Helicoil or tap for larger bolt??

[53burb]

First off, this is on a '55 Chevy Bel Air with an early 70s 350 I'm putting in it. As has happened many times to others, after changing the thermostat, the passenger side bolt hole on the water outlet stripped. This is the original cast iron intake. The bolt hole is so worn that the 3/8" bolt will just drop in for the most part. Do you think its easier to use a helicoil or retap it for a 7/16th bolt? I have an Harbor Freight tap and die set that I used on a riding lawnmower engine years ago. Thats the real only experience I have with it. Never have helicoiled anything. Thoughts?

https://www.amazon.com/Helicoil-5521...83463582&psc=1

[LS short box]

If a 3/8's bolt just drops in the hole it might be to big for a helicoil. If you go 7/16" I would drill and tap both bolt holes so they look the same.

[53burb]

It doesn't exactly just drop in, but it is fairly loose and doesn't tighten of course....think its easier to just tap them both for 7/16th? Shouldn't be too hard to tap cast iron, right? It is easily accessible....

[Dead Parrot]

Had to drill and tap an aluminum intake after one of the bolts corroded in place. If you have access to a drill press, use it so the holes are straight.

My vote is to drill and tap both holes. Should be good for another 40+ years.

[53burb]

I do have a drill press, but the manifold is already installed on the engine...its just a "temporary" 350. Of course temporary could be years. I want to get the 55 going, then decide how much more I wanna do to it....350/700 combo, lowered, A/C, etc. Or get the 350/400 I just dropped in up and going and start working on my '53 Suburban...finally....

[53burb]

This is the 55

[kwmech]

I've only used 1 or2 heli-coils in the past 40 years. I always go with these for a permanent repair

https://www.timesert.com/html/inchsert.html

If this outside diameter is too small they have a larger OD insert called a big-sert. Going with a 7/16 bolt is way over kill and reduces the amount of material available around the bolt hole on the t-stat housing.

[53burb]

Thx, Ill take a better look at it in the next couple of days and make my decision on which direction I wanna go...thx for the link....kinda pricey tho...but maybe worth it tho....

[53burb]

I was just reading the hole size or drill bit needed for a 7/16th tap....it says 11/32 is needed or 23/64. 3/8th is 12/32 and/or 24/64. Do you think the existing hole is too large to tap for a 7/16th bolt?

Here is a thread on the subject...

https://www.garagejournal.com/forum/...o-7-16.201965/

[Keith Seymore]

Originally Posted by kwmech

I've only used 1 or2 heli-coils in the past 40 years. I always go with these for a permanent repair

https://www.timesert.com/html/inchsert.html

If this outside diameter is too small they have a larger OD insert called a big-sert. Going with a 7/16 bolt is way over kill and reduces the amount of material available around the bolt hole on the t-stat housing.

How are these different than a heli-coil?

K

[Bigdav160]

Originally Posted by Keith Seymore

How are these different than a heli-coil?

K

They are solid rather than a coiled wire. I think they are less likely to pull out.

I am not sure a 7/16 bolt would work. You may not have enough room on the thermostat housing. Minimum would be the need for allen head bolts.

[Keith Seymore]

Originally Posted by bigdav160

they are solid rather than a coiled wire. I think they are less likely to pull out.

ty -

k

[A1971Blazer]

I own a machine shop and we use heli-coils frequently to repair threaded holes and also install some per customer specifications on manufactured parts.
If installed properly, they are very strong and will provide a permanent repair.
It's critical to drill the correct size hole for the heli-coil tap and to insure that the hole is drilled and tapped square to the mounting surface.

[67 twins]

Originally Posted by kwmech

I've only used 1 or2 heli-coils in the past 40 years. I always go with these for a permanent repair

https://www.timesert.com/html/inchsert.html

If this outside diameter is too small they have a larger OD insert called a big-sert. Going with a 7/16 bolt is way over kill and reduces the amount of material available around the bolt hole on the t-stat housing.

My late brother, who was a professional Harley mechanic told me about these probably 20 years ago. Told me then he'd never use heli-coils again.

[A1971Blazer]

Originally Posted by 67 twins

https://www.timesert.com/html/inchsert.html
My late brother, who was a professional Harley mechanic told me about these probably 20 years ago. Told me then he'd never use heli-coils again.

Those work well too.....the only problem with them is they have a very large outside diameter that's not always ideal in some situations.

[jeffahart]

you can clean the inside of the hole, blow it with air, then slather the threads with jb weld using a circular motion. What's remaining of the threads gives great surface for jb to grip. Tap it gently(basicaly a re-thread). It only needs to hold about 20-25 ft lbs torque.

j

[kwmech]

Originally Posted by A1971Blazer

Those work well too.....the only problem with them is they have a very large outside diameter that's not always ideal in some situations.

Not any larger than the hole required for a heli-coil. Only additional diameter is the small recess for the flange of the insert

[53burb]

Guys,
I did this yesterday....only took a few minutes....I didn't drill the holes any larger....filled the holes with Tap Magic (I already had it) and retapped for 7/16th, blew out the holes, got new gasket and reinstalled the housing....worked GREAT! Thx everybody for your opinions and sharing the knowledge!

[Troy Sr]

Now you're going to have to grab another wrench when you're working on the car!!!

[LS short box]

You don't need an extra wrench if you are using a vise grip. LOL

[87chevy.com]

Originally Posted by A1971Blazer

I own a machine shop and we use heli-coils frequently to repair threaded holes and also install some per customer specifications on manufactured parts.
If installed properly, they are very strong and will provide a permanent repair.
It's critical to drill the correct size hole for the heli-coil tap and to insure that the hole is drilled and tapped square to the mounting surface.

Trust this guy, he knows his stuff!

I've also ordered Holley brand LS and LT swap oil pans, every single one comes with a helicoil installed in the drain plug threads. Always thought it was weird to have an insert in it , but I imagine its for longevity, more durable than strait aluminum casting.

clint