240Z Aftermarket Itm Pistons Issues

[madkaw]

Zed,

not really mad, but making a statement that Z l motors are zero deck engines is just plain wrong. Maybe the the OP is getting this info from the builder that doesn't know. He wanted zero deck because that's what these engine should have which should not be put out there. .020 out of the hole is about perfect and very close to factory.

[Zed Head]

I think we're on the same page, as is redzed.  His builder has a comfort zone, as he should.  Good info though on the ITM L24 pistons.  They are, apparently, .020-030" taller than stock Nissan pistons.  Whether it matters or not.  That's what I got out of the thread.

[redzedsled]

The engine builder used Mitchel specs I believe he said, and insisted on 0 deck height. There is great deal of difference of opinion, for such a small amount of deck height.

 

What's done is done now...

[Zed Head]

All good.  Still interested in how it turns out.  Need to keep tabs on the best way to rebuild.  You, madkaw, and siteunseen all have some work going on.  Good stuff.

[redzedsled]

All good.  Still interested in how it turns out.  Need to keep tabs on the best way to rebuild.  You, madkaw, and siteunseen all have some work going on.  Good stuff.

 

I appreciate the mediation...

 

If I am at zero deck height and I have a stock gasket that compresses to, let's say 0.6mm, that is 0.023" piston to head clearance.

 

Perhaps with the new generation of head gaskets perhaps the compressed thickness is about 0.8mm, that is 0.031".

 

If stock minimum clearance as stated by Nissan is 0.035", how could you get any closer than that.

[Zed Head]

The stock gaskets are at 1.25 mm thickness, I believe ( I've actually measured my crushed factory fire-ring in addition to the general view).  So at zero deck, about .049".  Which is about where Monroe (the unofficial authority) recommends piston to head clearance.  So, an 020" pop-up puts a person at .029".  Which is tight.

 

It's an interesting discussion, because most of Monroe's work is on the Z engines, not the ZX.  The ZX, F54 flat-top, seems to be where the .020" (or .018" to be more exact) seems to come in to play.

[redzedsled]

After reviewing page 126 of the book how to modify DATSUN 510 610 240Z engine & chassis by H.P. Books, it states:

 

"Deck clearance should be from zero (piston flat even with block deck at TC) to +0.015 (out of the hole) with the piston centered in the bore. This assumes that you are using the standard Datsun gasket which is about 0.050-inch thick when compressed."

 

madkaw is right, after some thought, in that I could have gotten away with pistons that were 0.020" out of the hole (0.030" piston to head clearance).

 

At the same time, I went with zero deck height on good advice of others and also because that is the way I uncovered the engine to begin with.

 

If I have zero deck height along with a 0.050" thick compressed gasket, then I have more than Nissan's minimum requirement of 0.035".

 

This is my first engine rebuild, so I am learning alot along the way. Admittedly I don't have the same experience of other members of this club.

[73str86]

Just to add my bit of experience. 

 

About two years ago I decided to get a long block F54/E88 combo built up shortly after I purchased my '73 240z. I saved the original running block and the E88 went into the build. I chose a locally known engine builder, and had it built to a 2.9L ~10.0:1 comp ratio (heavily ported) masterpiece. It was fully balanced, blueprinted, etc.

 

My builder also said the pistons were protruding too far out of the block to his liking. He said my choices were were a 2mm head gasket (could have been less) for $220 or for him to mill the tops of the pistons in his shop for $150. I was a little nervous (he is mainly known for making American drag racing and circle track engines) about the milling but went with his advice and my gut. I'm glad to read Rebello does the same thing.

 

~1300 miles later, I have no complaints whatsoever. Did a proper break-in, 500 mile oil change, stayed under 4,000 rpms first 1,000 miles. Now I flog her and she's a blast. Still needs some suspension work, but the engine has performed wonderfully thus far.

[redzedsled]

Now you are putting out misinformation. What do the 4 cylinder motors have to do with this discussion anyway. Please read the attached thread and realize you turned down your pistons for nothing.

 

And who are you supposedly quoting?

 

 

http://forums.hybridz.org/topic/119593-pistons-protrude-from-block-thicker-gasket/

 

This is my source for my information:

 

http://www.jspecauto.com/files/jspecautotechcenter11d.htm

 

You did say and I quote "MOST Datsun motors have positive deck height(.020) for a reason"

 

Making mention of other L Series Blocks is relevant in this case.

[redzedsled]

I found this very useful calculator for Datsun L-Series Engines. Here is the link:

 

http://www.ozdat.com/ozdatonline/enginedesign/

 

With all the stock presets (E31 head, P30 block, etc) and a 1.25mm head gasket, it calculates the deck clearance at -0.100 mm (-0.004") below deck.

 

Note the stock Deck Clearance Presets with the different engines, L24, L26, L28 etc.

 

All dimensions on this calculator is in mm. Here is a link to a convenient length converter:

 

http://www.onlineconversion.com/length_common.htm