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M overhaul advanced question--valve train

L

littlefarmer

Member

I am overhauling the engine on my Farmall M. I would like to know what I need to check or replace on the valve train.

What should I check on the camshaft?
Should I replace the lifters?
Does the rocker arm assembly need to be disassembled and cleaned?
What do I need to check on the pushrods?

This is not a parade tractor. It is used to farm 160 acres. The last overhaul was in 1984 and it has done a lot field work. It will be doing more hard field work after the overhaul.
 
A machine shop should be able to measure and see if the cam needs turning or replaced, most are ok. You may need new cam bearings. Lifters are likely ok. You can take the rocker arms apart if you want to, I usually don't. I might clean the crud off with mineral spirits (sold as paint thinner). Pushrods just need to be straight, which you can see visually or rolled across the bench. The biggest problem is probably wear to the end of the rocker arms that does not allow the tappet measurement to be accurate. You may be able to get by with a narrow blade.
 
to to add: for the lifters when you remove them check the bottoms for wear. if they are worn as in a dished shape meaning centre is lower than edge they are junk or need to be resurfaced. new lifters have the centre slightly higher than edge. aslo resurfave the rockers if worn. if by chance cam is replaced then so are lifters , no used lifters on new cam! pushrods- for straightness and end wear. check gears for tooth wear.
 
You need to take the rocker arm shaft apart. The tips will at the very least need resurfacing. Many times the shafts are worn, some times very badly along with the bushings in the rocker arms. If they are loose you have two problem. One is getting an accurate valve adjustment that will stay accurate, second is excess oil will be thrown over the top of the valves causing oil consumption and valve stem carbon. You can put valve seals on to control the oil but that won't help the adjustment part. Often over looked part of rebuilding an engine.
 
Have your cylinder head redone to see if new guides are needed and if the valves will withstand
another grinding. I think 1/32 is the replacement thickness. Have the crankshaft measured for wear at your local auto machine shop. It may just need polishing and buy your bearings from them. It will be good for another 30 years or more. Hal
 
Pete, What causes the rocker arms to become off center and can they be straightened? On my Super M, which I haven't finished yet I bought a narrow spark plug gauge (that is maybe .001 more than the spec) that I used to adjust the off center ones -- not too late to change something, will that work, realizing that the whole surface is not used because it will not be accurate.
 
Check to see that all the cam lobes are the same height. Check the width of each cam at the shaft. The height minus the base circle is the lift. See how what you've got compares to the specs.

Keep the lifters in order in case you do not need to have the cam reground. If you have the cam reground, resurface the lifters. You might consider having the cam ground to Super M specs.

Like everyone else says, flatten out the lifter faces. Push rods should be straight. I like to keep them in order too.

Greg
 
Kind of depends on which ones are off center. The rocker shafts are pressed into the center oiler piece and may be pressed in too far or not far enough if it is the end rockers giving you trouble. Most likely though, just mfg's tolerence. If they are not the cast rockers you can bend them a little but they might twist when doing that and not push squarely on valve. I usually just position the supports to their best position and let it go at that. Have to make sure the rocker has a bit of side movement also so it does not bind.
 
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