Miller 225g welder replacement engine

[jayste]

Anyone out there ever replace the Onan engine on a 225g with another maker? These Onan's may be good engines but they are pricey to fix. I'm needing a crank, piston, rod, etc. I'd like to retrofit with another maker.

 

[BobG_in_VA]

Anyone out there ever replace the Onan engine on a 225g with another maker? These Onan's may be good engines but they are pricey to fix. I'm needing a crank, piston, rod, etc. I'd like to retrofit with another maker.

I'm guessing that you have a Bobcat...I've got a Trailblazer with the Onan 20HP...Yeah, parts are getting harder to find and more expensive...Miller has now gone to Kohler V-Twins...you might ask the local Miller dealer if a "swap" is possible...if not, see what they can do with your's....how many hours do you have on your Onan??? BobG in VA

 

[jayste]

Yes, it is a Miller Bobcat. I'm not sure of the hours. It's been used pretty hard by an oilfield company and not taken very good care of. I think it's worth salvaging if I can get the engine going for the right money. I'm considering going with another horizontal shaft engine if I can get the adapter to work. This one is a 16hp onan. I'm guessing this unit is a 90's model.

 

[AlanB]

I would look at the later model Bobcats, and go with the Kohler.

I am guessing, pure speculation, but guessing that you could use some of the controls from a later model on yours if they could not be adapted or fabricated from what you have.

I would look at a current one with a Kohler and get the model and that other # they use which escapes me at the moment, and that should get you base height and shaft diameter and length etc.

You are probably looking around the $1500 neighborhood for a new motor.

Small Engine Warehouse - Repower Outdoor Power Equipment is great too work with, but I have also had good luck working with my local tractor / mower dealer.

 

[Stimw]

I've rebuilt 4-5 of the Onan's on Miller Welders. If yours has an oil filter it is probably an Onan Performer. If no filter it is a CCK.
IIRC the crank can be turned .040 under but I might be thinking about the cyl bore.
You are not going to get a replacement engine cheaper than repairing yours if you are looking at new. And then you will need the engine adapter.
If you look around there are a lot of RV generators from scrapped RV's. I just bought one on craigslist for $160. that has the control PC board missing. These gens run at 1800 RPM so the engines last forever.
The crank is also tapered so a regular engine won't work, it has to be a generator version. The gen has no bearing on the engine end.

 

[jayste]

Stimw, are you saying that I could possibly use a generator engine for this welder? How about parts in your area? I like the idea of being able to find and engine online and using it. I thought of adapting another brand of engine to it but was unsure of the ability of making the adapter plate work.

 

[Stimw]

The Onan engines should be interchangeable from welder to generator. You would have to change sheet metal and some other parts but they will be interchangeable. They both use a tapered output shaft. Most direct drive generators use a tapered shaft.
The Onans will run almost forever if you keep oil in them and an air cleaner on them.
Do a search on ebay or craigslist for Onan and see what's available in your area.

 

[sandman2234]

If the RV's use 1800 rpm engines, they probably won't work in place of the 3600 rpm Onan. I don't know for sure the Onan is 3600, but they one I had purchased in early 90's was one fast running engine when it came off idle. Need to find a motor that runs the same under load, or your going to have to build a step up system for the generator.
If I thought an 1800 rpm engine would work, I would suggest that Kubota diesel I have out back...
David from jax

 

[Stimw]

The difference between a 1800 and 3600 RPM Onan engine? The governor! All you need to do is change the external governor linkage and the idle control solonoid.

 

[onanparts.com]

The primary difference is internal. A fixed speed 1800 RPM Onan engine has a 10 ball governor, 10 ball bearings in the cam gear.
A 3600/3750 RPM Onan has a 5 ball governor. The external governor spring is also different for the two engines.

As far as using an Onan genset engine on a welder it is possible if the cranks are the same. This is not always the case on Miller welders since they changed the design of the way the crank mates up to the rotor several times.

Early miller welders used a fat tapered shaft identical to the early Onan gensets. They then changed to a smaller tapered shaft and in the late 90's to a threaded straight shaft.

Other parts to consider are the oil pan/base and oil pump pickup tube. You may or may not have to drill and tap the PTO end of the block to match up the mounting points of the welder adapter/stator housing.