Date: Tue, 12 Feb 2002 16:24:10 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: Help setting deck height on Type 4 motor
Content-Type: text/plain; charset=us-ascii
Stock VW Heads require the head gaskets.
AMC Heads do no not require gaskets.
Base shims are .010 thick. Use one.
Check deck heigth by using a 1/8" or less thin wall brass tube and
crushing the end by turning the engine over with the tube dropped to the
bottom of the cylinder. The piston will crush the tube against the
cylinder head.
Mic the crushed end of the tube. Cut 1/2" off the tube and crush it in
the next cylinder, mic it again.
All you're trying to do in this exercise is get the deck height close.
You may need to use additional base shims of .010 to get the deck height
real close. Whatever you do you need at least one base shim to transfer
heat.
It is said that one base gasket/shim will give you 7.4 compression, two
gasket/shim will give you 7.1 compression.
----------------------------- Scan through this and see if it helps
----------------------------
Steve Blackham" <steph@uswest.net>
steph@uswest.net
801-510-4851
All right you expert mechanics, check my math. I'm getting ready to
put the barrels and heads on my 82/83? vanagaon aircooled engine
rebuild project. I decided to go with new AMC (no flames please, OEM
VW are not available for this engine to my knowledge) heads, and
Mahle (Brazilian) barrels.
Here's the math:
Deck height (w/ no gaskets or shims) = .025"
chamber CC = 56 cc
Piston Dish = 15 cc
Swept = 94mm x 71mm (1970 displacement)
My gasket set came with neither paper or metal bottom barrel gaskets
(interestingly it came with 8-.029" barrel to head gaskets which I
don't plan to use).
The AMC heads have a built in ridge at the contact point of the barrel.
Which way would you build these?:
7.53:1 CR with no gaskets
or
7.41:1 CR with .008-.010" metal barrel gaskets I have in inventory.
This Van probably will never go below 4200 Ft altitude and the fuel
mixture will be set towards the rich side (1.5% to 2.0% CO).
What do you think?
Steve Blackham sends:
Deck height (w/ no gaskets or shims) = .025"
chamber CC = 56 cc
Piston Dish = 15 cc
Your deck height is way low. Muir says no less than .040", a "high
performance" engine will have deck height of no less than .060", and some
guys are building engines with .250 deck height. I'd set it at no less
than
.125" to get the compression ratio down. (I'm putting .200" on the T4 I'm
building.)
--
I think you're missing something here. Compression ratio is the
ratio of the total cylinder volume uncompressed over the volume at
TDC or compressed. Look in the list library for more info on
calibrating this.
If you used the deck height you mentioned on this engine The CR would
be 5.64:1 w/ .200 and 6.30:1 w/ .125" deck height. They would run
but you wouldn't have any power. The factory specs on this engine
are 7.3:1 CR.
The Muir quote isn't taking into effect the larger chamber and dished
pistons on a two litre engine. With fly cutting of heads, etc, you
can't just look at deck height. You must do the math on all the
ingredients.
I can send you a excel CR & Deck height calculator if your interested.
>Steve Blackham sends:
>
>> Deck height (w/ no gaskets or shims) = .025"
>> chamber CC = 56 cc
>> Piston Dish = 15 cc
>
>Your deck height is way low. Muir says no less than .040", a "high
>performance" engine will have deck height of no less than .060", and
some
As usual don't listen to Muir or Wilson for a T4, that deck height
is right on typical for a T4. Do the math folks. Stock that would have
been 0.025" deck height + 0.009" shim + 0.030" head gasket for
0.064" or so deck, now at 6.94cc/0.040" (per mm) for a 2.0 liter 94mm
barrel, we get 11.1cc from total stock deck. 56 in the chamber (that is
on the high side BTW even for a set of AMC heads, make SURE it is
really there) + the 15cc is 82.1cc total in the chamber compressed or
(492.7+82.1)/82.1 = 7:1 CR, which is actually a tad lower than stock
using the stock head gasket and shim. Probably cause German heads
are usually closer to 52cc in the chamber. If one were to
wisely/unwisely
build this without shims or head gasket 0.025" is more than sufficient
clearance for moving parts BUT that would be only 75cc total in the
chamber all said and done for 7.6:1 CR. Whether that is too high, just
right, or whatever depends on your personal faith and what sort of gas
you intend to run. I would build it there for use in a Bus, in a vanagon
at least in my '82 with an auto tranny, that runs pretty hot and doesn't
really make a darn bit of difference to seat of the pants performance,
the difference between 65 and 68 hp trying to move 2.5 tons isn't a whole
lot of difference.
Regardless Muir's words are as often the case somewhere between
foolish or just not applicable to the T4 engine. 0.020-0.030 decks are
right common on the T4. Again my worry here is the 56cc in the heads,
if it is actually there fine, otherwise things may go together at closer
to
8:1 or so. Which again might be fine, but don't go thinking that a point
of CR is going to make a Vanagon any faster such that you'll notice it
volks, you'd get as much out of smoothing the ports or probably seem
to get as much having the engine spin balanced. The only thing you'll
likely see is an engine that runs 230F at 65mph instead of 215F. Real
words of advice from my last two Vanagon engines.
John
jander14@wvu.edu
I've got an 80 Westy with AC scheduled for another
rebuild (why I was trying to get a top quality crank
and rod set this time). The AC seems to pull a lot of
power from the engine (est 15 or 20 HP) so I figure I
should try to get as high a compression ratio as is
reasonable on the rebuild. I thought 130 to 135 psi
compression would be a reasonable compromise. Reading
your post several questions come to mind.
If an engine is built with an 8:1 compression ratio,
does this translate into a maximum compression test
number of 117.6 psi (8.0 X 14.7 psi)? You indicate
the loss of 15 psi in compression will not make much
difference in performance. Any estimates on what a 15
to 30 psi loss in compression means to HP or fuel
economy? Also as you've indicated there always are
uncertainties about the head displacement. Does this
require one to cc the engine to really know the
compression ratio after a rebuild?
On Tue, 12 Feb 2002 16:43:00 -0500 "G. Matthew Bulley"
<gmbulley@BULLEY-HEWLETT.COM> writes:
> Howdy all--
>
> I have a semi-stock Type 4 motor in my 1982 Vanagon for which I need
> a
> little guidance setting the deck height. Here is what I know.
>
> The motor has a stock dimension counter-weighted crank, stock
> (balanced)
> rods, stock heads (very slightly flycut), and set of slip-in,
> flat-top
> 96mm NPR piston/cylinders. I built it a few years ago and have a
> few
> thousand miles on the motor; today it has developed a head-to
> cylinder
> 'chirp' under full-throttle, low-speed acceleration that indicates
> a
> compression leak.
>
> I did not use in-head seals or barrel shims, but the deck height
> (eyeballed) was within .5 mm of the top of the cylinder. Between
> the
> flycut on the heads, and the flat-top pistons, it would appear the
> compression ratio is too high.
>
> The initial compression test (within 2k miles of building)
> indicated
> about 160 psi all around. However, the compression test now
> everything
> has settled in, (about 9k) indicates the compression is way high, at
> 185
> on two cylinders, and 170 on the others. I'm going to pull the
> motor
> replace the rings, and shim the barrels.
>
> My books give no help. How does one set the compression/deck height
> accurately, considering the modifications to this motor?
>
> From historic, walkable Mount Olive, NC,
>
> G. Matthew Bulley
> Bulley-Hewlett
> Corporate Communications
> Business: www.bulley-hewlett.com
> Alliance: www.ntara.com
> Home: www.MountOliveNC.info
>
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