396/325 hp BB piston orientation

[Richard D.]

Quick question - rebuilding a 396BB. It's from a 65 Impala 325hp. Going into my friend's "driver".

Installing the pistons, and they're marked with a hole (not a through hole, maybe better described as a notch) on one side of the piston top.

Which side does the hole face, top of motor (manifold), or bottom (oil pan) hen installing?

Thanks in advance for any help.

Regards,

Rich

[Joe L.]

Re: 396/325 hp BB piston orientation

Rich----

I'm not sure that I'm understanding you correctly but I'll offer this:

The "notch" or "hole" on the upper periphery of the piston, WHEN PRESENT, is always oriented towards the FRONT of the engine. However, I don't recall that 396/325 pistons used for any model year that engine was built actually have that notch or hole. These pistons have a dome and an "indented" valve relief on one side. The valve relief goes toward the top of the engine (i.e. towards the intake manifold).

If you are using aftermarket pistons, they may have the notch, I suppose. If so, the notch should be oriented towards the front of the engine AND the valve relief oriented towards the top. If it doesn't work out this way, then something's "non-standard" about this. If you're using aftermarket flat-top pistons, then the notch will usually be present and should still be oriented towards the front of the engine. However, if you're using flat-top pistons in this engine, they will yield a very low compression ratio and, in my opinion, are not necessary or advisable for any reason (except, possibly, if the engine is supercharged).

[Richard D.]

Re: 396/325 hp BB piston orientation

Joe, as usual, thanks a million.

We're in the shop now, and here's the answer we needed to keep moving along.

We're using all of the original parts from the engine, as they were all in good shape, except, of course, for the usual replacement parts - gaskets, bearings, rings, etc.

Again, thanks,

Rich

[Michael H.]

Re: 396/325 hp BB piston orientation

Joe,

Didn't low perf big block pistons have some sort of notch on them like small block base engine pistons? I'm getting to be an old geezer and I can't remember all this now but I thought there were LH and RH pistons on low perf big blocks because of wrist pin offset. I know the mech lifter 11.0 pistons had on center pins so one number services both sides but I thought the low perf had slightly offset pins which would have required two part numbers for left and right. That also would have required a notch somewhere on the dome to identify R & L.
There's a pic of a piston in the 66 Chev overhaul manual and it almost looks like there's a notch at the 12:00 position but it's difficult to tell for sure. I really don't remember a notch but I haven't worked on one of those for a lot of years. Thanks,

The Geezer

[Joe L.]

Re: 396/325 hp BB piston orientation

Michael-----

Yes, you are correct. The 396/325 and the 427/390 used pistons which were side specific and, thus, there would have needed to be some system to mark them for side specificity. Although I was previously aware of the side specific nature of these pistons, when I originally responded to this question I thought that the dome configuration would have been all that was necessary to identify them and I couldn't recall seeing the notches. However, I was incorrect; certainly notches would need to be present regardless of the dome configuration.

In any event, the correct orientation of the notches, if present, would be forward as I described.

[Michael H.]

Re: 396/325 hp BB piston orientation

Thanks Joe, I always enjoy reading your input on the forum.

Michael