What is the thread of V8 head bolts

[PhilipA]

I am currently preparing to change the heads and the cam on my 3.9 and I am now waiting for a set of ARP studs from the USA.

I have chased out all the manifold threads and was looking for the correct tap for the head bolt holes in the block.
It looks to me that the bolts are 12MM x1.75 with a 16MM(5/8) head. However my die is quite loose on the sample bolt . It is probably worn but does anyone know off the top of their head?LOL I cannot find a 12MM x1.75 nut anywhere to check.

If so it would be typical Land Rover as the manifold studs are 3/8 UNC ie Whitworth .
Don't get too enthusiastic to the extent of pulling your motor apart as I will be going to the nut & bolt shop for a tap anyway.
Regards Philip A

[p38arover]

Pretty sure they are UNC. I should have some head bolts in the garage if you want me to look. I've got three blocks.

[bee utey]

7/16 inch UNC on the 3.5, 4.4 and 3.9 engines. Please don't confuse UNC with Whitworth, you will weaken the threads.

[PhilipA]

7/16 inch UNC on the 3.5, 4.4 and 3.9 engines. Please don't confuse UNC with Whitworth, you will weaken the threads.

There I go trusting an engineer who told me they were the same when I borrowed his tap. This is a guy who restores cars for goodness sake.

Well the threads are only for the inlet and exhaust manifold and very little material came out, so hopefully they should be OK with only 20Ft lbs.

Darn it. I would hate to have to go and buy a heap of Whitworth bolts , If you can buy such a thing nowadays , and the spanners.
Regards Philip A

[bee utey]

There I go trusting an engineer who told me they were the same when I borrowed his tap. This is a guy who restores cars for goodness sake.

Well the threads are only for the inlet and exhaust manifold and very little material came out, so hopefully they should be OK with only 20Ft lbs.

Darn it. I would hate to have to go and buy a heap of Whitworth bolts , If you can buy such a thing nowadays , and the spanners.
Regards Philip A

It's to do with the thread angle, Whitworth is 55 degrees included angle, UNC is 60. Same thread pitch for 3/8 size. I think the Whitworth tap may take a whisker out of the deepest part of the thread but it should be OK for the manifold bolts. Most hardware store bolts are still WW (Zenith brand!) but as they aren't high tensile they are only found in engines assembled by newbs.

If any of the 3/8 UNC threads strip, just buy a Helicoil or Re-Coil kit. They are a good investment and handy to have around. I've used mine plenty of times for this exact purpose.

[clubagreenie]

Lee Bros engineering will have the bolts, they're in Dunlop St North Parramatta. Out of curiosity, how much were the studs in total fom the US?

[PhilipA]

Lee Bros engineering will have the bolts, they're in Dunlop St North Parramatta. Out of curiosity, how much were the studs in total from the US?

They were/are $206 landed with the ARP lube.

However I followed them up today ( Northern Auto Parts) and they NOW tell me that the kit is on backorder of 2-3 weeks.GRRRRRRRRRR.
I have asked whether that is from 8/2 when I ordered.
TRS is $290 plus freight for the kit only.

UPDATE- Northern Parts just came back to me that it is 2-3 weeks from now which is unacceptable so I have cancelled with them and ordered via TRS , who also sold me a set of Graphite headgaskets (for $58 EACH), correctly guessing that my problem with the Elrings is that water is drooling out of each end of the heads. they claim that the Elrings (OEM Landrover) are good for cylinder seal but awful at sealing the water in, which is my experience also.

Regards Philip A

[PhilipA]

I just went to Gosford Bolts and bearings and bought 2xUNC taps for the magnificent sum of $15, one for the manifolds etc and one for the head bolts.
I tried the UNC tap in the UNC holes in the head and without trying too hard it was tighter than the Whitworth Tap, both in holes that the Whitworth tap had cleaned and "virgin" holes.

I measured up the two taps and the Whitworth tap is .05MM smaller in diameter than the UNC tap.So maybe it is worn.
In any case I am now less concerned about the holes stripping.
Regards Philip A

[clubagreenie]

Before you shell out that much try Fabre in Lakemba. Mine were $125 plus about $10 freight and are kept in stock.

[Bigbjorn]

I just went to Gosford Bolts and bearings and bought 2xUNC taps for the magnificent sum of $15, one for the manifolds etc and one for the head bolts.
I tried the UNC tap in the UNC holes in the head and without trying too hard it was tighter than the Whitworth Tap, both in holes that the Whitworth tap had cleaned and "virgin" holes.

I measured up the two taps and the Whitworth tap is .05MM smaller in diameter than the UNC tap.So maybe it is worn.
In any case I am now less concerned about the holes stripping.
Regards Philip A

They are pretty cheap taps from a retailer. most likely Chinese or Indian carbon steel taps.

NEVER mix fasteners of differing thread angles on anything critical. OK to hold on cheap accessories or tinware but NEVER on mechanical items. Examples are BSW/BSF/BSB 55 degrees with NF/NC/NS/NEF 60 degrees, or BSB 55 degrees with BSC 60 degrees. The mismatch tends to be self loosening, crushes the crests of the threads, and will not achieve or maintain correct torque. People will tell you Whitworth and NC are "the same". I have even heard fitters who should know better say this. They are not the same for the aforementioned reasons. They may be the same pitch but don't mix them. You will find all the above systems on Land Rovers of various ages, plus BA and Metric.

Carbon or chrome tungsten steel taps are OK for cleaning out threads and cutting new threads in easy materials like grey iron, mild steel, soft aluminium and brasses. They also cut only to a generic tolerance. High speed steel taps should be used for accuracy. You will see on nearly all HSS taps a three character code which is a tolerance indicator. HSS taps should be/need to be used on difficult materials, tool steels, high duty irons, heat treated aluminium alloys, titanium, chrome nickel (stainless) steels, long chipping materials, and many plastics.

The price factor is usually three to one. HSS taps usually being three times the price of carbon steel ones from the same maker and supplier.

High tensile BSW & BSF bolts are nearly a thing of memory. Most places that still sell them are selling very old stock. They are probably still being made in miniscule quantities by specialists supplying restorers markets.