240Z Aftermarket Itm Pistons Issues

[redzedsled 6]

You milled .020 off the pistons that were .030 off the deck and now you are at zero deck?

 

I did say .020" piston out of the hole in my previous posts did I not.

[madkaw 542]

Okay-this thread has been a bit confusing. .020 it is, but why even shave the pistons?

I think I got 30 by adding the deck shave -which looked like there was a total off .011 taken off.

 

My question is, if MOST Datsun motors have positive deck height(.020) for a reason, why would you think you needed zero deck height? So now you have atleast .039 head to piston clearance, but maybe more like .049 with your HG. 

 

IMHO, you didn't or shouldn't have done a thing to the pistons. Not bashing, just stating.

[redzedsled 6]

I respect your humble opinion, but +0.020 deck height is not the standard from what I have known.

 

When I initially pulled the head off the block, the piston at TDC was at the very top of the block, zero deck height and no higher.

 

I have seen in engine calculators online and they suggest that the pistons should be slightly below the block at - 0.1mm, stock for the L24.

 

I have always thought it was the performance guys who wanted the positive deck height and therefore run thicker gaskets to gain the clearance.

 

The gasket I am going to use is about 1.1mm thick so compressed it should be about 0.6mm or so?

 

Nissan's requirement is 0.035" minimum clearance between gasket and piston top.

 

I respectfully take all opinions into account and then form my own decision, so I welcome your comments.

[Zed Head 2,212]

 

They measured the piston height to the old ones that came out before mounting (a slight difference of 5 thou) and after mounting them on the rod bolts and into the cylinder, they protrude about 20 thou above the block,

 

Did you edit this?  Because I went back and looked about an hour ago and I was sure it said "about 30 thou".  And I had the same question as madkaw.

[redzedsled 6]

Did you edit this?  Because I went back and looked about an hour ago and I was sure it said "about 30 thou".  And I had the same question as madkaw.

 

Yes I did. Initially in the first few postings I estimated at 30 over the block and in later posts I stated it was about 20 over the top.

 

Looking at How to Rebuild Your Nissan Datsun OHC Engine book, it states:

 

"although the piston may extend slightly above the block 0.001 for example clearance is required to prevent piston from striking the cylinder".

 

So what is the actual spec on stock deck height, is it really + 0.020? I have read differently.

[Zed Head 2,212]

I did say .020" piston out of the hole in my previous posts did I not.

 

Yes I did. Initially in the first few postings I estimated at 30 over the block and in later posts I stated it was about 20 over the top.

Thanks for being honest.  You were being misleading in your post above, to madkaw, though.  Not good.

[redzedsled 6]

No excuse for me to edit a posting (I changed it back to what is was), but I did later state it was 0.020 out of the hole, that I did not edit.

 

Getting back to the matter I found this bit of info on L Series Engines, very few with positive deck heights.

 

"Assembled stock engine deck height

L16 ('68-'73 510 and later years 521pickup)
piston deck height: 0.10mm (above block)

L18 ('73-'74 610, and 620 pickup truck)
piston deck height: -0.55mm (below block)

L20B (various '75-'80 610, 710, 200sx, HL510, pickup truck)
piston deck height: -0.45mm (below block)"

 

and further...

 

"most of the L, Z series have the piston slightly below the block deck at TDC"

[Zed Head 2,212]

No biggy, just a smally on your comment to madkaw,  Especially since you edited close to the time he asked.

 

Anyway.  The ZX F54 flat-top piston engines all seem to have a pop-up of about .020".  But there doesn't seem to be a lot out there about the early L24 flat-top engines.  Maybe they're zero pop-up (I'd use "deck" but it's hard to keep the +/- signs correct).  But they both use a similar gasket thickness so your .020" pop-up probably was fine.  The 030" that Diseazd had might have been in that worry zone, but even then, some guys like to run a really tight squish distance.  But that's with forged parts to minimize stretch at high RPM.

 

To top it off, somebody (madkaw maybe?) said that Rebello thinks the ZX P79 cylinder head "squish/quench" design was poor.  So, overall, it seems that keeping the pistons from hitting the head might be the main concern.  From there, you can get in to forged parts, and RPM, and all kinds of details.  Shaving the pistons for insurance is probably the way to go.  Too bad ITM is producing out-of-spec. product. 

[madkaw 542]

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/

[Zed Head 2,212]

Let's take a breather and get back on track.  The guy doing the work on this engine apparently wanted a zero-deck.  So he felt like machining the pistons was the way to go.  Sounds like he was working off specs. and not off what "could be".  He probably would have been okay with leaving the 020" pop-up.

[redzedsled 6]

I made a decision based on many people's opinion, including the engine builder, the members of this forum, and people in the business.

 

The builder felt more comfortable turning the piston tops down. I am aware that you can run your pistons over the top and understand that 30 over would be the danger zone.

 

I debated turning the pistons down versus leaving them as is for several days. I made the decision, and now I will have to live by it.

 

The goal of this thread was to inform others who could have potential issues with ITM pistons of their own.

[madkaw 542]

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 2,212]

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 6]

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 2,212]

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 6]

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 2,212]

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 6]

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 31]

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 6]

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 6]

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