Onans always use a little oil. Mine has since new. Others that bought new will agree...
If its noticeably burning it, then maybe your rings havent seated yet if they are new.

 

Compression tests are not very good at indentifying ring that pass oil. The same oil that passes by them also tends to seal them when compression is checked. Did you bore it and replace the pistons when you restored it? If not your new rings are not performing as well as they would have if you had bored it and replaced the pistons.

 

John,

The only engine work I did was to replace the starter. The engine is really strong and I don't mind feeding it oil, I was just wondering what would cause it to use oil. Also, at what point would it be a good idea to do a rebuild? Right now I think it is ok unless it blows up.

But at what compression + oil consumption should I decide to bore and replace the pistons?

Also, what is the typical cost of a rebuild?

This is curiosity right now, but I am preparing myself for the eventual showdown with the wife.

Michael of Winder-Barrow

 

i know it's not a tractor but when i was building my pro street camaro i would wait till the wife wanted to get stuff for the flower gardens all the way around the house than i would say ok if i can get what i need as the car never dies like the flowers

 

Michael,

When does the engine smoke? If it does it going up hills, when you first cut into some heavy grass, accelerate the engine or otherwise put a load on it then the oil is going past the rings. If it just smokes on start up, like a small block chevy often does then valve guides and/or seals would be the problem. From what I have seen on Onans I don't think valve guides/seal can ever really cause much oil consumption because there is not much oil to go there.

Unless

Guy do report excessive oil consumption on the Onans from crankcase breather problems; I am not sure why that occurs, perhaps someone that has experienced it and has it figured out can explain.

As for costs, based on my experience and what others have posted; $500-700 plus another $150-$200 if you want to replace the rods. That includes machine shop work and parts, your labor is extra.

 

Sorry John, but I'm going to question you in this thread. You keep recommending boring and new pistons. Why waste the money if the piston-cylinder clearance is within specs? I have a P218 engine that was using a pint of oil an hour. Smoked constantly. Everything was within specs, so I honed it out and replaced the rings. 9 hours later consisting of lawn mowing and a plow day, it hasn't burned a drop of oil and doesn't smoke at all. Just new rings will go a long way in freshening these engines. And it was only $68 for rings, head gaskets, and shipping. (I'm ashamed of myself, but here goes: I think it was BPHOPE on ebay. GREAT guy - has a lot of new Onan parts, reasonable) If anyone is interested, I can get more info. No connections to him, just a satisfied customer. He has his rings made, they aren't Onan parts. The oil ring is 3 piece like in a car engine instead of 2 piece like Onan's. He said they work really well in used engines. I'm happy so far. I'll be ordering another set here real quick for another engine I have.

Again, sorry John. I just don't think every engine needs to be bored out.

POST EDITED - The guys store is GP HOPE, not BPHOPE like I had earlier. His seller name or id is Garyh989.

Troy

(Message edited by Gunner on October 02, 2008)

 

For current price referance, I just priced .010 under rods, $78 and some change each, .020 over pistons, come with rings as a set, the only way they come, $123 and some change each. When someone else rebuild my B43, they used those 3 piece oil control rings, and screwed up, by either using a homemade ring compressor or being in a hurry, they caught and bent the upper of the 3 rings upwards between the piston and the cylinder wall, scorring the cylinder wall very bad on both sides. So, I am upgrading to a low hour P218 with my flywheel and oil pan. If I can find a place that can put new liners in the B43 block affordably, I will get it rebuilt in the future. I found the cylinder damage would require a .040 overbore to fix the left bore.

 

Troy,

Agreed, all engines don't need to be bored but I am surprised that an engine using that much oil had clearances within specs. Are you measuring the taper and out of round as well as the clearance? Both of these will cause premature wear of the new rings.

Piston ring lands also wear; if the rings have too much clearance to the piston the rings will initially seat well but will wear more than they should since it allows the ring to rock up and down in the ring land.

This is my experience with engines, yours may vary. It really depends a lot on if you are just trying to make it stop smoking for a while or if you want and engine that will give another 2,000 hours of service.

John

 

I have rebuilt a bunch of Onans and have found that for some reason the rings wear out and the cylinders are still within spec. which if you ask me is ok. I would rather just hone the cylinders and install a new set of rings then have to get them bored.

 

John,
Yes, I checked. The taper and out of round were good, ring land clearances and end gap checked, & no ring ridge to be removed. Everything was within specs. Just bad rings. The only reason I started this is because this is the 2nd post in less than a month I've seen you recommending the guy bore his engine or the rebuild isn't going to be any good. A lot of people don't have $500 to $1000 to throw at their engines. And most can get by a lot cheaper and have a very strong engine. I am in no way insulting you, your engine rebuilding skills, or your mechanical knowledge, so please don't take it that way. I just don't think we need to dash someone's hopes of having their engine running with no oil consumption, and will last a long time, without dipping into the grocery money.

Michael - As long as it's running fine, run it until you're embarrassed because you think others can see the cloud of smoke coming from your exhaust.

Or sometime before that happens. I think you're still ok though.

 

I was reading through your posts and I am thinking of repairing my B43. My B43 is actually leaking oil and it was getting worse. The compression is about 85 psi. It did smoke a bit when going up hills, and cutting heavy grass. What should I do? I was going to put new gaskets in and also new rings. But that was about all I was going to do. That is the danger though to only do the minimum when many other things could be done while you have the engine apart. What else should a person really look for and what can be done economically. Any thoughts for my situation would be appreciated.

 

I picked up my 318 not too long ago and it was using about a quart of oil in about 30 minutes I checked the compression and it was good so I was hessitant to think the rings were bad, so I cleaned the carburetor real good and used some seafoam hoping it would help but it didn't help as I thought, so I tore down my engine to replace the rings, the engine only had 350hrs on it when I got it, when I got into the engine I was surprised how much little wear was in the engine and there was no ridge at the top of the cylinder so I ordered some new rings and a gasket set from onan I think it was 298 dollars for everything, I took the block to a small engine shop and had it honed for about 30 dollars, I got the engine back together and running and now it doesn't smoke or use any oil at all, I read on this forum that if the filter is not kept clean the dust and dirt will wear out the rings, just my two cents worth I would look at changing the rings

 

i also picked up an onan (420) with very low hours like blake. i guess it had sat for ten years or so. it smoke like a chimney so i replaced rings and gaskets, had some valve work done and honed the cylinder. ($346.00 for everything.) my inside looked real good also. i do not have enough hours on it yet to tell about oil consumption as i am still in the break in period, but it does not smoke at all. time of course will tell....

 

Check the cooling fins on the engine for clogging. You need to remove the shields in order to access all of the fins. If the fins get clogged with dirt and oily residue, the engine will run on the hot side and use more oil.