I need to drill and tap Vortec 350 missing timing cover bolt holes. Help with size!!

[Nasty-LSX]

I am doing a aftermarket aluminum timing cover on the Vortec 350. I am missing 2 holes on the timing cover because the plastic
timing cover does not use them. What size drill and tap do I need? I decided to go all out with a complete overhaul of this engine
even when this was not the plan. I was suppose to just drop this in and drive it till the LS swap was ready. Well one thing led to
another as you all know it always happen this way LMMFAO!!!

This is NOT my engine picture but just a example. you can see the missing holes Thanks ALL!!

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[SquareRoot]

 

[Bextreme04]

1/4"-20

 

[Bextreme04]

Although, I would just keep the stock plastic cover or get a quality thick cover that won't need those bolts to seal up anyways.

 

[Nasty-LSX]

1/4"-20

That should be the bolt size Im Guessing. What about drill bit size? Thanks

 

[Ricko1966]

Your tap should have your drill size on it. Otherwise you can google tap drill sizes i would guess 3/16 th but just google a chart and post it for everyone. I keep my taps with the corresponding drill bit with each tap. If nothing rubs I'd go gasketless with ultra grey and ignore those bolt holes

 

[Bextreme04]

That should be the bolt size Im Guessing. What about drill bit size? Thanks

#7 or 13/64"
https://thetishop.com/tap-drill-size-chart

 

[Nasty-LSX]

Thanks everyone!!

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[Ricko1966]

Since you asked for drill size,I'm guessing you don't have much expierience with taps. In a blind hole if you bottom the tap but keep turning you will break the tap off in the hole, if it feels funny back out the tap clean the flutes investigate as to what's going on. You cannot drill out a broken tap with the tools you have at your disposal, so be careful. You really will need a bottoming tap also,but if you can get good threads as deep as the taps cross section as in 1/4 wide 1/4 deep you can stud and nut that. Do not overnighten. it

 

[Nasty-LSX]

Since you asked for drill size,I'm guessing you don't have much expierience with taps. In a blind hole if you bottom the tap but keep turning you will break the tap off in the hole, if it feels funny back out the tap clean the flutes investigate as to what's going on. You cannot drill out a broken tap with the tools you have at your disposal, so be careful. You really will need a bottoming tap also,but if you can get good threads as deep as the taps cross section as in 1/4 wide 1/4 deep you can stud and nut that. Do not overnighten. it

Note Taken!! Thanks

 

[Craig Nedrow]

Jon been a machinist 40 years and still machining, Like Eric said above. #7=.201, 13/64=.203. Could write a dissertation on tapping, but really Rick is telling you the truth. Leave it alone. Drilling cast, and tapping is no real mystery, but if the block came that way, I would leave it alone.