73 piston

[Diseazd]

L24 73 fly-cut pistons on L24 rods come out of the block by .030 inch. Does anyone know why the 73 pistons do this......why are they different from the 70,71 and 72 flat-tops as far as deck clearance? Is it OK to install these pistons with the early L24 heads without shaving the pistons since with the .030 positive deck clearance and the .060 gasket crush only gives you a .030 inch clearance.

Edited February 26, 2011 by Diseazd

[5thhorsemann]

Use the deck clearence specks for the head, if your too tall you may be able to get a thicker gasket from COMETIC's. I used their stuff on H-D motors in the past for this exact problem and their tech staff is awesome when it comes to this sort of thing.

[Diseazd]

I know you can use a thicker gasket or you can shave .030 off, but why is the 73 piston a different dimension? I can't find anything in any books stating that it is. A lot of people have noticed this but don't seem to know why there is a .030 difference in deck height........is it pin height different? Has anyone put these pistons in with without thicker gaskets or shaving the piston? Seems to me you'd pick up compression which is good, but is .025-.030 clearance enough? Most seem to think you need .060 clearance between the piston and head.......but is .030 good enough?

[Arne]

The '73 chamber in the head is different and larger, I recall. Probably has to do with that.

[ChrisZ]

Guy, do you have valve relief in those pistons?

Chris

[Diseazd]

Yes Chris.....the 73 pistons have valve reliefs.

[ChrisZ]

And they should have, are you sure the block haven't been decked?, i have a -73 block with aftermarked pistons, didn't even think about measuring the deck hight, but i have no problems, running a E88 head.

Hope it help

Chris

[Diseazd]

Chris.....No the block wasn't decked. I don't think a lot of people would even notice .030. It looks like you have the same .030 out that I'm talking about (just by sight). I've talked to people that say it's no problem with 73 pistons and E88 or E31 heads. I've also talked to people including Dave Rebello who say you should have .060 clearance. You certainly don't have .060 clearance if you come out .030 and the gasket is .060 inches, but I don't see why .030 isn't enough, and many are running this set up including you with success. Anyone else out there running the 73 pistons(valve reliefs) with the early E88 or E31 heads?

[Diseazd]

Chris....Are you running the early E88 or the 73 E88? As Arne mentioned....maybe the 73 head had a different combustion chamber with more clearance. I would like to hear from someone who could confirm this.

[ChrisZ]

Running open champer E88, probably the late model.

[Diseazd]

Chris.....That's the head the pistons were designed for.....You've got no problem.If you look at your block pictures,you can clearly see the .030 edge I'm talking about sticking out of the block. My question is......is it OK to run these pistons without modification with the early E88 or E31 heads where the chambers are designed for the "0" deck clearance flat top pistons. If anyone has used the 73 flycut pistons with the early heads, I'd like to hear from you. If the pistons you installed had valve reliefs whether Nissan or aftermarket, they are 73 pistons.

[pjoe]

Guy...Whats fly cut. excuse my ignorance. I think I have the the same set up as chris. guess you'll have to road trip up to the boulevard and give me some pointers on my engine in the shed.