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Date:         Tue, 12 Feb 2002 17:35:01 -0500
Reply-To:     "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM>
Organization: Bulley-Hewlett
Subject:      Re: Help setting deck height on Type 4 motor
In-Reply-To:  <20020212.162411.-879167.0.wilden1@juno.com>
Content-Type: text/plain; charset="US-ASCII"

Thanks! This gets me headed in the right direction.

Are you positive about the head gaskets though? Both from books, and from other engine builders, the word has been that from 1978 on up, put those gaskets in the trash. Thoughts?

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

-----Original Message----- From: Stan Wilder [mailto:wilden1@juno.com] Sent: Tuesday, February 12, 2002 5:24 PM To: gmbulley@BULLEY-HEWLETT.COM Cc: vanagon@GERRY.VANAGON.COM Subject: Re: Help setting deck height on Type 4 motor

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 > ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/.


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