Oman another onan

[Desko 608]

Well I picked up a 520 with 640hrs as a non runner and upon putting a battery in it and cranking it it was obvious it didn't have compression on one cylinder. So I went straight to thinking a typical valve seat.... WRONG rear cylinder had compression so I checked the front cylinder and found that it was at fault. No movement from the piston at all so follow along for the rebuild. Unfortunately Cummins/onan has discontinued the connecting rods for the 18-20hp onans but still produce the 16hp rods which is beyond me why but probably not enough market anymore for them. But first let's get this boat anchor out! 

[Desko 608]

Well it's out and on the bench. The rear cylinder looks okay for the most part but depending on how the bottom end looks it is going to need punched over not much cross hatching left. 

[Pullstart 62,843]

Oman is right!

[lynnmor 7,305]

Cross hatching goes away over time, all that matters is an accurate measurement.  Opening the bottom will reveal the extent of the damage.

[Desko 608]

Thats true and I will check it before deciding. Surprisingly enough it's not all scored up so a hone and new rings might just do it. But bottom end is opened up and there's not much rod left not really any chunks aside from the crank journal end just mostly flakes and shards. The crank looks a little worse for wear but I'll clean it up and check it if not I have a good in spec on on the shelf. No major damage to the block itself other then a gouge in no mans land when the rod bolt hit it and it also took out the oil feed line which is still available so no big deal. If worse comes to worse I do have a spare block though for just such an occasion. 

[lynnmor 7,305]

I’m sure that you know that the oil line looks like a wreck when it is new.

[Streetrodchev 798]

Who do you use for Onan parts?

 

I use Boomer. 

[Desko 608]

1 hour ago, lynnmor said:

I’m sure that you know that the oil line looks like a wreck when it is new.

Sure do lol 

 

16 minutes ago, Streetrodchev said:

Who do you use for Onan parts?

 

I use Boomer. 

I go wherever I can get them most of the time. Usually I've ordered them straight from cummins though 

[lynnmor 7,305]

I have purchased parts from onanparts.com, Boomer, Cummins and Colburn Power Systems.  Apparently Colburn went belly up, onanparts has a much smaller selection and Cummins has discontinued a lot of parts, Boomer tries to get good used and new parts as they become available.  .

[Desko 608]

Yea it's unfortunate that the parts are getting harder and harder to get. I always try to keep a spare of everything on hand just incase. Little red barn has a pretty good overall kit for them with pistons, valves, guides (I dont think they come with the kit) and gaskets but that's it for them. I'm remaining hopeful someone will start making rods and bearings (I think you can still get them yet?) for them since Cummins seems to be dropping whatever they can for them. I know isavetractors was supposed to be getting a kit made up for them also but haven't heard anything about it in awhile. 

[Bill D 1,920]

31 minutes ago, Desko said:

Yea it's unfortunate that the parts are getting harder and harder to get. I always try to keep a spare of everything on hand just incase. Little red barn has a pretty good overall kit for them with pistons, valves, guides (I dont think they come with the kit) and gaskets but that's it for them. I'm remaining hopeful someone will start making rods and bearings (I think you can still get them yet?) for them since Cummins seems to be dropping whatever they can for them. I know isavetractors was supposed to be getting a kit made up for them also but haven't heard anything about it in awhile. 

Contact Zach Kerber Machine about making some rods for you.  Billet aluminum would be much stronger.

[Desko 608]

1 hour ago, Bill D said:

Contact Zach Kerber Machine about making some rods for you.  Billet aluminum would be much stronger.

Fortunately I found a good set of used rods and matching crank on ebay but I will look into it! Maybe we could at least get a supply on the market because I'm sure this won't be the last onan to spit a rod. There's more pictures to come but I think I figured out why this particular one decided to take itself out. 

[Desko 608]

Onto the mystery this engine had two miss matched pistons one oe and one aftermarket. Being this engine wasn't low on oil my theory is due to the noticeable weight differences between the two it just ripped the one rod apart because of the imbalance or they assembled the rod wrong. The next question is even though there'll never be a true answer is why did they decide to change a piston in it. 

[RED-Z06 2,221]

How's the governor spacer look...when they take off for the moon its a dice roll

[Desko 608]

48 minutes ago, RED-Z06 said:

How's the governor spacer look...when they take off for the moon its a dice roll

Unfortunately I haven't gotten it tore down that far yet. Had to go out of town for grove/manitowoc training. 

[Desko 608]

Well got home today to some goodies my new crank and rod set showed up. It had some light surface rust that I just cleaned off but might chuck it in the lathe and polish it up better. While my mic set is at work I figured I'd check it with some plasti gauge to get a rough idea where it's at and it comes it right at .002 which is subject to small variations. The book calls for .002 min and .0033 max so it's looking like it should be fine. I decided to go with my spare block for a couple reasons but it will need punched .020 over due to previous water damage and thanks to onanparts I got a new set of pistons for less then aftermarket! Eager to hear this 520 sing with the 60"! 

[Desko 608]

We're back onto the onan! Engine is back from the machine shop with fresh .020 bores so it's ready for some reassembly! I got to checking out parts and had this feeling to check out the fly ball spacer and low and behold it was loose from the adhesive breaking down. No worries though I cleaned it up all good and got out the sleeve retainer and reinstalled with the key back in the center of the notch worth a shot at least vs spending $120 for the metal one and doing essentially the same thing. 

[RED-Z06 2,221]

14 minutes ago, Desko said:

We're back onto the onan! Engine is back from the machine shop with fresh .020 bores so it's ready for some reassembly! I got to checking out parts and had this feeling to check out the fly ball spacer and low and behold it was loose from the adhesive breaking down. No worries though I cleaned it up all good and got out the sleeve retainer and reinstalled with the key back in the center of the notch worth a shot at least vs spending $120 for the metal one and doing essentially the same thing. 

I think ive been paying around 75 shipped for my steel ones

[Desko 608]

10 hours ago, RED-Z06 said:

I think ive been paying around 75 shipped for my steel ones

That wouldn't be bad. I did a quick google search on them and the first couple that came up were about $120 along with the steel ones from the B series for $100 or less. 

[Desko 608]

Not much to report aside from its all back together. Gotta say it's definitely worth it ol girl runs like a champ and the 60" is a beast! I might have to do a carb clean and such though thought I could get away with not but it has a slight hunt down low but all in all couldn't be happier! 

[RED-Z06 2,221]

13 minutes ago, Desko said:

Not much to report aside from its all back together. Gotta say it's definitely worth it ol girl runs like a champ and the 60" is a beast! I might have to do a carb clean and such though thought I could get away with not but it has a slight hunt down low but all in all couldn't be happier! 

Back the needle out a quarter turn up front down low on the carb, see if it settles the idle 

[Handy Don 12,217]

On 5/12/2023 at 9:56 PM, RED-Z06 said:

Back the needle out a quarter turn up front down low on the carb, see if it settles the idle 

That may also help when you bump the throttle. 

Coming from mostly B&S and Tecumseh, I always tuned a bit on the lean side. My P218 likes it a tad richer (and yes, all those extra horses do slurp the fuel!)

The Kohlers I’ve touched seem to like it in the middle!

[Desko 608]

On 5/12/2023 at 9:56 PM, RED-Z06 said:

Back the needle out a quarter turn up front down low on the carb, see if it settles the idle 

I would but it's the good old accelerator pump emissions type carb so no adjustments to be made. It also get a hunt up high when it's not under load. 

[RED-Z06 2,221]

17 minutes ago, Desko said:

I would but it's the good old accelerator pump emissions type carb so no adjustments to be made. It also get a hunt up high when it's not under load. 

Oh man...i hate those things.  I fought mine for a couple months, tossed on an adjustable style and it purrs

[Desko 608]

19 hours ago, RED-Z06 said:

Oh man...i hate those things.  I fought mine for a couple months, tossed on an adjustable style and it purrs

As do I. My 416h has the good ol adjustable style and it never gives an ounce of trouble. I will try cleaning it out and giving it a fresh set of gaskets and seals and see what it does but if it continues I'll have to dig into my parts stash and throw an adjustable one on it.