Fitting a "freeze plug" question

[cranetruck]

What is the proper clearance for a freeze plug or cap in this case, before wacking it with a hammer? I need a solid fit and the cap will be drilled and tapped for a vent after installation.
The 2-1/16 cap is too large, so I'll have to grind it down to fit. The next smaller size cap that I can find is 2 inches in dia and is too loose.

Edit: Added image....

 

[doghead]

What is the measurement of the hole? There are several types of plugs, cup concave, etc.

Try Dorman Products? https://www.dormanproducts.com/cgi-bin/vm91corp30r/item-dtl.w?sid=xcwtkwbYxclDadsu009771701883011734&item=362563&icrid=&clt=hwrap1&vsrch_str=&vsrch_brand=all&vsrch_cat=Expansion%20Plugs,Cup%20Type%20Expansion%20Plugs&st_amount=0&end_amount=999999999.99&start=40&vfrom=&prev=yes&vnext=yes&category_list=1454:22:0


My local NAPA has a decent selection in stock.

 

[cranetruck]

Fair question, it's 2.025

Image shows what it should look like when finished.

Edit: Added image.

 

[doghead]

That looks like a concave disk. Did you remove the old one?

I found one that says it's 2.020" at my NAPA. It is either a Clevite or Dorman brand. They said the next size up was 2.062"

I can get it and send it to you if you think it will work.

 

[cranetruck]

Thanks Eric, I'll check with my local NAPA. The original was destroyed when I removed it....

 

[jwaller]

freeze plugs that I drive into the engine blocks go it with a moderate swing from a 3lb hammer. I'd say you want at least .002 of interference fit at 60deg F. yours can be a bit looser bc your not sealing water at 16psi over a 2sq in area.