Welder engine rebuilding advice

[gengine]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

 

[CJONE]

Kohlers have a tendancy to pop head gaskets. My 25HP did this last year and it was burning oil because of it. I would pull the heads first and check the gaskets over real well. CJ

 

[gengine]

That's good to know, I will check that out when I get home in the next day or two.

 

[brokenot]

Kohler has had most of the manuals for later-model engines online for quite a few years now.

Here's a link to the shop manual for a CH18:

http://www.kohlerengines.com/onlinecatalog/pdf/sm_24_690_06.pdf

You said you wanted to disassemble it without removing the generator head? You won't be able to do that unless the head is coupled onto the blower housing end. (Kohler does make stub shafts that bolt onto the blower/flywheel side. Toro Dingos are one application in which they're used. The machine function pump is coupled on to the "traditonal" pto end of the crank, and the hydro pumps are belt driven off of the stub shaft coming out the opposite end.)

If your generator head is coupled onto the "traditional" pto end opposite of the flywheel, you'll have to remove it in order to open up the crankcase to access the connecting rod bolts if you want to remove the pistons.

Kohlers are like most small engines....simple to work on. As already mentioned, the v-twin Kohlers are bad for head gasket failures. They issued a repair kit starting about 10 years ago or so that included studs to replace the head bolts, as well as an improved gasket.

 

[gengine]

So far I just plan on rebuilding the heads. I think the problem is the valve seals or a he'd gasket, but I'll find out more when I can take it apart. I was going to start it the day I started this thread, but a lot of other things have come up, and now I can't find the time to get into the shop. That day it was snowing and in the twenties, and now it is bright and sunny, and in the 50's. It's hard to be in the shop when it's that nice.

 

[gengine]

Thanks for the link! That is going to be a great help.

 

[RPW]

For the Bobcat 225nt's the shaft will be threaded on. It will require some angle iron and some bolts to attach to the flywheel and a big mucking wrench grasp the shaft at the end of the generator. Be careful as these are a "fine" thread and can be damaged easily. However if you are only working on the top end you probably won't have to go that far. Just remove all of the shrouds.

Good luck.