Farmall Cub engine issues

bdoss2006

Member
This is my second post about this tractor. Here is the link to the original so you can get more details:

https://forums.yesterdaystractors.com/viewtopic.php?t=1587083

I pulled 7 of the 8 valves out. One is stuck so tight I don't know if I will ever get it out. I am considering just replacing all the valves. They are pitted pretty badly, especially on the top. I can't even get a lapping tool to stick to them, and I would be surprised if I didn't damage them getting them out. Also, while cleaning the top of the block, I noticed that the piston has a lot of movement. (see video below) I don't know if that's normal or if that means it needs new rings. I also included some pictures of one valve after I cleaned it

mvphoto97646.jpg


mvphoto97647.jpg


mvphoto97648.jpg


[video play=false:10b0551edd]https://forums.yesterdaystractors.com/videos/mvvideo97649.mp4[/video:10b0551edd]
 
The piston movement when cold is almost normal. If the cylinder walls in all 4 are not rusted or radically pitted, I would run it. The top 1/2 inch of the
cylinder is not worn (rings are lower, and the top of the piston is smaller than the skirt). feel this unworn area with your finger nail ans try to catch your
fingernail under it where the top ring stops on its travels. If there is a clear and obvious step there, catching your nail easily, it needs to be bored out and
oversized pistons installed. these cant be honed out. A ridge reamer will be needed to get the pistons out the top as they catch on the ridge. Watch videos of
ridge reaming. If the ridge is just one or 2 thousandths of an inch, I would run it as is. The valves are toast. Though not worn at the face, they are too
corroded to use. Keep working the last valve it will come out. If the tip of that valve id=s hammered bigger it might need to be ground smaller with a dremel
tool and tungsten bit to get it out. Jim
 
first of all,... when then grinding valves they are chucked in a machine and the valve face is ACTUALLY GROUND. forget the lapping! nobody
does that these days that is from the 1930's. there is lots of margin there to have them reground. BUT the stem has damage so not a good idea
to reuse those valves. and you dont want to be dropping a valve on a rebuilt engine. and as for the piston movement it is quite normal on a
used engine. want to check it out better remove the pistons. plus check the cyl ridge at the top. that is where all cyl wear takes place.
 
I beg to differ, sir.
Almost every professional still hand laps valves. This accomplishes one important thing - it verifies that the seat and guide are centered and concentric. It also shows the width of the seat.
Personally, I hand lap every valve on every valve job for exactly those reasons.
Just like using prussian blue to read the pattern of a ring and pinion - to verify that they are set up correctly.
 
Probably a good idea to just replace the valves, you
might have a couple bent ones if they came out
very hard. You will still need to lap them in, to
sharpen up the seats a little bit... Im sure they are
as beat up as the face of the valve is. As jimg. says,
If you have an unbroken lapped ring in the seat with
your new valve, youre good. Dont be too
concerned about the seat width, theres nothing you
can do about it anyway without a Neway cutter. By
the look of those valve faces I doubt you will have a
problem like that anyhow.
 
(quoted from post at 19:51:59 09/25/22) I noticed that the piston has a lot of movement ..... if that means it needs new rings.
Just to clarify, excessive piston / bore clearance is typically worn / out of round cylinders, and to some extent worn pistons. Usally on the thrust side. New sleeves or overbore, and pistons would then use new rings with the rebuild
 

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