Engine.

Cost will be about the same. The Onan most likely will need to be bored, but get everything checked and measured by a engine machine shop.That will give you the list of things to be ordered. Then go shopping and pricing parts. Local JD dealer, Boomer's Onan Parts, Onan Parts.com and finally Jacks Small Engines. On re-power you will want a proven kit, otherwise you will have to do the drive shaft and adapter to engine, PTO to crankshaft adapter due to different size of crank, wiring changes, and finally the muffler/side panel fit.

It all depends on your $$$$/pain level.

Jackson1953 said:

My jd 316 with the onan p218 engine after 36yrs is starting to tell me it's warn out. What to do. Rebuild or replace. Please tell me your thoughts.

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I'd rebuild, the Onan isn't a bad engine, and it is the simpler solution because wiring and connections stay the same. If you have an interest in collecting JD garden tractors, a repower won't have the value an original-engined one does, and a collector won't pay you as much for a repower.

Honing the cylinders and replacing the rings isn't a great way to go, the bores wear egg-shaped (horizontal engines cylinder wear more affected by gravity). So, re-bore, new pistons and rings, valve seats and new valves. If bearings spec out, you could not replace them, but if you want to do it right, do the complete rebuild and not worry about it for another 36 years.

The 318 I have was a "partial rebuild" (bought it that way); valves and seats reground, cylinders honed with new rings, original bearings spec'd well enough to reuse them. It smokes when running, but gets less as the engine heats up, compression is good, makes good power, doesn't knock. It goes through maybe a pint of oil between 25 hour changes. There's enough soot and carbon in the oil that it needs the more frequent changes. 25 hours is about a full mowing season, this is mainly a backup mower and cart puller.

KHodges said:

I'd rebuild, the Onan isn't a bad engine, and it is the simpler solution because wiring and connections stay the same. If you have an interest in collecting JD garden tractors, a repower won't have the value an original-engined one does, and a collector won't pay you as much for a repower.

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100% agree on the resale comment and personally really liked my Onans, but....

If you are concerned about getting the most utility out of the tractor and not resale, I would strongly consider a repower. Parts for the Onan will likely be around for years, but they are only going to get more expensive and difficult to find. Also, while not a significant factor, a new engine will likely be more fuel-efficient.

I repowered my 318 with a Honda. I don't regret a thing as I feel that I have an engine that has good power, should run forever, and has replacement parts. If I had kept the Onan on it, I think I would always be at risk for little things like the coils, ignition system, carb etc. So I think I have a much better chance of a long, trouble free future with the Honda.

As for resale, I plan to be buried with the 318 - so longevity is more important than originality.

I do miss the sound of that Onan - great engines.