Valve height?

[Hugo]

Anybody know what the height of the valve stems above the head should be? Some of my valve seats were a bit off centre & I'm concerned that now that I've cut them & got them centered they might have sunk a bit, so I won't be able to set the clearances properly.

[angelw]

Hello Hugo,
Not off the top of my head, but easily calculated.

1/2 Base Diameter of Cam Lobe
+
Thickness through the top of Cam Follower Bucket
+
Mid range thickness of Tappet Shim (I also calculate for Thinnest and Thickest Shim in the range to achieve a Tolerance). This allows tappet shims in the range specified by Jaguar to be used, but out of that range are available off the shelf.
+
Mid of Tappet Clearance

The result of the above is the measurement from top surface of the Cam Housing (Split Line of Cam Bearing), to the end of the valve stem. A depth micrometer is the most convenient measuring tool to use, as the datum face of the micrometer will straddle the cam housing. If a digital, or vernier caliper is used, I measure from a parallel strip placed to straddle the Cam Housing. Obviously, the thickness of the parallel is added to the dimension if second measuring tool is used.

There is a limit to the amount of material that can be taken off of the end of the valve stem to compensate for greater stick through of the valve. The end of the valve stem must remain above the top surface of the valve spring retainer so the the Tappet Shim doesn't contact the top surface of same.

Regards,

Bill

[Hugo]

Hah! I never thought of doing it that way. Aston Martin 4 litre sixes have no tappet adjustment. You have to either grind in the valve or grind down the tip of the stem. A maximum .020" may be taken off the tip. Trouble is you never know if someone's done it before! If you're a long way out you can get selective thickness tappets. Expensive!
The horrid old Ford E93A 1172 sidevalve had the same (lack of) adjustment. Ford did it for cheapness, whereas Astons did it so there were no shims to fall out at speed. I prefer Jaguar's method. Hard to imaine a shim dropping out of place.

[malcolm]

The horrid old Ford E93A 1172 sidevalve had the same (lack of) adjustment.

How dare you! That was my first car! I got it because someone pushed it into the garage where my dad worked, said "if anyone wants it they can have the bxxxxy thing" and walked off.
So, after dad fixed the bent valves, it came to me! (17 years old and just passed my test)
Wind out front window, leather hanging straps (it was the Ford PREFECT, not a cheap popular) and vacuum windscreen wipers with no vacuum tank. As soon as you touched the throttle the wipers just stopped, but downhill they were a blur! Top speed about 50 mph if you were patient enough. What more could you want?

[Hugo]

Haha my first car too! Paid five Pounds for it. I was able to get it on two wheels round every corner with those transverse springs. One night the inevitable happened and it fell over (on a farm track of all places). We righted it & I drove it home, but what I hadn't realised was that all the oil had leaked out while it was lying prone, & it seized up half a mile from home.
How did somebody manage to bend the valves on a side-valve?

[malcolm]

No idea Hugo. Don't even know for sure that my memory is correct on the diagnosis - it was many decades ago! What I do remember for certain is that it wasn't running, it had to be pushed in, and my Dad had to fix the valves; thought he said they were bent.
BTW, I tipped mine over too. Going round a bend on a country lane. Fell onto a coppiced hedge, travelled round the bend at about 45 degrees resting on the hedge, then stood up as we came off the bend onto the straight. My dad scratched his head about how I could just damage the top nearside of the car!

[Hugo]

"Burnt valves" rather than "bent valves" perhaps?

[malcolm]

Could well be.

[abowie]

0.85"

[Hugo]

0.85"

Oh dear - my valve tips are roughly 1.4" above the face of the head.

[abowie]

The valve tip sits 0.85" below the machined face which mates to the cam cover.

This puts your shims around 0.100" +/- 5 thou.

[Hugo]

Aha - your measurement is upside down not downside up. I suppose that makes sense given where you are located :-)