VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 4" long enough for head bolts?

I've read in threads here where people have used the 4 1/2" and 4 5/8" bolts as head bolts (mine is a '31). I also saw where people were considering using 4" bolts, but never saw the response if this worked or not. Would the lack of the 1/2" make a difference? Also, the bolts I'm looking at from McMaster Carr have flanges. Other than being aesthetically incorrect, would the flange interfere in any way?

Thanks

McMaster Carr Bolt

Actually, I guess I answered my own question. I checked around on their website and found that they do offer 4 1/4" bolts. Grade 8 (8.8). I found this, but I don't understand why this bolt is more expensive than the link above:
McMaster Carr 4 1/4"

Is there anything that would lead someone to think the 2nd bolt I linked to would not work as a headbolt for a '31?

Hello Vetteman61,
I take it that you've looked at the Filling Station's head bolt offerings. Part# 835662 $11.50 each. Plain steel bolts back in 31. They suggest that whatever you use for head bolts, that you only use the torque value for plain steel. Torque value for 1/2" diameter bolts=67 foot pounds. If the stock length of the bolts where 4.586", using shorter bolts could result in failure and damage to the engine block threads, and all the other issues resulting from that. Thoroughly clean the engine block threads of crud down to the bottom of the holes. Use small diameter engine brushes with solvent and vacuum out. This will allow the proper length bolt to install completely without bottoming out prematurely. Nothing good comes with that happening. Are you replacing all the bolts? For using the flange headed bolts, you need to know the flange outer diameter and measure the bolt holes mating surface area for interference. Don't see any issues using stronger bolts if they match and are treated the same way as working with plain steel bolts. Edit: 4.586" is offered as the proper length for the 31. Use 4 1/2" long bolts.

Hello Vetteman61,
To add to the information about the proper length of the head bolts, measure the length of each head bolt hole from the top of the engine cylinder head to the bottom of the engine block's head bolt holes, after they are all cleaned and free of debris. Then you can make an informed decision as to what length bolt to use.

The proper length of the head bolts is 4 1/8" as listed in the Filling Station catalog.

Hello Doug Zeno,
The 29-32 Chevrolet Master Parts Price List under Motor: Cylinder Head Bolt, shows part# 835662. The Filling Station catalog for 29-32 Cylinder Head Bolt, shows part# 835662. This bolt is listed as being a 1/2" diameter- 13 threads per inch- and 4.586 inches long measured from under the head of the bolt. If this is incorrect, I'd like to know exactly where it's written differently, so that I can read it to set me straight.

My 29-55 parts book list the 835662 bolt as "1/2-13x4-1/8". My Feb. 1932 reprint parts book list the 835662 as the correct bolt for 29-32. Using a vendor catalog for specific technical information can some times be misleading as their reason for listing is different than the manufacturers.

Page 320 of the Nov. 2014 issue. The Filling station lists the length of the head bolts in whole numbers and fractions is 4 1/8". That converts to decimal length is 4.125 inches measured from under the head.

I also when having the head off any engine make sure the threads are clean from rust and other stuff buy running a tap into each hole to clean them out. Chuick

Hello Vetteman61, Doug Zeno, m006840,
My apologies to you all, I believe that I've been set straight once again. Looking at the 29-32 Price List, no measurements of the bolt is shown, just the part#. So the Filling Station shows the same part# with dimensions 4.586. That was the trap that I fell into, but thanks to your input, I am now rescued. I went to the 29-54 Chevrolet Master Parts to see if I would prevail in the issue, but sure enough, there was the cylinder head bolt dimensions 1/2"- 13 X 4 1/8". My humble thanks.

Check this post here: Hood latches and head bolt

Few discussions about length, and options to get them

No apology necessary. I find it's a learning experience every time I view the VCCA site. While the vendors don't really panic if they have made an error in there information the factory on the other hand can have some major issues. As for the 4" bolts being used in place of the original 4-1/8" I would advise against it. That would amount to about a 20 percent reduction in retention surface so it's possible that could cause pulling of the threads in the block.

Thought you all might enjoy this discussion on thread engagement:

http://fieldfastener.com/2013/04/23/rules-of-thumb-for-fastening-and-joining/

Cheers, Dean

Good information Dean, thanks for posting. I took a quick measurement of my 32 head and got 3.355. If you add the gasket thickness which I am guessing may be about .100 then you are awful close to the minimum requirement of .500 thread engagement. If it were mine I would like to have a little more for peace of mind.

I also went and got one of my bolts and measured it to be 4 1/8" however I'm still confused by the listing of 4.58 on The Filling Station website. We seem to have found the correct size, however perhaps they should update this as it could cause someone in the future some serious problems if they tried to use a 4 1/2" bolt for their head.

Here is a link:
Filling Station bolt info

Maybe The Filling Station's measurement includes the head of the bolt.

Perhaps it does. I almost took what their website information and ordered the bolts and I'm glad I checked here first. I'd hate someone else to get their bolts too long and damage their engine or head.

I just ordered 15 bolts from McMaster Carr. I'll have to grind 1/8" off each of the 15 bolts, but this is preferable due to the cost in savings.

Here is a link to the bolt I purchased in case anyone else is interested:
McMaster Carr 1/2-13 x 4 1/4

The bolts from McMaster-Carr came in today (that was quick). When I compared the two together (the original 4 1/8" with the new 4 1/4" I found that there is not an actual 1/8" difference. The difference is very small, possibly right at 1/16" or less. I'm going to measure the depth of each hole again as I install them and check each one to insure that it will work, but I believe at this time it may be possible to install the bolts with no grinding necessary.