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Roach 
Silver Level
Joined: 30 Jan 2013
Location: Wheeler, IL
Points: 280
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 Topic: 720 with Onan Overheating
Posted: 09 Jan 2020 at 8:58pm |
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I have an original 720 that is in very good condition and I have rebuilt the deck but having problems with it overheating then misfiring and then blowing oil out. It starts just fine and I have heard that it might be the timing but not knowing much about the Onan,(other than the parts are too high) I really don't where to start. All the small engine mechanics around me say to dump it and put in a Honda or Briggs kit. Any suggestions or advice will be welcomed. I do have all the metal parts around the engine in place as was also suggested.
Thanks
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1937 WC, 1948 G,1954 CA,1956 WD45, 1967 D17, 1937 M crawler, 1963 D-19, 1966 190XT, 1967 D-15, 1948 HG42 Cletrac, 1955 G456 Terra Trac, CAT 10 1928 and CAT 22 1938
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RLBPA1
Silver Level
Joined: 04 Mar 2012
Location: Somerset PA
Points: 285
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Posted: 10 Jan 2020 at 9:53am |
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Do you have the belly pan on it. That is important for cooling. Also check for mouse nests or other debris around the fan shroud. When everything is clean substantial air flow should occur around the heads and out through the front grill of the tractor.
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Roach
Silver Level
Joined: 30 Jan 2013
Location: Wheeler, IL
Points: 280
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Posted: 10 Jan 2020 at 11:40am |
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I do have the belly pan on and just had it completely apart to clean and run new wiring so that should not be a problem. Thanks for the reply.
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1937 WC, 1948 G,1954 CA,1956 WD45, 1967 D17, 1937 M crawler, 1963 D-19, 1966 190XT, 1967 D-15, 1948 HG42 Cletrac, 1955 G456 Terra Trac, CAT 10 1928 and CAT 22 1938
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PaulB
Orange Level
Joined: 12 Sep 2009
Location: Rocky Ridge Md
Points: 4858
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Posted: 10 Jan 2020 at 3:16pm |
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I had a WH that had an ONAN in it, with nothing but problems. After I finally got it running good, by replacing everything in the ignition and charging it had a valve seat come loose. Heed the advice of those who work on them, dump the ONAN on the scrap pile and install something reliable. I've seen a couple neat repowers with turbocharged little Kubotas
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If it was fun to pull in LOW gear, I could have a John Deere.
Real pullers don't have speed limits.
If you can't make it GO... make it SHINY
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AC720Man
Orange Level
Joined: 10 Oct 2016
Location: Shenandoah, Va
Points: 5070
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Posted: 10 Jan 2020 at 8:51pm |
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I well tuned Onan runs very well. Correct timing, points and plugs are key. I had that issue one time and my timing was off. I agree they require normal maintenance every 100 hours but we are talking about an engine that’s well over 40 years old in my case. It has 1,100 hours on it and still performes well. My other one has 670 hours on it. No electronic ignition means you need to read the manual to correct timing issues. Not hard, but the slightest movement of the breaker box makes a big difference. If you don't feel comfortable with the timing, spare yourself some grief and spend a little money and take It to someone who does. Won’t cost that much to have a good running engine if the internals are good. Timing issues cause over heating issues in any engine. Parts will become unavailable before I change out a good Onan. They can be very reliable.
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1968 B-208, 1976 720 (2 of them)Danco brush hog, single bottom plow,52" snow thrower, belly mower,rear tine tiller, rear blade, front blade, 57"sickle bar,1983 917 hydro, 1968 7hp sno-bee, 1968 190XTD
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Roach
Silver Level
Joined: 30 Jan 2013
Location: Wheeler, IL
Points: 280
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Posted: 10 Jan 2020 at 9:14pm |
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Thanks to all who replied. I would like to keep everything original if I can and will try to find a good small engine repair shop if I can. A friend of mine has a Onan on his Wood Miser Portable Band Saw and has a crap load of hours on it with no problems. I do know that it is a lot newer than mine but looks a lot the same. Why are the parts so high for these engines?
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1937 WC, 1948 G,1954 CA,1956 WD45, 1967 D17, 1937 M crawler, 1963 D-19, 1966 190XT, 1967 D-15, 1948 HG42 Cletrac, 1955 G456 Terra Trac, CAT 10 1928 and CAT 22 1938
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jaybmiller
Orange Level Access
Joined: 12 Sep 2009
Location: Greensville,Ont
Points: 23644
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Posted: 11 Jan 2020 at 5:48am |
maybe 'midnight' swap engines with your friend ?? 
as for parts $$... the law of 'supply and demand'. 'they' have the supply of parts and can demand a high price. Building something that has custom parts that fail or wear out means clients HAVE to buy from you. You'll pay $50 for a set of points to get your 2K$ rider running again but if they were $100, you'd think about it. Course the points only cost 50 cents so it's about squeezing as many coins from you AND keep you coming back.When I designed/built my remote energy control systems I used common,
generic parts, made by several manufacturers and sold everwhere so
parts were always cheap AND available.
Some things are outrageously expensive compared to acutal manufacturing costs. A typical current generation smartphone is less than $10 to MAKE, but high 100s to buy. GREAT profit in them.
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3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)
Never burn your bridges, unless you can walk on water
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Roach
Silver Level
Joined: 30 Jan 2013
Location: Wheeler, IL
Points: 280
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Posted: 11 Jan 2020 at 9:21pm |
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Jay, like your suggestion on a midnight swap. I think that I will start looking for a Kit Motor to change out and just keep the Onan so that someone someday may put back to original. Sure are a bunch of thieves out there for sure.
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1937 WC, 1948 G,1954 CA,1956 WD45, 1967 D17, 1937 M crawler, 1963 D-19, 1966 190XT, 1967 D-15, 1948 HG42 Cletrac, 1955 G456 Terra Trac, CAT 10 1928 and CAT 22 1938
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Steve in NJ
Orange Level Access
Joined: 12 Sep 2009
Location: Andover, NJ
Points: 11917
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Posted: 13 Jan 2020 at 9:23am |
There are a few fellows here that have repowers in them. I heard the Briggs VanGard motor is a nice motor. I think Small Engine Warehouse has a kit for the 616-720 Tractors. I think its $1500. or some where around there for the kit. I believe they offered a Honda engine also... Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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den/southern illinoi
Orange Level
Joined: 11 Sep 2009
Location: Sparta, Illinoi
Points: 2029
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Posted: 13 Jan 2020 at 2:57pm |
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Small engine warehouse dropped the Honda. Said they could not get warrantee wrk done on them. I repowered one of my 7 720s with the briggs. Works well. Den
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Own 4 wheel 20, 2-5015, 5020 and associated equipment and 2 electric forklifts.
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Roach
Silver Level
Joined: 30 Jan 2013
Location: Wheeler, IL
Points: 280
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Posted: 14 Jan 2020 at 7:35pm |
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Thanks Steve and Den. Think that is the way I will go with it. Neighbor has one with Honda but has to run with hood off to prevent overheating. Is that Small Engine Warehouse in Indiana?
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1937 WC, 1948 G,1954 CA,1956 WD45, 1967 D17, 1937 M crawler, 1963 D-19, 1966 190XT, 1967 D-15, 1948 HG42 Cletrac, 1955 G456 Terra Trac, CAT 10 1928 and CAT 22 1938
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