Setting Valve Lash

[Underwood]

Cub S/N 6697 Thought I would adjust the valve lash while I had the engine side plate off fixing an oil leak. Lash is measuring anywhere from 0.011 to 0.015 depending on which valve I'm looking at. I am holding the tappet with a 1/2" wrench and trying to turn the adjusting stud with a 7/16" but the stud does NOT want to turn. I am afraid to put too much force on it, if I twist it off I am in real trouble. Am I missing something or should I just leave well enough alone and run with the current settings? As always, your advice much appreciated, Thank You.

[Peter Person]

You can access the PDF Manuals in the Quick Links tab above.
1/3 down, click on Farmall Cub
Service Manuals
IH Service 1 Engine
Pages 1-15 & 1-16

[Underwood]

Thank you for the reply. I have the maintenance manual and was following it to set the valve lash to 0.013. The issue is that the the stud that has to be turned up or down in the tappet to adjust the lash seems frozen to the tappet and won't turn. I don't want to force it too much and wind up twisting it off so looking for suggestions.

[Dale Finch]

Did you set the engine at Top Dead Center (TDC) before you tried to adjust the valves? The Service Manual tells how to set TDC, and also the proper procedure for adjusting the tappets. This is an excerpt from the manual, and it only requires turning the engine twice:


Following the simplified procedure in the
chart below, all valves can be adjusted
accurately. Note that the engine does not
need to be cranked four times to position
the piston of each cylinder on T.D.C. All
valves are adjusted by cranking the engine
only twice.
Four valves are adjusted when the No. 1
piston is at T.D.C. (compression) and the
remaining four are adjusted when the
No.4 piston is at T.D.C. (compression).

- ADJUST VALVES WITH (Engine Cold)
No.1 Piston at T.D.C. (Compression) 1, 2, 3, 5
No.4 Piston at T.D.C. (Compression) 4, 6, 7, 8

1. Remove the intake and exhaust
manifold assembly. Remove the valve
tappet cover. Clean the gasket mating
areas to insure proper sealing when re-assembled.
2. Check the entire valve assembly
for rust and dirt. Inspect for looseness
in the valve assembly and for worn or
broken valve springs.
3. Remove the spark plugs from No.1
cylinder (nearest the radiator) and No.4
cylinder.
4. Place a thumb over the No. 1 spark
plug opening and slowly hand crank the
engine until an outward pressure can be
felt. Pressure indicates the piston is
moving toward top dead center of the
compression stroke.
5. Continue cranking slowly until the
T.D.C. mark (1) on the fan drive pulley
(3) is in line with the timing pointer (4)
on the crankcase front cover.
NOTE: Valve tappets have self-locking
tappet screws. Adjustment requires two
wrenches, one to hold the tappet and and one
to turn the tappet screw.
6. Insert the feeler gauge between the
valve tappet and the valve stem. The
specified clearance is .015 inch (engine
cold). Turn the adjusting screw in or out
as necessary to give a slight drag on the
feeler gauge. Adjust the four valves
specified in the chart on page 1-15.
7. Crank the engine until the No.4
piston is on T.D.C. (compression) and the
T.D.C. mark (1)on the fan drive pulley is
in line with the timing pointer. (Crank the engine ONE FULL turn and line up the pointer).
Adjust the
remaining four valves.
8. Install the valve cover being sure
to use a new gasket. Check for any oil
leaks.

[Peter Person]

Underwood,
It’s possible the last time the valve lash was adjusted, the individual that did it really cranked down on the wrenches.
I did mine 10 or 11 years ago and maybe a few of them took some extra oomph to break free.

[Rick Spivey]

I don't know exactly how the threads are cut and sized, but I have found that valves with this design for adjusting the lash are always hard to turn against one another. I believe it is on purpose so the lash won't change with engine vibration over time. You have no choice but to forge on, as I don't think there is any "secret". But again, I find those threads are made so the two pieces always adjust very tightly, requiring unusual force compared to a typical fastener.

[Winfield Dave]

Kroil them and let them sit awhile.

[Gary Dotson]

These tappet adjusters are an interference fit thread, to prevent them from moving while in service. Some will turn harder than others but all will require a pretty firm hand on the wrench. I seriously doubt that you’ll twist any off. Just make sure you’re using 2 good wrenches. I have special, thin, long handled tappet wrenches, made for the job but regular open end wrenches will work.

[Underwood]

Thanks to everyone for the replies. I will admit I haven't put any really significant force on the studs, just being conservative rather than sorry. A side note, I have a very old original Cub manual that states the lash should be set to 0.013" vs. the others referenced here that recommend 0.015". I will probably go with 0.015. Thanks again.

[Peter Person]

These tappet adjusters are an interference fit thread, to prevent them from moving while in service. Some will turn harder than others but all will require a pretty firm hand on the wrench. I seriously doubt that you’ll twist any off. Just make sure you’re using 2 good wrenches. I have special, thin, long handled tappet wrenches, made for the job but regular open end wrenches will work.

Gary,
I don't think the current generation of Craftsman, Husky, Kobalt, Harbor Freight, Dewalt, etc. regular open end wrenches are thin enough to fit.
Home Depot has this set; Husky Thin Head Access Wrench Set 6 Piece that would probably do the trick.
I picked up a set of Bluepoint Tappet Wrenches at a tag sale for $5 a few years ago.

[MilGunsmith]

I have some old tappet wrenches, but I also have the shop made ones that are ground down standard wrenches. Tip: grind the side without the size marking on it. Easier to rough on a bench grinder and then finish on a surface grinder if you can. This will ensure an even thickness.

[Gary Dotson]

When I was a much younger man, any decent Craftsman mechanic tool set included a set of extra long, thin, tappet wrenches. I still have mine and have picked up other brands from various flea markets, yard sales and such. These are handy for a lot of other projects besides valve adjustment.

[Bill Hudson]

When I was a much younger man, any decent Craftsman mechanic tool set included a set of extra long, thin, tappet wrenches. I still have mine and have picked up other brands from various flea markets, yard sales and such. These are handy for a lot of other projects besides valve adjustment.

You betcha!

Bill

[Underwood]

Well, as usual you guys were correct. I set the two worst valves, had a beer to settle my nerves and decided to wait on the others until I can find a set of tappet wrenches over this winter. I sickle mowed for the last time last week so I won't need the tractor again until spring. Thanks again.

[Peter Person]

...and to quote Art Chester (artc);
“If they’re tappin’, they’re not burnin’!”