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318 Onan P218 - Rebuild or Repower?


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109 replies to this topic

#31 JDBrian OFFLINE  

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Posted October 06, 2011 - 03:48 PM

This is an interesting thread. Thanks for posting the photos.
  • Toolpartzman said thank you

#32 shredwad OFFLINE  

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Posted October 07, 2011 - 12:58 PM

I'm glad I found this thread...someday I will face the same issue when my Onan dies!

#33 Lawnguy OFFLINE  

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Posted October 08, 2011 - 02:18 PM

Thanks for all the encouragement everyone :smile1: I've never rebuilt a motor before, so this is all new, scary, & fun at the same time! Hopefully I won't screw this up...lol Okay, today I checked the pistons. Wanted to find out what spec engine I had first because it matters when it comes to buying rings. Looking at the last letter in (pic 1) you can see I have spec A. There's a couple ways of measuring pistons and ring gap. The manual say's the top & middle compression groove needs to be within .08 to .081. Bottom oil ring has to be .188 to .189 After measuring the first piston, I was right at borderline on the top ring (.081) and right on for the middle and bottom groove. Now for the bad news, the second piston which I think was the one burning oil was out :wallbanging: Picture 2 shows I was at .085 and at one point upto .087 If you measure with the ring installed and use a feeler gauge, your max tolerance can be no more then .008 Sure enough I was over that as well measuring .011

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#34 olcowhand OFFLINE  

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Posted October 08, 2011 - 02:21 PM

And you are using one fine brand dial caliper to boot. Looks like new piston time! No aftermarket parts for these things either, but then you'd really rather have OEM anyway.

#35 Lawnguy OFFLINE  

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Posted October 10, 2011 - 05:46 PM

Not much going on tonight. Watching the grandkids ride the golfcart around the yard (they love that). weather is nice (mid 70's). I'm waiting on parts so thought I'd get into parts cleaning mode. Working on the heads tonight, did a quick clean on my bench grinder wire wheel to hit the big stuff and used my dremmel tool for the rest. I tried a new emery cloth type attachment for $10 bucks and it accualy worked pretty well. didn't wear out as fast as those little wire wheel attachments. My buddy with the dial gauge wasn't at work today, so couldn't measure the cylinder bores. If they spec out okay, I've got another friend that has a hone and said he'd clean them up for me. Nobody seen the budweiser in the pic right? lol

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#36 Tennblue59 OFFLINE  

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Posted October 12, 2011 - 09:44 AM

While you have the pistons out, measure the cylinder bores. Measure at right angles with/against the piston pin. Measure 1/2 " down from the top, mid bore and at bottom of stroke. You are looking for eliptical (egg shaped) bore. If too far out of specs, you will still burn oil, even with new rings/pistons - and your rings won't seal well.

Congratulations on doing this yourself! Engine work isn't difficult - actually pretty straight forward, you just need to keep things clean and pay attention to details. And by doing as much of it yourself, you save a ton of money on the process. Plus its kind of neat, once you get it back and running to realize "you did this"!

#37 Lawnguy OFFLINE  

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Posted October 14, 2011 - 05:46 PM

Measured the cylinder bores tonight. Spec's say 3.249 to 3.250 with wear tolerance of 3.255, also measured the taper (top of piston ring travel to bottom of ring travel) tolerance of no more than .005 I took four measurements horizontal & vertical about a 1/2' in from the top, and right at the bottom (still on the shinny side). as you can tell from pic number 1 & 2 I was using a "T" type gauge set. Its tricky (took several measurements) but think I'm close. I was real happy that I saw a max of .005 difference between the top and bottom, and not one dimension went over 3.251 Looks like I'll be able to poceed with de-glazing the cylinders now :)

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#38 Lawnguy OFFLINE  

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Posted October 14, 2011 - 05:57 PM

Wanted to mention a great deal I got today on ebay! I hadn't browsed in a few days, and I just happen to log in and find an ad with about one hour left to go! It was advertised as a valve set for a linkcon or Miller Welder, but it included both intake & exhaust valves, intake and exhaust valve guides, and both intake and exhaust valve guide seats. All the part numbers in the ad matched. Parts came out to $281 retail on an Onan parts site, but I won it for $42.50 with free shipping :) Pic below is the pic from the ad. It was advertised as new so I'm geeked :)

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#39 olcowhand OFFLINE  

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Posted October 14, 2011 - 06:51 PM

Wanted to mention a great deal I got today on ebay! I hadn't browsed in a few days, and I just happen to log in and find an ad with about one hour left to go! It was advertised as a valve set for a linkcon or Miller Welder, but it included both intake & exhaust valves, intake and exhaust valve guides, and both intake and exhaust valve guide seats. All the part numbers in the ad matched. Parts came out to $281 retail on an Onan parts site, but I won it for $42.50 with free shipping :) Pic below is the pic from the ad. It was advertised as new so I'm geeked :)


You fell right into one super deal there!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

#40 Lawnguy OFFLINE  

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Posted October 14, 2011 - 10:54 PM

My friend Tim came over honed the cylinders out tonight. I watched him do it and it wasn't as technical as I thought it would be. sprayed some WD40 and he ran the drill in and out maybe a dozen times, wiped the cylinder down and checked for high spots. He did this about 3 times and said we were all good. there was one little high spot, but he said it was nothing to worry about (taking his word on this). we took a rag and covered the crank to protect it. Cost me a few beers, but hey, what are friends for...lol

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#41 olcowhand OFFLINE  

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Posted October 15, 2011 - 03:31 PM

Hope he got a good cross-hatch pattern on the final run. Should have been a fairly slow spin, with fast in-out action.

#42 Lawnguy OFFLINE  

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Posted October 16, 2011 - 10:12 AM

Good call Cowhand, Looking at the cylinders there is a little cross hatching, but no where near 45 degs. Tim left the hone here because depending on how long it takes before I put the pistons back in, I may need to touch it up again. Will make sure I take your advise from above before I reassemble. I should have most of the parts this week. I still need to order piston rings 113-0314 (standard) or 113-0314-05 (.005 over), so if anyone out there has a couple sets for sale, or can point me to a place for a good price I'd appreciate it. As soon as I get the new valves I'm going to learn how to lap them this week, so stay tuned for that!

#43 olcowhand OFFLINE  

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Posted October 16, 2011 - 11:33 AM

My manual calls for anywhere between 30 & 40 degree crosshatch, but 45 is fine too.

#44 Lawnguy OFFLINE  

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Posted October 27, 2011 - 08:41 AM

Installed the new valve guides last night. I stopped over to hardware store and bought a 1/4-20 x 12" threaded rod, and then on over to the auto parts place for a new can of WD-40. I rumaged up some washers that were wide enough to lay across the valve openings without damaging them. I held the guide up square and ran the rod thru it, and then finger tightend it in place. I also threaded on two extra jam nuts, because you need them to keep the rod from turning as your tightening the other nut. I sprayed the WD40 on the guide and also inside the guide bore before I started tightning. Oh, I also made sure the bore was clean and clear of any debris as well. Everything worked smooth until I got the guide a little more than halfway in. I could feel the nut wanting to strip, and on one occasion it did strip. I had to readjust the rod to gain good threads again. I don't know if it was just a cheap rod or nut? Or maybe WD40 wasn't the best lubricant to use? I eventualy did get the guides seated though. There may be some better ways of doing this, but this was the only thing I could think of and it did work.

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#45 KennyP ONLINE  

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Posted October 27, 2011 - 08:52 AM

I haven't checked on this thread as you have a different model engine than mine. But the pics and all help to understand these a lot better. I'm glad things are going well with the rebuild. Thanks for the updates. I'll follow a bit more closely, now.




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