The Ford Barn

SoCalCoupe · 08-13-2023, 08:59 PM

Never thought this would be so hard.

Have an aluminum cylinder head with a 5/8" NPT female joint beside the radiator hose outlet. On the passenger side it's filled by a temperature sender. On the passenger side, well, it's unused.

Need a 5/8" NPT aluminum pipe plug to plug it. Can't find one anywhere. Spent hours on the internet.

Anyone know where to get one of these?

I have a blue anodized aluminum 5/8" NPT 90 degree elbow to heater hose fitting left over from a SBC project that I'll make work somehow with a cap but obviously, that will stick out like a sore thumb.

mcgarrett · 08-13-2023, 09:13 PM

Have you tried these guys?

https://www.mcmaster.com/products/pl...%2F8+npt+plugs

cadillac512 · 08-13-2023, 11:17 PM

Sure it's 5/8 NPT? Reason I ask is that 3/8 NPT measures very close to 5/8" and is a common size, and is used for most flathead Ford temp senders.

Terry

glennpm · 08-14-2023, 05:54 AM

Here you go

flatjack9 · 08-14-2023, 09:32 AM

I'm quite sure it will be 3/8 NPT. Never heard of 5/8 NPT and I am a plumber.

19Fordy · 08-14-2023, 09:45 AM

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The thread size for the temp. sending unit on your heads is 3/8-18 NPT.
It's the same size threads that are on 8RT (and other)water pumps.
Don't overtighten it.

You could also use a brass pipe plug instead of aluminum.

Bored&Stroked · 08-14-2023, 09:57 AM

You need a 3/8" NPT and don't for a minute use aluminum - you'll never get it back out.

I'd use a stainless plug if it was mine - with an allen head type receptacle. Also, use a Teflon type sealer - to lubricate and seal the threads.

glennpm · 08-14-2023, 10:17 AM

I never heard of 5/8 NPT either

petehoovie · 08-14-2023, 10:37 AM

Quote:

Originally Posted by 19Fordy

The thread size for the temp. sending unit on your heads is 3/8-18 NPT.
It's the same size threads that are on 8RT (and other)water pumps.
Don't overtighten it.

You could also use a brass pipe plug instead of aluminum.

SoCalCoupe · 08-14-2023, 12:06 PM

A 5/8"-18 tap runs down the hole with no cutting or resistance.

Quote:

Originally Posted by cadillac512

Sure it's 5/8 NPT? Reason I ask is that 3/8 NPT measures very close to 5/8" and is a common size, and is used for most flathead Ford temp senders.

Terry

Got out my KS temperature sender and fit's securely in the hole. Would have sworn it has 5/8"-18 NPT threads.

Quote:

Originally Posted by glennpm

Here you go

The picture measuring the distance across the threads is the key for me. Must be 3/8" NPT. 3/8" NPT thread count is 18 TPI which explains why the 5/8"-18 tap ran down the hole. Mystery solved.

Quote:

Originally Posted by flatjack9

I'm quite sure it will be 3/8 NPT. Never heard of 5/8 NPT and I am a plumber.

I believe you. Probably DOESN'T exist.

WARNING: don't ask me for help measuring threads.

Bob C · 08-14-2023, 12:24 PM

3/8 NPT is 18 TPI with .675 OD

Kube · 08-14-2023, 01:45 PM

I have authentic brass plugs for this.

Bored&Stroked · 08-14-2023, 08:23 PM

Also, given that this is a NPT type thread - it is tapered, not straight like a regular 5/8 18 tap creates.

cas3 · 08-14-2023, 10:09 PM

I like the brass plugs with a hex head for a wrench, not the square thing. And yeah, never heard of 5/8 pipe thread.

Jack E/NJ · 08-16-2023, 07:18 AM

SoCalCoupe>>>A 5/8"-18 tap runs down the hole with no cutting or resistance.>>>

This means that you can also use a 5/8-18 bolt or screw with a ring seal. Aluminum bolts & screws are available. The Brits mix & match tapered & parallel pipe threads this way.

glennpm · 08-16-2023, 09:04 AM

Quote:

Originally Posted by Jack E/NJ

SoCalCoupe>>>A 5/8"-18 tap runs down the hole with no cutting or resistance.>>>

This means that you can also use a 5/8-18 bolt or screw with a ring seal.

NPT threads are TAPERED, so don't do this, there is no need to. 3/8"-NPT are very common. Use the correct plug.

Glenn

Ol' Ron · 08-16-2023, 10:39 AM

It's interesting to see the confusion "Normal" people" react to mechanical things????
Gramps

Jack E/NJ · 08-16-2023, 10:52 AM

Sorry, no. Aluminum nspt isn't common. And aluminum is preferred in this case to help avoid electrolysis. He also said a 5/18-18 tap ran down the hole. So taper isn't causing an interference problem if the tap ran past its own taper. He just needs a ring seal and an 5/8" fine thread aluminum bolt or plug. Automotive aluminum plugs are in fact made for this purpose.

glennpm · 08-16-2023, 12:00 PM

Sorry, don’t use aluminum as has been mentioned here. Brass with anti- seize.

The original poster needs to tell us if he really re-tapped the hole because a 5/8 will go in a few threads and then the taper will stop it IF checking by hand and not using a tap wrench

JayChicago · 08-16-2023, 01:34 PM

Rather than find a plug for that hole, why not use it as intended, have a sender in each head. You will need to use this sender(actually just a switch) as the first sender:
https://thirdgenauto.com/product/new...original-type/

08-13-2023, 08:59 PM	#1
SoCalCoupe Senior Member Join Date: Sep 2021 Location: Point Loma, San Diego, CA Posts: 424	Cylinder Head Plug Never thought this would be so hard. Have an aluminum cylinder head with a 5/8" NPT female joint beside the radiator hose outlet. On the passenger side it's filled by a temperature sender. On the passenger side, well, it's unused. Need a 5/8" NPT aluminum pipe plug to plug it. Can't find one anywhere. Spent hours on the internet. Anyone know where to get one of these? I have a blue anodized aluminum 5/8" NPT 90 degree elbow to heater hose fitting left over from a SBC project that I'll make work somehow with a cap but obviously, that will stick out like a sore thumb.

08-13-2023, 09:13 PM	#2
mcgarrett Senior Member Join Date: Dec 2013 Location: Waxahachie, Texas Posts: 949	Re: Cylinder Head Plug Have you tried these guys? https://www.mcmaster.com/products/pl...%2F8+npt+plugs

08-13-2023, 11:17 PM	#3
cadillac512 Senior Member Join Date: Apr 2019 Location: Kansas Posts: 925	Re: Cylinder Head Plug Sure it's 5/8 NPT? Reason I ask is that 3/8 NPT measures very close to 5/8" and is a common size, and is used for most flathead Ford temp senders. Terry __________________ "It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302

08-14-2023, 05:54 AM	#4
glennpm Senior Member Join Date: Sep 2014 Location: Wiscasset, Maine Posts: 1,982	Re: Cylinder Head Plug Here you go

08-14-2023, 09:32 AM	#5
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,527	Re: Cylinder Head Plug I'm quite sure it will be 3/8 NPT. Never heard of 5/8 NPT and I am a plumber.

08-14-2023, 09:57 AM	#7
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,073	Re: Cylinder Head Plug You need a 3/8" NPT and don't for a minute use aluminum - you'll never get it back out. I'd use a stainless plug if it was mine - with an allen head type receptacle. Also, use a Teflon type sealer - to lubricate and seal the threads.

08-14-2023, 10:17 AM	#8
glennpm Senior Member Join Date: Sep 2014 Location: Wiscasset, Maine Posts: 1,982	Re: Cylinder Head Plug I never heard of 5/8 NPT either

08-14-2023, 12:24 PM	#11
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,756	Re: Cylinder Head Plug 3/8 NPT is 18 TPI with .675 OD

08-14-2023, 01:45 PM	#12
Kube Senior Member Join Date: May 2010 Location: Wisconsin, USA Posts: 9,012	Re: Cylinder Head Plug I have authentic brass plugs for this. __________________ "I can explain it for you. However, I can't understand it for you".

08-14-2023, 08:23 PM	#13
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,073	Re: Cylinder Head Plug Also, given that this is a NPT type thread - it is *tapered*, not straight like a regular 5/8 18 tap creates.

08-14-2023, 10:09 PM	#14
cas3 Senior Member Join Date: Jan 2011 Location: sw minnesota Posts: 4,578	Re: Cylinder Head Plug I like the brass plugs with a hex head for a wrench, not the square thing. And yeah, never heard of 5/8 pipe thread.

08-16-2023, 07:18 AM	#15
Jack E/NJ Senior Member Join Date: May 2010 Posts: 2,173	Re: Cylinder Head Plug SoCalCoupe>>>A 5/8"-18 tap runs down the hole with no cutting or resistance.>>> This means that you can also use a 5/8-18 bolt or screw with a ring seal. Aluminum bolts & screws are available. The Brits mix & match tapered & parallel pipe threads this way.

08-16-2023, 10:39 AM	#17
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,861	Re: Cylinder Head Plug It's interesting to see the confusion "Normal" people" react to mechanical things???? Gramps

08-16-2023, 12:00 PM	#19
glennpm Senior Member Join Date: Sep 2014 Location: Wiscasset, Maine Posts: 1,982	Re: Cylinder Head Plug Sorry, don’t use aluminum as has been mentioned here. Brass with anti- seize. The original poster needs to tell us if he really re-tapped the hole because a 5/8 will go in a few threads and then the taper will stop it IF checking by hand and not using a tap wrench

08-16-2023, 01:34 PM	#20
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 732	Re: Cylinder Head Plug Rather than find a plug for that hole, why not use it as intended, have a sender in each head. You will need to use this sender(actually just a switch) as the first sender: https://thirdgenauto.com/product/new...original-type/ Last edited by JayChicago; 08-16-2023 at 01:42 PM.