VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Head bolt trouble

Hi , i have a 27 tourer and farmed out the engine build . Just got it running the other day . But when i came back to it 2 days later all 4 cylinder where flooded with water . I dried them out and got it running again but noticed #4 and 3 cylinders blowing from the head gasket .(exhaust side). I check tightened the head bolts and found them loose / stripped . Some looked to have been helicioled before . My question is , can anyone tell me the largest thread size i can go to or what is the best to go to ? Before i break through anywhere ? Thanks Robbie

I am a bit surprised that the head bolts didn't strip or break before pulling out of the block. The original bolts are very soft and will not take much more than 50 ft./lbs. torque before stretching. Of course the builder may have found new bolts that pulled out of the block when tightened too much. He then attempted to cover up his mistake by installing Helicoils.

I would go back to the engine builder and ask him about what he did to destroy your engine? and how he proposes to fix it? After he denies everything and tells you to take a walk, you will need to find someone that understands the proper repairs. I would guess that installing studs into the block and then nuts to hold the head will be the fix as long as the block is still sound enough to hold the studs. Sorry but I don't know the block construction well enough to suggest sizes.

My experiance in old cast iron engine blocks tells me there will be a ton of material. They way over did the thickness almost everywhere. If it happens that you do go through, just patch the hole with JB weld or some type of epoxy before threading and spray the head bolts with graphite spray so the threads won't stick. Pipe dope can also seal the threads well. Use the old type dope, not the teflon type.

Thanks , could you tell me what thread the original bolts should be ? And do i need to remove the rocker arms or can i leave them on the head if i was to remove it to asses the damage ? Thanks Robbie

It is an unusual size, from memory I think it is 1/2"-12 (??) thread, whereas "standard" would be 1/2"-13 There are two different lengths involved.

You should be able to remove the head with the rockers in place.

I believe that the head bolts are 1/2-12 which is a British Standard size but think the thread angle is closer to US 1/2-13.

The '28 Master Parts Book calls the bolt thread," 1/2" X 12 U.S.S.",perhaps meaning United States Special?
The Whitworth threadform for 1/2" is 55 degrees angle X 12 threads per inch.The U.N.C. threadform for 1/2" is 60 degrees X 13 threads per inch.

New head bolts are available from the filling station. I was involved in the production of these bolts and they are a quality product.

I do believe the Filling Station also has the tap for this thread size.
Thanks
Woodbutcher