Farmall Super A Engine Missing When Hot

SnakNest

New User
I have a Super A which has recently developed an issue where it seems like the engine starts to miss when it gets hot.

It's a 6-volt positive ground system. I changed the coil, but that didn't solve the problem. I ultimately ended up changing points, condenser, rotor, and spark plugs as well, with no change. I also adjusted the valve clearance with no change in behavior.

I didn't change the plug wires yet, as I'm doubtful that's the issue since the problem doesn't seem to happen on just one cylinder (I can't duplicate it by pulling individual plug wires), and the wires are only about a year old anyway.

The problem shows up after the engine is hot, and doesn't seem to take more than a few minutes of idling or being shut off to make it go away. But after a short cooldown, the problem comes back again after only a few minutes of running under full load. The coolant level remains full; it was changed about two years ago and I haven't had to add any since.

Can anyone help me diagnose this issue, or offer any other suggestions as to what it may be? Thanks in advance!
 
Will it sputter and get worse to a stall or is it consent till you kill it? Have you recently fueled up...problem only started after new fuel, or doing before fueling.

Few things I can thing of...bad batch of fuel(as it warms the fuel burns different then in cold engine).

Lack of air or vaccume leak. (things stretch, twist, ect when warm opening or closing openings that are fine when cold)
 
It hasn't gotten bad enough to stall out so far. The engine RPMs generally don't even drop much when it happens. It just seems like a sputter similar to a misfiring cylinder or cylinders.

I don't recall whether it's still on the same tank of fuel as when the problem started, but I could try to drain it out and put new fuel in it.

I'll check the carb and hoses for anything loose or leaking, too.

Probably won't have time to work on it for a few days, but I'll follow up with results when I get the chance. Thanks!
 
Check the looseness of the distributor shaft. if you can move it (up down, away and toward the block) it is loose and needs a rebuild or bushing. Jim
 
Probably no related, but I'm going to mention anyway - since it caused me some grief, not being immediately obvious.

Make sure the rod from your governor is completely free. On my Super A, it runs very close to the block and was binding.

I wouldn't have any trouble until the tractor was under load, and the governor wouldn't keep up properly. Sometimes it'd work fine, other times it'd die. Conditions had to be right for it to actually bind.

Another thing to check that I didn't see mentioned here is your valve lash. These engines are pretty forgiving, but they can get worn to a point where the specs actually matter. The valve geometry does change with heat.
 
I checked everything that you guys have mentioned so far, and nothing seems to have helped. I had checked and adjusted the valve lash / clearance before my original post. Everything that should be tight seems tight, and everything in the carb / governor linkage moves freely with minimal play. The distributor post doesn't seem to have any appreciable play in it, either.

After checking everything, I drove it about 2 miles to the nearest gas station (I love the looks and occasional questions/comments I get from people when I do that) to fill up the tank in order to rule out the possibility of bad fuel, as I didn't have anything around to drain the rest of the tank. About a mile in, I could hear the issue starting; by the time I throttled down and pulled up to the pump, it was missing badly. In the 3 or 4 minutes it took to fuel up, the engine had already cooled down enough that it was running perfectly when I started it back up.

As expected, the issue started again not long into my return trip to the shop.

At this point, I'll say that by sound, it does seem to be unique to one cylinder. There's a definite rhythm to the sputter. But I still can't really duplicate it by pulling individual plug wires. I even tried spraying some starting fluid around the intake manifold when I got back to see if it made any RPM change that would indicate a leak in the manifold, and there was no change.

Any other ideas? Right now I'm afraid I might have to take it to someone more knowledgeable than myself to get the problem diagnosed. I still didn't change the plug wires yet, but I can't believe that a few minutes of cooling off could make that much of a difference in any plug wire issue. I'm really starting to fear that I've got something cracked / worn internally in the engine.
 
The issue you have where it runs worse and starts missing on a single cylinder can very much be related to improper (too tight) valve lash.
When cold, the valve is able to close, but when it warms up the gap closes up and then the valve is not sealing completely, leading to the miss.
The majority of the other mechanical issues typically cause the engine to run better as it warms up, except for piston to bore or ring end gap clearance set too tight, but those would only be the case if you had just rebuilt the engine and got some things wrong. I don't recall reading that you had done that.

The issue that you are having really sounds like valve lash set too tight on at least one cylinder.
You can narrow it down to the cylinder that is causing the problem by pulling the plug wires one at a time
(while the miss is occurring) and listening for RPM drop. The one that causes little to no RPM drop, will be the cylinder you want to focus on. If there is no one cylinder that stands out from the rest, then it is not an individual cylinder issue.

If you do identify the individual cylinder and you want to make sure it's a valve issue. Get the engine up to temp and the problem occurring, then pull the valve cover and start the engine, carefully open up the valve clearance on that cylinder and see if the engine smooths out.

If you cant' narrow it down to any one cylinder then you are back to a fuel delivery or spark problem.

There are lots of troubleshooting steps you can do on the spot to narrow this down, but it gets kind of tough to identify every scenario when you're not there.
 
I guess I'll have to check the valve lash again to be sure it's correct. When I did it the first time before my original post, the #1 cylinder seemed like it needed an appreciable adjustment, while the others not very much at all. So I was really thinking I had it fixed at that point, but not so.

Any tips on adjusting the valve lash, particularly when it comes to making sure the proper cylinders are at TDC throughout the process? I identified a mark on the flywheel that I think seems to line up with #1 TDC, but I can't positively identify it as the stamped mark that's shown in the manuals. Mainly, I want to make sure I'm using the correct engine rotation procedure for TDC across cylinders 2-4 after the adjustment on #1.

I have the operator's and service manuals that describe the procedure, but I've also read different sequences / methods for TDC location across various cylinders in the forums. I'd appreciate any clarification that you can offer.

One more thing; I know the valve lash adjustment is supposed to be done with the engine hot, but is there any valve lash spec for a cold engine on the Super A that I can try to adjust to before making final adjustments with the engine hot?
 
(quoted from post at 07:37:08 07/22/18) I guess I'll have to check the valve lash again to be sure it's correct. When I did it the first time before my original post, the #1 cylinder seemed like it needed an appreciable adjustment, while the others not very much at all. So I was really thinking I had it fixed at that point, but not so.

Any tips on adjusting the valve lash, particularly when it comes to making sure the proper cylinders are at TDC throughout the process? I identified a mark on the flywheel that I think seems to line up with #1 TDC, but I can't positively identify it as the stamped mark that's shown in the manuals. Mainly, I want to make sure I'm using the correct engine rotation procedure for TDC across cylinders 2-4 after the adjustment on #1.

I have the operator's and service manuals that describe the procedure, but I've also read different sequences / methods for TDC location across various cylinders in the forums. I'd appreciate any clarification that you can offer.

One more thing; I know the valve lash adjustment is supposed to be done with the engine hot, but is there any valve lash spec for a cold engine on the Super A that I can try to adjust to before making final adjustments with the engine hot?

Follow the procedure outlined in the operators manual. You can do it on a cold engine. Just add about .002" to the specification given for a hot engine.
 
My SMTA would miss when it got up to operating temp. I did a lot of checking things out and when a pulled the spark plugs out I noticed that one plug was nice and clean. I was getting antifreeze into that cylinder and the plug was getting steam-cleaned. I pulled the cylinder head off and found a crack. Good luck in your quest for a cure to your problem.
 
I just finished readjusting the valve lash. In the process, I did finally locate the TDC mark on the flywheel, so I'm sure that everything was in the proper position. I set valves 1-2-3-5 at #1 TDC, rotated the crank 360 degrees, then set valves 4-6-7-8 at #4 TDC.

I set to 0.016" cold, ran the engine at high idle for 15 minutes, then immediately readjusted everything to 0.014".

In regards to charlieu's post, I changed the plugs when this all started, and I didn't notice any difference in appearance between any of the plugs. So I still can't rule out a crack, but I'm keeping my fingers crossed for now.

As soon as the rain stops, I'll take it out for a test run again and see what happens. Thanks to everyone for your time and advice so far!
 
Finally got a chance to run the Super A to test it after the readjustment of the valves. Seems to me that the problem is getting worse. I only had to mow for between 5 and 10 minutes from a cold start before the engine miss began to show up.

I still haven't found any signs of a fuel or spark issue. So what now? Compression test? Is it possible to have a cracked head or bad gasket that could result in a compression loss without having an antifreeze leak? I'm not seeing any antifreeze loss or any visible smoke coming from the exhaust. Maybe a bad valve or valve seat?
 
If you have or can get ahold of a compression tester, that would be a good test to do. Do an initial test with the engine cold, if everything seems normal there, then get it up to temp where it starts to have the issue and do it again.

No matter which version of the engine is in the tractor, I would think you would want to see at least 85psi cranking, with the engine warm and throttle wide open. If it is a gasoline version, you would like to see over 100psi for a healthy engine in a super A.

If you get low numbers, try putting a couple squirts of oil in the cylinder and cranking it again, this will help seal the rings. If the numbers go up, then the rings are causing a lot of compression loss. If the numbers don't go up, it typically indicates a valve sealing issue.
 

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