Welder engine rebuilding advice

gengine · Mar 5, 2012

I've got a miller bobcat welder that I bought at auction and it has been great. This last summer it started burning a lot of oil. I've decided to rebuild it, but haven't ever done a small engine before. I have done an old stove bolt chevy, a couple small block Chevys, and a 4 cylinder dry sleeved diesel. Anybody rebuilt one of these? It is a ch18s kohler. Is there a rebuild kit somewhere? All I can find is individual parts, but no kits. Where is a good place to get parts?

rcowan · Mar 6, 2012

If you ever find out, let me know. My future son-in-law has a similar problem. He is trying to decide whether to rebuild or buy a new Kohler engine.

RC

yomax4 · Mar 6, 2012

I can tell you this, In order to remove the engine you have to remove the stator. When you remove the stator there will be very little left to remove because all that will be there is the frame. It's a Big Job. I did a stator swap in a different brand but very similar and it was all day with 2 guys and a fork lift to move the stator. Can you do it? yep. Just plan on some wrench time and get a roll of wire numbers so you can get everything hooked back where it goes. Miller can get you the rebuild kit or point you in the right direction. Good luck.

gengine · Mar 6, 2012

That sounds a little intimidating.... I had the generator part rebuilt, and it only has roughly 5 or 6 hours on it. Maybe I'll avoid the complete rebuild, and just replace the rings and valve guides. I'll check valve seats and all that while it's apart. I guess I can't hurt too much else. When it started smoking so bad, I shut it down, so it was never run low enough for it to shut down itself as long as I've had it. I guess we'll see what happens. Thanks for the replies!

crazyal · Mar 6, 2012

I would try to rebuild the head first and hope that it's bad valve seals. If it's a pushrod engine the head should come off easy. If it turns out you need to do more then the head will be done. If you can drop the oil pan with the engine in place then you could do the rings as well. Do you have an oil pressure gauge?

gengine · Mar 7, 2012

I got all the sheet metal off, and it looks like I can do pistons, rings, and the heads without removing the motor from the frame. Its like rebuilding a motorcycle engine without the frame in the way. I can pull the heads and the jugs as it sits right now. I think the crank and the connecting rods are fine, as well as the journals. I think I'll leave the pistons alone like you suggest and try to just rebuild the head to start with. Thanks!

RPW · Mar 8, 2012

Been there done that it's a tough job but it's doable . First, order the manual from miller. Second order the engine manual from either Onan parts or Kohler. Parts to rebuild are available but maybe pricey. I rebuilt mine for about 1k as I had a thrown rod.

gengine · Mar 8, 2012

I can buy a new engine for $1500, but the parts I should need are around $130 to rebuild the head. My suspicion is the valve seals are bad, but I don't know yet. It looks to me there are four bolts and the valve cover comes off, four more and the head comes off, and hopefully that's as far as I have to go. If that doesn't fix it and I still have low compression, I'll remove the 'jug' and replace the rings which are another $120. The welder still starts and runs fine, and sounds really good, just burns a whole lot of oil, and has never been run below the cross hatches since I have had it, about 120 hours of run time. This welder has 843 hours on it, and looks like it was taken care of. It was from an estate auction, so who knows if it was maintained. We have the exact same welder at work with 4000 some odd hours on it, and it's still running strong. I guess I better go to wal mart and buy a camera, because I suppose you folks will be wanting some pics. My last camera was destroyed when my horse rolled on it, and my rifle too.

RPW · Mar 9, 2012

What motor does it have? As far as that goes which Miller is it? What I rebuilt was a Bobcat 225nt. If it's an Onan then the "jugs" are not removable by themselves. I believe Kohler is done the same way. As far as replacing the motor be careful as the shaft mating is not a standard thing. In the case of my Miller the shaft had a taper threaded shaft.
Sorry to hear about your camera but horse have a tendancy to do the unexpected. Gee how'd I know that

We've got 7.

gengine · Mar 9, 2012

I'm not sure of which miller mine actually is, but the one at work is a bobcat 225, with the same ch18s motor, even the same spec number. So I assume it is a bobcat 225. I'll have to get back to you in the next day or two.