[alfa] Re: alfa-digest V9 #1086

[Nash Bap <nashbap@xxxxxxxxx>]

Hello:
 
I had posted a similar question on the Alfa Montreal group about two years ago. My friend Peter D. who is a machinist did some hardness tests on shims and I am including his responses here:
 
"The results of my shim hardness test is as follows:
First I tested 2 standard shims. One came up at 55 rockwell the
other came up at 48 rockwell, a little variation between them for
reasons I am not sure. Then, I machined 4 seperate shims. Results
are;

Thickness removed / Rockwell
.0025" 41
.005" 41
.010" 35
.015" 29

These shims are only case hardened and I wouldn't recommend taking
more than .002-.003 maximum off the shim if the correct shim cannot
be found. I hope these findings are helpfull. Regards, Peter."

"Ward, First of all, the shims were used, not new. The shims were
turned down on a lathe. How much do you have to take off? If its a
significant amount I would take it off the valve. They are through
hardened (consistanty hard throughout) and not case hardened (just
the very surface). Peter."

Date: Sat, 17 Jan 2004 10:37:14 EST
From: AlfaNeely@domain.elided
Subject: [alfa] Re: alfa-digest V9 #1082 - Valve shims 

In a message dated 1/14/2004 11:47:40 PM Central Standard Time, 
owner-alfa-digest@domain.elided writes:
Date: Wed, 14 Jan 2004 21:00:29 -0700
From: C M Smith 
Subject: [alfa] Valve shims

Don't these have to be of hardened steel to resist the pressure of the 
hardened cam faces? If so, then sanding them will take forever and be 
counterproductive in that the subsequent wear will increase the clearances 
pretty rapidly.


Michael Smith
White 1991 164L
Original owner
- ----------------

I have used a surface grinder to grind valve shims for years. I have a 
friend with a very nice machine shop including the surface grinder. It is so 
accurate you can grind shims to less than half of 0.001 inches. That is more 
accurate than you can get with a feeler gauge.
In all that time, I have had only one valve shim die. That was on my 84 
Spider SCCA race car that regulaly sees 7,000 + RPM. When I tore the engine 
down, the valve shim was gone, leaving only powder and a lot of damage to the 
top of the valve spring retainer, keepers and the inside of the cam follower. 
I had to weld a bolt to pull the cam follower. I had to replace the valve, 
the springs, the follower and clean up the bore for the cam follower.
So it could be that the valve shim cracked - possibly for reasons Mr. 
Smith states above. Or more likely, the valve could have floated, allowing the 
shim to move out of alignment and get hammered. The valve springs had not been 
replaced for some time prior to that incident, but are now new.

Ciao,
Russ Neely
Oklahoma City
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