MTFCA Forum

Putting new valves in 1922 engine. Should both valves be closed when No. 1 piston is at TDC.

if it's compression TDC, then yes

I suspect your question is just the tip of the iceberg as to what you're really wanting to know...as in: is the cam new or old?...and What clearance are you setting the valves to?

While both valves would be closed, that is not where you adjust the gap.
What is the rule of 9 valve adjustment?
To do that on a four-cylinder, eight-valve engine, use the rule of nine. Counting from the front of the engine if number eight valve is fully open, subtract eight from nine and the answer is one, so adjust the clearance on valve number one. If number six is open, then adjust number three and so on.
Unless the lifter bosses have been milled back a little and if using adjustable lifters (re lifters in most cases), it will take several rotations of the crank shaft to get each valve gap set. The flats on the lifter itself, will be below the top of the boss or if showing may require a very thin wrench, again depending on the lifters used.

Interesting stuff. Regarding Scott's question the crank is used and I was going to use .010 for clearance on both intake and exhaust.
I have read that exhaust clearance can be .012. As far as the rule of 9 that is completely new to me. Can you elaborate a bit on the
theory behind it?

BarnesvilleT wrote: ↑

Mon Feb 13, 2023 1:30 pm

Putting new valves in 1922 engine. Should both valves be closed when No. 1 piston is at TDC.

Not necessarily, depending on the cam grind & timing position. For clarification: Yes both valves are closed when the piston is on top of the compression stroke. If the piston was up (not on compression stroke), one or both valves can be just starting to open or close.

you want to set the clearance @ the cam heel. Get the valve to its full open position, Turn the crank 1 full turn & adjust.
This assumes a normal,correct cam lobe grind.

RE rule of nine. It has to do with the design of the cam. The exhaust cam boss is already on its way around closing the gap as the piston goes down on the power stroke with the intake valve fully closed. The exhaust valve starts to open before the piston reaches the bottom of the power stroke to help expel the burnt gasses.

Hey Mark, Just to be clear when you said No. 8 fully open and then said No. 6 Closed did you mean fully open on 6 or is it fully open or fully closed and that would apply to the valve you are adjusting.

If 8 is open you do 1 (9-8=1). Then subtract each open valve from 9. 9-6=3 would be 3 etc. I had copied it off the web and did go back and changed the closed to open for the number 6.

Easiest way is TDC per cyl. No 1 set lash with the 2 valves are rocking on No 4, set No 2 with No 3 valves rocking, No 3 with No 2 rocking and No 4 with No1 rocking. 10 inlet and 12 exhaust.

Hey Kerry, A bit new to this. Can you give a bit more detail on what rocking is.

Hi William,
If you are this far into your engine do you have the inspection cover off to look at the cam condition? You can look up at the cam from
under the car, the lobe you are adjusting needs to be pointed down. From 4:00 to 7:00, check the gap and adjust from there. If you have
adjustable tappets and the lifter bosses have not been shortened then you will need to rotate the engine until you can get to the
adjustment. I'm willing to bet someone has the degrees of rotation of the adjusting screw that + 0.001. If you haven't put the valve
springs on yet you may be able to slip the valve out and raise the tappet with a good magnet to make the adjustment. (or push up
from underneath) Use the magnet or a close pin to hold the tappet up while you make the adjustment. I add 0.001 to the gap if there
is no spring pressure on the valve.
Craig.

Rocking is that one valve is just about to close and the other is just about to open, so in other words if you turn the crank a little each way the valves are rocking on the seats in the block.