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F-20 missing issue for you advance problem solvers

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Pete L

06-12-2004 06:33:26

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Guys - - - Purchased a '36 F-20 last year with a missing problem in the engine. Much work has been done to cure this, but the tractor is getting the best of me and I'm about ready to shoot the dumb thing. Work done thus far is as such: new rings & sleeves, professional head rebuild, mag rebuilt, carb rebuilt, new wires & AC plugs, mag and valve timing verified by 2 other people, spark is consistand and hot, mag and carb were temporarily swapped from good running tractors with no change. All these things should result in a good running engine, but after all this work, the original missing problem is still there. It's eludeing me.

Here's the symptoms: 1) engine misses 20-40% of the time, at any speed. 2) engine runs smoother at full spark retard. 3) as load is increased, engine progressively runs smoother to near perfect at full load. 4) intake manifold pressure is 10-12" Hg, and drops as the engine recovers from missed firing. 5) Adjusting carb gives engine reaction as you'd expect, but doesn't effect the missing problem.

Need some help here! All of the basic stuff has been done and verified, but there's something on this engine that's still not right that I am missing. NEED HELP FROM YOU ADVANCED PROBLEM SOLVERS ! Will provide more information if you ask for it.

Thanx !

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F-Dean

06-13-2004 20:37:50

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Double check the timing. The fact that it runs better at full retard is suspicious. You may have to rotate the mag conection a hole or two.

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Tom Fesenmyer

06-13-2004 06:00:47

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Pete, these guys offered you some very good advice. The funny thing about what you described is that the tractor runs perfect at full load. I had an F-20 that I sold last year. It was a honey of a tractor. I had the head rebuilt(new valves, head machined, guides, the whole 9 yards), then sleaves, o-rings, etc. I reused the cam, but had it checked. After doing all of this, the tractor idled a little rough, but a full load smoothed out and pulled like a mule. The engine idled like a cammed up hemi. I guess what I'm getting at is, running a little rough might be the nature of the these tractors. Call me crazy and the other guys will probably lamb baste me for saying this. Good luck with your tractor, they are still one of the coolest old tractors ever made.

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lee

06-13-2004 08:05:50

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Re: Re: F-20 missing issue for you advance problem in reply to Tom Fesenmyer, 06-13-2004 06:00:47

nobody should lambaste but 0mone would think the motor motor should run smooth. Sounds like it's running like an old hit-and-miss engine.

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JRM

06-13-2004 07:03:34

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Re: Re: F-20 missing issue for you advance problem in reply to Tom Fesenmyer, 06-13-2004 06:00:47

My F20 has run like you describe for as long as I can remember. As you say, it idles like a cammed up hemi and smooths out and pulls like a mule under load. I've often wondered if it should run smooth all of the time. Mine still uses the kerosene carb, but I run gas in it. Is it possible that the kerosene carb puts out too much fuel at lower rpms and loads up the engine?

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Tom Fesenmyer

06-13-2004 10:01:40

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Re: Re: Re: F-20 missing issue for you advance pro in reply to JRM, 06-13-2004 07:03:34

My F-20 was gas and I really know nothing about Kerosene. Do you guys think that the model H tractors run smoother than the F-20s or is it just me? I noticed that when the outside temperatures are below 50 degrees or so that the F-20 liked to be choked just a little bit while running. That seemed to make the engine run a little smoother.

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El Toro

06-13-2004 05:46:01

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Hi Pete, Did you check that valve lash for correct clearances? If the engine still misses
after adjusting valves pull one plug wire off at
a time to see if you can determine which cylinder
is missing. If that cylinder head has had numerous
valve jobs, the valve seats may be to deep in the
head and should've had inserts installed. Run a compression check on all cylinders with the throttle wide open, the readings should be very close to one another. Did you use new valve springs? A weak valve spring will cause a miss.
I had a 57 Chevy that had a miss and I checked everything, but never could find the problem until
the spring broke. After replacing the spring it cured the miss. When I did the head I used the old springs, I always used new springs after that.
I know they say you can use valves when the valve
thickness are 1/32" thick. I replaced exhaust valves if they're that thin. Update us if you find the problem. Hal

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Hermit

06-12-2004 19:48:36

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

The vacuum reading indicates late valve timing.

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pete L

06-14-2004 05:00:45

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Re: Re: F-20 missing issue for you advance problem in reply to Hermit, 06-12-2004 19:48:36

Hermit - - I was suspicious of the valve timing last summer. The book said that on #1 cylinder, the exhaust valve should close just before TDC, and the intake open just past TDC. My tractor proved to be running 10-15 degrees late on all valve actions. The book also said that the starting crank pin in the nose of the crank shaft should be horizontal at TDC. It is 10-15 degrees off in the same direction also. Last summer, I moved the cam shaft timing gear 3 teeth to get the valve timing in line to the book. Problem wasn't apparently better or worse. Thoughts ? ? ? Pete

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Larry Martin

06-12-2004 15:57:09

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Try a set of Auto-lite plugs. I have never had any luck with AC.

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BURT

06-12-2004 15:18:36

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

QUESTION-----Does miss stay with same cyl. or does it move around? If same cyl. is probly valves, plugs, or compression. If moves around there is probly a leak somewhere as others have said.

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El Toro

06-12-2004 09:35:25

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Hi Lee, After checking that intake for leaks and
the compression on each cylinder and if this doesn't help check your valve adjustment. Make
sure you're on the compression stroke and rotate
engine until the rotor points to No1 and the timing marks are aligned. Adjust valves on No1
cylinder and then rotate engine to the next plug
on the distributor which should be No3 and adjust, then No4, then No2. You may not have enough clearances on your valves. You will lose
a little clearance as the engine gets to operating
temperature. Good luck, Hal

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lee

06-12-2004 10:09:36

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Re: Re: F-20 missing issue for you advance problem in reply to El Toro, 06-12-2004 09:35:25

This is a good point I assumed had been done several times. But I hate to make assumptions.
Verify also the firing order and correct wiring order to the plugs. A possible cracked distributor cap, Carbon fouled plugs, too rich,
too lean mixture. yada, yada, yada... This is a simple engine and you can fix it. DO NOT GVE UP!

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lee

06-12-2004 09:16:11

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Since you have swapped carbs and mags and the problem remains I will assume (and I hate to make assumptions) the problem is not there. You should pull the intake manifold and check it carefully for cracks and for uneven surfaces or leaks at the head and at the carby. This is easy and you need to be absolutely sure it is not leaking or cracked. Next I would do a very careful compression test, writing down the numbers, same number of strokes each cylinder, all spark plugs out, no leaks at tester, carburetor removed, or at least the air cleaner and throttle wide open, looking to see the compression is very good and consistent on each cylinder. Beyond that I'd be looking closely at the cam and valve train. You don't mention the cam at all. Have you inspected it closely? Are there any worn lobes. You can remove the valve cover and measure the lift at each push rod. I don't know the spec but they should all be the same. Verify each and every one.
Check all pushrods to insure none are bent. Many times a head builder does not get the valve geometry correct and consistent when he grinds and replaces valves. If the head is not re-done correctly the valves can be too deep in the head. The stem will stick out too far on top side and the rocker will be rolled over to cam side too far. Valves will open too soon. There should be a spec for the correct dimension from tip of valve to spring seat surface or similar dimension for a rebuilder to make adjustments and get the head to spec on all valves. All the valves should be checked to be in spec and free of travel, no broken spring coils, etc., etc. At this point, with all the things you/ve done it's time to start from scratch and not assume you've done this or that and it can't be this or that. You've got to re-verify everything. I did not mention cam timing. It doesn't sound like you have been in there. Odds are someone else has so it may not be right, who can say?

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Reido in Mo

06-12-2004 08:46:04

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Maybe you could try pulling plug wires seeing which one has the least ill effect, might be able to determine which cyl. if it is a specific cyl.If you can't make any determination this way, to my notion it's probably fuel, air flow related.
My .02

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Allan

06-12-2004 06:56:27

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Haven't got a valve too tight, do you?

Allan

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Allan

06-12-2004 06:47:00

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Re: F-20 missing issue for you advance problem sol in reply to Pete L, 06-12-2004 06:33:26

Hi Pete,

The thing that jumps out at me is that low vacumn. You don't have an intake leak do you?

But, then again, this could just be a reflective reading from that dead hole too.

Allan

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Pete L

06-13-2004 09:50:34

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Re: Re: F-20 missing issue for you advance problem in reply to Allan, 06-12-2004 06:47:00

Hey guys - - Thanx for the feedback, and lots of it. The missing situation didn't appear to get worse or better once the head was rebuilt, so I'm kinda ruling that out for now. The missing situation seems random between the cylinders, as no one cylinder seems to be better or worse than the others when plug wires are pulled.

Being it is a random missing situation between the cylinders, I have to assume is it something to that is shared between all the cylinders. I need to zero in on the intake system thru the carb and up into the manifold. Anybody have any idea what "adequate" vacuum should be? Also, how much looseness in the throttle shaft in the carb will affect this problem?

I'm off to the garage this afternoon (Sunday) to do some more exploring. Check back on Monday for updates. Thank all for your input thus far.

Pete

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