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AcFordHawk

Not good .....bad and ugly

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AcFordHawk
Doing snowblowing moving some of the snow banks along the lane back and had the 620 develop a heavy vibration and the engine died. Thought it was a bearing or something with the snowblower. Starter wouldn't engage and popped the hood up to look. Found the flywheel at angle and engine shrouds a little out of place. Pics show the damage. Have to decide on reworking one of the other two Onans or repower the 720 or P'max project tractors. Back of engine. .
[img]/club2/attach/AcFordHawk/onan1.jpg[/img]

[img]/club2/attach/AcFordHawk/onan3.jpg[/img]
Flywheel & Stator.
[img]/club2/attach/AcFordHawk/onan4.jpg[/img]
Flywheel & crank connection...crank broke at the shoulder area of the flywheel retention bolt.
[img]/club2/attach/AcFordHawk/onan5.jpg[/img]

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D-17_Dave
Bad thing is it took out the stator too. Maybe you can salvage it by soldering a few wire extensions. A Honda is an option, but remember it's not as straight forward as they want you to believe. I haven't ran mine enough to know if I like it enough to recommend it.

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AcFordHawk
Hope in about a week or so when have some more free time to look into it a little more. Haven't really looked at the stator but a quick glance looks like the flywheel did more than tear the wires apart. Will take a look at the other two engines for comparison and see if can salvage the stator at least. Would really like to keep an Onan in the tractor for originality. At least have one of the P'max tractors operational.

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PGL
What do you think gave out first? It looks like the shaft may have a bit of rust on the break from a crack? Did the fan break when the shaft went or did it break and the imbalance took out the shaft or???

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Time1992
If it were me I would use the 19.5 that I think you said you have, if its in good shape it is a great motor, if not then if you have the money a swap with a Honda, BS Vanguard or Kohler might be good, Look at B-17 Daves posts and others , there are tons of knoledge on this forum. Hey Cvans what Diesel would fit into a Power Max frame and clear the hood, thats also a great option.

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AcFordHawk
Peter, looking at the break I am inclined there may have been a crack in the crankshaft. The flywheel has fresh, clean, no-rust type breaks compared to the "dirty", rusty looking condition of the crank so believe the crank broke first. Tim, my first choice is the Onans. Luckily (or may be not $$ wise) there is a Cummins dealer in Des Moines I have bought a few parts from. Get a chance in a week or two and will spend some time working on the other two 19.5's and seeing what they need. Got one as a buy from a gentleman who did a repower and the other was running when I pulled it out of the 720 I got from Mike Wells (mwells).

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PGL
I thought probably the crankshaft went. You can see the break was at the end of the bolt, where the shaft size is smallest and where vibration from any slight off-balance of the fan/stator would concentrate and over time start a fatigue fracture and eventually give way. Note there are a number of balancing weights on the stator assembly - balancing is very important. I wonder how it could be checked if any disassembly or rebuilding or replacing parts is done? Like balacing tires?

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D-17_Dave
Question, what is the snap ring in there for. Non of mine have that snap ring that I recall. If someone cut a groove in the crank for the snap ring and didn't round the edges then the sharp groove is the cause of the failure.

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D-17_Dave
I've broken a crank on an ONAN in a 4041. It broke clean between the journal and the unfinished casting. It run perfectly up to that point and gave no warning. I couldn't find anything that caused that failure. That said, I'd run this engine in everything if I could. These engines are very well designed and built. They like any other engine have flaws and weak points from wear that were not exspected but they are heavy and over built for most applications. They are as close to automotive technology built engines in a small engine you'll ever see for this time period.

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AcFordHawk
I agree with Dave. Very good engine. This one was running great with no warning on the breaking. Keep them tuned up and I dont have many issues, they can be tempermental if carb, points, etc get a little out of whack but that is the same with most engines. Looked at the stator and flywheel when I brought it to work this morning (have some Non-destructive Testing (NDI) trained guys at the hangar who want to look it over - yeah little late for that) and saw the wire wrap for the stator is shot from the flywheel contact. Get it apart in another week and try to get some more photos of the crank area. May be have the NDI guys do a dye penetrant and see if other cracks appear. Paul, diesel is one idea I am kicking around for the P'max I got last May sans engine. Just another project waiting time to work on.

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