520H Carb

[parks416 22]

Hi all, long time stalker of this site, but finally joined and this is my first post. My son and I (he's9) have enjoyed playing with horses the last few years. We came accross a 1991 520H at auction and brought it home. have done some tinkering with it, have it running and mowing but the card is giving me some problems. It's running way to rich and blowing alot of unused fuel out the top of the card. I took it all apart, cleaned everything, checked the float and it seemed to be fine. Put it all back together, same thing. Anything else I should check or just try a new rebuild kit for the carb? The was the route i was originally going to go but my local Toro dealer didnt have one in stock this morning (plus it was $100).

Thanks

Ben

P.S.-once I take some pictures of all our horses I'll make an actual introduction post

[lynnmor 7,307]

 

In order to have an overflowing carburetor the float needle may have a problem, either condition or adjustment.  Rebuild “kits” are little more than new gaskets.

 

You mentioned checking the float, one that is defective can cause your problem.

 

I would start by checking compression to see if you have a healthy engine, an engine with blow by or leaking valves can show the symptoms you mentioned.  Report back with your compression readings.

Edited September 9, 2023 by lynnmor

[953 nut 55,259]

16 hours ago, lynnmor said:

checking compression to see if you have a healthy engine, an engine with blow by or leaking valves can show the symptoms you mentioned

                                                   

Many Onan engines suffer valve seat problems and if the intake valve on a cylinder is not seating completely the pressure leaking past it will cause the problem you are having.

[parks416 22]

Thanks, I will check compression and report back

[parks416 22]

Well not what i was hoping for. 125 pounds on the front cylinder, under 25 on the back. Looks like valve seats. 

[lynnmor 7,307]

48 minutes ago, parks416 said:

Well not what i was hoping for. 125 pounds on the front cylinder, under 25 on the back. Looks like valve seats. 

It could be, you need to pop the rear head and see what is going on.  Do not attempt to run it any more.  Some loose valve seats can be repaired, report back with your findings and photos.

[RED-Z06 2,221]

Always the rear cylinder, P220s were known for it, mine on my deere was 120/20 and was spraying gas up the carb, it had actually  unbeknownst to me at the time...split my intake manifold.  Block was trashed, could have been fixed with alot of custom welding and machining but i found a good used engine to go in it...which will inevitably do the same thing.

[parks416 22]

Our county fair starts next week and the kids have lots of animals to show so it'll probably be a few weeks before I can tear into it, but I'll let you all know what I find.

[lynnmor 7,307]

1 hour ago, parks416 said:

Our county fair starts next week and the kids have lots of animals to show so it'll probably be a few weeks before I can tear into it, but I'll let you all know what I find.

Just so you know, pulling the head only takes minutes.  Of course having the time to do cleaning and inspection will be much longer.

[parks416 22]

Well I had a little time today to start tearing into it today. Valves on both cylinders seem to move freely when i turn the engine by hand. Maybe I'm missing something but seems you would almost need to unbolt the engine from the frame and spin it to get the head bolts out from the back cylinder? 

[RED-Z06 2,221]

41 minutes ago, parks416 said:

Well I had a little time today to start tearing into it today. Valves on both cylinders seem to move freely when i turn the engine by hand. Maybe I'm missing something but seems you would almost need to unbolt the engine from the frame and spin it to get the head bolts out from the back cylinder? 

How much lash was on the rear valves?

 

When my p220 failed the intake side lost lash, reset it...and it quickly lost lash again.  

[953 nut 55,259]

12 hours ago, parks416 said:

need to unbolt the engine from the frame and spin it to get the head bolts out from the back cylinder

That is about the only way to get at the rear cylinder.

12 hours ago, RED-Z06 said:

How much lash was on the rear valves?

 

When my p220 failed the intake side lost lash, reset it...and it quickly lost lash again.

If the valve seat is the culprit that is a good idea for troubleshooting the problem.               Thanks for sharing this idea.        

[parks416 22]

Well with a little more time for inspection today (and a little better light)  you can see from the picture the intake valve seat on the rear cylnder is loose and there is some folded/mangled sharp steel behind it. I assume it's a piece of the block since the seat it's self loose and moves. You can kind of see it in the picture below. So what are my options.I know if read some on the forum about a machine shop maybe being able to press in anew seat if the block isn't to bad? Anybody have any good machine shop recomendations in Ohio? I bought the mower for $125 at auction. The hydo seems strong, hydraulic deck lift works, sheet metal is all straight, good tires, seat, belts, swept front end, 48" deck is pretty solid. I would hate to just junk it and give up on it. Wouldn't mind putting some money into it since I think it would be a solid mower with a good engine. I guess I would be hesitant to swap it with another Onan since it seems like a common problem among them. There is a Onan on marketplace, guy told me $400 and I can hear it run

[RED-Z06 2,221]

All depends on the machine shops you have...i couldn't find anyone locally to me who would touch mine.  

[parks416 22]

Did you end up swapping another Onan?

[RED-Z06 2,221]

24 minutes ago, parks416 said:

Did you end up swapping another Onan?

I did.  It was a 1991 Deere 420, had about 720hrs on it, i bought it at full market value with the understanding it needed deck work but was mechanically sound.  10 minutes...thats how long it ran before i discovered the governor spacer was bad.  I pulled the engine, replaced the spacer...put the engine back in..ran it about 30 minutes and it lost power, compression low on the right side..pulled exh and intake, found 0 lash on one..(and alot of new gaskets), so i lashed it..back together, ran about 35 minutes and...lost compression, no lash again.  Pulled head, pulled valve..seat fell out.  It was pretty beat up but fixable...9 months i gave up on machine shops jerking me around.  Found an engine in Indiana, shop assured me it ran fine but the starter was noisy.  I paid $600, got it home...jumped the starter and knew immediately the block was broken.  Pulled the flywheel, teeth half gone, pulled starter, it was okay..but the inboard starter mount was cracked.  I had that welded, put it all together, engine in frame...started and ran but no governor control..bad governor spacer.  Swapped that spacer out..put the engine back in..and its been fine.

 

 

[Handy Don 12,232]

12 hours ago, RED-Z06 said:

and its been fine

Wow, that is one dogged pursuit and glad to here you’re at a good place now.

A couple of years ago I bought a “doesn’t run, something is wrong internally” P220 cheap, mainly to have the “bolt on” parts as spares--muffler, starter, etc. Some day I might get it up on the bench and see what’s really going on with it!

[lynnmor 7,307]

13 hours ago, parks416 said:

 There is a Onan on marketplace, guy told me $400 and I can hear it run

 

Take compression readings on the $400 engine and buy it if all is well.  If it was on a Wheel Horse it will fit, if it was on anything else check the crankshaft measurements and starter position.  Also, if that engine sat outside for years know that corroded fasteners can cause much trouble if work is needed.

[parks416 22]

Well I guess the engine is going to have to come out either way so that'll be the next step. I called some machine shops around me today, no luck in any wanting to tackle the new valve seat. One that was recommended to me by our local Toro dealer (use to deal wheel horses), but they stopped doing the repair 3 or so years ago. Said to many he fixed were coming back with the same problem after the fix

[lynnmor 7,307]

23 minutes ago, parks416 said:

 Said to many he fixed were coming back with the same problem after the fix

Then he simply didn’t do it right.  Many do not understand that there should be a very tight press fit .0055 is the correct interference.  After the seat is installed, the edge of the block is to be peened over using a special tool.

 

My guess is that Onan didn’t get it right for some production runs.

[RED-Z06 2,221]

2 minutes ago, lynnmor said:

Then he simply didn’t do it right.  Many do not understand that there should be a very tight press fit .0055 is the correct interference.  After the seat is installed, the edge of the block is to be peened over using a special tool.

 

My guess is that Onan didn’t get it right for some production runs.

As common of a problem as it was...i think they got it wrong for a while.  What was odd was the P218 and P220 shared blocks, P218s rarely did it.

[parks416 22]

10 hours ago, Handy Don said:

Wow, that is one dogged pursuit and glad to here you’re at a good place now.

A couple of years ago I bought a “doesn’t run, something is wrong internally” P220 cheap, mainly to have the “bolt on” parts as spares--muffler, starter, etc. Some day I might get it up on the bench and see what’s really going on with it!

After thinking on it the last couple of days, that maybe what end's up happening to this one. I've got alot of other projects I would be leap frogging to start this one. Like I said I only bought it for $125 knowing it didn't run. I figured keeping the tires, deck, seat, belts, steering wheel, for spares were worth that. May take off what I can use on other models then sell what's left of it. I really don't need the mower, just bought a nice low hour 315-8 that I mow with every week. Would make my wife happier lol

[RED-Z06 2,221]

1 hour ago, parks416 said:

After thinking on it the last couple of days, that maybe what end's up happening to this one. I've got alot of other projects I would be leap frogging to start this one. Like I said I only bought it for $125 knowing it didn't run. I figured keeping the tires, deck, seat, belts, steering wheel, for spares were worth that. May take off what I can use on other models then sell what's left of it. I really don't need the mower, just bought a nice low hour 315-8 that I mow with every week. Would make my wife happier lol

If you were closer id offer to buy it, but 1600 miles round trip is a bugger.

[parks416 22]

Ok well I thought I'd do a follow up on this post. I had some time to unbolt the engine from the frame and take the head off. Block and head seem to be in pretty good shape, just the loose intake seat. I did manage to find a machine shop that would atleast take a look at it if I bring the block and new seats to them. Now, does any one have suggestions on where to buy replacement valve seats, or any preferences on which ones to buy?

Thanks

[lynnmor 7,307]

A good automotive machine shop has access to a wide variety of valve seats, after careful measurements the OD, ID and length can be determined.  Onanparts.com has some information and they did have very large seats so a shop can machine them to the size required, so basically they are simply raw material.

 

Onan did sell .010” oversized seats and you might still find them at online auction sites, however it is rare that they will be large enough to fix the problem.

Edited October 1, 2023 by lynnmor