l28build questions

[Diseazd]

Malibud.....I'm interested to hear what John Williams says is the max that can be removed from P79 (flat top pistons) safely. I've shaved as much as .025 inches from my 73 Nissan 240Z pistons which come out of the block by .030 inches by design, because they were designed for the open head late E88 head. I believe the minimum clearance between piston and head that Rebello recommends is .045 inches, which means a stock crushed gasket is .060 inches meaning your P79 piston would need to be milled .035 to get that clearance. .035 inches seems like a lot, but I'd like to know if John thinks that's OK. Also, I'd like to know what John thinks is an minimum allowable piston to head clearance is for the L series engine. Shaving the pistons is definitely the easiest solution and allows you to stay stock with your gasket. I agree with Madkaw on the front cover. Put some 220 grit on a flat surface and remove enough from the front cover to match the block.

Edited April 10, 2013 by Diseazd

[malibud]

I will let you all know what he says. I still have a long ways to go. I picked up someone elses project engine up. so i may end up needing a new block and start over we will just have to see. John williams and the machine shop next to him are in Sugar Hill GA I think it is up 75 just north of ATL his number is 770806 2926. I dont think he would mind putting his number up since I have seen it here before. A good guy does a lot of race stuff.

[madkaw]

Guy,

I think those numbers are a little off. Maybe Rebello would say .045, but I'm thinking it's more like .025-.035.

I also believe stock gasket is .047, not .060.

A 2mm gasket would give him .028- no piston shaving needed.

Just my 2 cents:)

[Lazeum]

I've measured stock head gasket (Ishino) at 1.00mm (0.039") compressed, same value for Felpro gasket.

[Diseazd]

Steve......I can't remember exactly what Dave said, but I thought he told me .045 inches.....but whatever he said, it seemed like a lot to me at the time. He deals with race engines, so street engines under 7,000 rpm will probably survive less. My questions are these. 1) What is the average gasket crush thickness for the stock Nissan gasket 2) What is the minimum allowable clearance between piston and head for L series engines 3) What is the max material that can safely be removed from the stock P79 and L24 pistons. No guessers please. I'd be interested in what John Williams or Dave Rebello or someone of equal knowledge has to contribute........it's probably already been discussed on Hybrid.

Edited April 10, 2013 by Diseazd

[madkaw]

As close as you dare on piston to head clearance.

1 fast Z on hybrid says optimum is around .022, I think he runs less. But he is a engine builder !

My Nismo gasket is 1.25mm and I thought was crushed size.

I did measure a removed HG and it measured .047.

No idea on piston shaving minimums

[Lazeum]

some info on my build if that could help some.

Madkaw, you were part of it.

Edited April 10, 2013 by Lazeum

[madkaw]

Great thread on engine building-almost forgot about that one!

[Diseazd]

some info on my build if that could help some.

Madkaw, you were part of it.

Great info......Seems like the P79 pistons actually do come out of the late block .020 inches from the factory and if you use Steve's .045 inch compressed gasket, you're running a piston to head clearance of .025 inches......that's interesting. Now if you do run into a situation where the block is milled or clearance is too tight, how much can you mill off of the P79 piston safely. Anyone know what the max material that can be removed from a stock P79 piston?

Edited April 11, 2013 by Diseazd

[malibud]

Good thread so it looks like .0025 is max to distance between piston and head

[conedodger]

I have been having conversations with Dave Rebello about this. I am going to be bringing him my block and internal/external rotating parts for prep and balancing. I may have him just build the engine though I certainly know how. I have done several Porsche motors and one other Datsun L6 a few years back. I just don't think I can replicate Dave's results in my garage. It depends on what he charges for an engine build of course as I have a two to three sports car habit at any given time. Right now it's just the 240Z and the 914 but that could change at any moment... Dave wants me to use my E31 BC Geralomy head with a little clean up and valve job. He says he has customers at my altitude (4500') running 10+:1 without pinging. I plan on selling the Webers and going with TWM triples and Microsquirt with crankfired ignition.

[Diseazd]

I talked with the Z Doctor in Roanoke yesterday......same question.....how much can you safely shave off of a P79 piston? He wasn't sure, but thought he remembered that you needed a minimum of .250 inches of material on a piston head to be safe. Does anyone have some type of caliper to measure the thickness of the material in a P79 piston, or can they confirm that number?