rootney

I need some guidance from some of you seasoned veterans please.

I'm about to install "C" heads back on 455 block and re-install in my '72 Cutlass.
This has been a Carb to oil pan rebuild for a hot street setup. Everything's coming together nicely with just a bit more to go before pulling the 350.

I just finished up some port and polish and Xover filling on the heads, Inspired by the "Home Porting Techniques" thread by 67 Cutlass Freak (thanks Dave). BTW, this forum has been absolutely awesome helpful. I'm turning 60 this year and this is the build I've always wanted to do. I'm having a ball.

Opening the oil drain back passages in the heads is something that I'd like to do now as well.
Beside needing a recommendation on drill sizes, any tips or techniques would be appreciated.
I've not found any detailed info in my searches. Some guys have reportedly broken into one or more of the Head bolt holes when doing this.

Thank in advance for the advise,

George

455man

http://www.robertpowersmotorsports.com/Tech1.html
I just used a 3/8 drill bit and smoothed out the holes. Also smoothed the openings going to the drain holes. There was a lot of sludge in them.

rootney

That's a good link.
Anyone agree/disagree?

George

costpenn

Could not agree more about cleaning out the holes well. A couple of years ago, a friend was finally putting together his 68 400. He sent his heads to Mondello to get some kind of super porting and polishing work, and was told that Joe himself did the work. Anyway, the heads sat for a few years before the engine assembly, so I pulled all the valves and looked at the seals/guides to check for cleanliness and contamination. Everything was fine there, but just as an afterthought ran a pipe cleaner through the two big drain back holes on the end. Thick wads of sludge, metal filings, green roto loc fibers and even a small piece of a red shop towel came out of those holes. I'd imagine the flow rate through the holes wasn't half of what it should be.

rootney

You mean all that crap stayed in there even with a bath post machining?

George

Smitty275

The Bob Powers link is basically sound information. Just be sure to head the warnings he gives about opening up the oil return holes. You must be careful to follow the existing hole because it is very close to water. AND its a bitch to fix it if you go through.

Run to Rund

I prefer to restrict oil flow upstairs with lifters that meter the correct amount of oil.

sbceater

Lol i just used a burr bit and got rid of the ledge

tonycpe

the ledge is there for a reason.

sbceater

What reason lol

Octania

I don't think breaking into a head bolt cavity would be a problem. Hot oil might get on the bolt. OOOH...

Now a water passage, that's s problem.

I have seen aft end of head drilled and tapped NPT then plumbed a drain tube down to the block near the oil pan. LH side, so the crank throws the return oil into the pan.

buzzbomb

Ya have to have somewhere to set your beer on!.

rustyroger

I'm thinking of all the threads concerning running hot while I'm reading this.
Just like a radiator that isn't partially plugged will be fine with any engine rebuilt to OE spec, so properly cleaned out oil return holes should have no problems with a near stock setup. If you have a high pressure, high volume pump I still think it shouldn't send more oil to the heads than it can cope with as long as the drains are clear and you aren't using high viscosity oil.
This is only my opinion mind, I have built precisely one non diesel Oldsmobile engine.

A head sent to an acknowledged builder coming back with clogged return holes?. I am rather surprised, and also a little disappointed to read that.
Always check everything when you get your parts back, no matter who did the work should be a mantra we all follow I guess.

Roger.