leeave96 487 #1 Posted October 19, 2013 I've got two 520H tractors I picked up recently. All I've done with them is drive the tractor off the trailer for another day. The BIG thing that jumps out to me is excessive vibration. My other Onan powered 520H tractors are silky smooth. I think vibration by the engines is being caused by them running on one cylinder. Haven't had time to trouble shoot - yet. Question is - when an Onan is vibrating excessively, is it generally due to running on one cylinder? Neither engine smokes or is hard to start, both idle fine and accelerate from it to full throttle without hesitation - but me thinks I'm running on one cylinder and probably due to a loose valve seat. Just curious as to your experience before I tear into it. Thanks! Bill Share this post Link to post Share on other sites
Sparky-(Admin) 19,674 #2 Posted October 19, 2013 Seems to make sense......why not fire it up and pull off one plug wire at a time to see if it makes a difference. Simple test to see if its firing on both cylinders. Mike......... Share this post Link to post Share on other sites
WH nut 553 #3 Posted October 19, 2013 If you have an infrared temp gun you can take some temp readings Share this post Link to post Share on other sites
sorekiwi 761 #4 Posted October 19, 2013 I bought my 520 running on 1 cylinder. I was surprised that it ran as well as it did, it sounded ok, but it did vibrate a bit and was down on power. I also assumed it was a bad valve seat, but soon discovered it had a broken rod. (I'd take an Onan with a broken rod over one with a bad valve seat anyday). Share this post Link to post Share on other sites
leeave96 487 #5 Posted October 19, 2013 Seems to make sense......why not fire it up and pull off one plug wire at a time to see if it makes a difference. Simple test to see if its firing on both cylinders. Mike......... Absolutely will do this test. That's an easy one. :) Share this post Link to post Share on other sites
ericj 1,576 #6 Posted October 19, 2013 compression test will detect a broken rod or loose valve seat real quick, but the infrared temp gun or the pulled wire will also tell the tale. my experience with broken rods is the motor seems to run smooth but hard to start sometimes, and the valve seat out the motor has a defined mis. i remember there was a thread on here about a vibration on a 520 before but i don't remember the out come of the problem maybe search the history and try and find it or somebody can provide a link to it. eric j Share this post Link to post Share on other sites
Kelly 1,028 #7 Posted October 20, 2013 I've had 2 Onans with broken rods, both ran pretty good, one the guy used for a dew weeks knowing it had a broken rod, and ran a 60" deck mowing a acre lot, a cheap way it to run it for a few min. and quickly touch the exh. pipes at the heads one will be very hot, the other cold, if not firing or no compression. Share this post Link to post Share on other sites
