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John Deere Tractors Discussion Forum
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valve or ?

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47B

12-24-2007 16:19:17




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newbie bought 47B told it was rebuilt wont start been through timing ect. Compression test 22 right 15 left by running starter any thoughts before I pull head? I am BLESSED CHRISTMAS EVE and I am working on my tractor, THANK-YOU ALL'




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P Browning

12-25-2007 05:14:57




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 Re: valve or ? in reply to 47B, 12-24-2007 16:19:17  
47B -- There is no question that you need to open the valve cover (front of the engine) and check things out. For openers, it sounds like at least one valve tappet lever on each side is set to close -- not allowing the valve to fully close. I say this because your compresseion is seriously low -- to the point where "NO", the engine will notstart!

The specified gap setting for your tractor is .020-inch, but to be on the safe side set them a bit more (say) at 0.22-inch when at room temperature. Set them and them double-check to see that the settings hold. Then button 'er up and re-run the compression test.

While you say you are a newbie, I am assuming you know your way around engines a bit - but I want to say this. As others have mentioned, open throttle (throttle lever full ahead) and also wide open choke (choke in running position) are essential so that you do NOT impede air-flow into the engine during the test. To be safe, you should also disable ignition by removing the plug wires from the magneto/distributor, marking at least one of them "top" (or "bottom") beforehand. The top terminal is normally No. 1 (flywheel side) -- at least that is the way it left the factory.

Merry Christmas! (PatB)

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skip33652

12-24-2007 19:16:38




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 Re: valve or ? in reply to 47B, 12-24-2007 16:19:17  
the throttle must be open and no restriction ice etc. in the intake to get compression reading.Paul



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BushogPapa

12-24-2007 18:07:30




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 Re: valve or ? in reply to 47B, 12-24-2007 16:19:17  
If you do have to remove the valve cover, take a small Brass hammer and tap the rocker arm ends over the valves, to bouch the valves off the seats... Maybe carbon is trapped under the valves and not letting them seal.. With the air cleaner oil bath bowl removed, listen for lots of leakage there, as the engine is turned over..same for listening at the end of the exhaust.. Using the air can be a great way too, but ya have to seat all the valves first by adjusting them out, or taking the rocker arms off..!

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BushogPapa

12-24-2007 18:07:21




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 Re: valve or ? in reply to 47B, 12-24-2007 16:19:17  
If you do have to remove the valve cover, take a small Brass hammer and tap the rocker arm ends over the valves, to bouch the valves off the seats... Maybe carbon is trapped under the valves and not letting them seal.. With the air cleaner oil bath bowl removed, listen for lots of leakage there, as the engine is turned over..same for listening at the end of the exhaust.. Using the air can be a great way too, but ya have to seat all the valves first by adjusting them out, or taking the rocker arms off..!

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jd b puller

12-24-2007 17:47:36




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 Re: valve or ? in reply to 47B, 12-24-2007 16:19:17  
Make sure the valves aren't so tight that they are staying open. Make sure when checking compression, you've got it at full throttle. If you have any way to pressurize the cylinder (maybe you can run shop air into the hose that your compression gauge uses (make sure to take out the valve in the end of the hose). Knock all the pushrods off and put 100 psi into the cylinder. If you've got a bad valve, you'll hear it out the muffler or the intake. SHouldn't be any. Might want to loosen those bolts that hold the crankcase cover on (in front of the gear shift pedestal) before you do this.

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