Anyone know the thread size? Try to repair an intake manifold


(Robert Thomas 68 FHC ) #1

Hello all,

I have a 4.2 triple SU intake manifold I’m trying to use on my 68 FHC. The water inlet on the back of the manifold has a steel fitting that screws into it. The threads are stripped on the aluminum manifold and my machinist can’t figure out the threads on the fitting. He says it’s not any of the usual suspects. SAE metric, etc. Does anyone know what this thread is? Even better does anyone have an idea on how to fix this?

I was hoping for a helicoil or something similar but not being able to identify the thread is making it impossible

Thanks for any suggestions


(Ray Livingston) #2

Plumbing type fittings are generally either BSP or BSPT - British Pipe Thread, Straight (BSP) or Tapered (BSPT).

Regards,
Ray L.


(peter balls) #3

If it is the heater fitting it is 3/8 BSP straight, the same as the banjo fittings on H and HD carbs.
Peter B.


(Robert Thomas 68 FHC ) #4

Thanks Ray. Any ideas on how to fix this manifold?


(Andrew Waugh) #5

You could have him bore out the hole until he finds solid metal, then cut a thread (possibly metric) and fit a new hose nipple with that thread and the right OD for the hose.

Tigging up a small hole that deep is going to be a PITA.

The other possibility would be to make a stainless plug which seals at the bottom (i.e. a thread) and fill the annulus with muggyweld or similar, remove the SS plug, then drill and tap for 3/8 BSP.

I’d go the muggyweld route if it were me.


(Huff) #6

I love, love, love Time-Sert for these type fixes. BSP is very similar to NPT if you want to run the risk:
http://www.timesert.com/html/taperpipe.html

If it is a brass nipple you could sandblast/file a bit of material off and see it it will thread into BSP.

This would all depend on if there is enough material surrounding the opening to hog out for the insert.

My $,02

Huff
69 2+2


(Old Ed) #7

Had a similar problem on my '62 3.8 water manifold. I found a compatibly sized barb fitting at a local air conditioning shop, aluminum material, cleaned up the damaged hole, and had it welded to the manifold.
Having trouble posting a photo, I will try to email you one…


(Old Ed) #8

Had a similar problem on my '62 3.8 water manifold. I found a compatibly sized barb fitting at a local air conditioning shop, aluminum material, cleaned up the damaged hole, and had it welded to the manifold.
Having trouble posting a photo, I will try to email you one…


(69 FHC ) #9

A bit pricy but look at the 4th item down if the original fitting is 3/8 BSPP. Just have your machinist tap the hold for 1/2" NPT and screw in the adaptor and then screw your original fitting into the adaptor.

http://www.stainlesssteelfittings.com/stainless_nptf_to_bspp_p/ss-9037.htm .


(Robert Thomas 68 FHC ) #10

Interesting approach. Does anyone know what size the male thread on the adapter is??


(Ray Livingston) #11

The correct fittings, and taps, are readily available. The correct fix is to have the hole welded, re-drilled, then tapped with the correct BSP thread.

Regards,
Ray L.


(Terry Sturgeon) #12

Bear in mind that BSPP fittings seal with a gasket, typically a copper washer, and not by the threads so when you are finished threading the manifold it needs an appropriate surface at 90 degrees to the thread for that.
P.S. a plumber friend says that most plumbers have BSPP taps so if you know one…


(Robert Thomas 68 FHC ) #13

So does anyone know a machine shop in the SF Bay Area that could weld up the existing manifold inlet and drill and retap it to the correct BSP thread? I’m in the east bay (Walnut Creek) but would be willing to travel.

Thanks!
Robert


(Robert Thomas 68 FHC ) #14

An update. Thanks for all the input, I was able to repair my manifold. I think. I don’t know if it’s water tight yet…

I sourced the correct British Pipe Thread Straight 3/8 tap ( $9 off Amazon )

I took a brass wire wire brush on my rotary tool and cleaned the threads, then got some oil and coated the id of the manifold and the od of the tap and just using my hand carefully guided the tap in straight, feeling my way through the cross threaded, damaged area. Not until I hit a firm stop did I put a wrench on it, and used it maybe a quarter turn, then went back to just using my hand. Doing this I was able to run the tap down, and then back out. Cleaned the threads with the rotary tool again, and reoiled and reran the tap. Then ran the brass wire brush through one last time.

The threads are still damaged quite a lot, but my thinking is that since with straight threads, the sealing takes place with the copper washer, I only need enough clean thread to firmly secure the washer to the flange on the manifold.

So I dressed the flange on the manifold with a small file, oiled the threads, and assembled it. It seems to have snugged down tight…