Cylinder base stud

[Jack K]

I need to make a fixture to aid in replacing a cylinder base stud that is pulling out of the crankcase on a 47 Chief. Anyone know the measurement from the center of the bore to the center of the base stud holes.
While I'm asking I'll go for a little more. I'm not a very good welder and have done very little of it but my limited experience tells me welding aluminum leaves it softer than before, sorta anneals it. With that in mind, I intend to use a thread insert for the repair,,, is that a good plan?

[Jack K]

If anyone could offer any measurements in locating the cylinder base studs in the crankcase of a 1947 Chief I would really appreciate it.

The reason I earlier asked for the measurement from center of bore to the center of the base stud was due to my recollection of an old engine blueprint that showed the dimensions in that manner. These drawings are either no longer in my possession or I can't find them.

Again, any help would be appreciated.

[exeric]

You should be able to determine that dimension by measuring the holes in the cylinder flange. You could use guage pins or use calipers to measure across to the tangents of two opposing holes and then add the radius of the holes, divide that by 2 and you have the radial dimension from the piston bore that you want. A helicoil is the only way to go for cylinder base stud repair. If you have just pulled the original threads you shouldn't have to do any welding as the helicoil will be stronger than original. You may want to helicoil all of your base studs if you have doubts about the others.

[c.o.]

That's excellent info to know Eric. I've got a buddy with a '48 Chief that may benefit by your post.

[Jack K]

Many thanks Eric. I can make those measurements.

I had hoped to have the fixture machined and ready for use when the engine got to my work bench. This is the second stud to pull out on this cylinder. The first one I just free handed in place. It work out OK but is canted inward ever so slightly so I really need to get this one in straight.

I think I will likely heed you advise and re-thread all the studs while I'm at it this time.

[exeric]

Jack, you may want to make a tapping block so can tap straight. If you're going to the trouble of making a fixture, make it from a piece of 3/4" steel or aluminum. Drill your 4 base stud holes in your fixture to the same diameter as your Helicoil tap. That will keep your tap straight, which is usually very difficult to do with hand tapping.

[Jack K]

Thanks again Eric.

My plan for this fixture is still forming. I'll either make two, one a drill guide, the other a tap guide or a plate threaded to accept a drill guide or a tap guide on one corner. Or maybe one plate with a drill guide on one corner and the tap guide on the opposite corner.

[exeric]

That's even a better idea Jack. You'll figure it out, it's obvious you know what you're doing.