Replacing PTO seal on a 520-H

[1990Onan520-H 15]

Hey all, I have a leaky PTO seal on my 520. How do I properly replace that seal? Last time I tried doing this, I unbolted the plate and pulled it out and scratched the main bearing. So really don't need a repeat of that. Any tips would be appreciated.

[lynnmor 7,815]

59 minutes ago, 1990Onan520-H said:

Hey all, I have a leaky PTO seal on my 520. How do I properly replace that seal? Last time I tried doing this, I unbolted the plate and pulled it out and scratched the main bearing. So really don't need a repeat of that. Any tips would be appreciated.

 

I guess that you mean the engine crankcase seal.. Just be sure that any burrs are completely removed from the crankshaft first and polish it with 400 grit paper to remove rust, paint or debris.  In other words, make it as smooth as a baby's behind before carefully pulling the housing out straight.

[1990Onan520-H 15]

7 minutes ago, lynnmor said:

 

I guess that you mean the engine crankcase seal.. Just be sure that any burrs are completely removed from the crankshaft first and polish it with 400 grit paper to remove rust, paint or debris.  In other words, make it as smooth as a baby's behind before carefully pulling the housing out straight.

The crank is inside the casing. I have no access to the crank. Let me see if I can post a picture of the seal someone graciously drilled 4 holes in before I bought the engine.

[1990Onan520-H 15]

[lynnmor 7,815]

Everything from the Holy seal out to the end is the crankshaft.  The surface that the seal rides on is what needs to be smooth before disassembly.  If the previous master mechanic nicked the surface and raised up a bit of material, that needs to be corrected first thing.

[1990Onan520-H 15]

10 minutes ago, lynnmor said:

Everything from the Holy seal out to the end is the crankshaft.  The surface that the seal rides on is what needs to be smooth before disassembly.  If the previous master mechanic nicked the surface and raised up a bit of material, that needs to be corrected first thing.

So the main bearing is the same size as the seal rubber and if there's a bur on the crank there it will scratch it?

[lynnmor 7,815]

I guess I was mistaken, only the seal rides on that surface but it does need cleaned up before assembly.  Since you had a bad experience previously I thought that it might have come from that surface gouging the bearing and that threw off my thinking..  As you pull the plate away from the block the crank will drop down a small amount, maybe that caused the problem.  Support the crank as you pull the plate out.

[1990Onan520-H 15]

3 minutes ago, lynnmor said:

I guess I was mistaken, only the seal rides on that surface but it does need cleaned up before assembly.  Since you had a bad experience previously I thought that it might have come from that surface gouging the bearing and that threw off my thinking..  As you pull the plate away from the block the crank will drop down a small amount, maybe that caused the problem.  Support the crank as you pull the plate out.

Ok so the proper way is to remove all 5 bolts, then as evenly as possible slide the plate out? That will allow me to knock the seal out the back side and replace? Which is what I thought but somehow it screwed up my main bearing last time.

[lynnmor 7,815]

3 hours ago, 1990Onan520-H said:

Ok so the proper way is to remove all 5 bolts, then as evenly as possible slide the plate out? That will allow me to knock the seal out the back side and replace? Which is what I thought but somehow it screwed up my main bearing last time.

Correct.  I use a round disk to press the seal in using an arbor press.  Since the seal is recessed into the housing, just tapping it in with a hammer is not a good idea.

[1990Onan520-H 15]

8 hours ago, lynnmor said:

Correct.  I use a round disk to press the seal in using an arbor press.  Since the seal is recessed into the housing, just tapping it in with a hammer is not a good idea.

Ok thanks. I've got a press so will do it that way. I was just kind of in shock when I found a big gouge on my main bearing last time so just wanted to make sure I didn't do something wrong. Sounds like I did it right but just had some bad luck somehow. I'll rip it off and pray the 4 holes didn't do any damage to anything. I know they drilled too deep though which has me worried about at the very least scratching the main.