Jump to content
stuppy62

520 acting up again!

Recommended Posts

My 93' 520 with the Onan engine is not running right at all. I've been mowing with it all season, not running right, and the last time I mowed it was idling terrible, but had good power running on both cylinders. Now today I thought I'd check the carb, everything good inside, no dirt or gunk. Next I pulled fuel line off after the filter and placed it in a jar, cranked starter, lots of fuel pumping. Tried starting it again, no go, for some reason I removed rear plug wire & now it started on 1 cylinder. When I tried to put second wire back on it made it worse & yes I tried starting it on rear cylinder only, no go. I'm really stumped at this point, coil?   

Share this post


Link to post
Share on other sites

I am not sure on these but some multi cyl engines use what they call waste spark technology. The  voltage travels from 1 coil tower thru the plug wire to a plug. It jumps the gap to ground (block) From there the other plug the voltage goes from the block, jumps the gap at the plug, travels thru the plug wire to the 2nd coil tower completing the circuit. Both cylinders fire at the same time but 1 of them is on the exhaust stroke hence the term waste spark. If you have a bad plug, bad  wire it can cause all sorts of odd things. 1 broken wire can kill the whole engine, while a grounded wire will knock out 1 cylinder. Try changing the plugs first, Then if it doesn't help I would go with both wires then the coil

Share this post


Link to post
Share on other sites

Hi Stuppy!
I would try three things right out of the box.
First: Your newer EPA carb on that Onan doesn't have an "exposed" Main Jet adjustment but it's there. Do a search under "Engines" on this TOPIC on RedSquare and there is a couple threads with details on how to find, remove & clean the main out. (Plus use Seafoam or carb cleaner to blow out the little orifices in those carbs).

Second: Pull your plugs and look at them remembering what was in the rear cyl and what is in the front. If the rear looks black and fouled but the front looks as it should, you should do a compression test on the rear and see if you don't have a loose or hammered valve seat. (Good compression on these Onans would be 90+ PSI in BOTH cyl. You don't want to be off in either cyl by more than 4 or 5 PSI). They will still run down to 30 - 40 PSI but starting is an issue.

Third: If your mowing a lot with an Onan, and God knows everyone is from the Ohio Valley through Pennsylvania and the Northeast! You need to keep the chafe/leaves/big grass off the flywheel screen. Wipe it off as much as needed while your mowing or it will over-heat and aid in the early destruction of the valve seats in the already compromised rear cyl. I would tear into the tins on that engine by unbolting it and turning it sideways in the tractor. Blow out the tins and then use a clothes hanger or thinner rod to get between the cooling fins. If you never did this and you mow with the tractor, this can be the problem that leads to the other problems which leads to your wallet bleeding green.

The priority is to do the compression test to make sure your no start issue isn't valve seat related.

Good Luck!

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for you're responses. Boovuc, I did the compression check first and unfortunately you are correct. I had 30 lbs. of compression, so I pulled engine and opened up to see. I've got a very hammered intake valve seat. Next questions is, is this repairable?

Share this post


Link to post
Share on other sites

Throw some pics up here and let the experts, (no.....not me), take a look!

Share this post


Link to post
Share on other sites

The valve seat is very loose, can move in & out with you're fingers. The third pic is inside where there the seat was scrubbing around in there. If I had a machine shop fix this could I get away with not pulling the piston's & sleeves? It has 1050 hrs. on it.

IMG_0214.JPG

IMG_0215.JPG

IMG_0216.JPG

Share this post


Link to post
Share on other sites

stuppy
can you post some pics that are MORE CLEAR?
especially needed, the one of the inside of the port.
thank you. boomer ( the used onan engine parts guy, also NOS and new )

  • Like 1

Share this post


Link to post
Share on other sites

At this point I'm going to drop off at local machine shop. Over the phone they said to bring it in they might be able to fix it. I'll keep you all posted.

Share this post


Link to post
Share on other sites

Keep us posted. Loose can be a good thing verses hammered and cracked.

Share this post


Link to post
Share on other sites

Ok, the valve seat is fixed, plus 4 exhaust bolt holes repaired. Cost $110, plus I'm getting gaskets & filter from boomers_influence. another $60. I don't think that's to bad for this fix, I just need to get everything together & hope for the best!

  • Like 2

Share this post


Link to post
Share on other sites

Good news! 520 is running & sounding better than it ever has for me. I mowed with it for about an hour & I couldn't believe how quiet it is. On a side note I was mowing with my 74' C-160 8 speed, (while repairing 520) which does a great job mowing, but getting back on the 520H is like climbing on a Cadillac.  

  • Like 2

Share this post


Link to post
Share on other sites

Ok, the valve seat is fixed, plus 4 exhaust bolt holes repaired. Cost $110, plus I'm getting gaskets & filter from boomers_influence. another $60. I don't think that's to bad for this fix, I just need to get everything together & hope for the best!

Just curious, did they repair the valve seat with the motor all together? And what kind of repair did they do. Over size seat or...???




 
  • Like 1

Share this post


Link to post
Share on other sites

Replying to Theroundhousernr , they put an oversized seat in, not an Onan, much larger, looks like it should last. Also, yes I was able to leave it all together.

Edited by stuppy62

Share this post


Link to post
Share on other sites

Did you have to pull the whole motor apart or where they able to do everything with pistons , crank and so on installed. Just wondering because some say they want it apart and other shops say they can do it together.

   Thanks Kyle

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

×