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Onan B48G Rebuild


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22 replies to this topic

#1 olcowhand ONLINE  

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Posted April 29, 2010 - 08:15 PM

Been in the process of rebuilding my B48G Onan...18hp. It will be replacing the 16hp BF Onan on my MF1655 w/FEL. The BF smokes all the time & stumbles now & then.
I was hoping to document the rebuild with pics, but had to do just a few minutes at a time & in a rush, so no "during pics", sorry. The bores were nearly perfect, & pistons/rods/journals all good. Bought several gaskets, but re-used the metal sandwich type head gaskets. New cam bearings, piston rings (std),intake/exhaust gaskets, pan gasket, oil pump gaskets, & valve cover gaskets. Valves & guides still had a great fit. I did put a longer bolt (1/8" longer) in the oil regulator to raise the oil pressure. Fired her up today & she runs smooth & quiet. I'll post pics of where I'm at before I put all the shields in place, and take a video clip to show how she runs. Spent $137 including shipping for the new parts. Spent about $60 or so more for some other used parts I needed as I had robbed some parts off this engine for the BF's. I could have taken them from the retired BF, but I wanted to keep it intact as an emergency spare engine. Got all my parts from Onanparts.com.
Had this engine backgrounded for at least 5 or 6 years, finally rebuilding her.

                       

#2 tractormike OFFLINE  

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Posted April 30, 2010 - 06:28 PM

I'd say Daniel that you got by real cheap for rebuilding an Onan :thumbs: Your time spent hunting parts saved you a bunch of money. They are a smooth running engine when all is right with them.

#3 olcowhand ONLINE  

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Posted April 30, 2010 - 07:46 PM

Went out just now to shoot a short video of her running, but have a miss in it now. I think it may be the OLD plug wire, so another day I'll put some new wires on it & see. They aren't the correct plugs, and I did flood it today, not noticing the hot wire clip had come off the coil, so was choking it thinking fuel problem. I know these AC plugs gas foul easily, so I'll check them also. I have new correct plugs coming in the mail too. I'll get a video when she's purring again.

#4 olcowhand ONLINE  

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Posted May 01, 2010 - 12:29 PM

Well, I now know why my engine is running ratty....well, now not at all. My ignition coil has went & died on me! No spare coil, so ordering a brand new one. Another $85 w/shipping! Dang, the total is going higher!

#5 NUTNDUN ONLINE  

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Posted May 02, 2010 - 11:56 AM

Well look at the bright side, it will have a new coil along with a new rebuild so it will last even longer without trouble :D

#6 olcowhand ONLINE  

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Posted May 02, 2010 - 12:51 PM

I haven't ordered the new coil yet, and may not. I might go with 2 separate auto style coils, each with a condenser. I have them already & seen people do it with great results. I always try to do with what I have.

#7 olcowhand ONLINE  

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Posted May 02, 2010 - 03:16 PM

WILL take a pic, but time to go feed & milk cows again....but NO having to buy a new coil. I had a couple auto style coils off Kohlers lying around, so cut a metal plate, mounted up the 2 coils & 2 condensers. Jury rigged the wiring to the engine & fired her up. Smoooooth as silk now! The plate will be welded onto the front edge of the battery tray, standing up. This will isolate them from most of the engine vibration too, so possibly longer coil life.

#8 olcowhand ONLINE  

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Posted May 03, 2010 - 11:17 AM

Here's a short video clip of the engine running. No air cleaner & cold engine, so on the lean side, but smooth still. Plus a pic of the mounting plate for the twin Kohler coils.
This plate will stand upright, welded to front edge of the battery tray. Will make for easy access to ignition. Gotta learn how to embed the movie to play here.
DSC00112..jpg

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#9 mjodrey OFFLINE  

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Posted May 03, 2010 - 12:44 PM

Hey, that onan sounds good.

#10 NUTNDUN ONLINE  

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Posted May 03, 2010 - 01:53 PM

In that coil pic it looks like you are running some kind of mad scientist experiment. LOL.

The Onan sounds good in the video. You will have to make a video of it working then once everything is back together :D

#11 olcowhand ONLINE  

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Posted May 03, 2010 - 02:14 PM

In that coil pic it looks like you are running some kind of mad scientist experiment. LOL.


I was! LOL The thing is...I found another parts coil....and it's good! Not sure if I'll use this setup, or the parts coil. Probably use the parts coil, then just set this setup plate back for emergency. At least I'll easier find the coils & condensers that way.

#12 olcowhand ONLINE  

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Posted May 04, 2010 - 09:16 PM

Put the spare Onan coil I found on engine this evening & she runs sweet! Then made some heat shields to block some of the heat off the exhaust pipes from reaching coil & carb. It originally had shields, but they didn't come with the engine when I bought it. "May" get started swapping the engines out on the MF1655 this weekend. Mother's Day is Sunday, so may not get nearly all done. Still have to find a 5 1/2" steel pulley so I can modify it to weld to the keyed shaft collar. The JD318's cranks are 1 7/16", so have to form my own pulley to drive the hydraulic pump. After work, I was so tired it's a wonder I did anything to the engine.

#13 tractormike OFFLINE  

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Posted May 04, 2010 - 09:22 PM

Good job on the onan, she sounds sweet! I've never tried the 2 coil trick but it's good to know that it can be done and will work.

#14 NUTNDUN ONLINE  

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Posted May 05, 2010 - 04:22 AM

Put the spare Onan coil I found on engine this evening & she runs sweet! Then made some heat shields to block some of the heat off the exhaust pipes from reaching coil & carb. It originally had shields, but they didn't come with the engine when I bought it. "May" get started swapping the engines out on the MF1655 this weekend. Mother's Day is Sunday, so may not get nearly all done. Still have to find a 5 1/2" steel pulley so I can modify it to weld to the keyed shaft collar. The JD318's cranks are 1 7/16", so have to form my own pulley to drive the hydraulic pump. After work, I was so tired it's a wonder I did anything to the engine.


I don't know how you do it as is, keeping up with all the farm work, finding time to work on the gt's and still post here LOL. You the man :thumbs:

#15 olcowhand ONLINE  

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Posted May 11, 2010 - 09:42 PM

Just won bids on a few parts to finish off the engine. I got muffler & exhaust pipe heat shields, and a flywheel screen for just $4.90 plus shipping, which should be around $10. These should help her run cool. The stationary flywheel cover this one uses can clog easier than a spinning screen, and since same seller had the shields, I got them also. It's Joe's Outdoor Power & he combines shipping.