seuadr 488 #1 Posted April 16, 2021 ok, so, maybe this is a stupid question, but i thought of it while i was in the shower. so my onan twin's "front" muffler is hotter than the rear muffler. I am not sure what can cause this - but one thing that occured to me is that i may not have hooked the coil up correctly and THAT got me wondering about the firing order - i assume that they don't fire at the same time? my train of thought was, if i were to switch the plug wires around, and the cooler muffler symptom followed the wire, then it might indicate like, a spark problem or something - at least give me a direction to start in, but, i don't know if that could potentially cause issues? thoughts? Thanks, Jared Share this post Link to post Share on other sites
pfrederi 17,147 #2 Posted April 16, 2021 Interesting Kohler twins fire both cylinders at same time even though one is on exhaust stroke ...Wasted Spark is the term. 1 Share this post Link to post Share on other sites
seuadr 488 #3 Posted April 16, 2021 7 minutes ago, pfrederi said: Interesting Kohler twins fire both cylinders at same time even though one is on exhaust stroke ...Wasted Spark is the term. maybe onan does the same - i've no idea Share this post Link to post Share on other sites
squonk 38,927 #4 Posted April 16, 2021 (edited) Cylinder lean. Intake leak perhaps. How's compression? Low cylinder = nofire =no heat Edited April 16, 2021 by squonk Share this post Link to post Share on other sites
seuadr 488 #5 Posted April 16, 2021 Just now, squonk said: Cylinder lean. Intake leak perhaps. oh good point - didn't think to check for intake leaks. thanks! Share this post Link to post Share on other sites
pacer 3,159 #6 Posted April 16, 2021 12 minutes ago, seuadr said: if i were to switch the plug wires around, and the cooler muffler symptom followed the wire, This is an excellent idea, because, yes, it does fire both both at same time. If it stays same, then pursue one of the other suggestions. 1 Share this post Link to post Share on other sites
squonk 38,927 #7 Posted April 16, 2021 (edited) If you switch the wires it will make no difference unless the problem is within the coil or wire. Both cylinders spark at the same time. Edited April 16, 2021 by squonk Share this post Link to post Share on other sites
Ed Kennell 35,769 #8 Posted April 16, 2021 Yep, both cylinders fire at the same time every revolution. One is on the power while the other is on the exhaust stroke. 1 Share this post Link to post Share on other sites
8ntruck 6,376 #9 Posted April 16, 2021 Have you pulled the spark plugs for a reading? That could give you some idea of what is going on. 1 Share this post Link to post Share on other sites
bc.gold 3,399 #10 Posted April 16, 2021 The twins motto, two at a time save time. Share this post Link to post Share on other sites
Handy Don 10,597 #11 Posted April 19, 2021 On 4/16/2021 at 10:03 AM, seuadr said: maybe onan does the same - i've no idea Onan has a single input to the coil and two outputs (one to each plug) with no distributor. That's how you can tell that both plugs are sparking together, as @Ed Kennell and @lynnmor noted. Share this post Link to post Share on other sites
bc.gold 3,399 #12 Posted April 19, 2021 When was the last time the valves were adjusted. Share this post Link to post Share on other sites
bc.gold 3,399 #13 Posted April 19, 2021 (edited) 11 hours ago, bc.gold said: When was the last time the valves were adjusted. A bad or leaking or burnt exhaust valve would raise the temperature of the cylinder, readjust the valves its also possible your engine has excessive carbon build up which could hang a valve from operating properly. Edited April 19, 2021 by bc.gold 1 Share this post Link to post Share on other sites
seuadr 488 #14 Posted April 19, 2021 @bc.gold so i checked the valves when i put the motor together, but, i haven't checked them since - but i've got less than an hour on the motor so far. Hopefully i don't have a valve problem yet, but is it possible that they could have "seated in" a little bit with running for the first time? i think i've got an extra set of valve cover gaskets so it wouldn't be hard to check them again. Share this post Link to post Share on other sites
seuadr 488 #15 Posted April 19, 2021 i forgot to follow up on this - I believe it was just me being dumb and forgetting to snug the rear plug up. when i pulled the plugs yesterday to see what was going on, it was wet, so i cleaned it off, put it back in and fired it back up (to see if it was recently wet or from the other day and wouldn't you know - turns out if the plugs aren't tightened in, it doesn't work very well! these picky motors - they want fuel, and spark, and compression. GAH it never ends~! Share this post Link to post Share on other sites
bc.gold 3,399 #16 Posted April 19, 2021 (edited) 7 minutes ago, seuadr said: @bc.gold so i checked the valves when i put the motor together, but, i haven't checked them since - but i've got less than an hour on the motor so far. Hopefully i don't have a valve problem yet, but is it possible that they could have "seated in" a little bit with running for the first time? i think i've got an extra set of valve cover gaskets so it wouldn't be hard to check them again. Didn't realize the engine had been overhauled while your at it re torque the head bolts. Air cooled engines require a much larger ring gap maybe a ring or two has been improperly gaped which is causing excessive drag which is causing the mystery heat on one cylinder. Edited April 19, 2021 by bc.gold Share this post Link to post Share on other sites
