has anyone cut a hole in a valve cover to run a breather / evac? I've got a set of nice alum valve covers that have no holes or punch-outs. I know the hole needs to be 1.22" for a moroso breather and grommet. Not sure about the best way to cut them.

 

after looking a bit more, it turns out that 1.22" is *very* close to 31mm. I guess I'll try and track down a 31mm hole saw at Home Dumpo

 

use a 1 1/4"" hole saw

 

The only problem with a 1 1/4" hole saw is hole saws tend to cut a little wider then you really want cause they want to skip around a bit. I know on mine it made the breathers a bit loose. I then sealed the grommets to the valve cover using permatex so they stay in place and it's unnoticeable.

 

Use a 1-1/8" and a die grinder.

 

can buy a 1-7/32" bit for around 60 bucks.... kinda steep for a 1-time only tool, but that'd get me within thousandths of 1.22. Also found a step-drill that is in 32nd increments, but again for like 40 bucks. might be cheaper to hit up a machine shop

 

There are several ways, you could throw a hole saw in a mill and get the hole more accurate. You could make a smaller hole and use a diegrinder. You could have the hole CNC milled. Lots of options, some are better than others.

 

right.... was just lookin' for "this is what I did, and it worked great" or "don't do this, I ruined my freakin' valve cover doing it" - like what Karps wrote. Figured someone might have done something I hadn't thought of. Thanks for the input guys

 

Also, if you know anyone that's an electrician, 1-1/8" is pretty close to a drag-out for ¾" conduit IIRC. That would make about the neatest possible hole.

 

I was just searching for a breather for my valve covers, and saw the specs as rated to be "for all factory and aftermarket valve covers, with typical 1.25" hole", so I figured a 1.25" hole say would work for ya. but yea, usually it's got that bent lip going in, so it's not a ragged gaping wound of a hole...

 

Even a drill is going to cut oversize. Use a 1 1/8 holesaw and file as needed. The hole saw will cut oversize to, so I think you'll find your right there.

 

XaviarRahl already gave you the solution. Use either a 1-7/32" conduit knockout or 1-7/32" drill bit, whichever is suitable for the thickness of the material. That is the standard size for the old pattern NEMA pushbutton or selector switch used for decades. They're still around in abundant supply.

 

I drilled under size and used a die grinder to make the hole a perfect fit.

 

Best DIY is cut undersize and enlarge via a die grinder. OR you can do as I did and find an engine builder / machine shop to machine the holes for you. Cost me a woppin 55 bux for (3) holes in my Dart covers.

 

Used a 1-1/8" bi-metal hole saw. Cut right through and made a surprisingly clean cut. cleaned up the sharp edges with a die grinder. Without grinding the hole any bigger, I test fitted the breather and it fit perfectly! (a little tight).

 

I used a Milling machine with a tool called a trepanning tool. I got it to within a few thous. and that is goog enough for automotive work. The tool was very hard to find though. You can drill the hole close to size and then use a boring bar on the mill to get it within a few thous as well.
Here is what I did for a buddy of mine. Yes it is a ford valve cover but you get the idea. I had to machine a shoulder in the tube as well for the breather.
T.J.

 

Isn't it great having access to this kind of equipment!