Lets brainstorm this Onan problem.

[RED-Z06 2,365]

Got this engine, a P220G, 870hrs, no smoke or knocks.  When i got it, it had uneven power between cylinders, right/rear cylinder being dead.  Compression was low.  Intake valve was quite hung open on 0 lash so i lashed it to spec...ran it about 2 hours with no problems...then noted spitback and hard starting, low comp again.  0 lash.

 

Pulled the heads, new gaskets, checked all 4 seats for any signs of failure and found none.  After relashing i had 115/120 Compression...and ran perfect.  For about 2 hours 

 

Now...im running out if lifter adjustment.  Seat doesn't appear to be hammering in...and I didn't see any signs of valve stretch.

 

Im going to have to pull the valve and grind it to get some adjustment back...but, ive never seen this

[WHX?? 49,652]

Tappet/cam issues is the first thing that comes to mind. Any chance the lash adjuster walking? 

[RED-Z06 2,365]

1 minute ago, WHX?? said:

Tappet/cam issues is the first thing that comes to mind. Any chance the lash adjuster walking? 

The adjuster is almost all the way in now, ot would have to walk out..i was hoping thats all it was but, doesn't appear to be.

[lynnmor 7,448]

Remove the spark plugs.

Turn the engine by hand till a valve opens the maximum amount.

Turn the engine one full turn.

Adjust that valve.

Do the same for each of the other three.

[RED-Z06 2,365]

Well...problem solved, its the seat...i guess the last time i messed with it; it wasnt bad enough, its bad enough now.  The seat moves independently of the block, but somehow still seals.

[WHX?? 49,652]

If the block isn't hammered too bad can you stake it back in.? Help of some green loctite maybe? 

[RED-Z06 2,365]

Seat measures 1.443"

Pocket is beat out to 1.460

 

Not even a +.010 seat will work

[WHX?? 49,652]

Crap... just out of curiosity was this in a 520? 

[lynnmor 7,448]

28 minutes ago, RED-Z06 said:

Seat measures 1.443"

Pocket is beat out to 1.460

 

Not even a +.010 seat will work

@onanparts.com sells blanks that need to be machined.  Also, a good automotive machine shop can make seats to fit and install them.  Do not depend on peening or adhesives, they need a very tight press fit, about .0050"

[RED-Z06 2,365]

1 minute ago, lynnmor said:

@onanparts.com sells blanks that need to be machined.  Also, a good automotive machine shop can make seats to fit and install them.  Do not depend on peening or adhesives, they need a very tight press fit, about .0050"

Yeah ive never liked staking/peening seats in myself 

[lynnmor 7,448]

2 hours ago, RED-Z06 said:

Yeah ive never liked staking/peening seats in myself 

Since Onan says to peen and they actually have a bit of metal upset into a small chamfer, I made a custom tool to do that.  Kind of a belt and suspenders thing.  I guess that a valve seat with a very tight press still may move if the engine is overheated enough, and that movement would be the beginning of the end.

 

I ran the numbers some time ago to see what the coefficients of expansion for the aluminum block versus the steel seat might be, and even .0060” press may be barely enough under extreme heat conditions.  I have read recommendations from .0045” to .0060” for a press, I chose to use .0055” as the target.  At that figure, heating the block with a heat gun for more than an hour and then quickly transferring the seat from a denatured alcohol and dry ice bath using a holder that is also cooled, it can easily be tapped in, if done quickly.  And I do mean quickly because the seat grows and the hole shrinks as soon as they touch.

[RED-Z06 2,365]

So...there is nothing so dangerous as a bored mechanic with a problem and a welder.  I made a jig to hold the seat centered and spin it slowly as well as support its shape.  Then setup my welder to 90amps, low wire feed, spun the seat about 45rpm...and grounded it, then in 6 bursts, built up the circumference, then while still held centered, ground away the excess to a smooth layer of weld that measured 1.461".

 

I cleaned the pocket with acetone, lightly heated the block, cooled the seat, put a bit of green holding compound on and it took 12 hits with a 2lb sledge and seat driver to seat it...its a snug fit.

 

I slid the valve in with the lash cap and it has some lash..i did build up some of the back of the seat so that helped.

 

Its absolutely a rigged fix at best...but thus far no local shops would help, they just work on motorcycle engines, power sports, and automotive engines.  If it works great, if not...thats fine too, was worth trying something different.

Edited March 9, 2022 by RED-Z06

[danweikert21 166]

does it have automatic compression release that would be my next step find that out if it does it could not be working right 

[953 nut 56,518]

Just now, danweikert21 said:

does it have automatic compression release that would be my next step find that out if it does it could not be working right 

Onan and Kohler twin cylinder engines did not have ACR.

[RED-Z06 2,365]

Runs.. runs way better, but still only 50psi on the right side, so its still hurt.

 

Guess ill have to suck it up, pull the engine, tear it down and beg a machine shop to put in a 1.500 seat

[Snoopy11 5,717]

Might consider buying a block. Various P220 blocks available on the web. Might be cheaper than a machine shop's work nowadays...

 

 

 

https://www.ebay.com/itm/384637863843?hash=item598e3407a3:g:1~0AAOSwC0Fhydqy

 

Don

 

 

[RED-Z06 2,365]

2 hours ago, Snoopy11 said:

Might consider buying a block. Various P220 blocks available on the web. Might be cheaper than a machine shop's work nowadays...

 

 

 

https://www.ebay.com/itm/384637863843?hash=item598e3407a3:g:1~0AAOSwC0Fhydqy

 

Don

 

 

Still doesnt fix the underlying seat problem.  Id love to find a P224G but adapting it...not sure.  For now, its out and im looking for a machine shop.

[Jeff-C175 7,203]

56 minutes ago, RED-Z06 said:

looking for a machine shop.

 

Good luck with that!  I've been looking for one here in NJ for quite some time now... nada.

 

 

[lynnmor 7,448]

2 hours ago, RED-Z06 said:

Still doesnt fix the underlying seat problem.  Id love to find a P224G but adapting it...not sure.  For now, its out and im looking for a machine shop.

 

If the replacement block is in good condition, how would it not fix the seat problem?

 

Of course the replacement block would need to be checked carefully and the cylinders should be honed so new rings seat properly.

 

Our local NAPA has a machine shop and did replace valve seats, I guess they still do.

[RED-Z06 2,365]

Just now, lynnmor said:

 

If the replacement block is in good condition, how would it not fix the seat problem?

 

Of course the replacement block would need to be checked carefully and the cylinders should be honed so new rings seat properly.

 

Our local NAPA has a machine shop and did replace valve seats, I guess they still do.

Because Onan 220s eat seats, if this one hasnt been "fixed" and still has the stock seats, its just a matter of time.  Been doing a ton of reading and the only conclusion i can come to is, the factory fit was just too loose, the seat to block tolerance, being too loose.  I found an old post in another forum where a guy bought a new old stock in the box wrapped in plastic short Block after his 220 ate both seats, he tore the valves out of the new engine and put a seat puller on the seats to see how tight they were, and was able to pull both seats out with very little effort, a couple taps with a slide hammer..compared to what should have been a tight interference fit.  

 

I found a local shop willing to at least take a look at it, im taking it in tomorrow hopefully.

[RED-Z06 2,365]

1 hour ago, Jeff-C175 said:

 

Good luck with that!  I've been looking for one here in NJ for quite some time now... nada.

 

 

Found a shop willing to hear me out, and willing to at least look at it.

[WHX?? 49,652]

17 minutes ago, RED-Z06 said:

Because Onan 220s eat seats, if this one hasnt been "fixed" and still has the stock seats, its just a matter of time.  

Your not very encouraging to a guy that's got four 520s. 

[RED-Z06 2,365]

2 minutes ago, WHX?? said:

Your not very encouraging to a guy that's got four 520s. 

Its incredible how widespread this problem is, i knew it was a thing but never saw the scope of how common.

[RED-Z06 2,365]

4 minutes ago, WHX?? said:

Your not very encouraging to a guy that's got four 520s. 

Worth doing compression tests...you would have never known this engine was on 115/50psi...seemed fine.  If you catch it early enough its not bad to fix

[Jeff-C175 7,203]

11 minutes ago, RED-Z06 said:

scope of how common

 

Keep in mind though...  you're not seeing reports from all the people that do NOT have problems!