Uh-Oh. No compression backfires

[1973Auto 80]

Well i've got trouble. Just got in from plowing. Got off my tractor to move my truck, got back on the horse reving pretty high and I see small blue flames coming out of exhaust and then dies. Tried to start but backfires. I can turn the flywheel by hand. So I got no compression. I think the old horse might be done. 12 hp Koehler.  Is she done or do I have a chance.

[benji756 341]

try pulling the spark plug and seeing if the piston is going up and down if so you may have sheared the flywheel key

[1973Auto 80]

Ok that will be my job this Saturday.  If it is moving the piston, how big of a job is it to fix the key to the flywheel. Thanks.

[953 nut 58,046]

I had a big chunk of carbon brake off and wedge a valve part way open once. Pulled the head, scraped the carbon off put on a new gasket and it was good as new.

[1973Auto 80]

953 thanks I'll look for that, hope all that it is. If it's not what else may be the cause. Just trying to get all my ducks in a row. Right now I have chunk of carbon and broken flywheel key. Any other ideas????

[Ed Kennell 40,566]

Broken keeper on the exhaust valve.

[squonk 42,605]

I hate to be a Debbie Downer but I'm voting for a rod.   Wish you the best though.

[AMC RULES 37,147]

I would think one would hear the rod let go.  

[953 nut 58,046]

        I've had a couple of rods let go and they were very noticeable events. Also, if it backfires it has enough vacuum to draw fuel/air mixture in and enough compression to help ignite it.    

[Ed Kennell 40,566]

                                                                                                        

Very low compression  +  backfiring through the exhaust = a leaking exhaust valve     I would pull the carb and breather first to check the valves.     

 

                                                                                             2 scents + 2 sense =  4 cents 

[1973Auto 80]

thank all for the replies. Now get this, before I left for work this morning I decided to try to start it just for fun.......guess what started right up. Didn't run it long because I had to get going but it ran just as before!!!!!  Now I don't know what to think??? Any thoughts on this?????

[Ed Kennell 40,566]

I would guess Richard @953 nut nailed it.  A piece of carbon holding the exhaust valve open and it dislodged itself.  You may want to schedule a head pull and decarbon.

[1973Auto 80]

Ed. That's what I was thinking, clean that up and get a new head gasket.

[Pollack Pete 2,273]

Had the same thing happen years ago when I owned a yellow and white tractor.It did have a 12 horse Kohler though.Would start right up.Run great til it got hot.Backfire and quit.Come back later,it would start right up and run great til it got hot.Then the same thing.Back fire and quit.One day I decided to hang around the tractor after it quit.I heared a small metallic click.I tried and it started right up.Come to find out,the exhaust valve had so much carbon around the stem that it was sticking open then slamming shut as the engine cooled down.Pulled the head,de-carboned everything and it was fine.Good luck.I'm sure you'll be just as lucky.

[clueless 3,118]

1 hour ago, Pollack Pete said:

Had the same thing happen years ago when I owned a yellow and white tractor.It did have a 12 horse Kohler though.Would start right up.Run great til it got hot.Backfire and quit.Come back later,it would start right up and run great til it got hot.Then the same thing.Back fire and quit.One day I decided to hang around the tractor after it quit.I heared a small metallic click.I tried and it started right up.Come to find out,the exhaust valve had so much carbon around the stem that it was sticking open then slamming shut as the engine cooled down.Pulled the head,de-carboned everything and it was fine.Good luck.I'm sure you'll be just as lucky.

Years ago had a B-80 did the same thing.