Rear head coolant opening

[studmobile]

My 1962 Harrington is getting a new head gasket, hopefully it needs nothing more. The rear opening that was originally hard piped through the intake has a 5/8 by 11 tpi bolt blocking it off. I'd like to add a fitting to run coolant from this opening to the "Y" at the water pump, probably 1/2" id. I have had no luck finding anything that matches the 5/8" with 11 tpi, everything is a finer thread. Thought I could get the bolt tapped so I could add a fitting with a barbed head to fit to a hose to the water pump. From the forum, looks like performance is better without the coolant running through the intake. But it also seems anything that promotes coolant flow through the back of the head would be helpful. Any thoughts appreciated. David

 

[puff4]

I’d definitely find a way to use that coolant port - it will help keep that #4 from preigniting and reduce damage to the piston and chamber. Seems to me the hole in the head is larger than 5/8, though?

 

[studmobile]

Using a tape, the hole is about 5/8" I matched the bolt out of the head with both a bolt and nut that was 5/8" 11 tpi. That was the only thing that had such a low thread count. Perhaps the hole was rethreaded to accomodate the bolt, to just cap off the opening. When I checked for a fitting for the opening, the sizes were all listed as smaller, about 3/8". But I honestly am confused with how sizing is different for bolts, hydraulic and air fittings, and the such. The replacement intake (the previous owner sourced an original ) for the Zenith carbs still has the hollow bolt and banjo fitting on it- wonder if that has the original thread? Either way, I have to deal with the tapped hole I have in the head.

 

[puff4]

British Standard Pipe would be 5/8-14, and to my knowledge there isn’t any 5/8” standard for National - it goes fro 1/2 to 3/4.

 

[husky drvr]

British Standard Pipe would be 5/8-14, and to my knowledge there isn’t any 5/8” standard for National - it goes fro 1/2 to 3/4.

Kevin,

It's British Standard Whitworth (BSW).

Not sure about finding fittings but here's a link to a hand tap:

Beta Tools 430ASW-5/8 Whitworth Hand Tap, 5/8x11 BSW | Pegasus Auto Racing Supplies

Come check out our Beta Tools 430ASW-5/8 Whitworth Hand Tap, 5/8x11 BSW at Pegasus Auto Racing.

www.pegasusautoracing.com

They list a die as well, if needed.

Also note this advisory notice:


Note: This British thread is not the same as any SAE thread. SAE UNC threads have a different thread angle and a shallower, squared-off thread root. Only use this tap when you intend to install a BSW threaded fastener.

 

[studmobile]

That at least would make sense. The bolt that was in there sealed tightly, so perhaps was "close enough". I would still love to find a fitting for the opening that we could connect hose to.

 

[puff4]

I would have thought it was BSP!

Well, in that case I very likely have the tap and die for this, as I do have a full set of Withworth (and BSP, for that matter). I’m traveling right now, but expect to be home next Tuesday. If you need it, and that fits your timeframe, let me know.

 

[husky drvr]

Whitworth thread chart:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwixisrh-f3-AhUGj4kEHcZMDlc4ChAWegQIBRAB&url=https%3A%2F%2Fwww.britishmetrics.com%2Fimages%2Fpdf%2Ftechnical%2Fbswstd_1.htm&usg=AOvVaw3omBBoCF0lnWcHquIMCYY_

 

[Barry]

David,

I suspect that the coolant port on the back of a Series Alpine head would have originally had British Standard Pipe (BSP) threads, probably tapered.

The smallest BSPx thread size with 11 TPI is 1"-11 which has an outside thread average diameter of 1.309".

Based on a hole size of about 5/8", it seems likely that the original thread was BSPT 3/8"-19 with an outside thread diameter of 0.656".

The available evidence suggests that someone plugged a BSPT 3/8"-19 threaded hole with a 5/8"-11 NCT bolt. Definitely crude, but apparently effective.

Unless using a BSP fitting is important to you, I think you could probably re-drill the port (using a 9/16" or 37/64" drill bit depending on who you believe) and re-thread the hole using a 3/8"-18 NPT tap with an outside thread diameter of 0.675". I would use a good thread sealer. The next (a lot) larger NPT size is 1/2"-14 with an outside thread diameter of 0.840" and which calls for a 23/32" drill size.

 

[65sunbeam]

This is the rear of the S4 engine that Mike S is selling. Does the rear of your cylinder head have the same design but it has a plug in it?
My S4 has the same connecting pipe to the intake but it was broken off as shown by the red lines and a rubber hose put in it's place.
I think I have that complete metal hose and banjo assembly or a set of broken ones like in this photo. Not sure if it will fit up to your S2 intake though.

 

[Barry]

Based on the picture that Eric posted, it it looks like the water port in the back of the head has a fitting with parallel threads and a metal gasket under the hex flange. Still 3/8"-19, but parallel (BSPP) rather than tapered (BSPT).

EDIT: It does not make a lot of sense for someone to have put an 11 TPI bolt in a hole with 19 TPI threads. On the other hand, an 18 TPI (National Fine Thread) bolt would probably match reasonably well with the 19 TPI BSPP threads. I suggest re-checking the TPI on the "plug" bolt. It is possible that the threads in the port have not been significantly damaged and may still work with the factory fitting.

I still think that the 1/2"-14 NPT "fix" should work.

I am not a fan of all copper lines that are subject to movement or vibration because copper work hardens and is likely to eventually crack. A section of rubber hose (as mentioned by Eric) pretty much eliminates the problem.

 

[husky drvr]

it looks like the water port in the back of the head has a fitting with parallel threads and a metal gasket under the hex flange.

Barry,

Here's a pic of that fitting. BTW, the finer threads on the outer portion are for use with a compression ferrule. Those threads measure 18TPI. My thread checker is limited to 13TP, which is smaller than the large threads.

 

[studmobile]

Thanks for all the input. I have the threaded fitting to the intake manifold and the copper? pipe toward the head, but am missing the original male/male fitting at the head. Counting the threads on the last picture looks like 11 tpi to me. Unfortunately, have not seen any fittings with 11 tpi, so the tap would be useless. Redrilling and retapping the hole for a more readily available fitting for adapting a rubber hose would do the trick. Was hoping to avoid the machine shop if possible. I greatly appreciate all the help. David

 

[studmobile]

Checking Amazon, they have a 5/8" UNC 11 tpi bushing, with 3/8" 24 UNF female fitting, which could be paired with a fitting to go to rubber pipe. Is the UNC thread close enough to the BSW of the same size/thread count? Lots of locktite? Or would you need to retap? If so, would you need to redrill?
Interesting to compare Eric's picture of Mike's engine, the original opening was at the base of the head at the corner, but the later head utilized an added cast boss for the opening.

 

[studmobile]

Sorry- forgot to post the link: https://www.amazon.com/Adapter-11-U...1684530792&sprefix=weiler+07746,aps,96&sr=8-3

 

[Shannon Boal]

Hmmm, just installed a new thermostat housing on Alpine V, and the temperature sensor was 5/8"-19......BSP

 

[studmobile]

I ordered the adaptor from Amazon, male 5/8-11 UNC, and female 3/8"-24. It starts to thread, but I'm hesitant to push it. Is it possible to tap the 5/8"-11 BSW opening for the 5/8"-11 UNC? This would allow a fitting to a hose, then looped to the water pump. Any thoughts or tips? Thanks again, David

 

[studmobile]

Here is what we eventually did to allow coolant out of the rear of the head on my Series ll (HLM). I could never find a fitting to fit the opening well. Luckily the banjo and fitting were still in the back of the intake manifold. This has the same thread as the head opening, so we put that into the opening. We attached a rubber hose to the hard pipe, and ran it over the carbs to the water pump. Looks reasonably good, just have to avoid the carb linkage. Now we have at least some flow from the back of the head to the water pump. David