Tapping 3/8 hole to 7/16
- Thread starter mike7
- Start date
volvo92906
Well-known member
I would just grab a tap and retap it....
djjsr
Well-known member
What's it holding?
7/16-14 thread tap drill size is 25/64" (.3906).
3/8" is .375".
Should be good.
7/16-14 thread tap drill size is 25/64" (.3906).
3/8" is .375".
Should be good.
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The question is "is there enough room on the block to support the larger threads" typically a nut has 1 1/2 the height as the diameter of the thread size. That would be a safe guide here as well. Keep in mind if you have to put an insert or helicoil in you are tapping it oversize anyway so you could just go to the larger bolt size. What about the flange you are bolting down over the thermostat? Will it accommodate the larger hole for a bigger bolt?
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djjsr
Well-known member
If it's an aluminum manifold the tap drill is different than what I posted for steel. You need a letter U drill, which is .368", so you probably don't have enough metal there to just tap for 7/16".
If it's a cast iron manifold, you should be ok. Use the same drill as steel, 25/64.
If it's a cast iron manifold, you should be ok. Use the same drill as steel, 25/64.
3/8-16 basic major diameter is .375
7/16-14 2A internal minor diameter range is .360 - .375 with a tap drill of size U (.368)
Answer: Drill out the thread and re-tap as 7/16-14. It'll work fine so long as the existing thread isn't augered out past it's major dia.
7/16-14 2A internal minor diameter range is .360 - .375 with a tap drill of size U (.368)
Answer: Drill out the thread and re-tap as 7/16-14. It'll work fine so long as the existing thread isn't augered out past it's major dia.
Murphy4570
Well-known member
I'd just drill and helicoil to restore the threads to the original size. A thermostat housing is a low torque application.
I just drilled and helicoiled a dozen 6mm threads a week ago, its a cakewalk if you take your time.
I just drilled and helicoiled a dozen 6mm threads a week ago, its a cakewalk if you take your time.
mikebramel
Well-known member
Epoxy and a stud the same size
porschedude996TT
Well-known member
Threaded insert 3/8-16 inside and 9/16-12 on the outside.
Or weld the hole closed and re-drill and tap.
Or weld the hole closed and re-drill and tap.
ChevyEFI
Well-known member
thread size minus pitch is the minor thread diameter and the amount that needs to be left to tap new (it can be slightly bigger but that's the basic idea.)
7/16" - 1/20" = .3875"
7/16" - 1/14" = .3661"
3/8" = .375"
If the threads of the 3/8 hole are boogered but the outer area is entirely intact, you have a bit more than enough meat to drill & tap for 7/16"-20. 7/16"-14 might work, but
Or coiled or solid thread inserts are an option.
7/16" - 1/20" = .3875"
7/16" - 1/14" = .3661"
3/8" = .375"
If the threads of the 3/8 hole are boogered but the outer area is entirely intact, you have a bit more than enough meat to drill & tap for 7/16"-20. 7/16"-14 might work, but
Or coiled or solid thread inserts are an option.
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619DioFan
Well-known member
Was thinking the same thing
That's also what I was thinking. Put a stud in it. I used to run into that problem a lot on aluminum intakes. Especially the carb mounts.
NHBandit
Well-known member
If it's Aluminum I would go with a Helicoil insert. Hard to guess though without knowing how "boogered" the hole is. It's like a woman asking if these pants make her *** look big without a picture of the ***... 
beerdog
Well-known member
Gluing it will be better than a threaded insert or retapping?
454ragtop
Well-known member
Better off just putting an insert in it, and it's fixed correctly forever. If you were around here, I'd pop a Heli Coil in for you.
Jim
Jim
mikebramel
Well-known member
Using the word glue I don't think you have much experience with epoxy
ilovevocs
Well-known member
The helicoil is such an easy option. Unless its a beater I wouldn't epoxy it, but that's just me. Would it work, likely.
beerdog
Well-known member
I was just being funny. Creating new threads is far better than holding it in with epoxy. Sure, it can work but the better way is to make new threads.