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eagle5473

AC 720 Onan is DEAD!!!!! (IT'S ALIVE)

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eagle5473
Well fellas was out today pushing some brush into the brush pile with my Ac720 and plow blade, and the CCKB made a CLUNKING sound and she has died.. Certanly sounds fatal.. She no longer has compreson..... My question is what do I do now? 1. Bite the bullet and call SEW for a Honda 24hp replacement $1700+ with shipping (this will not sit well with the wife) 2. Try to find all the parts I will need for a rebuild (pistons , Rings, Valves, Bearings, Piston arms, Maybe a crank or reground) pluse machine shop work on bore the cylinders and regrind the vales.....I can do the rest $500+ At leaste 3 take the $1700 and buy something else and sell the 720 as is What should I do?

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D-17_Dave
To make the correct decision you must first identify all the problems. Will it still spin over? Pull both heads and see if both sides are moveing. If both pistons move and the cyl. walls look OK then look for a broken valve, or correct valve movement showing possible broken cam or drive gear. It's certainly possible and even more likely that you've broken a rod. But you said NO compresion. It should still have comp. on one side if you just broke one rod. I've even ran them one one cyl. but it sounds pretty bad. I'd definatly look at the whole thing a diagnos it before makeing any snap disition. Finding out what all is broken may help lead to what to do next. Hope it's not too bad.

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Guest
I disagree with Dave. If it were me, I would first panic. Then make a rash decision and throw money at the problem. After you've done all of that by all means take the logical and sensible approach as Dave suggests.

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JP
Hey Guys.... I'm flattered! 8-) I do have a shortblock that could be looking for a home. It was going to go into a unit on a waiting list for a transplant (LOL). See the other Onan owner in the same boat & review comments in the forums. Glad to help! I have a road trip coming up to pottstown pa on 12/3, if that helps....... JP

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eagle5473
Thanks For all the help guys Dave I will pry off the heads this morning, but JP's short block sounds good I am waiting to see how much bling he needs for it.......I does turn over,and spins freely after you let go of the ignition....

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JP
One other thing...... When you pull the oil filter side head off (do that side first....) Look down into the flywheel/alternator area. Did a magnet cover come loose & spin the stator? It happens occasionally. Sometimes 'painlessly' others, With a bang......... JP

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eagle5473
Well I pulled the heads and they did not move when cranked over by the starter, but would move when I turned the front PTO, appears I have a broken crank shaft......Now I had just replaced the matched set of drive belts and this was the first time I was using the tractor since they were installed, How on earth can the cranksaft break? its over and inch wide ? JP got any spare crank shafts?

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D-17_Dave
I've got a broke crank in one right now.

There was nothing wrong with it before and it didn't do any further damage to the engine block or rods. But it was due for an overhaul so I too am searching for a resonably priced crank.

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Roy
Material defect? Maybe torsional/rotational fatique. Look closely at the picture and you will see it had a crack for a while before the final break. Crack/break angle looks to be the classic 45 degree failure. Cannot tell from the picture but maybe they forgot to radius the crank at the rod journal which would create a stess riser. Just some educated guesses.

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JP
Hey Aaron, Dave has asked the same questiion. The only way to know is with a set of digital calipers & a way to check the keyways for timing issues. The boggle is Onan used the CCK in SO MANY applications. I think the flywheel side from most will work. It's the PTO side is the most item of concern. JP

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SMC17
Aaron, I've got a complete CCKB that I'm going to either part out or sell complete either on this site or on ebay. I'm in CT as well so we might have a match. I sent you a PM. If your're interested give me a call and we'll set something up. Sean

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john-holcomb
I don't know if this help anyone and I don't know anything about Onan's. But, My neighbor has a brand new old stock Onan 16.5 hp sitting in a crate in his garage. It sure looked like the exact engine as the power max when I had him helping me work on one for a friend. I pretty sure this could be bought right as he has no use for it, he bought it at a sale because he couldn't pass up the deal. If anyone wants his number let me know. John

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eagle5473
Well.....It only cost me a few dollars and about 3hrs helping out Sean get his new Honda bolted in, and I have a donor /transplant/spare CCKB for myself and it was only 45 min away.....I will let you know how thinkgs go once I have time to work on my own tractor and get it back to life........Thanks Sean

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