Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
> Deck Height Question
clarkcou
post Nov 28 2020, 09:16 PM
Post #1


Member
**

Group: Members
Posts: 115
Joined: 17-October 03
From: Peoria, Arizona
Member No.: 1,257
Region Association: Southwest Region



Building a 1.7, 90 mm piston/cylinder. With no base gasket, deck height is .013in. Shouldn’t the head gasket/ shim be included in the deck height.

Barrel shim, not yet installed, is .21mm. Head gasket is .068.

Seems to me that deck height would be.082 without barrel shim. I.e. .013 plus .068.

Thoughts on this please?

Randy
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Montreal914
post Nov 28 2020, 09:48 PM
Post #2


Senior Member
***

Group: Members
Posts: 1,532
Joined: 8-August 10
From: Claremont, CA
Member No.: 12,023
Region Association: Southern California



I am sure others will chime in but per Porsche bulletin many years ago, head gasket are not recommended. 0.040" is the "standard" deck height you are looking for. Shims should go under the barrels. I had a custom thickness one machined for me on my rebuild. Not sure multiple stacked ones are recommended, I doubt it.

That being said, head chamber volume, and deck height should all be considered to calculate your compression ratio, assuming you have flat pistons.

Good luck with the rebuild.

Edit: Sorry, to answer your question, yes under barrel shims should be considered in the deck height measurement and cylinders should be held down on the block with head torque value simulating assembly.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Robarabian
post Nov 28 2020, 10:10 PM
Post #3


914 A Roo
***

Group: Members
Posts: 588
Joined: 11-February 19
From: Simi Valley, Kalifornia
Member No.: 22,865
Region Association: Southern California



They sell a kit to help with it... a deck height measurement kit. No head gaskets / shims. Put the base shim and assemble the cylinder. Using the kit, it will bolt down under pressure (torque spec not necessary but likely used) and measure the deck height. You want .040 to .060.. somewhere in that range. Do the math and calculate the base shim you will need to meet the deck height. Make sure you take the CC of the heads into consideration for compression ratio calculations...

Have fun!


QUOTE(clarkcou @ Nov 28 2020, 07:16 PM) *

Building a 1.7, 90 mm piston/cylinder. With no base gasket, deck height is .013in. Shouldn’t the head gasket/ shim be included in the deck height.

Barrel shim, not yet installed, is .21mm. Head gasket is .068.

Seems to me that deck height would be.082 without barrel shim. I.e. .013 plus .068.

Thoughts on this please?

Randy

User is offlineProfile CardPM
Go to the top of the page
+Quote Post
VaccaRabite
post Dec 1 2020, 11:59 AM
Post #4


En Garde!
**********

Group: Admin
Posts: 13,405
Joined: 15-December 03
From: Dallastown, PA
Member No.: 1,435
Region Association: MidAtlantic Region



QUOTE(Robarabian @ Nov 28 2020, 11:10 PM) *

They sell a kit to help with it... a deck height measurement kit. No head gaskets / shims. Put the base shim and assemble the cylinder. Using the kit, it will bolt down under pressure (torque spec not necessary but likely used) and measure the deck height. You want .040 to .060.. somewhere in that range. Do the math and calculate the base shim you will need to meet the deck height. Make sure you take the CC of the heads into consideration for compression ratio calculations...

Have fun!

The old school way to do this is not to use a kit, but to use 2 sockets that fit over the stud and use them to bolt down the cylinder to measure deck height.

Also DON"T JUST PICK A DECK HEIGHT!

Deck height is only a part of your Compression Ratio calculation. You want to pick a CR, and then use Deck Height to get to it. Don't just build to the smallest deck height and hope for the best. I've done it. And I've torn the engine down a few months later too.

.040 is the minimum safe deck height in terms of valves not hitting pistons. You can build an engine with too little deck, which equals too much CR, and be constantly battling overheating heads. Being forced to drive around in 4th all the time or watch head temps hop over 400 degrees SUCKS.

Zach
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



- Lo-Fi Version Time is now: 28th March 2024 - 05:51 AM