What should an Onan sound like?
 

I fell into a John Deere 318 with a B43G that the PO said was non running. I didn’t ask too many questions because it was in good shape and clean and really cheap. So I bought it and brought it home. The battery was from 2011 and swollen. So I put a good battery in it, put some gas in it and turned the key. I saw fuel go through the filter and it fired right up. It sounds pretty good but it sounds like a Diesel engine almost. Is that how they sound? I’ve never heard one running and it sounds different from my Kohler M20 in my Cub Cadet. It’s not a knocking sound or anything like that. The oil is good and clean. It has 1900 hours on it. The tractor had a good clean deck and everything. I feel like a thief!

Well, the few experiences that I have had with Onan, they similar but different than the Kohler Twins. Maybe a good thorough Tune Up is in store.

:bigthink:

It sounds strong, throttle up and down is responsive. It doesn’t smoke. Inside the air filter is clean and not oily. I’m going to look at the plugs and change the oil and stuff before I try to use it. I also have to change the rear tires, I have a good spare set but one of the rears has a plug in it that isn’t holding and they’re worn down. The hole looks pretty big and there may be two plugs in it and it leaks down a day after pumping it up. Oh, and it had JD wheel weights mounted on it also.

Most of my experience with Onans have been in generators, but they do have a " different " sound than most gas engines. Here is a video of one running. Fast forward to 4 minutes ;

https://www.youtube.com/watch?v=Sq4WJE4x1SU

Sort of hard to compare a video to real life but mine sounds like that I think. Maybe I’ll record a video of it running and compare that way...:bigthink:

They have a bit of a more throaty sound esp under load.... 1900hrs is pretty good as i have normally repowered the JD 318/420 with other Kohlers at the 1500 mark for the Onans… Check the compression on both banks to get an idea of the internals....

Also the split intake manifold has been known to be a PITA....

One thing I did not ask is what oil are you using ? My Onans have called for 30wt, & that is what I have used. I also use a NAPA/Wix oil filter.

I haven't had much time to play around with this tractor but I did mow with it once. It wants to bog down under load, and it surges and dies at idle without the choke on. It almost sounds like a misfire. So, doing my research on this issue it looks like it's probably a carb issue or an air leak in the split intake seal. I haven't checked the compression yet, I tend to do things backwards. :biggrin2: Both sides definitely have compression, I replaced the plugs and turned it over with the plugs out and both sides blow air forcefully out the plug holes. I have a compression test kit somewhere, but just haven't taken the time to pull it out. I put my timing light on both sides and the flash is smooth with no misfiring down to idle when it dies, so I don't think it's a misfire. Last night I finally pulled it apart to look around at the intake. It didn't look terrible to the naked eye, I cleaned it up and looked it over good. So then I decided to get my super bright mini maglight and turned off all the lights and shined it up in both sides of the intake and voila... there was light peeking through the seam in several places. So, following the guides online I took it apart and cleaned it up good and resealed it and put it all back together. I'll give it a good 24 hours to cure and then fire it up and see what happens.

I think the split intake has to be one of the worst ideas ever conceived. I wonder what was their reasoning for this design?

split manifold is less expensive to manufacture.

Figures...

I finished reassembly of the tins and covers and stuff and started it up and it still did the exact same thing. So, into the carb I went. I found one of the jets had been plugged and I cleaned it out, and put it all back together and fired it up, and no more surging. But, the top end power still seems weak, with the deck engaged it drags the engine down and it has to wind back up, and when I get into thicker grass it bogs down. I guess I'll start looking at the governor now... :bigthink:

That front bowl jet is known to get clogged and cause surging...Have you done a Comp check yet to see the condition of the internals??

The jet that screws in from the top is the one that was clogged, and there wasn't any dirt in the bowl. I've not done a compression check yet. One of the easiest things to do, and I haven't dug out my kit to do it yet. I've been very preoccupied with building my pole barn to move all my tractors and equipment into.

I did notice that the governor spring was in the third hole from the end, and the engine was maxing out at 3100 RPM's according to the tachometer app on my phone. So I moved it up one hole (both appear to have the paint worn a little so the spring has been in both holes at some point) and now I'm at 3600 RPM, and it seems a little better, but I didn't have time to run it in grass yet, that was after dark and the headlights on it are pretty much useless, they don't make much light at all. I'll take it for a stroll today and see how it is, and maybe I'll even get the compression test kit out.

The clock has 1900 hours on it, but it looks like a clean 1900 hours if that's accurate. It's not dirty/oily/gross like I've seen from lower hour machines, and the engine does not smoke at all. It fires right up as soon as I hit the starter now that I've gotten the carb cleaned out.

While I'm working on stuff around the place, I got around to checking the compression on this. I'm around 70PSI on both sides, so it looks like the engine is tired. I read places where it should be around 100PSI min for a B43G.

If it is not using oil, let alone. Was it warm/hot both plugs out and open throttle? As it should doing a test.

No, it was cold and throttle closed. I’ll check it again. It’s a dog under load, the engine just bogs down. I set the governor spring right and went through the carb and cleaned it to solve a surging issue, but it had no power before and after. It doesn’t smoke, I’ve not used it enough to see if it’s using oil over time.