520H needs help

[chargerrt 0]

I am an new member with a compression problem on my 1993 Wheelhorse 520H. It starts, but has no power since I started it this spring. The cylinder closest to the battery wasn't firing. It has a strong spark, I checked the compression and it reads 0 the other cylinder reas 115#. I thought I had a stuck intake valve as I am getting a lot of gas pushed up into the air cleaner and the machine was idle for a while. I removed the intake and exhaust manifolds and valve cover. Both intake and exhause valves are moving as the engine is turned over by hand. It appears that I will need to remove the engine to remove the head to get a visual on the condition of the valves and seats. The 520H has only 392 hours on it and has been a great machine over the 15 years I have owned it. I previously had a B80 for 15 years. Is it a big job to remove the engine? Is there an easier way to access the head near the battery? Am I overlooking something I should try before removing the head? Could I have a blown head gasket and get 0 for a compression reading? I appreciate any advise I can get. I hate to lose my 520H.

Thanks

[nylyon-(Admin) 7,860]

Welcome to RedSquare sorry you're here because of this problem. I have heard of some Onan engines having valve seat problems where the seat comes loose, which sounds like is a possibility in this case, but it makes sense to check everything else as well. Unless the head gasket is physically blown out, I would think that it would show some compression.

I would suspect that you may have a valve seat issue. I don't know what the repair to that is though.

[Jim_M 179]

It could be that a valve seat has let loose, it could also be possible that the intake valve is stuck open due to carbon build up on the stem. I hope it's just stuck, there's no sure way to lock the valve seat back in. You can peen the area around the valve seat to hold it in, but it's only a matter of time before it comes loose again.

Either way, you'll have to pull the head to know for sure. The easiest fastest way that I've found is to pull the engine off or a least rotate it 90 degrees on the frame.

[Bow_Extreme 549]

I also have a 520H. I've never removed the engine but I've been thru the tractor quite thouroughly. That engine comes off there very easy. First remove the drive belt cover on the right side of the tractor. You can remove the engine from the bottom plate or remove the plate & engine from the frame. 4 bolts for each one. Disconnect the fuel line and disconnect the main engine wiring harness. That will take around 15 minutes or so to do. There are 2 lifting hooks on the top side if you have a hoist or lift. Sorry to hear about your problems. I'm personally working out the last minor bugs with my 520. Good Luck.

[T-Mo-(Moderator) 4,589]

I can't really add anything constructive here that hasn't already been mentioned. But, I do want to you and Bow Extreme to the site. :WRS:

[chargerrt 0]

Thanks for the information and advice. I'll try to get the head off this weekend and let you know what I find.

[refracman 167]

Chargerrt

I would have to concure the valve seat has let loose. But it can be fixed. Our local small engine guy has had many Onan's valve seats repaired with it being a permenate fix. Your local engine rebuider should be able to repair it. But be ready for the cost, the gasket kit costs about $120 and the valve seat repair is about $60.

If your in the northwest ohio area i can turn you on to the shop that does his.

Lets hope its just a sticky valve.

And :WRS:

[chargerrt 0]

I did get the engine disconnected and turned so I could access and remove the head. The valves had heavy carbon build up on them and I found the intake valve staying open about 1/16 of an inch. There was no valve clearance. I was able to adjust the valve clearance to get the valve to close, but I decided that while it was apart I should remove the valve and clean the carbon from the seat and back of the valve. when I removed the carbon I found the valve seat loose. It slides in and out. I tried measuring the seat pocket and valve seat with verniers, but it measured the same. If I wrap 3/4 of the OD os thr valve seat with cellophane tape (mics at .0015") it is a press fit in. Can I get a .002 - .005 oversized valve seat? Should I try and stake in the existing std valve seat? The seat height or depth seems to be approx. .020 below the angle lead in to the valve seat and maybe that is why the valve wasn't closing. Looking for some advice on best way to make the repair without getting deaper into the engine. Chargerrt

[546cowboy 302]

I have a P220G at the machine shop now with that problem in the same cylinder. They can get an oversized seat and replace it. It's really not that big a deal to do for a good shop.

I have heard of staking it back in but I didn't know if that would be a permanent enough fix. I would rather have a shop fix it now than have to do it again later.

Good luck