[Mjoe7]

Here are some Before and After pics, after cleaning up the heads and piston/valve areas.

 

[Rob_P]

What did you use for the cleanup?

 

[heatseaker1]

I did mine this past supper right after I bought it at from a swap meet. It was as bad if not worse than what yours was. I really don't think the valves were able to seat all the way with all the build up I had.

Not sure what you used but I used generic oven cleaner for mine. Worked like a champ too. Spary it on, go over it with a bass brush then let it set for a but then repeat. Two maybe 3 rounds of that and it was done and clean as a whistle. Would have been a simple afternoon job too if I hadn't busted 2 of the head bolts off on each side. :crying:

Hard to believe that I still see posts that this is not a requirement anymore due to better fuels. Prior to doing mine my Onan didn't even have enough power to run the deck of the tractor was moving. Now I have power to spare :grin:

 

[animalsonly]

How long has it been since you did it? Is this the result from poor fuel mix or improper point plup gap? I had my engine rebuilt last year. Should I check to seeif mine is that way? Pulling it would show me the ammount of build up over just one year.

 

[Mjoe7]

What did you use for the cleanup?

I used a scraper and wire brush, and for the hard to get spots a small pointed tool to scrape it clean.
The nice thing is this is easy to do. Just be sure to have a set of gaskets available. I re-used mine, but I ordered some just in case.

 

[Mjoe7]

How long has it been since you did it? Is this the result from poor fuel mix or improper point plup gap? I had my engine rebuilt last year. Should I check to seeif mine is that way? Pulling it would show me the ammount of build up over just one year.

It's up to you if you want to check it out. I wouldn't bother, but it's easy enough to do, and with your recent rebuild you could probably get away with reusing the gaskets. It would be interested to see what it looks like. How many hours did you put on it since the rebuild?

To the best of my knowledge this engine has never been apart. Still has standard pistons etc. I bought it on ebay 3 years ago. I installed it, crossed my fingers :fingerscrossed: and it has run excellent for the last 2 years. I use ethanol free fuel in my tractors.

I checked the plug gap on mine while doing this and found it to only be about .010 practically touching, so I put in new plugs (because I dropped one on the floor :facepalm: ) and adjusted the plug gap to the proper spec of .025.

I tightened the bolts on the front timing cover because one of the bottom bolts had backed out and was causing lots of oil leakage. Easy fix for once. :thumbup:

Next is to clean the whole block well and then reinstall it. :thumbup:

 

[animalsonly]

I would say about 50 hours. It doesn't have a hour meter on it.

 

[Mjoe7]

I would say about 50 hours. It doesn't have a hour meter on it.

Yeah that's not much. Maybe wait a couple years or until you reach the recommended hour limit to check them out. It's up to you of course. Anyone remember what Onan recommended for hour intervals on decarbonizing? My books in the shop. No it's not getting repaired. :lol:

 

[jojotigerman]

The manual on my 1983 448 Onan say "Remove cylinder heads and clean combustion deposits every 250 hours or yearly. Period may be extended to 500 hours if unleaded fuel is used exclusively". Wow!....Guess I better get busy. Last time I did it was in 2004, over 500 hours ago. Note that I discovered that there are two kinds of head gaskets, viz., "Rigid #110-2287" and "Soft #110-3181". The OE gaskets were Rigid. I don't know what difference it makes however. Now, if I just knew how to adjust valves, I'd be a rocket scientist. :sidelaugh:

 

[case680rob]

Might it be necessary to recalculate the cleaning interval with today's E10? Might it burn differently than fuel on the market in the 80's?

And what about the Kohlers? Would it be necessary to do the same task on these engines as well?

Rob

 

[1031d]

Rob, its in the tractor manuals for the kohlers too. Actually killed my engine. There was such a large growth over the top of the cylinder that it hammered the top of the piston down past the first ring groove. Was like it when I bought it.

 

[Hydriv]

Rob, its in the tractor manuals for the kohlers too. Actually killed my engine. There was such a large growth over the top of the cylinder that it hammered the top of the piston down past the first ring groove. Was like it when I bought it.

That's how you turn cast pistons into forged pistons. :sidelaugh:

 

[burrhoes]

Is there step by step instructions on how to decarb the engine?

 

[Hydriv]

There are several manuals in the Library that deal with Kohler and Onan's. De-carb'ing is described.

 

[Bob MacGregor]

Once you do a decarb you can keep it that way by regular use of carbon softening fuel additives like ValvTect Carbon Free. This is a Marine Engine additive but it lends itself to any aircooled engine that consumes engine oil during operation This additive with regular use keeps the carbon in a softer state and it will pass thru the engine as it runs. Cleaning the engine cooling system particularly the cooling fins around the base of the cylinders and using 89 or higher octane fuels will increase engine life.
Mad Mackie in Taxonnecticut :mrgreen: :lol: :mowlawn: Soon!!!

 

[Mjoe7]

I thought I'd share some other things I did while the engine was out and apart.
I took the intake off and adjusted the valves. All but 3 were way to tight. Proper settings... 008-Intake .013 Exhaust.
Then I thought I'd get crazy :rockon: and lightly ported the intake valve area on the block. I took off the cast flashing and lightly rounded some edges along with a slight polishing to increase flow characteristics. It should be interesting.
I also checked the Points and found them way to close. I adjusted it back out to the proper .021 setting.
The plugs were also to close for tolerances, so I gaped and installed new ones as posted earlier in this thread.
This thing ran great before this maintenance, so it should really run great now! I can't wait to try it out! :thumbup:

Ported Intake Areas.

 

[oleblu72]

Now you did it you really went and stepped in it this time. There's a written law somewhere ( please don't ask me to find it)that says when you do a high performance port job like this you have to go ahead & turbocharge add N.O.S. and a big fricken hood scoop & install a narrowed Ford 9 inch rearend not to mention all the chrome stuff you have to start adding to her. Did I forget to mention the fuzzy dice & a 8 track? :thumbsup: :thumbsup:

Mark