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Rebuild Onan 318 engine


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#1 TerryD OFFLINE  

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Posted January 13, 2012 - 02:37 PM

I've ran across a 318 with a knocking Onan - not sure what year yet. I found rebuilt Onan's on ebay for just over $13oo, but I am interested in a winter project and doing the work myself. Just curious what machining and parts would run if I wanted to rebuild this thing myself after it's been sitting for 6 years or so.....worst case scenerio.

Like everyone else, if it can be saved from the scrap yard I'd like to try.

Thanks,

Terry

#2 olcowhand ONLINE  

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Posted January 13, 2012 - 03:18 PM

Worst case scenerio.......$1300. On the brighter side, I've went through them & got by with $200 and had a solid reliable re-rung engine. Been a long time since getting any cranks turned, but I'd say at least $100 to $150, maybe more just to turn all the crank journals. I have a B43G (318'S engine) on my bench now, waiting for me to look into it. I've never had to turn an Onan crank yet, so never put over $300 into a rebuild so far.
Even a non rebuildable engine is worth saving from scrap, as there is always some good parts left in them.
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#3 TerryD OFFLINE  

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Posted January 13, 2012 - 03:25 PM

Thank you. It's been years since I tackled anything like this and with winter here I was toying with the idea of picking it up if the price is right just so I can occupy my time.

#4 TerryD OFFLINE  

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Posted January 13, 2012 - 08:35 PM

Dang, already sold.

#5 olcowhand ONLINE  

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Posted January 13, 2012 - 09:13 PM

Dang, already sold.


Sorry bout that, but there will be more, just be patient.

#6 dgphelps OFFLINE  

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Posted January 14, 2012 - 08:17 PM

I just got a 316 with a P218 that apparently has some ring issues - haven't done a compression test yet...

Other than rings - what would be expected to need checked when rebuilding. There aren't any odd noises and it appears to run fine just blows smoke when increasing throttle speed.

#7 olcowhand ONLINE  

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Posted January 14, 2012 - 08:55 PM

I just got a 316 with a P218 that apparently has some ring issues - haven't done a compression test yet...

Other than rings - what would be expected to need checked when rebuilding. There aren't any odd noises and it appears to run fine just blows smoke when increasing throttle speed.


Check everything! Seriously, you need to check as much as possible. If running still, I like to install a pressure gauge into the port in the oil filter adapter. See how much oil pressure there is at full temps. You need to have 25 to 30psi at full rpm's hot. If not, this means either a worn oil pump, faulty pressure regulator, or worn main &/or cam bearings....or combination of some or all of these. Check crank for up/down play...best to use a dial indicator for accuracy . Onan manuals in our "Manual Section" should give you specs on everything. Oil usage could be just as much from worn valves/guides as it is the rings, sometimes more-so. This is just some of what you need to check. When you get into it, start your own thread & we'll help all we can.
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#8 TerryD OFFLINE  

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Posted January 15, 2012 - 05:58 PM

Hey, good info and good advice. It's always what you don't know that will bite you. Check everything.....twice. Only when you know, will you know that everything is fine.

#9 Deere Green OFFLINE  

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Posted January 16, 2012 - 10:16 AM

make sure to post pics for these guys!!! They were awesome help on my 317 rebuild. Now I have to find time to paint the thing so it looks half as nice as the other tractors on this site.

#10 Lawnguy OFFLINE  

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Posted January 17, 2012 - 12:59 PM

As well when I rebuilt my P218G. Still running strong and no worries :)




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