I guess size doesn't matter ?

[Reg Evans]

This is the head on my 39 Chrysler Royal.  I've never seen such small head bolts before.  They are 1/2" and every other L6 I've seen has 11/16" bolts.

Anybody here seen this before ?

 

 

[Niel Hoback]

Nope, never saw one that didn't have 11/16 head bolts.

[Don Coatney]

Not me...

[RobertKB]

Nope. Weird.

[Ulu]

They look like Briggs & Stratton head bolts to me.

 

(Did they own the Briggs Body Works?)

[plyroadking]

The 39 chrysler engine sitting in my shed has the 11/16" bolts. I'll unbury it in the spring and do the compression check for you.

[Reg Evans]

Thanks Plymouth Road King.

 

This engine runs smooth and has even compression.....90-95 psi in all 6.  My plan is to raise the compression ratio some by shaving the head .070. 

Sure hope these smaller than normal bolts don't snap off.

[Young Ed]

They look like the modern ones that GGdad ended up with. You can kinda see them in a few of the pictures in his build thread.

http://p15-d24.com/topic/26461-ggdad1951-truck-project-montage-fef/page-1

[Reg Evans]

Hey yeah Ed.  I see what you mean. Thanks, I don't feel so alone now.

 

 

[greg g]

are the bolts actually smaller or just the heads?

[junkers72]

They just have smaller hex heads. Same shank and thread size.

[Don Coatney]

This is the head on my 39 Chrysler Royal.  I've never seen such small head bolts before.  They are 1/2" and every other L6 I've seen has 11/16" bolts.

Anybody here seen this before ?

Per the standard US bolt head size chart found at this link below both 1/2" and 11/16" are not standard head size for a 7/16" bolt. Should be a 5/8" head size.

 

http://www.engineeringtoolbox.com/us-bolt-head-wrench-size-d_1457.html

[Reg Evans]

Well ain't that weird. 

I took my 11/16" socket around to all my flatties including 3 engines on the floor and all 11 are 11/16" with the exception of the '39 Chrysler.

[Young Ed]

Well ain't that weird. 

I took my 11/16" socket around to all my flatties including 3 engines on the floor and all 11 are 11/16" with the exception of the '39 Chrysler.

I don't know the history of your Chrysler engine but I know Ggdad had his engine fully rebuilt and knowing him I would be really surprised if he didn't get all new headbolts. I would suspect these flange type ones are a modern replacement. The only flathead I've ever seen that didn't have 11/16 besides these 2 is the one I got from Merle. Someone replaced all those headbolts with hardware store stuff and they are a 5/8 head.

[greg g]

wonder if it a strategy to prevent overtorqueing?

[Reg Evans]

Me too Greg.  I also wonder if the torque spec is the same as the larger one.

[Niel Hoback]

I wonder if the shanks are undercut.

[Ulu]

I think they are just cheaper roll-formed bolts and not the highest quality cut-thread bolts.

 

You can tell by the threads being fatter than the shank, with no obvious relief cut to reduce the shank diameter.

Head bolts often have a reduced shank, I believe, to avoid seizure in the head.

 

Also the "heavy-pattern" head bolts will have an 11/16" head, same as the typical SAE nut.

 

The typical 7/16"-NC  bolt head would indeed be a 5/8" hex (but the nuts would be heavy pattern 11/16" nuts x 3/8" thick, if it had studs instead of bolts.)

[DJ194950]

I have read articles in car magazines that said Cold Rolled thread bolts are stronger than cut thread bolts.

 

There is also a Big difference between hot rolled threads and cold rolled. Attached just one of many posts on the advantage of cold rolled threads.

 

What are the bolts that started this post??

 

 

Advantages of Rolled Threads _ Atlanta Rod _ Bolts _ Rods _ Studs - Atlanta Rod & Manufacturing.htm

 

 

 

 

[Ulu]

I have read articles in car magazines that said Cold Rolled thread bolts are stronger than cut thread bolts.

 

They can be, but aren't automatically so.

It depends on how they were made & what from.

 

The state does not allow us to use roll-formed bolts to anchor buildings or most structures.

That is partly due to the infiltration of cheap foreign bolts too.

 

I don't ever recall seeing roll-formed bolts used on jet engines either, though I am no jet mechanic.

I just used to get lots of free bolts off old scrapped ones.

[Plymouthy Adams]

rolled threads are the rage for strength and fit as the very bottom of the thread is not fractured by the point of a cutting tool being it hand die or machine cut...I have a couple cars here that they are the specified grade for bolting the suspension cradle to the frame..a read on the subject will give you a better insight to the why's and wherefores

[Ulu]

Well they're certainly faster and cheaper to make, once you have the tooling that is.

But they don't work where the shank must be larger than the threads.

[Plymouthy Adams]

basically the very cost of machining will dictate the method for mass production items based on the very purpose and use...even in cutting of bolts you still have class of fit...very little is a cut and dry process one size fits all..

[DJ194950]

ARP brand of strictly hi-perf. bolts uses cold rolled threads on their Mostly(?) automotive bolts. They also use American made steel to higher than most specs. They used to have a very detailed story of their why and how on their website.

 

Does an old mopar flattie require this level of hi tech bolts? I think not!

 

Have read many stories about how they make them and why they use the processes they do.

 

Other uses of threads vary so much as to use psi requirements/ stretch, etc  I cannot begin to comment. Average use bolts available today at most local suppliers is a big unknown.

 

Just saying.

[Plymouthy Adams]

todays head bolts with the use of aluminum heads require a special bolt..they are very prone to stretch due to the fact that they are angle torqued....the special washers used with them are cup and allow for displacement without galling...even at that many mankers..(mainly foreign) are having great amount of problems with ripping threads out of the block...enter only one thing...poor design..