabricate myself? (mainly just brackets) or are we talking new driveshafts and things of that nature? It seems like quite a bit gets tacked on to the price when an adapter kit is included. Anybody who has repowered i would love your advice and reviews!

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 -http://www.smallenginewarehouse.com/RepowerItems.asp?Brand=John%20Deere&Model=318

I am more-or-less in the same boat with a 318 I bought for $250 knowing it needed work. My B43G runs, but poorly. It will only run on full throttle and it has low compression (70 psi) on both cylinders. Like Ams4life, I am hoping to get away with rings and a few other parts and have a nice running engine. Fortunately, we have the good fortune to be able to find out what is needed before we buy anything, other than investing a little at the machine shop, which is worth the gamble.

In my case, I plan to weigh the rebuild price tag with a Vanguard repower once all is known and decide from there. After all, my engine has got to have some value, since it is still running, and if I need to part it out or sell it as a core, it can offset the repower. Best of all, the LOML is on board, mainly because when the 318 gets useful, I can sell my 165, which is a great tractor that's runing like a deer.

Here's a pic of the 318 with her new seat...

marcuskelley35 said:

Oh man it's painful to watch all these old Onans die a slow death but to be honest it's time has come and gone.

Click to expand...

marcuskelley35 sure has that right! There are no modern small engines manufactured anymore with the high quality of an Onan.

The picture here is just one example comparing the Onan to a "modern" Kohler V-twin.

The first thing you notice is that nice big 100% iron & steel oil pump used by Onan for over 50 years. Note the pickup is also made of steel. The Kohler oil pump is made of aluminum with a PLASTIC drive gear! Even the pickup is PLASTIC.

Can you find the cam & main bearings for the Kohler?....Look closer...that's right! The crankcase is the bearing! Run it low on oil or just normal wear and you toss out the "disposable" modern kohler V-twin. Go buy another one. Kohler made it to be replaced not rebuilt.

Just above the Onan oil pump is a "replaceable" Onan main bearing. Cam bearings are also replaceable in the Onan's. Break or damage the oil filter mount on the Kohler and you are looking at replacing the entire engine cover, not cheap! Plus the fact you have to take the engine half way apart to do it!

The Onan filter mount? Two bolts and an easy swap.

I'll start a new thread soon comparing the Onan, Honda, B&S, Kohler etc. internal engine parts.

For some folks repower is the only way to go if you don't have the time, tools, skills etc. to rebuild your Onan. Just don't expect a "modern" engine to have the same quality as an industrial Onan or last as long. It won't. Facts are facts and the cold hard truth is nothing is made to last anymore.

The good news for those who choose to keep their Onan's going is that new replacement parts are still made right here in the U.S of A! Just need a good deal on some used parts? Millions of Onan's were made so finding used parts in good shape is easy.