"High" Nuts vs Standard for Cylinder Head

[GrahamPaige29]

Hi guys.  Several 7/16-20 nuts are missing for both my cylinder head studs and manifold studs on my '29 Graham.  I noticed the old ones are longer or taller than a standard type you would buy (cat 5 or 8).  Other than the look of them being mismatched once they're all on, is there a need to seek out these "high nuts".  I think they could get a bit more of a grip on the threading and avoid stripping better.  Any thoughts?  Thanks.

 

Geoff

[PFitz]

McMaster-Carr has them. Called "high hex nuts".  https://www.mcmaster.com/#hex-nuts/=19d6wao They are grade 8 but you have to use the torque value of the weakest part and in this case that would be the old stud bolts. Grade 2 torque on cars from that era is safer without risk of stripping a stud bolt.   Better to have to retighten because of too-loose than have to replace from too-tight.

 

McMaster-Carr also carries the "wide hex" (aka "heavy hex") that are used on some makes of cars from the 20-30's.

 

Paul

Edited September 13, 2017 by PFitz (see edit history)

[Spinneyhill]

If the car came with High nuts, the designers obviously chose them for a purpose. Put them back. Short nuts have fewer threads holding and are thus not so strong. Unless you know better, use high nuts. Short nuts of higher grade don't cut it either, you still have the old (low grade steel) studs and the old cast block.

Edited September 13, 2017 by Spinneyhill
added a phrase (see edit history)

[PFitz]

You would think using a longer nut that it would be stronger, but a caution from this site says no.  https://www.fastenal.com/en/78/screw-thread-design

 

" .....................Caution: It appears that one could theoretically increase the thread strength by increasing the length of engagement. However, as illustrated in the Load Distribution chart above, the first thread will be taking the majority of the applied load. For carbon steel fasteners (including tapped holes) the length of engagement would be limited to approximately one nominal diameter (approximately 1-1/2 times the diameter for aluminum). After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession. ........................"

 

Paul

[joe_padavano]

18 minutes ago, PFitz said:

After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession. ........................"

 

Paul

 

That is not entirely true.  It depends on the ductility of the bolt and nut materials.  The statement is more accurate for hardened steels, like Grade 8 bolts.  More ductile materials will yield slightly and allow better load sharing among the threads.  Aluminum threads are the opposite extreme, for example.

[Spinneyhill]

5 hours ago, PFitz said:

You would think using a longer nut that it would be stronger, but a caution from this site says no.  https://www.fastenal.com/en/78/screw-thread-design

 

Interesting. Thank you!

[edinmass]

The shorter nuts will bottom out before you reach proper torque for crushing the head gasket. Thus, your torque wrench will read correctly, while in fact you won't have enough clamping force, and the gasket WILL fail. We see it all the time. Pierce Arrow used a special nut, which today are CNC machined to proper profile and length out of stainless. They cost three time more than off the shelf nuts, and the cheap guys buy them all the time, and then need to do their gaskets over again. At current prices for head gaskets, they end up spending almost a thousand dollars more for using the incorrect nuts, especially expensive on the twelve, as your buying two new gaskets. 

Edited September 14, 2017 by edinmass (see edit history)

[Spinneyhill]

If the car has cap nuts, you must use the right height nut else when you bottom in the nut, you will probably brake the stud before you reach the right torque (if you use a torque wrench). Or have the problems edinmass talks about. But it has open-ended nuts according to the O.P. picture.

Edited September 14, 2017 by Spinneyhill (see edit history)

[Friartuck]

I made my own:

http://www.secondchancegarage.com/public4/acorn-nuts-1.cfm

 

[Bhigdog]

8 minutes ago, Friartuck said:

I made my own:

http://www.secondchancegarage.com/public4/acorn-nuts-1.cfm

 

 

This is what I love to see.....................Bob

[jpage]

Most all original head nuts as well as most bolts and nuts on any early car are only grade 2. Early nuts and bolt heads were a little thicker than their modern counterparts. You might try a Model A Ford supplier as "A's" used the heavy pattern nuts, so you might find a match.

[GrahamPaige29]

Obviously, there's some controversy about this topic.  It's always good when we explore issues like this.  I'm going to re-use as many original nuts as possible and use ones of similar height for the missing ones.  I'll have to guess at my torque setting as I don't have a chart for a Graham. 

[PFitz]

 They didn't use torque values back then.

 

However, you can look on line for a nut/bolt torque chart and use the value for the sizes that your dealing with.  Always pick the value of the softest/weakest metal involved. As I said above, with many old cars it's safest to assume grade 2 bolts and studs, .....  unless you have original factory info showing otherwise.  

 

Also look up cylinder head  bolt tighten sequence charts. Cylinder heads have to be tightened in stages and a proper sequence, or you risk having the head  warp and leak.

 

Paul

[JFranklin]

Usually a head  is tightened center out with x cross pattern. Tighten all fasteners evenly in stages of about 15 ft# until around 50-55 #. Re-torque after running a few times. 

[edinmass]

Sorry, on my phone I couldn't see the open ended nut, so I thought the discussion was on acorn nuts. I'm getting to the point I shouldn't try and read this forum on my phone......sure sign of age!

[Terry Wiegand]

This has been an interesting discussion for sure.  Here is something to think about.  Geoff mentions in his original post that the head nuts are 7/16-20 thread.  The original engineers wanted fine thread for a reason - more thread surface to share the load.  I have always felt that it is a very good idea to replace fasteners like this when things come apart for any reason.  The reason being that the original threading has been 'stressed' or 'pulled' if you will to a small degree.  I agree that replacing all of the cylinder head nuts might seem unnecessary, however, replacing the head gaskets twice seems like a really unnecessary situation.  Also, the metallurgy of 100 years ago doesn't even begin to come close to what is available today.  Just some things to think about.

 

Terry Wiegand

South Hutchinson, Kansas 

[Spinneyhill]

8 hours ago, Terry Wiegand said:

The original engineers wanted fine thread for a reason - more thread surface to share the load.

 

I never thought about this. I find it easier to get higher tension on a fine thread, but...

 

http://www.katonet.com/article/coarsevsfine.html  gives a rundown of fine vs. coarse threads. In brief,

 

"Coarse threads are more durable and have greater resistance to stripping and cross-threading. The height of each thread is greater than the corresponding fine thread so there is more material between each thread making flank engagement greater.

Coarse threads are less susceptible to being nicked or damaged, so they do not have to be “handled with care” as much as fine threads."

 

and

"Fine threaded bolts are stronger than the corresponding coarse threaded bolts of the same hardness. This is in both tension and shear due to the fine threaded bolts having a slightly larger tensile stress area and minor diameter.

Fine threads have less tendency to loosen under vibration due to their having a smaller helix angle than coarse threads. Fine thread Locking Insert grip coils are more flexible than coarse thread insert corresponding size grip coils, and are less likely to take a set under vibration conditions.

Fine threads because of their finer pitch allow for finer adjustments in those applications that need this characteristic.

Fine threads can be more easily tapped into difficult to tap materials, and thin walled sections.

Fine threads require less tightening torque to develop equivalent preloads to the corresponding coarse thread bolt sizes.

 

[Terry Wiegand]

So, at the end of the day, each thread pitch has it's good and bad points.  I think it would be really unfair to say that one is better than the other.  It all comes down to the individual application.  The demount-able, split rims on my 1920 and 1922 Buicks are held onto the wheel rims with 7/16"-20 Heavy Hex machine nuts holding the rim wedges in place.  This is a very good example of threads not loosening under vibration and wheels certainly are the subject of constant vibration.

 

Terry Wiegand

South Hutchinson, Kansas 

[Graham Man]

Geoff,

    You mention you are missing some studs and bolts.  I would replace all the head studs and bolts together for all the reasons listed.  You have to be careful because sometimes they extend into water jackets so they need to be sealed when reinstalling new ones (I think a waterproof thread lock is the tool of choice?).  Yes all Graham cars had the tall nuts, and fine thread, well except into the head where they are coarse thread (another topic of discussion?).  The only Grahams I have seen with acorn nuts is the early large 8 engines just to mix it up they used short acorn nuts....

[GrahamPaige29]

21 hours ago, Graham Man said:

Geoff,

    You mention you are missing some studs and bolts.  I would replace all the head studs and bolts together for all the reasons listed.  You have to be careful because sometimes they extend into water jackets so they need to be sealed when reinstalling new ones (I think a waterproof thread lock is the tool of choice?).  Yes all Graham cars had the tall nuts, and fine thread, well except into the head where they are coarse thread (another topic of discussion?).  The only Grahams I have seen with acorn nuts is the early large 8 engines just to mix it up they used short acorn nuts....

 

Hey Graham Man!  I examined the studs and they weren't so bad.  I did have to replace some of them with ones that my friend out west sent me.  I ended up using 7/16" fine thread new nuts with flat washers below them and I was able to torque to 50 lbs with no problem.  I was careful to clean out the course threads on the engine with a tap.  There was some rust and crud there.  I added a little anti-seize paste when I installed them.  Hopefully, this will work out ok.  Here's pic of the install...

[Taylormade]

I'm no expert, but I rarely, if ever, see washers under the head nuts.  it may be perfectly fine, but I have to wonder why they weren't used originally.

[Graham Man]

The normal "Head Bolt Washers" are about 0.120 in thick (about 2x-3x a normal washer thickness) two camps, first dissipate the pressure over a larger area, second "hard" washers so there is less galling between the bolt and head theoretically more accurate torque readings.  All Graham engines used "Head Bolt Washers" most used tall head bolts.

 

[Taylormade]

You learn something every day.

[mcdarrunt]

I keep long (high) nuts in a drawer that I have pulled off of leaf spring U-bolts. Most are 1/2" fine but some compacts had 7/16 and big trucks use 9/16 and larger. They are usually TOO long but are easy to face off on a lathe.

[70sWagoneers]

Many straight 8 type manifolds have a relatively low torque value to allow for heat expansion and to account for the small clamping surface area.