417-8mule 23 #1 Posted 7 hours ago This is a new to me 520-8, I don’t really know the history of it but supposedly it’s been rebuilt. Noticed this ticking soon after purchase and really haven’t used it much or had time to dive in. To the Onan pros on here does this sound like the valve seats? To me it sounds like it’s coming from the front, and fairly consistent. Tips on where to start appreciated, big plans for this machine for this coming winter and spring. IMG_0882.mov Share this post Link to post Share on other sites
ri702bill 13,139 #2 Posted 6 hours ago Hmmm... I'm not hearing a ticking sound, but I detect a possible surging issue. Onans are known for intake manifold leaks... and carbs that require multiple baths in the Ultrasonic Cleaner to get them right... 1 Share this post Link to post Share on other sites
417-8mule 23 #3 Posted 5 hours ago 25 minutes ago, ri702bill said: Hmmm... I'm not hearing a ticking sound, but I detect a possible surging issue. Onans are known for intake manifold leaks... and carbs that require multiple baths in the Ultrasonic Cleaner to get them right... the surging might just be me messing with the throttle. I had sped it up and slowed it down the original video was longer I had to trim it down. I will say it starts pretty easy and idles fine, little smoke on start though especially when cold out Share this post Link to post Share on other sites
lynnmor 9,044 #4 Posted 5 hours ago Always start with a compression test, that won't always find a loose valve seat, but if the compression is low pull the head. The front head is easy, just unplug the headlight wires and pull the hinge pin and remove the hood, then the head access will be wide open. What I heard, in the all too brief video, sounds like the noise is at engine speed, a valve issue will be half the engine speed. You might want to engage the PTO and see if the noise changes. 1 Share this post Link to post Share on other sites
417-8mule 23 #5 Posted 4 hours ago 12 minutes ago, lynnmor said: Always start with a compression test, that won't always find a loose valve seat, but if the compression is low pull the head. The front head is easy, just unplug the headlight wires and pull the hinge pin and remove the hood, then the head access will be wide open. What I heard, in the all too brief video, sounds like the noise is at engine speed, a valve issue will be half the engine speed. You might want to engage the PTO and see if the noise changes. so I did try that engaging the pto because I was thinking it might just be something loose there, but didn’t seem to have any effect. I haven’t loaded the pto with any belt or attachment so maybe that’s the next step. Compression test is easy as well just need to find my tester so I’ll give that a shot too Share this post Link to post Share on other sites
Ed Kennell 47,502 #6 Posted 3 hours ago I often pull one plug at a time on my twins when trying to locate a problem. They do run on one cylinder. Share this post Link to post Share on other sites
