Farmall A engine knock

[rick pa]

Hello, I am working on an A that has run great for years,the other day I started it and let it warm up a few minutes, I started driving and noticed a miss in the engine with a very concerning knock. The knock sounded like it was coming from the upper part of the engine.
Later in the day I pulled the valve cover and checked for stuck valve but didn't see anything noticeable, did compression test cold, all 4 had same pressures, I then started engine again,ran without knock for about 5 minutes when knock started again. The knock isn't constant, it comes and goes.
Today I started it and warmed it up,it knocked for about 2 seconds,then was quiet, I adjusted valves, they weren't far off, drove for about 15 minutes without any issues.
I am thinking it may be a sticky valve but was wondering if there is something I should look for. thanks

 

[ih560]

Did you notice if the knock goes away when you push the clutch in? If it does that would rule out the engine. I have heard the coupler in front of the transmission get loose and make noise.

Another possibility is a timing gear with a broken tooth, I have had this happen on more than one tractor, one being a 1945 Farmall A that I have (belonged to my great grandfather). It was about 25 years ago and I had restored the tractor with my grandfather, I was driving it through a parade when a random slick knock started. It went away, only to return later. Finally, it started jumping time and would start running poorly, I took the front end off and found the cam gear and the governor gear both missing teeth. I replaced them both and it has been fine every since.

 

[rick pa]

Thanks for the response, The knock is present when clutch is in,or out. I was thinking it could be something at the front of engine,I removed belts to eliminate noise from alternator and fan hub, but will still knock.I was also thinking about timing gears or governor/magneto. The knock seems to come from area of camshaft,middle of engine.
The reason I was thinking valve was that when it isn't knocking it runs good but when it knocks it seems to miss.

 

[Charlie M]

My M had a knock several years ago and it was caused by a bent rod that operates the valves. If you pull them out and roll them over a flat surface if they are bent is shows up easily. I don't know how it got bent. I also had one bent on my W30. That one was bent enough it sometimes held the valve open. That motor was set up when I got it so maybe that had something to do with that.

 

[dewy]

pull pan an check bolts an bearings on rods.....dewy

 

[used red MN]

Rick welcome to YT! Pull the air inlet off the carb and see if both screws and the backfire valve are in the choke plate. One of the screws or that valve could have came loose and got sucked up on top of a valve. The IH diagram calls it an air shutter, number 41 in the link. The Zenith carb has a backfire valve as well it is just not shown separately. To see the Zenith carb breakdown you will have to push ..back to manual.. and select it on the list. FYI the IH parts page does not view real well on a phone, you can but it is tricky.
A carb break down

 

[grandpa Love]

This won't help you much but my A had a strange rattle- knock. Hunted for several days. Pulled oil pan. Pulled valve cover. Listened to it with a stethoscope. Decided to drive it until it blew up. Pulled out of the barn and noise stopped!!! What?? Drove it for 30 minutes, no noise. Backed it in the barn. Noise is back. Ughghbb. Give up. Couple days later I was using the bench grinder in the lean-to. Turned it off went in barn and heard that odd rattle- knock!!! Tools on the peg board. The A engine was making them rattle. So did the grinder..... Ahhhhh. Fun times.

 

[Janicholson]

Carbon can accumulate on the backs of intake valves. it can also flake off and get on top of a piston to be smashed into the head where there is little room. It can stay there for a while, and or disappear then return. If all the screws are in the carb choke and throttle plate (throttle plate is less likely unless it has speed control issues from a loose plate) it is likely going to be OK. Jim

 

[rick pa]

So today I pulled the carb loose, and one of the choke butterfly screws is missing, shiny metal where screw should be. Ended up pulling head off but can't see screw or marks from screw going through. Might need to look in intake ports better.

 

[chevyman29]

i just had a issue where the valve cover was leaking, took it off inspected it nothing wrong , put it back on and tightened it down tighter .
started the engine has a dead miss , after lots of trouble shooting it ended up being the baffle inside the valve cover barely making contact with 2 rocker arms keeping them from fully closing......

it was a easy fix , but dont over look the littlest thing.

 

[used red MN]

Wow, you hopped into action on pulling that head. If it were me since it was quiet for 15 minutes I would have pulled the plugs to see if any were marked or smashed, then run it. It probably worked it way through and out the exhaust. Now maybe if I used it for tractor rides or it was another bigger tractor I depended on to be reliable for major farm work yes more investigation may have been warranted. Well at least you got the bolts all limbered up. Hope it treats you well now.

 

[rick pa]

If it were mine, I would have done more, but it belongs to an archery club so I didn't want to chance anything.
Mine is a 50 ferguson TO 20. thanks for all the responses

 

[rick pa]

Today since the engine is this far open, we checked rod bearings, at some point dirt wore a groove in bearing but everything looked good and crank measured good,and still standard, so I will put in new bearings and close it up again. thanks for all the help.