Date: Mon, 5 Jun 2000 08:13:22 -0700
From: "Tom Young" <tomyoung1_at_home_dot_com>
To: "Alex Wisniewski" <icehenge_at_hotmail_dot_com>, <type2_at_type2_dot_com>
Subject: Re: Barrel shims

Alex:

You're on the right track here... Install the cylinder with the shim in
place and measure the deck height from the flat top of the piston to the top
of the cylinder.  If the deck height is .04" or greater, you're probably OK.
I say "probably" because there's at least a couple of things going on here:
1) the issue of compression ration and 2) the issue of the proper rocker arm
geometry.  I've read conflicting information as to whether you need to
torque the head nuts down to "spec" torque when making this measurement;
Hoover says you have to, Wilson certainly indicates it's not necessary.  As
a practical matter, unless you can somehow machine a "dummy" head setup to
torque into place to take this measurement, you'll have to settle for using
some spacers between the head nuts and the cylinders and tightening down the
nuts "snug enough."

As to the compression ratio issue, I'd advise you to cc your heads to ensure
the final compression ratio comes in somewhere in the 7.0 - 7.5 range.
Unless you know the complete provenance of these heads, they may have been
machined somewhere along the line, altering your final compression ratio.
With an average combustion chamber size of 55cc's (that's a guess I heard
somewhere; my average over 8 combustion chambers was 54.3cc's), an average
piston dish of 15cc's (that's what I measured mine at, others have reported
14cc's), an area of 492.7cc's for the piston swept area (calc) and a deck
area of 7.05 (calc based on deck of .04") you come up with a CR of 7.4,
which is good.

Any machining that's gone on where the head meets the top of the cylinder,
or any change in the barrel shim from "stock" alters the effective "length"
of the pushrod (well, not really, it alters the "stacked up" height of the
shim/barrel/head combination, but you know what I mean) which alters the
rocker arm geometry.  This can be brought back into spec by putting spacers
under the rocker arm pedestals or machining material off the bottom.

I just wish we could see the original, complete specifications for these
engines; we're all struggling with a certain lack of information when it
comes to rebuilding these things.
Tom Young                  tomyoung1_at_home_dot_com
Lafayette, CA 94549    '81 Vanagon
From: "Alex Wisniewski" <icehenge_at_hotmail_dot_com>
To: <type2_at_type2_dot_com>
Sent: Monday, June 05, 2000 1:31 AM
Subject: Barrel shims


> Every thing was going really well on what I call my engine
> mini overhaul. Engine: type IV-2000cc in a 77 bus
>
> So today I was looking over every thing today I noticed a shim
> on the bottom of the cylinder that went between the cylinder
> and case. For some reason this part I never noticed and now
> I am sitting here banging my head on the desk(just kidding).
> O well next time I wont make the same mistake. Live and learn!
>
> I tried comparing the shim to my feeler gauge but its
> to hard to tell. Could I install the cylinder and check
> the deck height(it has to be 0.040 or more right?).
> My cylinder has a dished out center so would I measure
> across the cylinder top and the outer portion of the piston.
> So then I would order the appropriate shim to bring it to specs
> right? If I am wrong please let me know, this is all very new to me.
>
> I checked busdepot for some barrel shims.  After searching for
> spacers I found "BRL SPACER" but no specs such as the size of
> the shim.
> RON if your read this let me know if you stock these or not
> please :)
>
> Any one thats got some words of wisdom send it my way please!
> Thanks
> Alex,
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