Bolt length spec
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,554
Likes: 381
From: Strongsville, OH
2016 C2 of the Year Finalist
Bolt length spec
64...is there a general accepted bolt length spec when replacing undercar bolts such as for bumper brackets, gas tank crossmember, etc. Specifically how much of the bolt end should be showing after a washer and nut are installed. My P.O. liked using 2-3” bolts in a bunch of places and it looks nasty. If I knew how much bolt thread should generally be left exposed I could figure out what lengths to buy. I’d like to correct it.
Weird question, I know.
Dave
Weird question, I know.
Dave
Last edited by dkleather; Jan 9, 2018 at 01:01 PM.
Burning Brakes
Joined: Aug 2013
Posts: 1,071
Likes: 322
From: palm springs ca
Dave,
I can say there is a guide to that in aircraft that I also use when locating the proper bolts for my cars.
It reads at least 1 1/2 threads MUST show. For me no more than 1/8" on average. Some larger 3/16".
Dom
I can say there is a guide to that in aircraft that I also use when locating the proper bolts for my cars.
It reads at least 1 1/2 threads MUST show. For me no more than 1/8" on average. Some larger 3/16".
Dom
Melting Slicks
Joined: Sep 2009
Posts: 3,382
Likes: 1,258
From: MI
2023 C2 of the Year Finalist - Unmodified
2022 C2 of the Year Finalist - Unmodified
2017 C2 of Year Finalist
In general, the last 1.5 threads of a bolt are less than full height and therefore, not structurally sound (this varies, depending on the type of bolt point being used). Additionally, the first internal nut thread usually is not full height, so is unusable. So, if the last trace of bolt thread is 1.5 threads outside the edge of the nut, you have a good safety margin.
If you have a modern Corvette, with modern bolts, this does not hold true. PM me if you need an explanation
If you have a modern Corvette, with modern bolts, this does not hold true. PM me if you need an explanation
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
The Corvette Illustrated Parts Breakdown used by dealers shows both bolt part numbers and dimensions. This document changed over the years and does not cover everything for every year.
I don't know if they are reproduced, but it's a handy reference to have around.
Duke
I don't know if they are reproduced, but it's a handy reference to have around.
Duke
Race Director
Joined: Jun 2006
Posts: 17,901
Likes: 751
From: Inverness FL
St. Jude Donor '07
In general, the last 1.5 threads of a bolt are less than full height and therefore, not structurally sound (this varies, depending on the type of bolt point being used). Additionally, the first internal nut thread usually is not full height, so is unusable. So, if the last trace of bolt thread is 1.5 threads outside the edge of the nut, you have a good safety margin.
If you have a modern Corvette, with modern bolts, this does not hold true. PM me if you need an explanation
If you have a modern Corvette, with modern bolts, this does not hold true. PM me if you need an explanation
anything else is a waste of material and $.
Bill
Last edited by wmf62; Jan 10, 2018 at 10:07 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,554
Likes: 381
From: Strongsville, OH
2016 C2 of the Year Finalist
Dave
Last edited by dkleather; Jan 10, 2018 at 11:29 AM.
Le Mans Master
Joined: Feb 2008
Posts: 5,214
Likes: 447
From: NJ Hockey beer league
Dave, there are a couple of ways to get the correct lengths on the bumper bolts. If you want the correct heads, just get the bumper bolt kit from one of the vendors. Another way if you don't care about the markings is to get a hold of one of the old GM parts manuals and look in the back (green pages 7-13 & 7-14 from the 1982 book) and they have pictures which list the bolt sizes and lengths for the locations. 
PM me if you need a copy of those pages and I'll get them for you.
PM me if you need a copy of those pages and I'll get them for you.
Last edited by Pilot Dan; Jan 10, 2018 at 06:56 PM.
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,554
Likes: 381
From: Strongsville, OH
2016 C2 of the Year Finalist
Dave, there are a couple of ways to get the correct lengths on the bumper bolts. If you want the correct heads, just get the bumper bolt kit from one of the vendors. Another way if you don't care about the markings is to get a hold of one of the old GM parts manuals and look in the back (green pages 7-13 & 7-14 from the 1982 book) and they have pictures which list the bolt sizes and lengths for the locations.
PM me if you need a copy of those pages and I'll get them for you.
PM me if you need a copy of those pages and I'll get them for you.
I do have the unmarked head bumper bolt kits to install. There are other bolts underneath I’d like to correct as well.
Thanks for your offer to copy the pages. I’ve sent you a PM.
Dave