Onan P220 Decarbon - replace rings and/or hone ?

[seuadr 489]

Hi all,

 

been thinking about my new to me 520H - it has a nebulous maintenance history, so i am thinking i'd gonna do a decarbon partially because it is a good idea, partially because i plan on checking the valve adjustment at the same time and partially because i wanna see if anything looks amiss on the inside.

 

the motor has 748 hours on it currently.

 

logically - would it make sense to hone the cylinder and put new rings in while i am in there?

 

it burns oil - a pretty fair amount. i'd say i'm adding around a pint per tank of gas, possibly more. my initial guess, if this were a motorcycle motor would be either rings or valve stem seals. It smokes when you start it up for a moment, which would seem to suggest that it is possibly valve stems leaking when the motor isn't running, but it also smokes when you run the throttle from low to high.

 

it may not be needed - but is there any harm to be done by giving it a (very) light hone and new rings?

 

seems like, if i am going to be in there anyhow..

 

thoughts?

 

[Fordiesel69 271]

Decarboning and valve work is much different than a complete tear down.  I would start with the decarbon and check for valve guide wear.  Also verfiy the breather is working correctly.  Other than that, these are EXPENSIVE to overhaul, and the parts you will need are going to be costly.

[seuadr 489]

Decarboning and valve work is much different than a complete tear down.  I would start with the decarbon and check for valve guide wear.  Also verfiy the breather is working correctly.  Other than that, these are EXPENSIVE to overhaul, and the parts you will need are going to be costly.

forgive me if this is a stupid question, but can't you just separate the rods from the crank without pulling the crank and just replace the rings with stock sized rings and deglaze the cylinder while you are at it?

[Fordiesel69 271]

Yes, but you still need to take quite a bit of the engine apart.  Repalcement parts are not cheap.

[seuadr 489]

Yes, but you still need to take quite a bit of the engine apart.  Repalcement parts are not cheap.

fair enough - but the rings are only another 40 dollars on top of what i'd be spending on gaskets and valve stem seals, etc to do it, seems worth the small expense while i am in there anyhow.

[Martin 2,133]

Have you priced a gasket set or individual gaskets yet? You will also need a crank gear puller if you have to take off the timing cover.

If you take it down far enough to do rings properly and don't ignore other issues that will come up, I would be very surprised if you don't throw at least $200 at a rock bottom bare minimum. These are tight tolerance engines and they will bite you in the end if you overlook worn items, not as forgiving as a cast iron single kohler.........

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Edited May 20, 2014 by Martin

[seuadr 489]

Have you priced a gasket set or individual gaskets yet? You will also need a crank gear puller if you have to take off the timing cover.

If you take it down far enough to do rings properly and don't ignore other issues that will come up, I would be very surprised if you don't throw at least $200 at a rock bottom bare minimum. These are tight tolerance engines and they will bite you in the end if you overlook worn items, not as forgiving as a cast iron single kohler.........

Sent from my iPhone using Tapatalk

ya, i'm at 104 dollars for rings, valve stem seals and gasket kit for the decarbon. weighing my options, really. No nibbles on my N52M for buyers, but a couple nibbles from people selling the bits i need. of course, no one close that i can just go compare parts at - so my train of thought is, the decarbon needs to happen anyhow sooner or later (and who knows if it has ever been done, so why not now) so how does that figure, cost wise, to buying a "big block" onan for the exterior parts. I've priced them all out seperately - that'd be somewhere in the area of 500 dollars, used.

 

Possibly i'm over-thinking it, but i'm burning more oil than i was, and i have a real or imagined knock so i kind of feel like it is pushing my hand in regards to what i'm going to do for a motor.

 

what other wear issues should i consider? 

[shorts 182]

Just do the top end service-decarbon and valve adjustment, and don't open up an expensive can of worms by opening up the crankcase like Martin said.  All of the vintage air cooled engines burn some oil think of it as lube for the rings and valve guides.  you can add lots of oil for the $200 in consumable parts that it will take if you open up the bottom end of the engine and you will still probably need to add oil at a regular interval

[seuadr 489]

thanks for all the responses guys, just trying to do the best job that i can while i've got the motor off once. what are some of the additional things i'd need to replace if i opened up the bottom end? (i've never done any work on motors besides simple stuff like valves ,etc.)

[Desko 623]

My dads saying is do it right the first time so you don't have to do it again to re ring it all you need to do is just take the oil pan off and pull the rods and pistons just watch when you hone it you don't hit the crank because the drill is going to talk back but its more simple than you think I've been building an onan p220 from the ground up no manuals just common sense there pretty self explanatory. Not arguing with anyone here but that's just my 0.02 cents

[Wh416H 24]

I would go all the way if you are burning oil Do it right or don't do it at all

[seuadr 489]

thanks for the responses, people.

 

I am still possibly getting parts for the N52M that may turn into a re-power project, but if i don't, i think i will tear this down in the fall and do it up before snow-blowing season.

[546cowboy 302]

Like everyone says parts for Onan's are very pricey. I bought a 520H from a guy once and he said it used oil but he didn't know how much. He said it was at his mother's house and he didn't use it. Well I bought it and it did smoke some and you had to put oil in it every time you used it but I mowed with it for a year or more before I found another engine to put in it.

You say there may be a noise in the engine? Any knock in that Onan means a rod is fixing to let go and cannot be ignored. That's when it gets expensive. It has been several years since I checked but s I recall rods were about $90 ea., pistons w/rings $120 ea., complete gasket set was something over $200 and then if you have to have the crank turned you add that cost. But you will have essentially a new engine. There is only one place to get new parts and that is from Cummins/Onan.

There is someone who did one on here a year or so ago and posted his progress on the site. He is from Michigan too. He called it his "Super Snow Chucker" as I recall. Contact him and see what it cost.

Once you open that engine up be prepared to spend the money because that is what it will take and a repower with a Honda will be close to $2000.

Edited May 30, 2014 by 546cowboy

[seuadr 489]

Like everyone says parts for Onan's are very pricey. I bought a 520H from a guy once and he said it used oil but he didn't know how much. He said it was at his mother's house and he didn't use it. Well I bought it and it did smoke some and you had to put oil in it every time you used it but I mowed with it for a year or more before I found another engine to put in it.

You say there may be a noise in the engine? Any knock in that Onan means a rod is fixing to let go and cannot be ignored. That's when it gets expensive. It has been several years since I checked but s I recall rods were about $90 ea., pistons w/rings $120 ea., complete gasket set was something over $200 and then if you have to have the crank turned you add that cost. But you will have essentially a new engine. There is only one place to get new parts and that is from Cummins/Onan.

There is someone who did one on here a year or so ago and posted his progress on the site. He is from Michigan too. He called it his "Super Snow Chucker" as I recall. Contact him and see what it cost.

Once you open that engine up be prepared to spend the money because that is what it will take and a repower with a Honda will be close to $2000.

thanks for the insight. i'd rather know and have to spend the money while it is still technically a runner than have it catastrophically fail so if i go that route, i will definitely tear it down. hopefully my N52M re-power works out and then I've got the time to leisurely decide what i want to do.