Onan Carbon

[deputyrpa]

Well, I started off on carb rebuild. When I removed the carb and manifold, I saw quite a bit of carbon buildup in the manifold and the jug. Here's some pics. Soooo, i popped a head off and I'm glad I did. More pics...yeah!

I decided to try our household steamer to see if that would soften the carbon deposits. I remember the old mechanic's trick of decarbonizing with steam by misting water into the carb. I'm sorry to say it only had a minor effect. I guess there's no easy way out o this one - I'm gonna have to apply some elbow grease.....

I have to figure out how to clean the cabon off the jug intake area. I don't really want to get much further into teh engine because I don't have my garage built yet, and I'm doing this under a carport (well, tractorport). I suppose I have to pull the valves and clean them up too...and then there's the seats..... What have I done? I have to mow the lawn by Saturday!

I'm also a bit concerned about the intake manifold. The rubber-type sealant between the halves looks a bit old. It could be sucking air. Is there any practical way to separate it so I can reseal it? I suppose the little peaned-over studs could be knocked thru, since it's only aluminum....yes?

I noticed a wear line in the cylinder wall too, but I could not feel any scoring. There's a pic of that too.

[deputyrpa]

I cleaned up the heads and the valves of the B48G. I'll be danged if I couldn't get the clips off the valves to remove them, so I had to clean them and the seats in place with a pick and a Dremel. The seat contact is bright and even, so I think it'll be fine.

I removed some "imperfections" by taking a little bit off the heads with some fine emery paper placed on my cabinet saw deck. Upon reassembly I achieved 105psi compression in the left and 100psi in the right cylinder. There was more valve crud in the right cylinder, as the pic shows, peobably accounting for the lower compression. I'll run some Seafoam through it for a final rinse, and then change the plugs and oil.

I'm almost done with the carb rebuild, but have a cork gasket and a O-ring left over. Funny that the carb says "Onan mfg by Walbro", and not Nikki. It' s a Walbro LUA 8. All the gaskets seem to fit, but I hate it when I have leftover parts! This may be a dumb or obvious question, but what are the oiled fiber pads in the rebuild kit for - the shafts?

Thanks......

Nice job.

Scott

[deputyrpa]

I rushed to get the Onan back together to mow the lawn today. We're supposed to get rain all week, and it's already out of hand.

Sooooo....it has much more power, but it doesn't run as smoothly as I think it should. It burbles from idle to full throttle under no load, yet smoothes out quite a bit under load (with the deck engaged and mowing). Is that normal? My Kawi twin was damn smooth all around in comparison. I have to fine tune the governor too, as there was some doggin' delay.

After I mowed for about 1/2 hour, smoke was pouring off top of the block. I think I melted the RTV that I used between the carb and manifold, because I didn't let it cure long enough. I failed to order that gasket, so i did what I had to to get her mowing. Looks like I have a slight leak in the front somewhere too. When it cools I'm going to degrease with Gunk and see where it's coming from. The engine seemed really hot too. I ran it without the shrouds. Do they make that much of a difference for cooling? I hope so, because if not, it has another problem.....

I replaced the coil, fuel pump, fuel lines and clamps, filters, plugs (and cracked the thin aluminum plug lip on the head!), points and condensor. I rebuilt the carb as well. The only thing I left was the plug wires. They don't look to bad, but looks can be deceiving, so I'll change them.

I guess I'm a bit disappointed with the outcome, and have to stick my head into it more than I expected and wanted. ONAN = $$$. I wound up finishing (read: scalping) the lawn with the '68 Ford 120 (K301!).

Any advice would be greatly appreciated. Thanks.

[aagitch]

If you're talking about the black shrouds/ducting that bolts up around the engine, it will overheat without those on. Those keep the air flow directed where it should be, helps cool heads/jugs. I would make sure and use the proper gasket between the carb and manifold that could be part of the problem causing it to run rough. Your carb may also need adjusting as well.

[deputyrpa]

Thanks aagitch. I thought so....that's why I didn't run it too long. Phew!

I'm just about to place an order for the carb (spacer) to manifold gasket, valve cover gaskets and head gaskets. I cannot find a source for the spacer to carb gasket.

I think I may be developing internal pressure from sucking air thru the old head gaskets I reused. I read somewhere that the head bolt torque is 16 ft/lbs. Is that correct?

Thanks for your help.

[Matt G.]

That doesn't seem like enough. Assuming the cylinders are cast iron and your bolts are 3/8" then the torque should be like 35 ft.-lbs. Don't reuse head gaskets, either.

[ajgross]

Assembly torques according to the Onan manual say:

Asbestos Gasket 16-18 ft.-lb.
Graphoil Gasket 14-16 ft.-lb.

AJ

[RPalmer]

Well it's not been said yet so it's my turn. Run the engine for about half an hour then let it cool off and re torque the heads. You have to do this.

[deputyrpa]

Thanks guys. I'll wait until I get the new gaskets.

I was considering getting the service manual for the Onan from that fellow on eBay who can email it instantly, or provide it on a disc for $13. Seems to have too many pages (200) and different engines (6) on it though: http://cgi.ebay.com/Onan-Engines-Ser...3A1%7C294%3A50 Yeah? Or should I get the real deal paper copy? Is there a free copy available online at the Cummins or other sites?

Is my Walbro carb a replacement, or did some 1980 IH 982s come with Walbros too? I can get a NOS Nikki for $80, because it'll probably run better without all the schlop and wear I saw in the shafts. Thanks.