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Farmall & IHC Tractors Discussion Forum
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When does a head need rebuilding on an F-20 ?

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Pete L

03-03-2004 10:30:51




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Guys -

What are tell-tale signs of a head needing rebuilding on an F-20, short of leaking valves?

Engine runs well, spark advanced, under a load, but misses frequently without load, at any speeed. Engine has been checked out by numerous people and fuel/spark/timing are all in order. Indicators point to the head, but I don't know the effects of a worn head.

Seeking your wisdom & experience. Thanx !

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Pete L

03-03-2004 13:31:27




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 Re: When does a head need rebuilding on an F-20 ? in reply to Pete L, 03-03-2004 10:30:51  
Guys - Thanx for the quick feedback. The tractor, as purchased, would run well, spark advanced, under a heavy load at any speed. Remove the load, at any speed, and the engine misses 30-40% of the time, but those cylinders firing sound fine as an advanced spark timed engine should. Retard the spark to TDC, and it runs near fine, at any speed without the load. An overhaul was deemed necessary.

Yes, the engine had been torn down by myself for 2 sleeve replacements (due to water damage pitting), new rings all around (cylinder-to-piston tolerance well within specs now), carb rebuilt, mag rebuilt, valves ground (some seats were very pitted and marginally sealed), wet & dry compression test done and hovered around 60psi after rebuild, intake system tested for leaks and all is well, new gaskets upon overall reassembly, Autolite 3076 plugs, new wires, spark and valve timing was verified several times, spark checked with timing light on all cylinders and it is constant and steady. Upon starting up and running, the missing situation described earlier had not changed. All work had not affected the problem. A mag and carburator from a good running tractor were temporarily installed and the missing problem was still there. This ruled out the mag and carb as the issue. Am running out of things to check. All work done till now has not bothered the missing problem. When last run, I was noticing that as the tractor missed, a light "popping" was heard thru the carburator, but never a back fire. This link has lead me to believe I have a head issue. Yup, I'm aware of the manual oiling needed to the valve train and have kept it wet, along with replacing the wicks. With this feature, I can see worn valve guides as possibly being an issue. Also, during the regrinding of the valves, the head & valves were cleaned and valves hand ground in, but not professionaly, nor did I check them for warping. This is where I think my problem lies, and why I was looking for tell-tales on failing head operation.

With all this background, what's your thoughts now ?

Thanx for your time and thoughts.

Pete

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Bob Kerr

03-04-2004 21:00:51




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 Re: Re: When does a head need rebuilding on an F-2 in reply to Pete L, 03-03-2004 13:31:27  
Just a thought, but did the governor have any wear? That might let the throttle get slightly sucked open too far and then the speed picks up enough for the gov to push it back closed causing a sputter. It might be right at that fine point where it it isn't an obvious gov problem, but enough to make it sputter off load. You might be able to rotate a half turn or so, that pot metal part that is on the gov and see if that helps. There is a spring inside that I think tensions the flyballs.I also thought about valve guides and throttle shafts worn, like a few of the other guys mentioned.

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Bruce

03-04-2004 17:49:03




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 Re: Re: When does a head need rebuilding on an F-2 in reply to Pete L, 03-03-2004 13:31:27  
I had the same problem on my F20. I replaced the valve guides and exhaust valves with new. Also
installed hardened valve seats so can run on
unleaded gas. Did 4 years ago. Haven't had a problem since.



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F-man

03-03-2004 15:17:07




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 Re: Re: When does a head need rebuilding on an F-2 in reply to Pete L, 03-03-2004 13:31:27  
Be sure to check for manifold leaks. With the tractor running, spray some starting fluid around the manifold gasket around the two intake ports. If the engine speeds up then you have a leaky manifold gasket. You can also check for valve seat problems buy holding something thin over the exhaust. A dollar bill works great for this test! With the tractor running, the dollar bill should not go down the exhaust at all. You can tell if the exhaust is trying to pull on the dollar or not. If it is then you have valve problems. Do this chek on the intake as well. It should be a constant pull on the bill and at no time try to blow it out. Be sure to take the air breather pipe off and do this test right at the carburetor. Another thing to check for is worn throttle plate pivots. Good luck!

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Bill Smith

03-03-2004 12:02:48




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 Re: When does a head need rebuilding on an F-20 ? in reply to Pete L, 03-03-2004 10:30:51  
Burnt valves ussually will make a popping noise when engine is running. The sound will either travel out the exhaust or back through the intake. Bad seats or valves can incorporate a mis. F-20's are natorious for sticking valves also. You want to be darn sure that you don't have a valve or valves that are sticking open all the time or even once in a while. Remember that the stuff under the valve cover needs to be oiled every so many running hours. As Dave said, you might want to do a compression test. If you come up with low readings, squirt some oil in on top of the pistons and do it again. If you still have low readings, you have bad valves or seats. If the readings were low and oil brings the compression readings up to normal, you are losing compression at the piston rings (either bad rings or to much sleeve wear). If you pull the head to do a head job, be sure the valves, seats, guides, and everything is checked out in the head. Also check the head for flatness (most likely will be alright) and you will most likely want to use all new gaskets when you put it back together.

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brianh

03-03-2004 11:51:11




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 Re: When does a head need rebuilding on an F-20 ? in reply to Pete L, 03-03-2004 10:30:51  
Generally speaking, an engine that runs OK under load but misses without load is running too rich. Many small engines, particularly old Kohlers, will do this when the mixture is set correctly under load. Those Zenith K-5 carbs are pretty crude. Can you minimize the miss by leaning it out slightly? The toughest test for any engine is when it is put under load. If it runs OK under load it is hard for me to believe that there is anything seriously wrong with the head.

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Dave_Id

03-03-2004 11:07:13




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 Re: When does a head need rebuilding on an F-20 ? in reply to Pete L, 03-03-2004 10:30:51  
Did you check compression?



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