Valve tappet setting rule of thumb

[Gary Mitchell]

Is there a "rule of thumb" for setting valve clearance on older solid lifter engines if you don't have the specs? Something that uses pushrod length x diameter, solid vs hollow, for example? Just curious. gm

 

[Janicholson]

No. Cam to lifter relationships are drivers of the clearance. The camshaft lobes are designed with a base circle that extends more than 180 degrees around that particular lobe. when turning, the lobe and lifter are separated by the clearance for the entirety of the base circle. as the lobe approaches the lifter (flat, or roller) there is a ramp like change in the lobe profile. this ramp is designed to close the clearance gently such that the lifting of the valve off of its seat begins with no noise or clatter. The closing of the valve, as the valve seats, also has a ramp, but this ramp is more attenuated, assuring the closing, and limiting the slapping of the valve into the seat, but not taking its time doing it. The designer of the cam and lifter assembly make the clearance account for heating of the valve stem, mechanisms, cam, head, and block. so that at operating temperature the clearance is reliably quiet and valve operation is accurate. Jim

 

[Butch(OH)]

As Jim said ramps and angles vary too much for a rule of thumb. Clearance must be taken up by the ramp before the can lobe accelerates the lift but not be so small that the valves are held open under the highest operating temps. Lacking any specs open the clearance until they get noisy when warm, then close up the clearance until the clatter stops plus a bit more.

 

[JOCCO]

That's a tough one. I would strongly recommend researching and finding the proper clearance for the engine. You risk issues like burning valves, lack of power if to far off.

 

[Southern Ray]

an old Farmall mechanic told me to use a hacksaw blade. let them clap.
I set my Farmall M twenty years ago and still working.

 

[Mcrafty1]

an old Farmall mechanic told me to use a hacksaw blade. let them clap.
I set my Farmall M twenty years ago and still working.

Better to have them clap a little then run them tight.

 

[BarnyardEngineering]

If you can fit your thumb in the clearance, it's too much clearance.

Sorry, couldn't resist.

Seriously, why are you keeping the engine secret? Share!

 

[560Dennis]

Good question ,

 

[Watthour]

Pushrod length, deck height, metallurgical differences (expansion rates), valve stem and guide design, and some minor factors will affect the cold versus hot clearances. Set them hot and you will likely be safer, yet that is no small feat in some applications, particularly L-head engines. Air cooled radials also come to mind as a prime example of that.

 

[sotxbill]

18 and 22 seems to be common on older stuff....But many of the valve tops and rockers are worn in a round pattern, meaning you will end up setting a bigger gap... " )) " shows the wear pattern on older engines thus the settings will always be more.

 

[Janicholson]

18 and 22 seems to be common on older stuff....But many of the valve tops and rockers are worn in a round pattern, meaning you will end up setting a bigger gap... " )) " shows the wear pattern on older engines thus the settings will always be more.

With respect, Proper resurfacing of the rocker tip works very well. A thin feeler gauge that does not lap into the unworn area also works. A dial indicator is another method to get it right. Jim

 

[Gary Mitchell]

No. Cam to lifter relationships are drivers of the clearance. The camshaft lobes are designed with a base circle that extends more than 180 degrees around that particular lobe. when turning, the lobe and lifter are separated by the clearance for the entirety of the base circle. as the lobe approaches the lifter (flat, or roller) there is a ramp like change in the lobe profile. this ramp is designed to close the clearance gently such that the lifting of the valve off of its seat begins with no noise or clatter. The closing of the valve, as the valve seats, also has a ramp, but this ramp is more attenuated, assuring the closing, and limiting the slapping of the valve into the seat, but not taking its time doing it. The designer of the cam and lifter assembly make the clearance account for heating of the valve stem, mechanisms, cam, head, and block. so that at operating temperature the clearance is reliably quiet and valve operation is accurate. Jim

Thanks Jim, for another well thought-out and well-presented response. gm

 

[TheBartman47]

The manual on my JD730 says to tighten until contact, then back off 1/3 turn. The tappets seemed to be a little too loose with that much back-off, so I only did 1/4 turn back off and is running fine, has a little bit of valve noise but seems within normal.

 

[620 John]

About the only "rule of thumb" I can think of is the exhaust valve is usually set with a larger gap than the intake due to more heat on the exhaust side. But a lot of older engines like the JD two cylinders.022"(?) was used for both valves.

 

[timcasbolt]

When you've got high compression pistons, aluminum rods and aluminum castings to work with, backlash becomes a pretty big deal, but with these old antiques I'll bet a soup can lid would be close enough.

 

[Dan in Ohio]

The manual on my JD730 says to tighten until contact, then back off 1/3 turn. The tappets seemed to be a little too loose with that much back-off, so I only did 1/4 turn back off and is running fine, has a little bit of valve noise but seems within normal.

I back mine off two flats rather than measure with a feeler gauge. I was told that accounts more for wear on the old two cylinders.

 

[T.R.K.]

Tell us what engine are you working on. That would be the place to start.

 

[TheBartman47]

I back mine off two flats rather than measure with a feeler gauge. I was told that accounts more for wear on the old two cylinders.

Yes, 2 flats on a hex nut is 1/3 turn, which is what the manual says. I was going to go that far but it just seemed a little too loose that far out, so I did 1 - 1/2 flats. I didn't bother with a feeler gauge, as the manual also says worn tappets might not gap correctly with a feeler.

 

[drsportster]

Engine should be cold not hot

 

[kencombs]

Better to have them clap a little then run them tight.

Like we used to say about the old chevy stovebolts, clicking valves are happy valves.