DE-CARBON ONAN P216

[km3h 543]

Since I had to move the engine forward to replace the fuse block on one of my 416H's, and the engine now has 532 hours on it, I decided to pull the engine and remove the carbon from the heads and valves. I am very glad I did. I have torn down a lot of engines but I don't believe I have ever seen one with this much carbon on it. It looks like I will spend the winter months de-carbonizing the other Onan engine and my two KT17's.

Engine runs perfectly,idles smoothly and fires up instantly, so the carbon was not causing any problems. There were some places that the buildup was sort of knotted up and I don't think it would have helped any if these pieces had broken loose and gotten into the bore which is still like glass.

Called Boomer and ordered the gaskets and will do some other work while waiting for them to arrive.

By the way, what should I use to remove the carbon. I tried carburetor cleaner and brake cleaner and neither works well. There must be something that will dissolve this stuff.

Edited July 29, 2014 by km3h

[boovuc 1,090]

I used brake cleaner and I also used MEK. (Methyl Ethyl Ketone). I also used some small pieces of heavy duty polyethylene, (HDPE), and scraped it after soaking it with MEK. It takes a lot of time and elbow grease but it will come off. just don't use any metals to scrape with. You can buy MEK at most paint supply stores.

[Hodge71 663]

If you're in no rush I would spray it with a mixture of 50/50 acetone and transmission fluid. Its works great as a penetrating oil as well. Spray it every day for 2 or 3 days and it should scrape right off. I have also heard of people using easy off oven cleaner with good success. I have never seen that much build up on pistons. I usually just throw the heads in my glass header and blast them clean then take a piece of glass and wet sand paper or a really good file and face the head flat, install a new gasket and torque her down to spec.

[km3h 543]

I was very surprised when I pulled the heads and saw all that carbon. As I said before the engine runs perfectly, with no obscene noises. Almost as if it was run on leaded gas. I have been doing some research on the subject and a lot of folks seem to use Easy Off oven cleaner. I am not sure if that stuff will hurt aluminum.

Tomorrow I will pull the valves out and give them a good cleaning. I checked the valve clearance and even after over 500 hours they were right on specs, .005 for the intake and .013 for the exhaust.

[Martin 2,130]

normally i use a plastic scraper. got to be real careful with any metal objects.......

mek is ok, but you need to protect yourself with the right equipment, not good for the skin and to breathe in.

 

i have also used a real wide metal blade (wider than the bore) to scrape the whole piston at once. keep the blade perpendicular and drag it across the surface, won't cause nicks in the soft metal. i blast the heads and remove the rough surface with scotchbrite afterwards. this also helps to remove embedded media in the head. (don't want that stuff floating around in the bore)

scotchbrite can be used on the carbon too, just takes a lot longer. check out some of the pics of the Onans in the 416 thread of mine for how they looked and turned out using these methods.....

[km3h 543]

I read that thread and the heads looked like someone had polished them. I have a pack of plastic spreaders for Bondo that are probably hard enough to do the trick. I never thought of that. I might take the heads to the local machine shop and have them dipped.

[Martin 2,130]

put the heads in some thinners for a few days, then hit them with some scotchbrite, you will be surprised at how much they will clean up......

 

that polished look was all scotchbrite (red) and elbow grease........

 

and sore fingers......

Edited July 30, 2014 by Martin

[km3h 543]

Thinners and Scotchbrite it is. Since I have to wait for parts anyway, I have nothing but time. I am painting the bottom of the 48 inch deck tomorrow morning and then the rest of the day will be spent putting away my tools and whatever. I should get the rest of the parts to fix the fuse block tomorrow.

[MalMac 1,328]

Well now you got me convinced to de-carbon my 520. Like you said it runs perfect and starts at the blink of a eye. It's good and strong. I only use it for snow blowin duties. After seeing yours I guess it's time to de-carbon and adj. valves. It's just I hate tearing into Onans. Expensive to tear into. Expensive to fix if you don't. It's a catch 22. Like the ol Fram commercial "Pay me now or Pay me later"

[km3h 543]

Yes, it's a catch 22 kind of deal. After seeing the inside of this engine, I think I will do the same to some of the other tractors I have around here. All except one are at least 20 years old and I know they have not been opened since new.

I ordered the gasket set from Bob Kummer, AKA Boomer, who is a member of Red Square, cost of $56.00 including shipping. You need six gaskets to do the job. You have to remove the intake and exhaust manifolds.

[km3h 543]

Worked on de-carbon the heads and pistons today. Cam out nice. Still have a little work to do on the valves. I may take them out to make sure everything is absolutely clean. Lot of scotchbrite and brake cleaner along with some thinner. Rub, Rub, and Rub. 

Edited July 31, 2014 by km3h

[JackC 616]

Thanks for the update.  Looks great.

[Martin 2,130]

Nick, looks like you put some time in there.......

 

sore fingers tonight?

[km3h 543]

Yes they are a little sore but it has been worth it. Not as nice as the job you did but good enough for government work. I will do a bit more tomorrow. I still have to install that fuse holder too.  

[boomers_influence 106]

nick

BEAUTIFUL job.

thank you boomer

[km3h 543]

nick

BEAUTIFUL job.

thank you boomer

Coming from an old pro like you, I really appreciate that.