Wheelie horse 90 #1 Posted June 13, 2021 Hello, I have a few questions I have a 416-h a 520-8 and a 416-8 all with Onan engines they all start right up but I have noticed lately that the 416-h runs the smoothest out of all, it has a few hundred less hours, my other 2 are both pushing 800, when I start them up they both run well but you can hear them popping a bit noticeably not running as smooth as the H dose. I have cleaned the carbs on both of them but doesn’t seem to make a huge difference also changed file filed and new plugs, any input would be great thank you! Share this post Link to post Share on other sites
horseyheaven 113 #2 Posted June 13, 2021 2 things come to mind. The intake is a two piece design and can sometimes begin to leak, causing them to run different. An easy way to tell is to spray carb cleaner along the seam where the intake goes together while it is running. If the intake is leaking, or will cause it to surge when it sucks in the carb cleaner. If it does not affect it, it most likely is not leaking. To fix this, you remove carb and intake, then take intake apart. You can use Permatex gasket maker to seal it up by putting it on seams and then putting the pieces back together. Another thought is the valves may need adjusted or checked to see if they have the correct lash. If memory serves me right, I believe they are to be adjusted every 600 hours and decarboned every 1000 hours. Hope this helps. Share this post Link to post Share on other sites
Tuneup 1,452 #3 Posted June 13, 2021 Having a 516H, I'm inclined to agree but my 520 doesn't have a running engine so what can I know? Like Horseyheaven, you'd best do a comparison from a similar starting point. You could decarbon, replace the intake seals, run a little gray sealer on the intake seams and then get your baseline. You might find that the 520s become sweet runners as well. I have to get back to that 20... Share this post Link to post Share on other sites
Wheelie horse 90 #4 Posted June 13, 2021 4 hours ago, horseyheaven said: 2 things come to mind. The intake is a two piece design and can sometimes begin to leak, causing them to run different. An easy way to tell is to spray carb cleaner along the seam where the intake goes together while it is running. If the intake is leaking, or will cause it to surge when it sucks in the carb cleaner. If it does not affect it, it most likely is not leaking. To fix this, you remove carb and intake, then take intake apart. You can use Permatex gasket maker to seal it up by putting it on seams and then putting the pieces back together. Another thought is the valves may need adjusted or checked to see if they have the correct lash. If memory serves me right, I believe they are to be adjusted every 600 hours and decarboned every 1000 hours. Hope this helps. Thank you I will try these things maybe they will help ! Share this post Link to post Share on other sites
Wheelie horse 90 #5 Posted June 13, 2021 40 minutes ago, Tuneup said: Having a 516H, I'm inclined to agree but my 520 doesn't have a running engine so what can I know? Like Horseyheaven, you'd best do a comparison from a similar starting point. You could decarbon, replace the intake seals, run a little gray sealer on the intake seams and then get your baseline. You might find that the 520s become sweet runners as well. I have to get back to that 20... I’ll have to spend some time in the garage is all and see what I can come up with there is a good chance it could be the intakes Share this post Link to post Share on other sites
Tuneup 1,452 #6 Posted June 13, 2021 Mine looked good but I did have it removed at the time so applied gray RTV to it. Working well and looks just fine - when you're careful. Share this post Link to post Share on other sites
oliver2-44 10,711 #7 Posted June 13, 2021 Start with a compression test to have a baseline of each cylinders condition. Do the maintenance suggested above. Check intake for leaks/replace seals Decarbon head Check valve clearances (since your this far into engine) use a magnifier glass and with each valve open inspect the seat and valve surface to determine if you need to lap the valves While you have it apart, clean the engine, especially the rear fins good. Consider ventilating the belt guard to help with air cooling the rear cylinder. Share this post Link to post Share on other sites
WheelHorse520H 708 #8 Posted June 14, 2021 I agree with everyone who said to try to decarbon the heads, my 520-H had an issue with surging and I took the heads off and they could use some good cleaning. This machine had around 650 hours so for you around 800 I would decarbon and see if that makes a difference. Share this post Link to post Share on other sites
Wheelie horse 90 #9 Posted June 14, 2021 2 hours ago, WheelHorse520H said: I agree with everyone who said to try to decarbon the heads, my 520-H had an issue with surging and I took the heads off and they could use some good cleaning. This machine had around 650 hours so for you around 800 I would decarbon and see if that makes a difference. Yes i have tried a few things since this post new plugs non ethanol fuel and a fuel system cleaner non seem to really help so looks like I’ll be tearing into the mother to clean the heads is this a difficult job on the Onans? Share this post Link to post Share on other sites
WheelHorse520H 708 #10 Posted June 14, 2021 2 hours ago, Wheelie horse said: Yes i have tried a few things since this post new plugs non ethanol fuel and a fuel system cleaner non seem to really help so looks like I’ll be tearing into the mother to clean the heads is this a difficult job on the Onans? Not very difficult, a word of advice though remove the hood from the hinge to get batter access to the front cylinder. The back one I pulled the battery and the plastic tray it sits on just be careful to not cut yourself on the metal battery tray that is under the plastic one. Once you remove the engine shrouds/tins over each cylinder there are 9 bolts. Don’t do what I did and miss one because you didn’t kneel down to look, if you try to pry the head off you are likely to break a cooling fin. Don’t ask how I know… Happy Cleaning, Andrew Share this post Link to post Share on other sites