WHEEL HORSE 312-8 52 #1 Posted April 19, 2015 A friend came to me saying his 520 is only running on front cylinder can any one guess what's wrong y back is not firing Share this post Link to post Share on other sites
daveoman1966 3,586 #2 Posted April 19, 2015 Fouled plug, loose plug wire, could be many things. I had same issue and found that the intake manifold gasket was shot, letting too much air to cylinder. Share this post Link to post Share on other sites
312Hydro 473 #3 Posted April 20, 2015 Switch the plug wires and see if the other cylinder fires. I had 1 cylinder firing on my 520h and it turned out to be a bad coil. 2 Share this post Link to post Share on other sites
WHEEL HORSE 312-8 52 #4 Posted April 20, 2015 It has a BLOW connecting rod to piston Share this post Link to post Share on other sites
ericj 1,576 #5 Posted April 20, 2015 that's why i do a compression test first when i have one only running on one cylinder eric j 3 Share this post Link to post Share on other sites
BESTDOGEVER 218 #6 Posted April 20, 2015 That happens a lot to the 18 and 20 horse onan engines if you are lucky the crank is still okay but you will probably have to replace both rods because they have changed them and they would not be balanced. I had the same thing on my 518h when I got it 1 Share this post Link to post Share on other sites
BESTDOGEVER 218 #7 Posted April 20, 2015 Hi all please excuse my lack of manners I am new to the forum but have been a wheel horse owner since 1988 when I got my 310-8 I recently got back into them with a 518h that needed the rear cylinder rebuilt after the previous owner let it run out of oil. I owe you guys a big thank you for the info I got here that made rebuilding it a lot easier. Also I wanted to say don't be too quick to give up on the crank as they are pretty strong mine had a layer of melted aluminum from the rod on it and cleaned up pretty well .Good luck with your 520 4 Share this post Link to post Share on other sites
WHEEL HORSE 312-8 52 #8 Posted April 20, 2015 Everyone is so awsome here Share this post Link to post Share on other sites
elliot ness 1,916 #9 Posted April 21, 2015 One thing that kills a cylinder is fins that are full of debris, I take an air hose and blow out all the fins on the cylinders after every 2 or 3 hours of use. The debris that collects in the fins create hot spots inside the cylinders, by not letting out the heat. and on the twins, always keep the screen on the fly wheel side clean, Its where the motor get all the forced air to cool the cylinders. And lastly change the motor oil often, it's a lot cheaper then a new motor. Share this post Link to post Share on other sites
BESTDOGEVER 218 #10 Posted April 21, 2015 That's true and with the onan they tend to get the screen covered up with grass really fast add that to the high hour machines using a bit more oil and you have a recipe for disaster Share this post Link to post Share on other sites
