Hobby Horse 2 #1 Posted June 5, 2013 Hi all. I'm a new member and found this forum while looking online for an answer to the problem that I'm having. I have a 1991 Wheelhorse with a 416 Onan motor. The problem is I have no compression in the rear cylinder. Zero. I've read about carbon build up possibley holding a valve open, or a valve seat insert that could have come loose. I'm going to take the head off and look for something obvious. I am the original owner and have no intention of getting rid of this tractor because I've had it for so long. I was really happy when I found this forum today because I plan to restore it soon. In the meantime though I have to fix this problem, so any advice that anyone may have would be greatly appreciated. Thank you in advance for any replies. Tom Share this post Link to post Share on other sites
WH nut 553 #2 Posted June 5, 2013 Open it up and do some exploritory. If it has Zero compression you will see what the problem is when you open it. Any symptoms before she went dead? Share this post Link to post Share on other sites
Hobby Horse 2 #3 Posted June 6, 2013 Thanks for replying WH nut. The only symptom that it had was that last Summer it seemed to run with less power, and rev to speed less quickly. This Winter when I went to start blowing snow it would barely run and would backfire through the exhaust. Share this post Link to post Share on other sites
WH nut 553 #4 Posted June 6, 2013 When it felt like less power is when you lost the cylinder. No noises or bangs? Share this post Link to post Share on other sites
Hobby Horse 2 #5 Posted June 6, 2013 No unusual noises that I can remember. I was surprised to get a response so early. Thouhgt I was the only one up at that time. If I don't respond right away, I'm working. Share this post Link to post Share on other sites
MalMac 1,331 #6 Posted June 6, 2013 Sounds like you have a valve problem. Look for the valve not seating and the valve seat loose. The seat may be down and look seated just fine so make sure you crank it over by hand so you can check it. Some of them will fool you when you first take a look at it. Others will be evident right away. What ever you do don't run it anymore so no more damage can occur. 1 Share this post Link to post Share on other sites
Hobby Horse 2 #7 Posted June 7, 2013 Thanks Mal Mac. Will check this weekend. I hope it's just carbon buildup. Not sure what to do if it's a loose valve seat insert. I guess I'll cross that bridge if I get to it. Share this post Link to post Share on other sites
ericj 1,578 #8 Posted June 8, 2013 it is either a valve seat or rod let loose. back firing through the carb sounds like valve seat, but it could be a rod also let us know what you find when you pull the head eric j Share this post Link to post Share on other sites
Hobby Horse 2 #9 Posted June 8, 2013 Thank you to everyone for your replies. I took the head off yesterday and this is what I found. On the compression stroke, when both valves are closed, the exhaust valve can still be spinned. I'm thinking it's the exhaust valve because it's the smaller of the two. That's all I had time for to work on it yesterday. I guess the next step will be to try to get the valve out. Is the valve or seat worn so bad that there's a gap between the two? Thanks for following. Share this post Link to post Share on other sites
WH nut 553 #10 Posted June 8, 2013 Im not following you when you asked about the gap. With the valve closed there should be no gap anywhere. Share this post Link to post Share on other sites
Hobby Horse 2 #11 Posted June 8, 2013 Right, but with the piston at TDC on the compression stroke I'm able to spin the one valve which makes me think that it's not making contact with the seat. The other valve is not spinnable. Share this post Link to post Share on other sites
MalMac 1,331 #12 Posted June 8, 2013 Is the valve shut but the seat is possibly spinning? Share this post Link to post Share on other sites
Hobby Horse 2 #13 Posted June 8, 2013 I guess that's possible. I'll have to check it out closer today. Share this post Link to post Share on other sites
Don1977 604 #14 Posted June 8, 2013 The clips holding the valve may have come off or the valve spring broke. I should have enought pressure from the spring that you could not turn it. Share this post Link to post Share on other sites
Hobby Horse 2 #15 Posted June 8, 2013 Thanks Don 1977. I'm going to dig a little further tomorrow and see if I can figure anything out. Share this post Link to post Share on other sites
Hobby Horse 2 #16 Posted June 9, 2013 I took the valve out today and was able to remove the seat insert very easily with my fingers. Not sure where I'm going to go from here. I guess with all the crud that was built up on the motor it caused it to run too hot. I had no idea that it was that dirty or I would have cleaned it out. Any suggestions as to what I have to do now. As always, thanks in advance for any ideas. Share this post Link to post Share on other sites
Hydro 131 #17 Posted June 15, 2013 Your issue is the most common problem with the Onan. They pop the valve seat on the rear cylinder when they overheat. There is no guarantee it won't happen again after an expensive repair. Share this post Link to post Share on other sites
Hobby Horse 2 #18 Posted June 15, 2013 Thanks for the reply Hydro. I imagine that the expensive repair is to machine the block for an oversized seat. Tha old seat is intact and someone suggested to dimple the block to hold the seat in place and readjust the valve. I'm going to give that a try today. Share this post Link to post Share on other sites
Hydro 131 #19 Posted June 15, 2013 If that's the extent of it you're lucky. Mine had the cross hatching worn out of it too on the back cylinder. I was pretty careful or so I thought but there were times when my wife would mow and I was not home. They can overheat pretty quickly especially if the flywheel screen cloggs up with grass which of course they always do. Good luck with it. Share this post Link to post Share on other sites
Hobby Horse 2 #20 Posted June 15, 2013 Thanks Hydro. I think that mine overheated because of all the crudd that had accumulated on the motor under the shrouds that I couldn't see. I blow it out with compressed air peiodically, but unless you take of the motor covers you can't get at it let alone know it's there. I'll post the results after I get it back together. Tom Share this post Link to post Share on other sites
WH nut 553 #21 Posted June 15, 2013 Thanks for the reply Hydro. I imagine that the expensive repair is to machine the block for an oversized seat. Tha old seat is intact and someone suggested to dimple the block to hold the seat in place and readjust the valve. I'm going to give that a try today. If you can pop the seat out far enough I would use some high temp locktite on it before you peen it in. And make sure you dont get any on the valve face or seat face. It will stick your valve and then you will have problems. Share this post Link to post Share on other sites
Hobby Horse 2 #22 Posted June 15, 2013 Great idea Hydro. I have the valve out so no problem getting at the seat. I just picked up some high temp locktite. Share this post Link to post Share on other sites
Hobby Horse 2 #23 Posted June 16, 2013 I used the high temp locktite to put the seat back in, put the valve and spring back in, readjusted the valves, put everything else back together and let the locktite sit overnight. Started it up this morning and it seems to be running fine so far. What a great forum. I can't thank all of you enough for all of your help. 2 Share this post Link to post Share on other sites
ericj 1,578 #24 Posted June 17, 2013 sorry i didn't get to respond to this sooner i have had 2 onans that i have had the valve seats put back in i took them to napa here in York pa which is just a little far for you i know but they put the intake seat back in the 1st 1 for about $100.00. the 2nd motor ended up needing intake and exhaust seats and they only charged me about $ 130.00 for that job. plus the gasket set that's $ 50.00 from onanparts.com so it's not a real expensive repair if you can pull the motor off and apart yourself eric j Share this post Link to post Share on other sites
