stripped coolant drain

[Joshua Mitchell]

I am having a bear of time with the drain for the coolant in front housing. the previous owner apparently siliconed the plug in because there are no threads. i have broken 3 bits trying to drill for tapping. does anyone have a solution for this. its supposed to be 5/8" 11 bolt and i am trying to tap to 3/4" 10. 21/32 drill bits are expensive and i was thinking of maybe welding a nut to the inside.

Thoughts?

[CSA_CUB]

HAVE YOU THOUGHT ABOUT USING JB WELD? YOU COULD DO A SIMALAR REPAIR AS IN THIS CARB REPAIR POST FOR REPAIRING THE INLET THREADS. viewtopic.php?f=139&t=100192&p=791631&hilit=threads#p791631

[tst]

the correct thread size is 3/8" NPT

[Joshua Mitchell]

it had a 5/8" 11 bolt and i am assuming it was drilled previously. i would just like to get it solid so no problems with the restoration and be as close as possible to original.

[Joshua Mitchell]

i like the thread repair idea with JB Weld. never thought of that. i wonder if it will work with pressure of the coolant system though.

[Dale Finch]

I have used this to repair threads... it's easy and quick. There shouldn't be any pressure on the system (later Cubs did have low pressure cap), so I think this would work.
https://www.napaonline.com/en/p/NCB28654

[CSA_CUB]

I THOUGHT OF SOMETHING ELSE BOTH JB WELD AND LOCTITE MAKE A STEEL PUDDY/STICK THAT CAN BE DRILLED AND TAPPED. JUST RECOMMEND EVERYHTING BE VERY CLEAN (SANDBLASTED OR WIRE BRUSHED). IF THE RAD IS OFF, TAPE OFF THE HOLE AND FILL IT FULL FROM THE RESEVIOUR SIDE. LET IT CURE, DRILL AND TAP.

[Nelson 634]

Just a little information about drilling cast metals. Cast metals have hard spots in them. You'll be drilling along and boom, very fine metal particles where seconds before they where clean shavings. It's very hard to get off the drill pressure or speed quick enough. Have extra bits and all ways use cutting fluid or cutting oil. Start with small bits and work your way up. Be ready to get off the drill. Also be ready to slow down drill speed. The only thing harder to drill is stainless steel. That's another story.

[Clemsonfor]

I am having a bear of time with the drain for the coolant in front housing. the previous owner apparently siliconed the plug in because there are no threads. i have broken 3 bits trying to drill for tapping. does anyone have a solution for this. its supposed to be 5/8" 11 bolt and i am trying to tap to 3/4" 10. 21/32 drill bits are expensive and i was thinking of maybe welding a nut to the inside.

Thoughts?

I am about 99% sure it should be 3/8 NPT and have a 3/8 pipe plug.

[tst]

yes, early post state that it is a 3/8 NPT, it is NOT a 5/8 11 bolt hole can be helicoiled

[Joshua Mitchell]

you guys are correct, it is 3/8 npt. I was able to chase the threads with tap and it works great now. thanks for the help and I will remember the jb weld idea for future issues