I have a freashly rebuilt N42 head that I am planning on installing on my 240 block. I have seen a few posts explaining that the cylinder bore must be notched so the larger intake valve will clear it.

Does anyone have any information or tips on the size and positioning of the notch to be made?

Does the bore only need to be notched on the intake valve side or does the exhaust valve have a clearance problem as well?

Thanks in advance for any advice.

I can't remember where I read it but if you went atleast .10 over on the bore then you should be okay if you have 280 valves.But please verify that because I 'm not a machinist.

My advice is even if you bore the block you should notch the block anyway. If the valve just barely clears then you won't get any flow around that side of the valve, not to mention the valves might get closer than you think when they're flopping around at 7000 rpm. General idea is to lay the headgasket on the block and mark where the fire ring sits (scratch it with a pick). Then take a die grinder with a burr and grind away the block up to the fire ring line. According to How to Modify you can go to about .040 above where the top ring stops.

You might also want to do the same thing on the head. Not sure how the head will line up with the 280 chambers, but if you can remove any "extra" alumimum on the head around the valves it will help. Your valves are going to be so close to the cylinder walls that it's a good idea to get every little bit you can.

Just finishing machine work on a rebuild. I took a fun photo of the combustion chamber from where the crank sits:

I am notching the block with a hand file as my better half drove to work with my die grinder in the back (My fault

The head is a stock N47 from a Maxima.

The block is an E31 from a Jan 1971 240z

I figured I would add to this older post to help others who have recently searched as I have for these details

Here is a nice picture from Madkaw:

Key words: eyebrow, eyebrowing, eye-browing, notch, notching, notching block, datsun, zcar.

Edited May 31, 201113 yr by Blue

It can easily be done with a Dremel and grinding attachment. Do it before you get the block honed to prevent contamination and put several layers of tape on the top of the block in case the Dremel rides off across the top of the block.