8n Engine Block Coolant Drain

[Gumbi]

Howdy, first time posting here, but have been reading and looking around for a while. I got a '49 8n that I have been going through for a couple months as time permits. It sat for 2-3 years before I got it so have been doing all the typical maintenance, rewire, plugs, distributor, fluid changes etc.
As I was doing a coolant flush the other day when I went to drain the block I found the threads on the block are just about completely stripped. I was hoping it would be the brass plug that was stripped, but replacing the plug with a new petcock I found it definitely is the threads in the block. I put some teflon tape on the new petcock hoping that it would help, and it does help, but not enough. When installing the new drain I can push the plug in almost 3/4 of the way in before it will catch any threads to screw in and then only get about 2 turns before it bottoms out. I does hold but this morning I noticed that some water had seeped past. Is there a way to fix this? I have not tried re-tapping the threads yet, but didn't really think that would help with how worn they are.


Anybody have any ideas?
Thanks

 

[TheOldHokie]

(quoted from post at 10:53:15 03/27/19) Howdy, first time posting here, but have been reading and looking around for a while. I got a '49 8n that I have been going through for a couple months as time permits. It sat for 2-3 years before I got it so have been doing all the typical maintenance, rewire, plugs, distributor, fluid changes etc.
As I was doing a coolant flush the other day when I went to drain the block I found the threads on the block are just about completely stripped. I was hoping it would be the brass plug that was stripped, but replacing the plug with a new petcock I found it definitely is the threads in the block. I put some teflon tape on the new petcock hoping that it would help, and it does help, but not enough. When installing the new drain I can push the plug in almost 3/4 of the way in before it will catch any threads to screw in and then only get about 2 turns before it bottoms out. I does hold but this morning I noticed that some water had seeped past. Is there a way to fix this? I have not tried re-tapping the threads yet, but didn't really think that would help with how worn they are.


Anybody have any ideas?
Thanks

Easiest?? Drill and tap next oversize (3/8 NPT???) and screw a 3/8 to 1/4 NPT reducing bushing into the hole.

TOH

 

[tcarlson40]

Where on the block is the drain located? I didn't realize there was one, I would agree with TOH - drill out and retap next size larger as long as you can get to it.

 

[Gumbi]

For some reason this didn't even dawn on me as an idea. Although drilling a hole into the side of an engine block isn't exactly something I want to do, but is the only way I see to fix it.

Would there be any concern with the hole getting bigger and the casting getting thin on the bottom side of the hole? I know these blocks are probably much thicker than anything these days, but I don't want to accidentally be drilling through the coolant passage and into the bottom of the block where oil is present.

Thanks

 

[Gumbi]

It is on the left side just above the dipstick and behind the starter motor. And there is plenty of room to do something like that.

 

[TheOldHokie]

(quoted from post at 15:28:06 03/27/19) For some reason this didn't even dawn on me as an idea. Although drilling a hole into the side of an engine block isn't exactly something I want to do, but is the only way I see to fix it.

Would there be any concern with the hole getting bigger and the casting getting thin on the bottom side of the hole? I know these blocks are probably much thicker than anything these days, but I don't want to accidentally be drilling through the coolant passage and into the bottom of the block where oil is present.

Thanks

I don''t see any solution that does not involve drilling. It should be an easy job and no danger of drilling into anything bad. Just don't break the tap. That would turn it into an exceedingly nasty job ;-)

If you are truly concerned and want to minimize the amount of material removed then you can go uptown repair ($75) using a helical thread repair insert (aka HeliCoil). The major advantage here is that using a helical insert you will only need to increase the hole size by .078 (to .516 from .438). Here is a link to a 1/4 NPT thread repair kit with STI tap, installation tool, and 10 inserts. You will need a 33/64 tap drill in addition to the repair kit. And for good measure I'd also use Loctite high strength thread locker when installing the insert.

Recoil 36048 1/4" Pipe Thread Repair Kit

TOH

 

[Gumbi]

A helicoil was something that I had initially thought I would need to do, but also did not know they made them for pipe thread.

I'll most likely just drill and retap it for 3/8 npt and use a bushing. Cheaper and could pick up the tap on my way home today.

Thanks for the input!

 

[Phil Tibbetts]

If you drill it out and retap it to 3/8 make sure your drill bit is ground properly to drill cast iron or it will grab into the cast.

 

[Bob]

(quoted from post at 09:53:15 03/27/19) Howdy, first time posting here, but have been reading and looking around for a while. I got a '49 8n that I have been going through for a couple months as time permits. It sat for 2-3 years before I got it so have been doing all the typical maintenance, rewire, plugs, distributor, fluid changes etc.
As I was doing a coolant flush the other day when I went to drain the block I found the threads on the block are just about completely stripped. I was hoping it would be the brass plug that was stripped, but replacing the plug with a new petcock I found it definitely is the threads in the block. I put some teflon tape on the new petcock hoping that it would help, and it does help, but not enough. When installing the new drain I can push the plug in almost 3/4 of the way in before it will catch any threads to screw in and then only get about 2 turns before it bottoms out. I does hold but this morning I noticed that some water had seeped past. Is there a way to fix this? I have not tried re-tapping the threads yet, but didn't really think that would help with how worn they are.


Anybody have any ideas?
Thanks

Clean the threads in the block with a 1/4" pipe tap, and get them clean of antifreeze and/or any oily residue with brake kleen.

Then slather a little JB Weld (or equivalent) on the threads of a new petcock, and snug it in place.

Let the epoxy cure for 24 hours and the junction between the block and the drain fitting will be good and leak-free for another generation of owner.