metzep 5 #1 Posted September 21, 2022 Have a onan 220 with 1100hours. Completed a valve check and clean.. With new gaskets.. put back together. Barely started.. with carb and exhaust backfire.. Stopped.opened valve covers..and rotate engine. Now left and right cylinder. Are open and closing valves oposite of each other. ..they are suppost to be in sync. Firing at the same time.. Question..what happened.how to correct...and is this even possible? 1 Share this post Link to post Share on other sites
BESTDOGEVER 218 #2 Posted September 21, 2022 They should be opposite each other hence the name opposed twin. The valves would have to work alternately ,the coil fires when one is on power stroke and the opposite one is on exhaust Share this post Link to post Share on other sites
Handy Don 10,557 #3 Posted September 21, 2022 (edited) 15 minutes ago, BESTDOGEVER said: hence the name opposed twin Opposed actually means that they are in the "boxer" configuration with the cylinders 180º apart on the same crankshaft. Different than a "V-twin" where the cylinders are often at or near 90º apart. Edited September 21, 2022 by Handy Don 1 Share this post Link to post Share on other sites
metzep 5 #4 Posted October 15, 2022 Thanks for all your input... 40 years in this landscape field and dont know how a twin engine works yet.. oh boy... I got confused ... it has to be in balance...or it would tear it self apart... the ignition fires both plugs at the same time is where i got off track... the waste spark on the opposing side is during the exhaust..stoke totally benign... so there you have it..... thanks guys 2 Share this post Link to post Share on other sites
