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D-17_Dave

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D-17_Dave
I really hate it when stuff like this happens. And it's not even mine. But it is one of my friends that I just fixed the 4041 for. It was running fine when he said it made a noise and he shut it down. It would still crank and run but I told him we had better find out what all broke instead of trying to mow with it like this. It wore the edges of the front main and the thrust bearing but did no damage to the rods or block. I'm really surprised it didn't take out something else. It could have been a lot worse.

Anyone else ever had this problem w/ the cck series? In all the discusion I've seen on these onan's I've never heard of a broken crank on one.

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iweld
I'm suprised there isn't more, since they designed a 16 hp engine and then coaxed it up to 20 with intake and carb modification. What an opportunity to do do a repower with something better and more economical.

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BLT
On the big engines that I work with, a break like that is called a torsional break. The side opposite the break is generally where the culprit was. So, on the PTO shaft was there more power taken off then what was designed to do, i.e., more pulleys , ect?

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D-17_Dave
JP, It was stock. He was half throttle bladeing the drive when it went. Bob, there wasn't any load. No belt on the pto and no added stuff. I checked the hydro drive shaft and it had no problems. I'd love to see something stronger in there but we lucked out and I have a crank. It'll just need regrinding and bearings . I'll have to see if the block needs boreing, I think it needs it.But I think I can get him out for way less than a repower at this point.

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BLT
OK then was that crank re-ground? If it was a lot of machine shops forget to roll a fillet on the journal ends and this can also break cranks. Square cut journal ends weakens the crank and also causes lubrication problems.

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Chris727
That looks like terrible news. I think I'm going to stick to single cylinders on all my tractors. I read somewhere about a KT17 doing the same thing, was running fine, well maintained and suddenly breaking the crank.

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Al
Hi, I would like to agree with BLT, The radius on the journals is crucial when a crank is ground. If the radius is not correct the sharp corner becomes a stress point and then there is potential for cracks. This is why when they fix water cooled blocks they find the end of the crack and drill a hole in it and pin it. Without a round hole, the crack will keep running. One other thing I wanted to mention was I was looking at repowering Miller welders. A year ago I was talking to a rep in the engine industry and he told me that there had been some problems with cranks in Onans breaking apparently from a harmonic vibration in an occasional welder and that if I decided to try the repower to assess this problem up front. I have worked around environmental analysis for many years when I worked as a technician for Rockwell Intl. We do not have all of the equipment I would need to really evaluate this issue to see if it really exists, and if it would appear on a V twin with its Harley Davidson type firing sequence. About a half hour later Warner Frazier the Chairman of the Board at Simplicity saw me and stopped to talk a few minutes and asked what I was doing. I told him about my repower endeavors. He took me over to a person standing in the Kohler booth and introduced me to a very good friend of his Richard Schumaker the president of Kohler. Warner mentioned that we went back about 20 years and I was always doing something. Then mentioned the repower activities. One of the questions Mr Schumaker asked was: "Have you thought about welders? I explained that there could be problems that I probably didn't have the expertise or the equiment to deal with these issues at this time. Thank goodness I had the conversation when it did and not an hour later. I might have jumped into something that the water was too deep for me to swim properly. Al Eden

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D-17_Dave
I certainly can understand about the sharp edges and have seen hot rod engines get heads, cranks, rods,and blocks all ground to the point of makeing weak spots. This crank was stock and the engine not under load w/ no deck hooked up. I have been unable to locate anything in the tractor or the engine that may have even contributed to the dimise of this crank. Other than the fact that this engine with less than a 1000 hrs on it was worn out and the cam had around 1/4 " of endplay. I saw no gear problems where anything could have bound up, only the fact that the "FLOATING" cam wouldn't let the govn. react right. It would idle fine, and run high rpm's fine w/ govn. control. But mid range rpm's the gear tourqe against the govn. weights and spring was enough to loose most of the throttle response from just off low idle to 2/3 throttle. It wouldn't over rev, it hust didn't have mid range throttle control. I've seen cranks break in the journals, but if you look closely the crank broke outside of the edge of the rod journal. We have put I'd guese close to 50hrs on this engine since I worked on it and sent it home to him. And he's not blameing me for any problem. It's just one of those unexplained things..... Unless it happens agian...

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iweld
Did you happen to check the bottom pulley bearings? If they turn very freely they might have done an occasional "lock-up" that you might not even have heard, but still put a big instant load on the engine. Just reaching for straws here, but just a thought. There also might be more to the cam end play problem.

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