Onan Engine Question

[muz123 1,191]

I recently picked up a 520-H with only 150 hours on it, yes the meter works. When I got it, I changed all the fluids on it. The only problem is when the tractor is running there is a loud tapping noise coming from the front of engine(Front of the tractor). Is that a rod problem or a valve issue? It becomes louder as the RPM's are increased. It is a very loud tapping noise and I have no idea what it could be. Would a valve adjustment fix the issue? Assuming the low hours do not help as it sat a lot. Any input would be great.

Thank you.

[Achto 27,569]

2 hours ago, muz123 said:

Would a valve adjustment fix the issue?

 

This is what I would start with. Does it sound like it is at cam speed (1800 RPMs) or crank speed (3600 RPMs)? Cam speed would more that likely be a valve issue.

[kpinnc 12,012]

First, I wouldn't run it until you take the heads off and inspect it. 

 

An Onan that sits for a while like yours can get a buildup of crud in the cylinders from condensation and carbon. It then can get pushed up to the head where it makes contact when the piston reaches TDC. It absolutely will break a rod when it builds enough.

 

It's a simple thing to check, and always a good idea on any "new" Onan you get to do the decarbon procedure. All you need are a few gaskets.

[JoeM 7,873]

10 hours ago, kpinnc said:

It's a simple thing to check

Yeah the tins are the toughest part of the job.

Tapping front or rear needs immediate attention. 

Tapping noise from the top is the valve lifters. 

[lynnmor 7,305]

The valves may have rusted from non-use and they may be sticking in the valve guides.  Pull the heads to see what is going on.  Hopefully pulling the valves, polishing the stems and running a reamer by hand thru the guides will take care of the noise.  Take some photos while apart.