VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Head Bolts

Has anybody discovered a source for 1/2-12 head bolts for the old 4-cyls?

Thanks,
-R

Nothing firm at this point, however at least two parties are looking into cost, feasibility, ECT.

If you decide to use the old ones you can torque to 50-55 pounds and have a satisfactory seal. If you use the old head gasket coat it with a light coat of grease. If you use a new one coat it with the Permatex "Copper Spray-A-Gasket" or similar product.

During my last rebuild project, I did at least make an attempt to cut my own bolts.



However, on my first attempt, I didn't feed the bolt in straight and the result was a 5 1/4" bolt with a wobble. On my second attempt, the die broke (possibly from feeding two grade 8 bolts through it.)

-R

Rusty Fender, What about using soft bolts and having them case hardened after threading? Dan

Hi Dan,
I thought about that too but I found it was extremely difficult given the limited equipment at my disposal to feed the bolt straight into the die so I gave up. It looks like I may have to make another attempt.

Incidentally, I did some research on the 1/2-12 Whitworth standard. The Whitworth threads feature a 55 degree thread angle which is different from the UNC 60 degree thread angle. Although such bolts may appear to thread in properly, it would most likely cause considerable loss in holding force, fatique resistance, and strength. Therefore I don't see Whitworth as a viable option.

Cheers,
-R

Threading grade eight bolts to 1/2 X 12 tpi, purchase bolts at least one inch longer, plus the threads, than you need your finshed bolt, cut off threads, chuck bolt head in 3 jaw lathe chuck, use a brass jawed chuck [like you would use to hold a starter or generator shaft] in tail stock, cut threads to 75% depth, remove, cut off where your threads start, finish threads with 1/2 X 12 adjustable die [like your picture]. You will be able to make a fit as precise as you wish. If you don't have a lathe, hunt up a friend that does.

There are several solutions to this problem but none seem satisfactory for all cases. Following is a summary of the situation.
1. NOS bolts - This should be an ideal answer but there are almost none available and NOS bolts are just too short. Old bolts are usually stretched and if fully torqued will break and new ones are apt to pull the threads out of the block. Only about four full threads will be in contact if a new copper gasket is used.

2. Long Class 5 or Class 8 bolts - These can be cut to desired length and re-threaded but should be annealed before and re-heat treated after re-threading. I would make them at least one half inch longer than original and bottom tap the threads in the block. The drawback to this approach is the bolt heads are incorrect ( ie too short ) if the car is to be a show car.

3. Bolts made from chrome moly hex stock -This is feaseable but requires turning the 3/4" hex down to 1/2" bolt size which is very time consuming. You should heat treat after threading and the length should be as in Item 2. above.

4. Studs made from chrome moly steel rod - Studs are heat treated to class 8 equivalent after threading and Class 8 (1/2-20) nuts and washers should be used. I have been using this combination for about two years with good results. Mine are heat treated Type 01 Tool Steel but I would prefer chrome moly. I have about 8 threads fully engaged in the block and 80 pounds of torque on the fine thread nuts provides an equivalent of about 130 ft-lbs.
I thread the studs in my lathe with soft metal between chuck and workpiece. The threading die is held in a right angle fixture which eliminates the wobble that Ron ( ie. Rusty ) reports. I make two passes with different dies. First a die adjusted to maximum size and second the final fit.

Again the stud and nut combination is visibly incorrect and would cost points for a show car, but for me this is the best overall solution.

Herb

Hi Herb,
Great ideas you have there. Your comment about pulling the threads out of the block reminded me there is one other solution that has not been brought up yet. That is to install a thread repair kit in the block. This would bring the threads to 1/2-13 which allows the use of conventional bolts while adding strength to the threads. I believe the bosses on the block are strong enough to support being drilled to the required size.

-R

A while back I checked with the local fastener supplier and was told about the Whitworth 1/2-12 bolts. As related by Herb the head was not correct and the angle also not the same as the threads in the block. They then said that new bolts could be made with the proper threads, head and strength. They would have rolled threads like new bolts. The cost? depends on how many are ordered. The estimate was $ 5 each if several hundred were ordered. Since I didn't have a current need nor extra $$$ I did not persue further. Anyone check lately on having new ones made?

Chip I feel the same as you about investing a couple of grand to get several hundred head bolts made . I would either thread studs and use nuts or get extra long bolts and thread them with a couple of hand dies, why do you need grade 8 bolts? I figure grade 5 will hold as much as is needed. I think the key is to clean and chase the threads in the block before you ***** something in or ***** something up.
(I wonder what other word we should use for schrreew This anti-foul language thing is absurd

chip,

guess I'm weird, but these are some of the discussions I find most interesting at this chat site...

so, is "several hundred," 300?..

and, not owning a four, how many head bolts are required per engine?..


epi

Hi epi,
There are four 5 3/16 bolts and four 1 15/16 bolts, all too short.
Mack
I certainly agree that screwed is a perfectely acceptable automotive and engineering term. The couth file seems a little limited; however, and you can screwe something in or fornix something up, or just thread it in and scroue it up.
Herb

herb,

what did you mean "all too short?"...


epi

epi
I am simply emphasising what I said in my first statement above to the effect that four threads of engagement in a 75 year old casting using bolts of the same technology is a recipe for failure.
Herb

herb,

so are there &, if so, how many more threads are available in the bore?..


epi