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Old 22-02-2012, 22:26   #1
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Crack Discovered LOL Seriously

i am in the process of getting a new to me boat ready for the summer
the generator ( ONAN First Mate 3.0 MAJB ) was not starting and we discovered that the harmonic balancer has a crack in it. the crack starts in the center where it slips over the crankshaft but stops a little shy of the half way mark ( from the outer edge )

1.how dangerous would this be to continue useing
2 is there a way to fix it ( it is cast iron )
3 any idea where i can find a part ( i will be calling cummins but i dont have a lot of hope )

on the inside it looks like the part number is 170-3943 but it could be 3843 really hard to tell for sure

i got my fingers crossed

thanks
Dwain
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Old 23-02-2012, 07:18   #2
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Re: crack discovered LOL seriously

ok the actual part name is a fly wheel (not a harmonic balancer) and the actual part number is 160 1353 ( although the number that is on the part is different but that may be a factory part number )

does anyone know if , how or where i can be repaired ? or where i may find one?

thanks
Dwain
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Old 23-02-2012, 07:27   #3
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Re: Crack Discovered LOL Seriously

Please do not use the generator while the harmonic balancer is in this condition, believe me if it comes apart and its at high rpm. it will do serious damage to Vessel and body,,,think very heavy grenade!!!
Onans are easy to get parts for,,even used,,and any machine shop can make you a new Balancer to fit.

Best of luck..

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Originally Posted by BentWheel View Post
i am in the process of getting a new to me boat ready for the summer
the generator ( ONAN First Mate 3.0 MAJB ) was not starting and we discovered that the harmonic balancer has a crack in it. the crack starts in the center where it slips over the crankshaft but stops a little shy of the half way mark ( from the outer edge )

1.how dangerous would this be to continue useing
2 is there a way to fix it ( it is cast iron )
3 any idea where i can find a part ( i will be calling cummins but i dont have a lot of hope )

on the inside it looks like the part number is 170-3943 but it could be 3843 really hard to tell for sure

i got my fingers crossed

thanks
Dwain
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Old 23-02-2012, 07:32   #4
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Re: Crack Discovered LOL Seriously

might be best identifying the engine make and model first.
a lot of the onan gensets are perkins engines,onan only assemble the complete unit,and buy in the engines.

many of these industrial engines are used in industrial applications like compressors,pumps etc,
the sort of thing you find rusting away in scrap yards.

once you have found a scrap engine go and get the fly wheel of it,most scrap yards will weigh the item and charge the scrap steel price.
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Old 23-02-2012, 07:41   #5
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Re: Crack Discovered LOL Seriously

The risk is significant and damage would be severe if it exploded.

Witnessed a flywheel explosion years ago in a race car. The firewall and most of the floorboard disappeared in a blink of an eye. When the dust settled the drivers foot was uninjured but dangling in an open space large enough to crawl through.

The driver and by-standers were very lucky that day.
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Old 23-02-2012, 07:47   #6
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Re: Crack Discovered LOL Seriously

I had a clutch explode in a car with no scatter shield and got a nice slice in my leg as it exited the car roof. Do not run that engine in that condition...
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Old 23-02-2012, 07:55   #7
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Re: Crack Discovered LOL Seriously

If you have to use it, drill a hole at the end of the crack, otherwise - get a new one!!
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Old 23-02-2012, 08:13   #8
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Re: Crack Discovered LOL Seriously

Dang!! ok i am convinced that i need to try my best to locate another one or possibly have one made i found some places online that advertise they can fix cast using a metal stitch method i will investigate perkins and maybe find some luck there

does anyone know of a place that might have older parts like this? my internet searches so far have not produced very much but i am determined to keep trying i want this thing to work LOL

thank you all for your words of wisdom i will not use it in its current condition
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Old 23-02-2012, 08:16   #9
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Re: Crack Discovered LOL Seriously

Best not to try and repair it, because being a balanced part,,any addition of metal such as the weld itself will throw the balance off.
Phone around any RV repair depots,,as these gensets are typical in a lot of motorhomes. G'luck..

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Originally Posted by BentWheel View Post
Dang!! ok i am convinced that i need to try my best to locate another one or possibly have one made i found some places online that advertise they can fix cast using a metal stitch method i will investigate perkins and maybe find some luck there

does anyone know of a place that might have older parts like this? my internet searches so far have not produced very much but i am determined to keep trying i want this thing to work LOL

thank you all for your words of wisdom i will not use it in its current condition
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Old 23-02-2012, 08:17   #10
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Onan part # 160-1353 flywheel
My list price is $552.01
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Old 23-02-2012, 08:18   #11
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Re: Crack Discovered LOL Seriously

has anybody ever used one of after it was repaired or welded? if so how long did it last? still gonna try to find a new one or have one made....but just in case
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Old 23-02-2012, 08:25   #12
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Re: Crack Discovered LOL Seriously

Even if the repair is possible, the balance issue still trumps anything else,,,dont forget this thing is on the end of the crankshaft,,and its job is to absorb vibration from the crankshaft,,,if for any reason it stops functioning (such as cracking again) and you do not notice it,, it could very well destroy the main bearings,,,this is a small problem compared to the physical injury you will receive if it comes apart,,not to mention the boat.
Getting a used balancer should be easy if you reside in North America.


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Originally Posted by BentWheel View Post
has anybody ever used one of after it was repaired or welded? if so how long did it last? still gonna try to find a new one or have one made....but just in case
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Old 23-02-2012, 09:23   #13
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Re: Crack Discovered LOL Seriously

thanks nemo safety comes first boat second if this thing was a little heavier i could use it for an anchor LOL i found someone parting out a 5.0 majb onan genset i wonder if the fly wheel would fit mine? i will be checking that out too

still stricking out finding a parts source that has that fly wheel but i will keep checking.....

really apreciate the advice i really dont want anyone hurt

Dwain
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Old 23-02-2012, 11:39   #14
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Re: Crack Discovered LOL Seriously

Dwain, your best bet is to make a few phone calls (i.e. to Onan) and see if you can get a good price on a replacement. If there are any machine shops in your area, they can certainly make up a new one but I'd expect it to cost more. (Maybe not, who knows these days?)

The balance of the flywheel is critical to proper engine operation and bearing wear, thus the new one not a repair. And if it was properly designed, it has just enough mass and weight to make the engine turn over smoothly without wasting energy. Since Onan generally have a good reputation, I'd expect the flywheel was designed reasonably well, so an exact replacement, or something very very similar, would again probably be the best way to go.

Now the other side of the question is what cracked the flywheel, and is the rest of the genset (shaft & bearings) OK inside as well? Depending on how inconvenient a complete failure might be, you might want to look into that, or ignore it.
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