Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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#476495 11/28/22 05:43 PM
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Grease Monkey
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I have a question on head bolt replacement, has any one cut down a grade 8, 5” 1/2-13 to 4.586 and used as head bolts. Does anyone see an issue? Seems like they would work fine and much stronger than original. Let me know your thoughts. Thanks in advance

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There is no reason to spend the money for Grade 8 bolts. Plus they are a lot harder to cut.

The threads in the block will fail if you torque to Grade 8 values. The clamp load to hold the head to the block is determined by the torque. So even if you use Grade 8 bolts the head will not be clamped any tighter to the block if you use the regular torque value for a 1930 engine.


Rusty

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How bout grade 2 or 5? I just hate spending $11.50 e for new head bolts. Mine are pitted and I’ve already had one break.

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I will defer to an early 30’s expert about the strength of the original head bolts. Most of the hardware in that time period was what we now know as Grade 2.

If you do not use original style bolts do your research to make sure the thread length as well as the un-threaded length are correct. A bolt stretches differently in the threaded portion compared to the unthreaded portion.

You also need to compare how the bolt head fits into the head.

You might post in the Wanted forum for used bolts.

My experience is that redoing work because I was “saving” money is expensive.


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Not trying to confuse anyone here and I hope a more knowledgeable person will pipe in but I thought I read or was told the head bolts were 1/2” - 12 and not 13 pitch.

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they are 1/2-13 as when i did mine I did a ton of research on using alternatives. I used some off the shelf grade 2 1/2-13 bolts with the heads cut off for guide pins when setting my gasket and head on my rebuild :)

if not using original repros i would use grade 5 plain steel and torque as VCCA recommends (see below). the original head bolts are close to grade 2

just know that the HEAD is completely different on the original head bolts vs an off the shelf bolt. original and the repros have a taller head !! plus it is plain and flat, no markings or concave shape. no one produces a bolt with the head height of the originals, they can be custom made but no where near the price you want to pay nor the quantities you want to buy !! being in the Mechanical Design Engineering Field last 20+ years i talked to many of our suppliers around the world.

VCCA recommended Head Bolt Torque:
***tighten them in steps and follow pattern per the Chevrolet repair manual***
Cylinder Head Bolt OLD: 55 to 65 ft-lb
Cylinder Head Bolt NEW: 65 to 75 ft-lb

just an FYI partially threaded 1/2 bolt starts partial threads around 2.00" long under this length typically fully threaded, and at2.00" long they have approx 1.25" portion of thread, stays that till around 7" then goes to 1.50" of thread and stays there. Thread length is standard per ASME for bolts, all in the Machinery handbook and ASME standards. sorry have them on my desk :) and the thread length on the repros and original are around 1.25" long.

if you need a head bolt or 2 let me know i have some old ones in my stock, i replaced all of mine with new ones, I will gladly ship you a few.

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For your guide pins any headless bolt of correct thread would suffice as the main purpose is to guide the gasket and head into correct place and then removed.
Tony


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There was a guy who used to make the head bolts for many old cars. He now owns a bicycle shop in NH. Last I knew he still had some in stock. Cant remember the name of the shop.


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