fireman 1,022 #1 Posted June 23, 2010 I transplanted an Onan 20hp out of a 1989 520H into my C-81 as most of you know. Got the exhaust all modified today. When we started it up after welding the muffler to the existing pipes, we noticed the joint we made on the rear cylinder pipe turned blue and the front cylinder pipe didn't. It was also noticeably hotter than front pipe even after running for a few minutes. We checked for spark to make sure we had it on the front, which there was. Anyone have any idea why one would be hotter than the other? I have no experience with Onan engines. I want to bring this tractor to the show but not if it's not running right. Share this post Link to post Share on other sites
WH nut 553 #2 Posted June 23, 2010 If you have a temperture gun check and see how close the temps are. Is the moter clean under the tin and getting good air flow Share this post Link to post Share on other sites
Save Old Iron 1,571 #3 Posted June 23, 2010 Check to make sure the large rubber gasket is present around the oil filter. Loss of that gasket can disrupt the full airflow to the engine cooling fins. Share this post Link to post Share on other sites
wh79d160 52 #4 Posted June 23, 2010 I would think the hot cylinder is too lean,not firing correctly, not getting enough fuel. Or you could have a bad spark plug, check the gap, The coil may also not be working right, bad wire??? good luck, Tom, Perry Ks. Share this post Link to post Share on other sites
