sonic testing, minimum wall thickness - Pontiac GTO Forum
User Tag List

LinkBack Thread Tools Display Modes
post #1 of 5 (permalink) Old 07-13-2016, 11:05 PM Thread Starter
60sPontiacs's Avatar
Join Date: Jul 2016
Location: St. Louis
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
sonic testing, minimum wall thickness

What's the minimum cylinder wall thickness for a Pontiac 455?

After much reading, I saw .100" on non-thrust and .160" on thrust side, but it wasn't specific for Pontiacs. Block is std bore now with .132" on one cylinder's non-thrust side and I want to bore .030". I always heard .060" can be done on all Pontiac blocks, which would be close on this one.
60sPontiacs is offline  
Sponsored Links
post #2 of 5 (permalink) Old 07-14-2016, 06:11 PM
PontiacJim's Avatar
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,541
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 361 Post(s)
I'm no math expert, but boring the block .030" over does not take .030" out of the cylinder walls because you are talking diameter, so it should be half of that or .015", which should be within the specs you provided - and I can't verify those numbers, only your machinist can do that.

That said, if you went .060" over, .030" would be removed from the walls which would still put you right at the maximum safe bore for that block according to your figures.

Again, not an expert in this area, so don't believe me. Ask your machinist who should be able to give you a qualified answer.
PontiacJim is offline  
post #3 of 5 (permalink) Old 07-15-2016, 02:48 AM Thread Starter
60sPontiacs's Avatar
Join Date: Jul 2016
Location: St. Louis
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Your math is right.

If .100 IS okay, then I'm good with .030 removed from the diameter - would leave .117 wall thickness from .132. Allowing for (hopefully no) damage, someday I may need .040, then .060. At 60 years old, I don't think I'll be doing 3 rebuilds on the motor considering it won't be daily driver. I was just curious if .060 could be removed as I'm trying to learn.

While searching, I'd seen .125 and .130 min all around - any boring on my block goes below this. Some Mopar guys say .160 min all around (I don't know where they start). "My" machine shop engine tuner/carb/intake expert (who's learning machining details from owner who's about to retire) said it "should be fine" because thrust sides were .200+ min, but he's not Pontiac. I'd asked on a different forum, and was told to PM Mr. P-body, but never heard back. The info I'll go by came from a guy with screen name CNC BLOCKS NE who seems most experienced.

Have some bad vibes after reading about Eric's 67 GTO nightmare. This shop is similar - been around 45 years, 70-year old owner got sick a few months, work stacked up, my block's been sitting there 6 weeks (was said they could do it in 2-3). Want it cleaned/magnafluxed, bored/honed, zero-decked, and balanced - so far it's just been sonic tested. They want to test bore a corroded cylinder/water setting before proceeding - said if it's bad, may want to sleeve that one. Still need to get pistons so he can match to cylinders (planning on SRP 149721 lightweight forged +.034). Will see how it goes.

Wasn't sure I was going to keep the GTO (had it 30 years), but after coming here, I got the fever again...

Last edited by 60sPontiacs; 07-15-2016 at 03:04 AM.
60sPontiacs is offline  
post #4 of 5 (permalink) Old 07-15-2016, 06:21 AM
Super Moderator
BearGFR's Avatar
Join Date: Aug 2008
Location: Springtown, TX
Posts: 5,731
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Originally Posted by 60sPontiacs View Post
Wasn't sure I was going to keep the GTO (had it 30 years), but after coming here, I got the fever again...
The best one can hope for is occasional periods of remission. There is no cure. (thank goodness)

Please keep us informed on how things go.


Springtown, TEXAS
BearGFR is offline  
post #5 of 5 (permalink) Old 07-15-2016, 01:09 PM
Join Date: Jan 2015
Location: Injun Territory, 'Merica!
Posts: 1,611
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 121 Post(s)
.060 over overbore can't be done safely on all Pontiac V8's, not all, always sonic test. Have gone through the "thin cyl wall on the thrust side" frustration with one of my original HO cars engines. ended up sleeving one hole and hard blocked to the bottom of the freeze plugs. Block was then bored, slightly offset in two cylinders, and then finish honed with a BHJ plate.. Light weight forged pistons and 6.8" rods will help in the longevity. Heavy old school forged 455 pistons & 6.625 rods experience cyl bore wear much quicker.
Pinion head is offline  
Sponsored Links

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

Quick Reply

Register Now

In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
Front Suspension Minimum evanpatchay Drive train, suspension, alignment and brakes. 3 02-11-2013 01:20 PM
1964 Convertible Frame Thickness ??? Dual Tempests 1964-1974 Tempest, Lemans & GTO Convertible Top, Interior, Glass and Trunk 7 01-02-2013 03:09 PM
Minimum offset GTO will except? crccobra Wheels and tires 3 03-16-2007 02:57 PM
rotor thickness gman26 1964-1974 Tempest, Lemans & GTO General Discussion 2 10-23-2005 02:28 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome