bubbling a/f inside spark plug recess

[ArtJ]

I ran my spare A4 today and checked for the source of coolant collecting
in the spark plug socket nearest the output shaft end of the engine.
I checked for the source being a thread leak from a nearby stud as
mentioned by Don Moyer in a recent service note.
The leak appears to be bubbling coolant out of a specific (small hole?)
on the side of the plug recess. Can this be repaired in a way that will
hold up rather than replacing the head?
This engine was acquired as a spare engine and the PO said it
had been rebuilt. The engine is one of the very later late model versions build as it
has the flat plate covering the front of the engine. The engine was S/W cooled in prior use but I would use f/w if needed as a backup


Comments appreciated

Thanks Art

[Al Schober]

Sounds like a pinhole porosity in the head. Personally, I would try a repair.
There's obviously coolant on the far side of the pinhole, so it doesn't get that hot. I'd drain down the coolant, clean up the area with a small drill bit (make a dimple at the leak site) then fill the dimple with JB Weld. An alternative would be to fill the dimple with braze metal.

[jcwright]

Your pinhole leak sounds similar to one I had. IIRC, the leak occurred where wire was attached to the head during casting. I drilled and tapped the hole and filled it with a stainless socket plug. I used the engine for several years after that with no leaks.

[ArtJ]

By a ss socket plug do you mean something like a short allen plug?

[jcwright]

Here's a description and link to a plug like the one I used. I'm not sure if was a 1/8 plug. I used the smallest one I could get that would fill the hole. I have the old head in the basement (I replaced it during an overhaul due to that at the lifting bracket). Let me know if you want more details.

316 Stainless Steel Hex Socket Plug, MNPT, 1/8 in Pipe Size - Pipe Fitting
Item #4WPL2 Mfr. Model #4WPL2
UNSPSC #40142313 Catalog Page #2782

This GRAINGER APPROVED hex socket plug is 316 stainless steel construction with a higher nickel content for better corrosion resistance.

https://www.grainger.com/product/4WPL2?gclid=CjwKCAiA4o79BRBvEiwAjteoYNakxfQ02Futb3QGqvCcPEdQQwFbxJa51bKD79SFjxE-OHbpTfkTyxoCEggQAvD_BwE&cm_mmc=PPC:+Google+PLA&ef_id=CjwKCAiA4o79BRBvEiwAjteoYNakxfQ02Futb3QGqvCcPEdQQwFbxJa51bKD79SFjxE-OHbpTfkTyxoCEggQAvD_BwE:G:s&s_kwcid=AL!2966!3!281698275765!!!g!472905489838!&gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231

[jcwright]

Art: Here's a photo of the head. The arrow points to the plug. Hope this helps.

[ArtJ]

JC Wright
Thank you for the great responses and photo.

Unfortunately, my leak is not at that pointed to by the arrow

It is actually in the slope of the circular "bowl/ well " that surrounds the threaded spark plug hole, Almost exactly where the brown rust colored streak is in
your photo.

AL

What size bit would you use and how deep would you go to prep for
JBWeld? E. G. if a 1/4 area then bit size= ?? if a 3/16 area or larger bit =??

Note the head has scale on it notably in the wells for the plugs not sure how much scraping can be safely done

Many thanks to you both
Art

[jcwright]

Art: If you or others think of measurements I could take of my head, let me know. Also, I’ve tried before to give my head to someone who could use it, without luck so far. The engine was running fine when I took the head off. You’re more than welcome to the head if you want it.

Jack

[ArtJ]

Jack
Please let me know when you have the phone number recorded so can remove it from the post

Thanks
Art

[jcwright]

Hello Art.

I have your number. I'll aim to call later today. In the meantime, feel free to use my email address: jack dot c dot wright at gmail.com.

jack

[ArtJ]

Thanks Jack

Art

[jcwright]

Happy to help. I hope the head finds a new home on your Tartan 34c.