Elimination of all cylinder base shims - yes/no?

356 Porsche-related discussions and questions.
Message
Author
User avatar
Steve Hatfield
356 Fan
Posts: 793
Joined: Wed Mar 26, 2008 8:54 am

Elimination of all cylinder base shims - yes/no?

#1 Post by Steve Hatfield » Tue Aug 06, 2019 12:12 pm

I’m dealing with a set of S90 heads nicely prepared and machined to 30degree bevels which now cc at 66.

If I eliminate the only .010” copper I’ll still have a safe squish of .040” and a deck height of .95mm and I can achieve a respectable 8.727:1 CR which should work well with the high duration wide lobe cam and cast NPR 30 degree 86’s and cast iron cylinders.

So my question is: OK to assemble with no shim/gasket?

If I go with one ten thou shim my CR drops to 8.42:1. Not great.
Steve Hatfield
Fort Walton Beach, FL
'63 S90 Sunroof Coupe
'06 997S Coupe

User avatar
DonCichocki
356 Fan
Posts: 423
Joined: Thu Aug 22, 2013 4:29 pm
Location: Lafayette, NJ

Re: Elimination of all cylinder base shims - yes/no?

#2 Post by DonCichocki » Tue Aug 06, 2019 12:20 pm

Steve,
I didn't use any shims on my last rebuild, just used a small bead of Yamabond at the base of the cylinders. 9:1 compression, .040" deck height, and all has been well for over 5,000 miles.

User avatar
C J Murray
356 Fan
Posts: 7676
Joined: Fri Oct 23, 2009 7:24 pm
Location: 30MI WEST OF PHILA

Re: Elimination of all cylinder base shims - yes/no?

#3 Post by C J Murray » Tue Aug 06, 2019 12:58 pm

I often go without base gaskets. Yamabond or similar.
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car - Finally Finished!
'63 GS 2133 coupe
'64 Elva Courier mk4T
'67 911 S Original Owner

User avatar
Steve Hatfield
356 Fan
Posts: 793
Joined: Wed Mar 26, 2008 8:54 am

Re: Elimination of all cylinder base shims - yes/no?

#4 Post by Steve Hatfield » Tue Aug 06, 2019 1:33 pm

Thanks guys
Appreciate your inputs
steve
Steve Hatfield
Fort Walton Beach, FL
'63 S90 Sunroof Coupe
'06 997S Coupe

Tim Berardelli
356 Fan
Posts: 355
Joined: Wed Apr 30, 2008 7:02 am
Location: Washington DC Area

Re: Elimination of all cylinder base shims - yes/no?

#5 Post by Tim Berardelli » Tue Aug 06, 2019 6:05 pm

Steve,

Yep on no shims. How did you determine your CR? What was your technique?

User avatar
Eric Wills
356 Fan
Posts: 134
Joined: Thu Mar 27, 2008 10:54 am
Location: Fairfax, VA
Contact:

Re: Elimination of all cylinder base shims - yes/no?

#6 Post by Eric Wills » Tue Aug 06, 2019 6:14 pm

Well, I'll try this for the second time......Computer or internet acting up.

Steve, Not that you need anymore confirmation, but sealant instead of copper gasket works fine. We use Threebond 1184. Supposedly the same as Yamabond/Hondabond. But CCing an S-90 head to 66 seems very large, even if modified. How is that done without cutting into the exhaust seats quite deep? Just asking, cause I'd like to know.....

EW
Eric Wills

User avatar
Harlan Halsey
356 Fan
Posts: 442
Joined: Fri Mar 02, 2012 2:05 pm
Location: No Cal SF Peninsula

Re: Elimination of all cylinder base shims - yes/no?

#7 Post by Harlan Halsey » Wed Aug 07, 2019 5:33 am

I think you have your answer, but I'd machine the cylinders enough to get 9.5:1 with a gasket. CR is where the power is. (Dema Elgin told me in answer to my question that 9.5:1 is about the maximum with todays street gas. And that is what I shoot for.)

MICHAEL FOSTER
356 Fan
Posts: 236
Joined: Tue Mar 25, 2008 6:14 pm

Re: Elimination of all cylinder base shims - yes/no?

#8 Post by MICHAEL FOSTER » Wed Aug 07, 2019 1:48 pm

I go with Harlan on this one, machine cylinder base to up your compression to 9.5 with proper shim. Otherwise someone will be calling you a previous turkey owner who left out shims.
MICHAEL FOSTER

User avatar
Steve Hatfield
356 Fan
Posts: 793
Joined: Wed Mar 26, 2008 8:54 am

Re: Elimination of all cylinder base shims - yes/no?

#9 Post by Steve Hatfield » Wed Aug 07, 2019 1:54 pm

I’ve been called worse ... but
Thanks
Steve Hatfield
Fort Walton Beach, FL
'63 S90 Sunroof Coupe
'06 997S Coupe

MICHAEL FOSTER
356 Fan
Posts: 236
Joined: Tue Mar 25, 2008 6:14 pm

Re: Elimination of all cylinder base shims - yes/no?

#10 Post by MICHAEL FOSTER » Wed Aug 07, 2019 2:05 pm

Hey Steve, I didn't call you a Turkey owner....just saying SOMEONE may call you that in future.

Michael Foster
MICHAEL FOSTER

User avatar
Steve Hatfield
356 Fan
Posts: 793
Joined: Wed Mar 26, 2008 8:54 am

Re: Elimination of all cylinder base shims - yes/no?

#11 Post by Steve Hatfield » Wed Aug 07, 2019 2:06 pm

Capish
Steve Hatfield
Fort Walton Beach, FL
'63 S90 Sunroof Coupe
'06 997S Coupe

User avatar
C J Murray
356 Fan
Posts: 7676
Joined: Fri Oct 23, 2009 7:24 pm
Location: 30MI WEST OF PHILA

Re: Elimination of all cylinder base shims - yes/no?

#12 Post by C J Murray » Wed Aug 07, 2019 3:43 pm

Gee wiz, I'm a Turkey! :x
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car - Finally Finished!
'63 GS 2133 coupe
'64 Elva Courier mk4T
'67 911 S Original Owner

Mike Horton
356 Fan
Posts: 750
Joined: Thu Feb 05, 2009 8:13 pm
Location: Texas Panhandle South Plains

Re: Elimination of all cylinder base shims - yes/no?

#13 Post by Mike Horton » Wed Aug 07, 2019 4:20 pm

Steve, the S90 I just finished, using the 86mm AA cast iron 22*cylinder set, and a (-17cc dome) volume number, for the hypereutectic pistons, as published by AA, and once cut .010" heads, with the original 22* head angle, cc'd at 59.5, and with 3 ea., .25mm/.010" shims, calculated at 8.94:1, C/R... , a cross country cruiser, and in deference, to the "10% ethanol fuel" out on the roads, today,
Mike

User avatar
Steve Hatfield
356 Fan
Posts: 793
Joined: Wed Mar 26, 2008 8:54 am

Re: Elimination of all cylinder base shims - yes/no?

#14 Post by Steve Hatfield » Wed Aug 07, 2019 5:04 pm

Mike etal
The truth is I’m saddled with a pair of S90 heads that thirty years ago a previous owner thought he/she could both improve glow and eliminate the 22 deg sculpting. So they now cc 84 vice 60. With a deck height of 1.5 mm (new old stock NPRs), I don’t have much room to trim the barrels. If I did cut the fins which I’ve done in the past to match up a set, I’d only trim 8-9 ccs and still have 76 ccs to reduce with enlarged dome volume pistons. But then I may have flow issues.

So following Leonard’s (Shasta) advice I’m looking for new heads? Preferably SC heads.

This engine otherwise has been a sheer delight discovering near perfect bottom end and unused period NPR set.

Here’s a pic of the enlarged chambers on the Buret bench
Attachments
404CF621-2D85-44DE-BB82-2D45A9BB57DB.jpeg
404CF621-2D85-44DE-BB82-2D45A9BB57DB.jpeg (2.55 MiB) Viewed 867 times
Steve Hatfield
Fort Walton Beach, FL
'63 S90 Sunroof Coupe
'06 997S Coupe

MICHAEL FOSTER
356 Fan
Posts: 236
Joined: Tue Mar 25, 2008 6:14 pm

Re: Elimination of all cylinder base shims - yes/no?

#15 Post by MICHAEL FOSTER » Wed Aug 07, 2019 5:12 pm

So you can blame the previous owner of the heads . Your not the Turkey, it's the previous owner who mistakenly cut the heads. Capish?

Michael
MICHAEL FOSTER

Post Reply