Newer Heater Box in Older Car - Need bigger holes

[calw]

Lets say you want to put a newer heater box, with the larger core and water hoses, in an older car...  And decided to do this this after your body was painted...  The problem is the diameter of the holes in the top of the firewall where the hoses go thru inside large grommets.  How to enlarge the holes without damaging paint inside the water trap ..er.. well behind the firewall. 

 

Hole saw ?  File ?  Sawzall ?  Chisel ?  Not without some repainting.

 

Use a chassis punch of the correct diameter.  A 1 1/4" Greenlee chassis punch did the trick for me.  The actual hole diameter needed is 1 1/4" as measured on a '76 body shell.  The size is not to be confused with the sizes marked on chassis punches made for electricians to use for conduit, which are larger than the stated size to account for the thickness of the conduit.  It needs to be pretty well centered on the existing hole to make this work, which can be done by looking inside the well when doing the initial tightening of the punch.   

[TobyB]

Oh.  yeah.  but do touch up the paint under the grommet, as it'll rust if you don't.

 

I do love square chassis punches, too- you can do all sorts of creative stuff with them.

 

And the heavy- duty ones with bearings under the drive bolts can punch through any metal on a 2002.

 

t

 

[irdave]

Ah!  I didn't even know these were a thing!  Thank you.

 

P.S.  You should see the holes in my car to fit all that e30 HVAC crap.  I really need to learn to weld thin sheet metal.  Although, to be fair, the e30 heater core is huge- so nice on the cold days...

Edited July 7, 2020 by irdave

[Mike A]

Yes indeed, they come in handy. I found my set at a flea market about 30 years ago that my wife forced me to go to. Not too much use on an 02 but Wouldn’t be without it if you are building a race car