520H bogging down and stalling engine

[Rob R 958]

So... I got cabin fever and against my best judgement, picked up from my brother a 520H Model # 4120OE02; Serial 1033076 (1991) that he got from a Friend who claim it ran but hasn't been used in years and was in dry storage. Included was a 48-inch triple blade mower in very good condition, total cost $250 ..... I figured that even if the tractor was no good the deck was worth the coinage....... and it had a good new battery....... So got it home fixed the one flat tire, replace the cooked fuse in the fuse holder. Cranked the engine over it cough a few times and then quit, was not getting fuel, replace the fuel line from the tank to the pump, pump not pumping, replace it with a B&S pump, cranked her over and she started right up ran and idled decent with no noticeable smoke. p.s. the hour meter is disconnected but you can tell she was run hard and put away wet but overall, in fair to good condition. 

 

So without doing anything else time for a test drive. It moved forward and backwards took her out into the yard got about 50 feet and the motor started laboring to me was like the transmission was putting a heavy load on engine, I tried to shift into neutral, but it wouldn't let me do that and then the engine bogs down and shuts off. Wait like 10 seconds start her up again and the issue repeats.... In all my years I have never had anything close to this issue hence my call for help.

 

I did all the normal stuff trans fluid looks clean added some 10-40 weight to top her off, did not change the filter yet as I do not have one in stock.  You can start the engine without engaging the transmission and it will run fine until the cows come home..... put it in gear forward or reverse and it will go an little ways and then the load condition occurs, the engine loads up and is dragged down into a stall. 

 

Appreciate all your advice as this one has me stumped...... 

 

 

Edited March 29 by Rob R
typing error

[Ed Kennell 36,795]

I will be following this.    I have all Eaton 1100s.    Wish I could help.

[lynnmor 7,096]

I would start with a transmission oil and filter change.  Drain in a clean pan and look for water and debris.  Jack up the right front to get more old oil out.  Likewise, remove the filter and cut it open to see if there is metal or other debris.  Be sure it had the correct filter.  Report back.

[kpinnc 11,293]

I would also check both engine cylinders for spark. Opposed twins will run on one cylinder, albeit weaker. 

 

If your transmission is in a bind, it should whine considerably. All hydros have a little whine, but it will be alot if it's in a bind. Check you make sure the brake isn't too tight. 

 

Question- can you roll the tractor fairly easy with the DCL forward? 

[Rob R 958]

On 3/29/2024 at 9:49 PM, kpinnc said:

I would also check both engine cylinders for spark. Opposed twins will run on one cylinder, albeit weaker. 

 

If your transmission is in a bind, it should whine considerably. All hydros have a little whine, but it will be alot if it's in a bind. Check you make sure the brake isn't too tight. 

 

Question- can you roll the tractor fairly easy with the DCL forward? 

Yes rolls easily with DCL in forward. Brake good NO whine my GT14 has a little whine this one none. 

Edited April 1 by Rob R

[Rob R 958]

4 hours ago, lynnmor said:

I would start with a transmission oil and filter change.  Drain in a clean pan and look for water and debris.  Jack up the right front to get more old oil out.  Likewise, remove the filter and cut it open to see if there is metal or other debris.  Be sure it had the correct filter.  Report back.

Agree need to get the correct filter and do what you said. Ditto chk out the current old one. Thanks 

[Rob R 958]

So my stump was a DUH. Had some time this morning to really go thru the machine. What we have here is a dead cylinder (back) which has NO compression, as some of you indicated, and I guess worse then that the Piston is NOT moving up and down so must be a broken connecting rod....... So now decision time regarding what to do and where to start. Assume remove engine tear down see if the block and or crank is journal is damaged etc. etc. also assume parts are basically in the scarce or unattainable status. I guess I could put in a K301K engine which I have and is in perfect condition?  any thoughts please share. Thanks for all the good input. 

 

When I remove the engine what is the MINIMUM I need to remove to get the piston out and observe the damage etc.?

Edited April 1 by Rob R

[ebinmaine 64,972]

 

My 

 

If you want the tractor for the full working potential I think a B&S or Honda transplant could be a good consideration.  

 

 

If you don't NEED the whole 20 HP it would benefit from whatever is readily available. 

 

 

[Ed Kennell 36,795]

Whew, I'm glad to hear it's not an Eaton 1100 problem.     Should be a lot of Onan Gurus willing to help.    Is Boomer still around?

[kpinnc 11,293]

2 hours ago, Rob R said:

What we have here is a dead cylinder (back) which has NO compression,

 

If you weren't so far away I'd give you my P220.  the stator stopped charging last year and I'm tired of dealing with it! If my old back survives removing it (again), I'm repowering my 520-H. 

 

I have a plethora of decent parts for Onans, and two P220 engines that I'm not going to rebuild. Just too expensive! 

[Rob R 958]

So pulled the engine today and broke her down, the back connecting Rod was busted into many pieces, I could not see any damage to the other internals or the block itself. It must have been broken a long time at the piston while in relatively good condition had one stuck ring (light rust) bore was fine. The crankshaft had the normal aluminum connecting rod embedment which I am dissolving with muriatic acid, you can see the improvement in the pics but more to do tomorrow.

 

Next step is the parts and gasket chase. Kevin Pinnc has been great and thinks he can help me with what I need and perhaps some back-up. Feeling much better today about the machine but still a long way to the finish line. Comment as always appreciated and Kudos in advance for all the assistance. 

I can still NOT believe how well the engine ran and sounded on ONE Lung.......... !

 

Edited April 2 by Rob R

[ebinmaine 64,972]

1 hour ago, Rob R said:

 

 

 

 

 

 

This might be the most pieces of rod I've seen in a 2 cylinder engine! 

 

[kpinnc 11,293]

3 hours ago, Rob R said:

The crankshaft had the normal aluminum connecting rod embedment which I am dissolving with muriatic acid, you can see the improvement in the pics

 

I'm curious how the valve seats on the rear cylinder look. Have you gotten that far into it yet?

[Rob R 958]

They look fine Kevin (initial look), full of gunk but intact, I will be working on them today and getting into the cleanup of the block as well as bore honing etc.  Now that I'm committed it also needs a lot of electrical refining and wire replacement and quite a bit of Rube Goldberg replacement and abject maintenance..

[ebinmaine 64,972]

1 hour ago, Rob R said:

Rube Goldberg replacement

 

 

 

 

 

That needs to be used more often 

[onanparts.com 181]

Another Horse worth saving! Using a mix of new and used parts the Onan can be brought back to life without breaking the bank. And a LOT less than a disposable repower.....

 

Regardless of where you get them, avoid the imported garbage gaskets and seals. Failure rate is very high, recycled cereal boxes make lousy gaskets.....nothing worse than having to go back and replace a failed gasket or seal after time and $$$ to repair/restore/rebuild any engine. OEM Onan gaskets etc. really are that good, zero failure rate! Good luck with your 520H. Do it right and your Onan powered Horse will be good for another 20-30+ years.

 

 

[Bill D 1,770]

If you decide not to rebuild or take Kevin up on his offer of the free P220, consider locating a good used P216.  The P216, in my opinion is a much more reliable choice.  Little to no issues with valve seats and less likely to break rods based on what I've seen.  If you find a good used engine adding the temp sensor and tach connection make it a plug and play replacement.  Also consider changing the governor flyball spacer as a preventative measure.  If used with a 48" deck it's unlikely you'll miss the four horsepower.  

[Rob R 958]

So making headway should have this puppy buttoned - up shortly waiting for the parts i need gaskets etc. I came across this disconnected little square black cube (like one inch square) with two push on disconnected wires this is located in the battery box (battery removed). Anyone know what this is?    Thanks 

[Ed Kennell 36,795]

4 minutes ago, Rob R said:

Anyone know what this is? 

Dirty air cleaner sensor?

[cleat 5,461]

That is a little vacuum switch for monitoring the air filter.

If the air filter is clogged the vacuum goes up and this switch senses that and turns on the air filter light on the dash.

 

However, yours has the nipple broken off as most do that the hose from the air cleaner hooks to.

 

Under the air filter housing you should have either a hose connected or a hose nipple.

 

You can simply plug this hose and be done with it then just check the air filter just like any other engine.

 

I do not have this working on any of my 520's.

Edited April 7 by cleat

[lynnmor 7,096]

Part is available here as well as several other places.  You want part number psf101-8111-150.  You will find prices all over the place.  I have repaired several of those switches by sanding them flat and screwing on a metal plate with an integrated nipple. Tiny screws go thru the rivets on each corner.

[Rob R 958]

You guys baring NON are the fricking BEST! tomorrow I put the Piston and Rod in, button her up say a prayer to the WH Gods and hit the start button!

[Rob R 958]

As promised here she is running PROUD!

 

 

 

[lynnmor 7,096]

I get this:

 

Oops, something went wrong.

[Blasterdad 2,608]

Me too....