Re: Block Thread Repair

Fri Aug 02, 2013 8:28 pm

Ken, Not to complicate matters, but McMaster-Carr carries the 3/8-16 size in 4 different lengths. I don't know off hand how long the threads are in the block, but for strength I would think you should use the longest helicoil that you can.

Bob

Re: Block Thread Repair

Fri Aug 02, 2013 8:38 pm

Bob McCarty wrote:Ken, Not to complicate matters, but McMaster-Carr carries the 3/8-16 size in 4 different lengths. I don't know off hand how long the threads are in the block, but for strength I would think you should use the longest helicoil that you can.

Bob


Bob, that's one of the problems with the threads in the block, they go through into water jackets. The actual thread length is not more than 1/2" if I remember correctly. Normal standards says thread engagement should be 1-1/2 times the diameter. Add to that the high torque specification and the minimal threads in cast iron, the factory threads are at best, marginal.

Re: Block Thread Repair

Fri Aug 02, 2013 9:40 pm

ricky racer wrote:
Bob McCarty wrote:Ken, Not to complicate matters, but McMaster-Carr carries the 3/8-16 size in 4 different lengths. I don't know off hand how long the threads are in the block, but for strength I would think you should use the longest helicoil that you can.

Bob


Bob, that's one of the problems with the threads in the block, they go through into water jackets. The actual thread length is not more than 1/2" if I remember correctly. Normal standards says thread engagement should be 1-1/2 times the diameter. Add to that the high torque specification and the minimal threads in cast iron, the factory threads are at best, marginal.


Howdy Ricky - I measured them today - they come in just under 3/4". The original bolt did not quite use all the threads. I ordered 3/4" helicoils...I'll keep everyone posted.

Re: Block Thread Repair

Fri Aug 02, 2013 9:43 pm

Ken, Sounds like you've got it covered.

Bob

Re: Block Thread Repair

Sat Aug 03, 2013 6:15 am

Bob McCarty wrote:Ken, Sounds like you've got it covered.

Bob


Bob - thanks for the vote of confidence - to be clear I'm nervous as all %^&$, about this. Never used a helicoil before. There will be lots more checking and verification before drill is placed to metal. Also, I'd not have ever made it this far on Rex if not for the support of the members of this forum. Thanks to everyone. :thanx: :thanx: :thanx:

Ken

Re: Block Thread Repair

Sat Aug 03, 2013 11:31 am

I am reasonably certain that I can remember when Helicoils were first invented. Now the patent has expired and anyone can offer the inserts-- but not using the Helicoil name, which is copyrighted. Studying the concept, any coil that fits the thread must be identical to any other of the same thread size. So they all are interchangeable for a given size and shopping for price is productive.
When I tear down a single cylinder engine with aluminum block, all the holes get a coil insert as a routine. Some makers of aluminum engines, perhaps a outboard engine maker, can't remember, use coil inserts in the engine as original from the factory. Their confidence inspires confidence in me.

Re: Block Thread Repair

Sun Aug 04, 2013 1:37 pm

In fairness to the person who posted suggesting drilling and tapping for the next larger size, the tap drill for the 3/8-16 coil insert is 25/64. The tap drill for 7/16-14 ( no insert) is 23/64. So that does remove less original material.
However, the use of 7/16 necessitates drilling the hole in the head larger and using a different bolt in that position. Additionally, a given torque on the bolt with 16 threads per inch and 14 threads per inch yields different clamping pressures on the head with the 14 thread having the lower pressure at that given torque. In many cases it is a good and workable solution.
But I much prefer the coil insert if it will work in a particular situation.
Drilling and tapping for 7/16-14 locks out forever the possibility of using the 3/8-16 coil insert.