need HELP WITH L28 BUILD

[joewood]

so i bored my n42 l28block out to 0.60 over because thats what it took to get rid of the rust. and now that i am trying to find pistons i cant... because unless you special order them 0.40 over is all they go. but z22 pistons will work if i go 0.20 more which i will gladly do but my cr will be low or high? please any comments will help

[Rays74]

In any of the rebuilds I've ever done (automotive all the way down to small bore MXr's) when ever I had a bore done, the machinist had the pistons in hand BEFORE the boring was started. With this type of precision machine work, you have to mike each piston to fit each bore.

Never heard of it done without.

 

GL :)

--Ray

[datzenmike]

The L series pistons have a piston pin height of 38.1mm the Z22 is 35.5mm . What this means is that if you put Z22 pistons on your L28rods the top of the piston will stop 2.6mm below the top of the block. This space above the piston adds up to over 15cc of extra volume added to the combustion chamber plus the 9.32cc of piston dish for a total of over 24 cc on top of the combustion chamber itself. Your compression will be way down in the 7s.

[Xnke]

All hope is not lost.

 

You say you had the block bored .060"

 

Your machinist is either a dumbass, or he's not finished with the job. Nissan pistons are metric. 1mm=0.039", approximately.

 

Get Z22S pistons, 35.5mm pin height, L24 rods, 133mm rod length. Stock 79mm L28 crankshaft. Cut the block to fit the pistons AFTER YOU HAVE THE PISTONS IN HAND!

 

This configuration will give you pretty close to the stock configuration. You'll pick up a smidge of compression, not even enough to worry about. What cylinder head are you planning to run? That matters MUCH MUCH more than what block you're running.

 

Or, get out the ITM piston catalog, and order pistons with a 38.1mm pin height, in anything up to an 88mm bore, with the dish you want. choose the dish size based on the head you have. If it's a stock N42 or N47 then you want a 10CC dish. If it's a P79 you want a 0CC dish. If it's a turbo car, you need to decide on the compression ratio...stock engines run a 10CC dish on a P90 head and run 7.4:1 compression.

[banzai510(hainz)]

nissan might have .060 which will be listed as 1.5mm

 

2mm =.080

1.5mm= .060

1.0 = .040

.50 = .020

 

or find a Z car site. they might be able to help source pistons.

 

I ran in to this when I ordered soem .060 rings then find out the pistons were NLA. I was stuck with the rings.

[Xnke]

2mm is NOT 0.080". 2mm=0.078". It can be the difference between a piston that slaps when cold and a piston that seizes in the bore when hot. Not trying to be a jerk about it, but You Must Know when you put these things together. Would you run a rod bearing 0.002" out of tolerance? (Not for long!)

 

Another thing to consider is the type of piston, if you buy stock cast replacements, are they "pressure cast" or "hypereutectic", or both? Pressure cast can mean plane jane cast piston, or hyper...hypers are harder, stronger, and expand less when they heat up...so they fit in a tighter bore spec. Bore the block for hypers and fit standards and you can get piston scuffing, shortened piston life, or if you're just shit out of good luck it'll sieze and tear everything else up too. (I left out forged, because they are EXPENSIVE, and use a bore sizing tolerance based on alloy they are forged from, cross section of the piston, wall thickness, skirt design, and a bunch of other things that we don't need to get into here.)

 

Stock L-series pistons will either have a blank top, or a "2", "3", "4", or "5" stamped in the top. These refer to the piston size, being 0.002mm, 0.003mm, ect over marked bore size. Nissan sized these things VERY closely, and it shows in the longevity of the engine.

[datzenmike]

Hyper-eutectic pistons are used in almost every car made.They have extremely high silicon content, more than the 12% (eutectic point) that can be mixed naturally into the molten aluminum. Usually 14-16% is optimal for strength. Hyper-eutectic pistons expand very little when heated so they can have a closer clearance in the bore and thus are quieter on cold start up. (and are also cheap to make) Because of the silicon content they are very strong but brittle.

 

Forged (low silicon) aluminum pistons must have much more cylinder clearance to allow for expansion and are noisy on cold start up. They cost more to make but are more forgiving of abuse.

[Xnke]

Exactly; but hypers were not commonplace in cars till the early 80's...a LOT of cars didn't have them before that. A lot of manufacturers still make non hypereutectic pistons for stock replacement purposes; it pays to check when you order. ITM is a good, inexpensive brand that IS hypereutectic for these cars, and is a very strong piston for being a cast type. I think I paid 27$/piston delivered when I built the engine in my Z, and 22$ delivered for the Ford.

[FricFrac]

+1 on the ITM hypereutectic pistons. Very good for an aggresive street build/DD.