SBC Temp sensor plug removal from head

JED

Well Known Member
Supporting Member 5
You may know from my previous posts that I recently acquired another '33 Ford Roadster, in addition to my old '33 Ford Roadster project with the 348. The new roadster is a "complete, running" car with an older SBC "Mr Goodwrench" 350 ci engine. After thorough inspection of the car (this is the first hot rod that I have not built myself and I wanted to be sure that the car was screwed together correctly and was safe), I found a number of punch list items that need my attention (6 pages & 89 issues so far), but most are minor clean-up items and will not effect my putting the car on the road. There are about a dozen items that need to be fixed (or have been already) before I feel comfortable with putting the car on the street.

The current problem is a coolant leak from the driver's side head where a threaded plug is installed to block where a temperature sensor may be installed. I need some suggestions from the group on how best to resolve this problem.

Head sensor plug leak-1.jpgHead sensor plug leak-2.jpgHead sensor plug leak-3.jpg

As shown in the first picture, the driver's side head has a threaded port that has a 2-piece pipe plug installed where a temperature sensor could be installed. The large part of this 2-piece plug is leaking coolant and needs to be replaced. I have removed the headers and spark plugs from this head and removed the small hex-headed pipe plug that was threaded into a larger threaded plug that is screwed into the head itself. The small pipe plug came out fairly easily and did not require any major effort to remove.

The question I have is how do I remove the larger threaded plug from the head (see pictures 2 and 3)? It appears to be brass, based upon the color of the head of the plug. Apparently, it was screwed into the head by installing the smaller pipe plug into the larger threaded plug, and then using the small plug to tighten the larger threaded plug into the head. As I noted, the smaller hex-head pipe plug came out easily, but now I have nothing to grab on to the larger plug to unscrew it from the head. Do I put a large EZ-Out into the small threaded hole and hope I can get enough bite to break the larger threaded plug free from the head (with the knowledge that I will totally screw up the smaller plug threads in the process)?
Or, do I JB-Weld the smaller pipe plug back into the large plug and hope it stays tight enough in the larger threaded plug to let me use it to un-screw the large plug from the head? Or, ????

The engine is installed in the car and the head is about 6" from the inner fender apron. There isn't really enough room or clearance to get a torch in there to heat the plug. Nor is there room in there for me to get a drill in there to drill it out. I don't want to remove the head unless I absolutely have to do so.

Does anyone have any suggestions? Do either of my suggestions above sound like good options?

Thanks for any help you may have.

John
 
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La Hot Rods

Well Seasoned Member
Supporting Member 15
Maybe one of those stubby easy outs. Not sure how you would drive it in though.
 
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Jim Sullivan

Well Known Member
Supporting Member 10
I would also suggest the stubby style easy outs like James mentioned or the extractor set Brian suggested. There are also internal pipe wrenches available, but they may not be small enough for your application. If drilling is needed, an angle drill with a stubby drill bit may work.
 

blkblk63ss

Well Seasoned Member
Supporting Member 5
Put the plug back apply this locker ,let it cure. Clean all threads first with brake clean.
LOCTITE® red threadlocker

LOCTITE® red threadlocker is the highest strength of threadlocker adhesive. This product cures fully in 24 hours and is available in both a liquid and as a semisolid anaerobic. The red high strength threadlocker products are so powerful they may require heat to be disassembled
 

wristpin

Well Known Member
Mix acetone and ATF in 50/50 mix. Pour a little around that plug then red loctite plug into it. As said let cure then turn it out. If the brass plug wont come its should be do able to drill it out ONLY REMOVING BRASS then use pipe tap to rethread to cast iron.
Good luck
 

JED

Well Known Member
Supporting Member 5
Update:
Thanks to everyone for the great help. The short story is that I got the plug out., but it took a couple of tries. I cleaned up the little plug's treads, put some Red threadlocker on it and installed it in the larger plug, but the small plug was a tapered plug and did not get enough thread bite into the larger plug. After letting the Red threadlocker cure for a couple of days, the little plug came right out without moving the large plug. So before I tried an extractor and chewed up the hole, I decided to tap the larger plug's inner hole and thread a 3/8-14 hex bolt into it. I put Red threadlocker on the hex bolt and threaded it into the larger plug tight enough to see it slightly rotate the larger plug, just to ensure the larger plug wasn't frozen in place. After letting the threadlocker cure for 24 hours, they both (large plug & bolt) unscrewed as one piece. Success!
Now to clean up the head and install a new plug with a hex head so I can remove it later if I need to. Hopefully, this will solve my coolant leak problem.
BTW, in hindsight, my idea of using a torch to heat the plug would have been a bad idea. Although I have drained the radiator and removed the lower radiator hose, there is still antifreeze in the head up to the level of the bottom of the plug. Antifreeze is flammable! Glad I didn't try that option.

Thank you all again for your help.
2023_07_12-Head sensor plug leak-Large plug removed-IMG_6906.jpg2023_07_12-Head sensor plug leak-Large plug removed-IMG_6907.jpg

John
 
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