Head Bolts

[Rod]

Hi All,

In cleaning up my motor and looking in the spare parts department I thought I would share some useless trivia that I have searched for on this forum but havent' found reference to.

As we are aware there are two different lengths of head bolts . I looked in my master parts catalogue which goes up to EK and there is only reference to one part number for each length. This is what I have found:

Short Bolts. I have found three different types.
      1. Slightly Domed bolt head with Ajax 70 on top. The shaft of the bolt is uniform thickness.
      2. Flat bolt head with a Star Pattern on top. The shaft of the bolt is uniform thickness.
      3. Flat bolt head with a Circle on top. The shaft has a shoulder under the bolt head (as if to assist in the centering of the head on the block) which is the same diameter of the bolts above. However, the majority of the shaft is slightly smaller in diameter.

Long Bolts. I have have found two different types.
      1. Flat bolt head with a Star Pattern on top. The shaft of the bolt is uniform thickness as with the first two short bolts.
      2. Flat bolt head with an ever so slightly different Star Pattern. This bolt has a shoulder under the head like the third short bolt with the majority of the shaft slightly smaller in diameter.

I know this is useless trivia but it has me thinking. The bolts may have changed once the EJ motor came out (I haven't got a parts catalogue for the EJ). However, I don't think that this would be the case considering there are three short bolts versus two long types. Possibly different suppliers. I wonder if the bolts with the shoulder and slightly smaller diameter shafts made way for a "stronger" uniform lengthed diameter shaft.

Anyway thats enough from me on bolts. I am now paronoid about bolts, especially broken ones.

Cheers

Rod

[Harv]

GMH made both “long” cylinder head bolts (part number 7401119), and “short” ones (part number 7401120) for the grey motor. The GMH cylinder head bolts have a very short thread length. The idea behind this is that you only cut enough thread to do the job – any unengaged thread acts as a localised stress riser, leading to fatigue failure of the cylinder head gasket joint. The bolts are also reduced in diameter (they should be 7/16” diameter, but are less than that). This reduces the bending stiffness of the bolt, increasing fatigue strength.

Cheers,
Harv

[Rod]

Hi Harv,

Thanks for offering additional information. Based on what you have provided would indicate the third example I had for the 'short' bolt and the second example for the 'long' bolt are GMH ones. This makes sense as the marking on the head of each bolt (circle and star) and shoulder under the head of the bolt, being 7/16 with the rest of the shaft narrower, being consistent with the markings on the Main Bearing bolts as I have found.

Interestingly, the threads on all of the bolts are relatively short for the reasons you indicated but the GMH ones are slightly longer. The shoulder under the head is 7/16 in diameter (a length of about a 1/3 of an inch) which runs into the main shaft which has a diameter of 7/18 (if there is such a diameter).

Thanks for your post. I have learnt something about the strength of these bolts. I was going to run with the bolts that had uniform shaft diameter thinking these would be stronger.

The other bolts I have listed must be after market ones ie: Repco etc...

Cheers

Rod

[ardiesse]

Rod,

You've just described the history of Holden cylinder head bolts.

There are "early", "mid" and "late" head bolts.
"Early" head bolts have stars on the heads, for both long and short bolts, and full 7/16" shaft diameter.  This style was used for FX and FJ.
The "mid" head bolts were made by Ajax, have domed heads, and I think the full 7/16" shaft diameter.  I have an FC motor with these head bolts.  Can't recall now if the long bolts also have domed heads.
The "late" head bolts (at least B and J motors) have O on the short bolts, * on the long bolts, and reduced shaft diameter.

I'd say all your head bolts are OEM.  But GMH would have had at least two suppliers.  And years of engine rebuilds will have randomised things further.

Rob

[mcl1959]

I’m sure I’ve seen head bolts with GMH on the top, I’m going to go look to see if I have any.
Ken

[ardiesse]

Ken,

Head bolts with the GMH logo - that rings a bell with me, now that you mention it . . .

Rob

[my8thholden]

Rod ..Have you advanced with the motor rebuild,I am interested to know how its going if you have managed to work on it over this period..thanks Vern ..

[Rod]

Hi Vern,

Thanks for your interest. I have been slowly working on the motor. I would like to be a little quicker. Tomorrow I am dropping the head off to get crack tested. It has done very little miles since it was last done but as you know that is a lot of years ago now. While it had no symptoms prior to pulling down, I want to be safe not sorry. It cleaned up a treat. It looks as if the surface has just come off the milling machine as the face in smicko. I would love to get bigger valves, a little radius relief etc.. but I figure it is not worth the expense as I drive the car very rarely. I have identified what may be a crack but as I said I have had no symtoms. It almost looks like it is a casting mark.

The reason for the slowness is I have been cleaning, oiling, putting brushes in, painting etc... all the ancillory items to the motor. This includes where needed soaking the manifolds, thermostat housing, water pump(only up to the level of the seal as I was unsure what the citric acid may do to the seal) in citric acid. Gee this stuff is amazing! The manifolds, particularly the exhaust came up like new. Likewise the interior of the thermostat housing and the water pump around the impeller etc...looks like it has just been cast. I have thoroughly flushed the block after removing the welch plugs and putting the pressure washer through etc.... I am now wondering if I should fill the block with citric acid and the do the pressure clean trick again.

I hope to start cleaning up and painting the engine bay shortly.

Cheers

Rod

[Errol62]

Hi Rod
I love the citric acid too. I have a large wheelie bin I fill with solution for longer panels and such and now looking at the old claw foot bath in the garden to soak some guards in.

I thought about using citric in my block as well. Oxalic acid is what is commonly used and should be readily available.

Keep at it. You’re doing a thorough job.
Cheers
Clay


Sent from my iPad using Tapatalk

[my8thholden]

Hi Rod ..I haven't used Oxalic acid ,I have used Citrus based paint stripper on alloy parts like carby / fuel pump / generator end plates/ very happy with that,especially old dried up fuel in a carby ..we have a molassis bath at the museum workshop ,it does a fair job on something that is in good condition but dirty ,it doesn't etch in at all ..the machine shop where you took your head ,do they have a pickle bath ,when I had my head done , just standard ,they put in hot bath for couple days along with the engine block ,its good..Jack said if I want a " like New " he sends them out to someone in Blacktown ,not cheap at all..I just want it clean as it will be painted any way...cheers Vern

[Rod]

Hi Again Vern and all,

While the title of this thread has moved off track, I thought it best to respond to some of the points above re the head etc...

I took the head to the engine rebuilders shop. The owner wasn't too fussed about what I identified as being a crack. He said while it was in a classical spot for a crack to appear, he was sure it was a casting mark as I thought it maybe. Initial inspection indicated that maybe a basic rebuild was required. Anyway after it had been hot bathed and pressure teset I go the call I was hoping not to get. The "casting mark" was indeed a crack but another two were located. There were no concerns about doing a repair but the rebuild was going to be more substantial including new valve seats (current ones recessed too much), red motor valves and valve guides.

I possed the question about testing a couple of other heads I have, to see if we could find a better head. The owner was great and said there is a point that the expense of testing additional heads is outweighed by doing a repair. Anyway I dropped another two off today. One was a virgin head in that it had no sign of having the head shaved (full thumb print). It had a lot of surface rust and the seats were too far gone (rusted signifcantly due to no valves being present). If it comes up ok it will still need a full rebuilt. The second one was much the same but had less meat. The owner wasn't concerned about how much was left (thumb print was still present)as the motors weren't high compression anyway. This head is interesting in a couple of ways. Firstly when taking out the valves they seemed to be "very" tight. More than just gummed up. As I worked through I found two guides that were cracked and one broken off at the head. I have never seen that one before and it semi confirms my belief around the tight valve to guide clearance. Once again if this head comes up a full rebuild will be needed. The other interesting part around this head I will discuss below.

When we were looking at the heads I spoke about the great work that Rob and then ultimately Harv did in getting the New Improved Head Gaskets made. The business have done many grey heads over the years and continue to do so. I spoke about how Holden modified the gaskets in 1963 and then how Harv has got these remanufactured. He hadn't heard about these gaskets. He spoke at length about heads in general and the antomy of how they are made in order to improve coolant flow particularly to the back of the head. This made a lot of sense in regards to why the gaskets, in this case the grey holden, were modified particularly with the larger hole in the head and block. I said I would show him the differences when I collect the repaired head. As you know I can get long winded but here comes the second interesting fact about the second head spoken about above. In its past life it must of had one of the original modified gaskets installed. How did we come to this conclusion. The owner identified that it has a larger hole at the back of the head compared to the other one. Initially he thought it was corrosion but on closer inspection this didn't seem to be the case. I am hoping that if this is the case that the gasket did its trick and that there are no cracks with this head. If this one gets rebuilt at least I won't need to redrill that hole.

Cheers

Rod