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Tractor Talk Discussion Forum

engine not firing on all cylinders

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Mark Riggs

11-17-2003 13:27:53




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Have a super C with a c123 engine that dosn't seem to be firing on the #3 cylinder. Did a compression check and got around 145 to 149 PSI on all but the #3 that read 125 LBS. Took the plug out of that cylinder and put in a little oil on top of the piston and picked up an additional 10 PSI which I suppose indicates the piston rings are leaking on that cylinder. But should the cylinder fire with 125 PSI of compression? Getting spark there, checked that. Don't really want to do over haul because engine has hair line crack in block behind the water pump area where I understand they are prone to crack. Any suggestions?

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Mark

11-18-2003 06:19:04




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  

Check to make sure the distributor shaft isn't all worn out. Sometimes they get so much wear that the shaft moves around too much and they won't fire on all cylinders.



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kjm

11-17-2003 21:26:04




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
Mak, I just went through this with a Super M, it was a bent rocker arm. (Gave 500.00 for it because the dealer thought the valves were bad)



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Ol Chief

11-17-2003 17:34:29




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
There is a lot of good advice in all of the other posts.If all of it has been put to use without results except Bobs suggestion then it sounds like he may have the answer to your problem.An intake manifold crack or leaking gasket is not common but I have had this problem and chased around all the other possibles and found a leaking gasket last.



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Revredneck

11-18-2003 09:51:33




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 Re: Re: engine not firing on all cylinders in reply to Ol Chief, 11-17-2003 17:34:29  
If the intake gasket is leaking, you can find out by spraying carb cleaner around the joint where it mates to the head with the engine idling. If the RPM's pick up when you spray it, there's a leak. It's pretty simple to find, and easily overlooked. Gook Luck and God Bless, Tommy



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john

11-17-2003 17:18:09




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
Change plugs with another cylinder. I had a brand new plug that would not fire right out of the box. Changed cylinders and the miss changed too.



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Joe Evans

11-17-2003 15:33:53




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
Just fixed a problem JUST LIKE yours on an MF-50. Pulled the vavle cover and discovered that the adjusters on #4 had come loose and had fallen on top of the head. Found all the goodies, re-installed, adjusted, and them proceeded to wipe out the drive shaft of the mower the 50 was making so much power!



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redrig

11-17-2003 14:22:39




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
Thanks for the input guys. I have replaced the plugs with new ones and the wires are new copper core. Could be the distributor cap although I can't see any defects. I belive I have wires in the proper order. I assume the #1 cylinder is nearest the radiator, if so I should have it correct. May neeed to have someone check the push rods on that cylinder to make sure the valves are operating correctly. Thats a little out of my range of limited expertise. Thanks again

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wdTom

11-17-2003 16:32:52




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 Re: Re: engine not firing on all cylinders in reply to redrig, 11-17-2003 14:22:39  
You can check the operation of the valves. It is easy to doa basic check. Remove the valve cover. With the piston for that cylinder at the top and the rotor pointed to that cylinder, the valves should be closed-you should be able to very slightly wiggle the rocker arms, and insert maybe a .010 feeler gauge between the valve stemand the tip of the rocker arm. Now hand cranking the engine over the valves should both (at different times) open as much as the other valves on the other cylinders. Rig up some simple gauge or method of measureing this. This will tell you if you maybe have a worn camshaft. This won't tell you if you have a burned or leaing valve, or slightly worn parts, but it will tell you if things are probably OK.

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Bob

11-17-2003 13:32:58




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 Re: engine not firing on all cylinders in reply to Mark Riggs, 11-17-2003 13:27:53  
Have you replaced the spark plug? 125 psi should be more than enough to fire. Are you certain wires are on plugs in correct firing order?

Check for intake leaks, and verify that pushrods are properly operating both valves for the #3 cylinder.



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Kevin (FL)

11-17-2003 14:06:54




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 Re: Re: engine not firing on all cylinders in reply to Bob, 11-17-2003 13:32:58  
That engine will run with less than 100 PSI compression. I agree with Bob--replace the spark plug with a known good one and check firing order and also check the plug wires. I find carbon type plug wires installed on tractors all the time instead of the solid copper type. They will work but also have found they can cause misfiring or no firing of the plug. I use an inductive-type timing light to do a quick check and then replace any suspect wires that are intermittent firing.

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