The dreaded Onan seat and the fix!

[Greentored 3,220]

Halfway through a chassis up resto on my 91 520H, I yanked the heads to do a decarbon and bet you know exactly what I found. I had a speed shop for awhile and still have some equipment, I have already fabbed up adapters and will be cutting in oversized seats right on the tractor and thought this may be of interest to some. Sometimes its not how we get there, its knowing what the end result needs to be and finding a way to do it.

On another note, this 1308 hour, obviously poorly maintained P220G engine was otherwise pretty impressive! Bores are beautiful, guides are tight, valve adjustments were within a few thousandths (aside from the zero lash rear intake, indicating the seat issue).

Note #3- As an experiment, I warmed this engine to operating temp, ran it up to 2200rpms, and trickled half a bottle of seafoam right down the throat, shut it down, let it sit 30min, and did it again til the bottle was empty, then ran the hell out of it for 15 minutes. Look at the carbon in the pic, or lack thereof! No I cant conclude the seafoam did this as I do not know the maintenance history or 'before' carbon, but judging by the rest of the tractor, I highly doubt the heads have ever been off it. Anyone else ever tried this?

[WHX?? 50,862]

I guess it can't hurt to try your seafoam experiment. 

Be careful about advertising your seat repair... you might come home to find a dozen blocks needing it on your steps! 

[lynnmor 7,617]

How much press are you going to use to retain the seat?  I was able to use a .010" oversize Onan seat by boring a very small amount on a Bridgeport milling machine and leaving .0055" press.  Of course the block was not worn much.  I warmed the block for about an hour with a heat gun while the seat cooled in dry ice. Using this method and working very fast the seat will go in with very little persuasion.  If you hesitate for more than a couple of seconds, the block will shrink while the seat grows.  I made tools to stake a bit of metal around the seat for additional retention rather than using a prick punch, Onan made such a tool.

 

The carbon looks about the same as any Onan that still runs well, I never use Seafoam.

[Greentored 3,220]

3 hours ago, WHX24 said:

I guess it can't hurt to try your seafoam experiment. 

Be careful about advertising your seat repair... you might come home to find a dozen blocks needing it on your steps! 

I thought about that before posting, then thought 'hell, if this works, bring em on! Its a nice 'side gig' and gets me away from the same old car crap

[Greentored 3,220]

3 hours ago, lynnmor said:

How much press are you going to use to retain the seat?  I was able to use a .010" oversize Onan seat by boring a very small amount on a Bridgeport milling machine and leaving .0055" press.  Of course the block was not worn much.  I warmed the block for about an hour with a heat gun while the seat cooled in dry ice. Using this method and working very fast the seat will go in with very little persuasion.  If you hesitate for more than a couple of seconds, the block will shrink while the seat grows.  I made tools to stake a bit of metal around the seat for additional retention rather than using a prick punch, Onan made such a tool.

 

The carbon looks about the same as any Onan that still runs well, I never use Seafoam.

Ive always used .008-.010 on aluminum heads and .006-.007 on iron and havent lost one yet, so shooting for the same. Believe it or not, always made my cuts, tossed the seats in a cup of ice water, centered them up and knocked em in. The key was to not have ANY sort of rough edge on the seat chamfer, and Id make a VERY light chamfer cut on the head as well, and knock any edge off with a scotch brite. Kinda dig your idea and may throw some heat on the block to facilitate things a bit.

 I lucked out as well, the seat did 'sink' about .020 but the bore measures .001 larger than the seat. If I were patient I believe a +.010 Onan seat would be just fine and save some hassle.

I nicked a seat on a set of Harley heads once while porting and needed to replace. I froze the seat, tossed the head in the gas grill at 300, and the seat literally fell in- that was at .010 interference at room temp. Still amazing how much materials 'grow'.

[PeacemakerJack 10,743]

Thanks for the great post...I’ll be following along on this one be for sure.  Have you posted the story behind your avatar name?  I’d like to hear it if you haven’t...sound like a “real page turner”

[squonk 42,777]

Seafoam works as advertised.I know there are guys around who cry "Snake oil" but this stuff works! 

[Greentored 3,220]

4 hours ago, PeacemakerJack said:

Thanks for the great post...I’ll be following along on this one be for sure.  Have you posted the story behind your avatar name?  I’d like to hear it if you haven’t...sound like a “real page turner”

Came from a family of Deere, 3 generations, at least 90% anyhow. Being the black sheep I had to be different and those reds always caught my eye. Tell ya what, as new as I am to all this, there’s still no doubt these Horses are simple, no frills machines and built like a tank! Couldnt be happier with the switch! 

[Greentored 3,220]

New seat installed, refaced the valves at 44 degrees per the book, stoned the seats at 45, and she’s back up and running! This procedure worked very well but as I’ve seen before, the aluminum on these small engines (and import vehicles/some fords) is apparently of different quality and tends to almost smear versus a nice clean cut. It hasn’t presented a problem in the past and hopefully doesn’t here either. Set up for at .010 press, then heated the block, froze the seat, and drove it home. 

Coming from a lifetime of hotrodding, the sharp edges in the ports drove me nuts, so it got a quick port touch up, mainly in the exhaust short turns. More concerned with efficiency and perhaps a touch cooler running than power increases. 

Has anyone ever hopped up one of these Onans? 

Edited January 2, 2020 by Greentored

[WHX?? 50,862]

1 hour ago, Greentored said:

ever hopped up one of these Onans

Not that I have heard of Green... power is God awful enough stock! Long as it's this far I wouldn't be beyond a little porting and polishing just to smooth things out tho. 

What are your thoughts on using the green "ain't never coming out" locktite on the seats?

Just to throw it out there we use liquid refrigerant to ice down things with  bearings on Harley cranks... propane works in a pinch but 

Edited January 2, 2020 by WHX24

[WHX?? 50,862]

On 12/31/2019 at 1:20 PM, Greentored said:

I thought about that before posting, then thought 'hell, if this works, bring em on! Its a nice 'side gig' and gets me away from the same old car crap

Lol ..you sound exactly like my guy who does my Kohler blocks! Gets him away from complicated race motors, does it for fun and says cash is king! 

[Greentored 3,220]

8 hours ago, WHX24 said:

Lol ..you sound exactly like my guy who does my Kohler blocks! Gets him away from complicated race motors, does it for fun and says cash is king! 

Hit the nail squarely on the head!

[tom2p 2,394]

when I repower I'm going with a Kistler 410

 

 

[Greentored 3,220]

19 hours ago, WHX24 said:

Not that I have heard of Green... power is God awful enough stock! Long as it's this far I wouldn't be beyond a little porting and polishing just to smooth things out tho. 

What are your thoughts on using the green "ain't never coming out" locktite on the seats?

Just to throw it out there we use liquid refrigerant to ice down things with  bearings on Harley cranks... propane works in a pinch but 

 

I actually use loctite green on every seat ever done, including this one. Can’t believe it would stay there especially on the exhaust side, but it sure can’t hurt. I do it more to lubricate things a bit.