16 hp Onan valve seats

[Pettybilt 3]

While cleaning the carbon out of  my 16 hp ,i noticed the intake valves would spin even though they was closed. So pulled the valves, then proceeded to pull both intake seats out too.

The engine was running great before i tore it down, I guess i should feel lucky that i caught it before it tore anything up . I miced the seat, and the seat bore, i have .0004 to .0005 clearance. The seats are not egg shaped, neither is the seat bore. The bottom of the seat bore is beat up a little, which explains  why i didn't have but .001 clearance on the intake valve.  

 

 

So my question is, does anyone know how much of a interference i need. Cummins  sells a  .010 over size seat. If i heat up the block and chill down the seat, you think it will go?  I work at a machine shop, just not an engine machine shop. However i can spin grind the new seats down, just don't know how much of a press fit i need. 

 

I appreciate your help.

 

Doug  

 

[Jim_M 178]

If you already have .005 clearance they .010 over seats should fit pretty easily. I would do just as you say, heat the block and throw the seats in the freezer, I'll bet they'll almost fall in.

[sorekiwi 761]

He said he had .0005 clearance Jim, not .005"

 

Sorry I cant help with a number for the fit.  Perhaps try contacting an engine rebuilding shop and ask them for their advice?  And maybe an air cooled engine needs a little more interference than a water cooled engine?

 

Onanparts.com sells even bigger oversize seats as well, maybe they can give you some numbers for the proper fit.  It would be reasonably easy to set up an onan on a Bridgeport to cut the pockets.

 

Years ago I worked in a shop that sometimes fitted new seats in aluminum heads.  I never got involved in the machining, but sometimes helped with the install.  The head was heated in an oven, and the seats were cooled in liquid nitrogen.  We'd do about 4 seats and then return the head to the oven to heat up again for the next 4.

[Jim_M 178]

Oops, looks like it's time for new glasses! In that case I think you'll have to ream the block to get those .010 over seats to fit. All I can tell you is, try it, if it's too tight then ream the block a couple thosandths at a time until you get the right fit.

Edited September 7, 2013 by Jim_M

[Pettybilt 3]

Thanks guy for the the replies.

I was able to find a site where a guy apparently has replaced onan valve seats .He said .006 press is what it needs l..I might call a regular automotive machine shop to see if they can get a seat the right dimensions.

 

 So other than the valve seats flying out, the onans are pretty good engines right?

I've never had any problems with mine, and those onans sound nice under a load.  I would like to get some more hours out of it. 

 

Thanks , Doug 

Edited September 7, 2013 by Pettybilt

[Jim_M 178]

The valve seats seem to be their weakest point and to be honest it's not as common for the 16's to lose a valve seat as it is for the 20's.

[Pettybilt 3]

From what I've read, it's seems that the rears seats give more problems. Both of mine came out. At least I caught it before any major damage

[MalMac 1,328]

Just my opinion, I would not mess with it. Find you a 16 Kohler and be done with it. That way you will get way more life out of your tractor. There have been some members on here that have rebuilt and have had good luck. A lot have rebuilt and have the motor turned right around and do it again. If you look at most of the overall complaints the Onan leads the way by far. Again this is just one persons opinion and it's each to there own.

[Pettybilt 3]

I'm considering a Kohler, finding  one in good shape seems to be the hard part. I would hate to spend the money to fix the onan only to have it let go later. I bought a walk behind to mow the yard cause the onan is like an vacuum sucking everything into the fan. 

 

Maybe i can trade a the walk behind for a good Kohler, now that's a thought. 

[sorekiwi 761]

Since the motor was running well before this problem, then I'd fix it.

 

Since you can do the machine work yourself, its not going to cost you much to fix it.   Cerainly less than what you would have to pay for a 16hp Kohler, and then you don't know how good the Kohler actually is until you fit it.

 

I like the big Kohlers, but I like my Onan as well.  Love the sound of it when its working hard.

Edited September 7, 2013 by sorekiwi

[Pettybilt 3]

They have a nice sound for sure. Incredible power also.  How  does a 16 hp kohler matches up? I would think the Onan would have more torque. 

 

I'll fix the Onan which should be less than $100 for the seats and gaskets. I have the tractor tore apart to repaint, wasn't planning on doing much to the engine. Guess it all going to work out though. Glad i was able to tear it down on my terms.

 

Thanks guy for your input.

 

Doug   

[woodchuckfarmer 333]

I had a engine machine shop do both intake valve seats . It cost me $130 and he guaranteed them never to come out.

[Dieselcowboy 210]

Onans power reefers with thousands of $ of produce on board. They power gen sets that run for days without shutting off. Also running welders on industrial equip. Why because of reliability, especially of the reefer units. Not Kohlers, Or even diesels. I love kohlers a lot too but there is some reason these Onans are on most industrial applications. Fix it right and use it.  

Edited September 8, 2013 by Dieselcowboy

[Pettybilt 3]

I know that a welder application is a lot different that out tractors, but this quote from a guy on a welder forum is impressive!

Maybe after getting it warmed up, keeping around 3/4 throttle would help cooling and carbon build up. I sure most of the 3000 to 4000 hrs on his welders was at full throttle under load. 

 

 

I've had three Miller bobcats with the Onan 16hp engines and sold all of them when they had between 3000 and 4000 hrs on them. never had a major problem with them. that welder has some good life left in it!