welch plug 21 stud engine.

fftoddster

fftoddster

Senior Member
I know the welch plug at the bottom of the block is 3/4". The trouble I am having is getting it to seal good because there is some corrosion in this area. I have tried sealant but think it is still weeping.

Does anyone know or have a block available to measure what the inside diameter of the bore is that the 3/4" welch plug goes up against?

I am thinking of trying to find a freeze plug that will fit up in there and then back it up with the 3/4" welch plug with sealant.

Is it 5/8" ? I do not and will not have access to it for several days and I would like to start hunting down a plug to fit it.

Thanks
Todd
 
fftoddster said:
I know the welch plug at the bottom of the block is 3/4". The trouble I am having is getting it to seal good because there is some corrosion in this area. I have tried sealant but think it is still weeping.

Does anyone know or have a block available to measure what the inside diameter of the bore is that the 3/4" welch plug goes up against?

I am thinking of trying to find a freeze plug that will fit up in there and then back it up with the 3/4" welch plug with sealant.

Is it 5/8" ? I do not and will not have access to it for several days and I would like to start hunting down a plug to fit it.

Thanks
Todd
Click to expand...

Todd, once the plug is in hole you need to whack it in the center with a ball peen hammer, etc, to spread it to fit. I used Permatex "The Right Stuff" to help seal it. Hope that helps you.
 
Another possibility is tapping the hole, closest NPT without going to big. Seal the plug with a quality sealer, then machine or file it down so pan gasket seals.
I've done this before on motor that's still running strong.
 
Mark's 37 said:
Todd, once the plug is in hole you need to whack it in the center with a ball peen hammer, etc, to spread it to fit. I used Permatex "The Right Stuff" to help seal it. Hope that helps you.
Click to expand...


Yes I understand that and have done that. The problem is that the car sat for 30 years and the corrosion of the weeping welch plug ate away at the surrounding block area. Also ate a hole in the oil pan but I welded that up.

The area just above where the welch plug sits appeared to be in good condition, so If I figure out what size that bore that is I believe a cup style freeze plug would fit and seal nicely there.
 
fftoddster said:
Yes I understand that and have done that. The problem is that the car sat for 30 years and the corrosion of the weeping welch plug ate away at the surrounding block area. Also ate a hole in the oil pan but I welded that up.

The area just above where the welch plug sits appeared to be in good condition, so If I figure out what size that bore that is I believe a cup style freeze plug would fit and seal nicely there.
Click to expand...

I would be a little concerned that the corrosion has weakened or eaten further into the pan rail, especially on the inner and outer wall margins. Without seeing it it's hard to say but doing a little "dental" work to clear out the cancer to bare metal and see what's what. If that is ok and you think it could be drilled and tapped for a threaded NPT brass plug with thread sealer and filed down as RalphM suggested would be a good choice.
 
No inside the engine actually looks pretty good. It was just the little area outside of area where the welch plug sits outwards.
 
fftoddster said:
No inside the engine actually looks pretty good. It was just the little area outside of area where the welch plug sits outwards.
Click to expand...

I have a 37 engine with the pan off on the engine stand. I will pop one of the plugs out tomorrow and see if I can size the hole.
 
All of the blocks that I rebuild with those plugs, get drilled and tapped for 1/2 pipe
thread. I remove the center main studs or bolts and drill with magnetic mount drill.
After drilling chuck up a large center drill to start the tap. Use flush pipe plugs and
565 Loctite to finish the job. Gary
 
fftoddster said:
Thanks that would help a lot.
Click to expand...

Todd, the hole below the seat step for the 3/4" welch plug on mine is 5/8" ID. If yours hasn't been corroded beyond usefulness, a freeze plug might be the way to go with some sealant. If not, it could be possible to tap it to next NPT size up and use a flush top brass threaded pipe plug.
 

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Mark's 37 said:
Todd, the hole below the seat step for the 3/4" welch plug on mine is 5/8" ID. If yours hasn't been corroded beyond usefulness, a freeze plug might be the way to go with some sealant. If not, it could be possible to tap it to next NPT size up and use a flush top brass threaded pipe plug.
Click to expand...


Mark,

Thank you. That is exactly what I was looking for. I remember looking inside on mine and thinking boy that is in really good shape in there. The corrosion and pitting were only on the outer part of the block right where the welch plug was supposed to seal.

Todd
 
Sometimes those shoulders are about eaten out inside the hole, clean the hole out and use 3/4 cup plugs instead dish plugs, smear some RTV in the hole, drive the plug in, fill the plug with RTV. Don't forget the install the pan before you pour the oil in. LOL Walt
 
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