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Hello to all. . .  I just received an L24 engine a few days ago that I was intending to use for backup parts but I'm thinking it might be a better engine than the L26 that's currently still in my series 1 car. L26 was parked with the fluids in for about 18 years and I expect trouble when I get in there so I bought the L24 cheap. I tore the new L24 down yesterday and the cylinder walls look perfect as does the crank and pistons. Shop will need to confirm. Lots of carbon crap caked on everything and an inch of sludge in the pan.  I'm  wondering if anyone in the community that's more experienced than I (which is everyone) can tell me about these pistons. Previous owner raced Z's in the midwest 15 years ago and he's now getting rid of some stuff. He couldn't say much for sure about this engine so I took my chances and the price was right. Any info is appreciated. Thanks in advance.

Piston01.jpg

Piston02.jpg

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Might just be OEM Datsun pistons.  Not uncommon for old cylinder walls to show little wear.  Apparently the blocks are made from pretty tough metal.

Are there any markings on the bottom of the piston tops?

https://maseraticompound.com/products/datsun-240z-pistons-rods-bearings-and-rings

http://datnissparts.com/x-1973-240z-l24-oe-oversize-cast-pistons-1-0mm-040-84-0mm-12010-h2716-set-of-6-also-fits-l26-l16/

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Thanks Zed,  Photos included. One side says AMP00 and the other has a symbol followed by 221. I was surprised that the pistons are vented on the sides thru the 3rd ring down. Wow. Is that typical??

Piston03.jpg

Piston04.jpg

Piston05.jpg

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Thanks Zed, Just looked at your reference links. . . That's pretty much what they look like. . . I guess they're stock after all.

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On 8/30/2020 at 4:57 AM, Zed Head said:

Might just be OEM Datsun pistons.

I've got a new set of original nissan oversize pistons still in stock and i don't recall they have those indents for the valves.. (i think pics of them are on page1-2 of my 280zx slick roof 1979 restauration topic)

Also the "Ampco"  tells me it's not stock?

On 8/30/2020 at 6:41 AM, ToolBoy said:

One side says AMP00 and the other has a symbol followed by 221

AMP00  is Ampco  and the symbol is the NISSAN sign!  ampco made these pistons for nissan i assume..  I'm almost sure i never seen pistons for z cars with the indents in the piston! So NOT OEM.

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2 hours ago, dutchzcarguy said:

Also the "Ampco"  tells me it's not stock?

 

2 hours ago, dutchzcarguy said:

AMP00  is Ampco  and the symbol is the NISSAN sign!  ampco made these pistons for nissan i assume..  I'm almost sure i never seen pistons for z cars with the indents in the piston! So NOT OEM.

AMPCO was/is a majority Nissan-owned affiliate company, making parts for use on Nissan vehicles.

Whilst the H2716 'Pop-up' pistons were not OEM on any S30-series Z, they were supplied by Nissan as a service replacement part on Nissan L-series engines. They are not 'aftermarket' or custom.

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Thanks Guys,    I've read about a valve swap to take advantage of the slightly larger valves from the more recent Z cars. Could the indent be to accommodate  the bigger valve? Just a wild guess. . . 

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2 hours ago, ToolBoy said:

Thanks Guys,    I've read about a valve swap to take advantage of the slightly larger valves from the more recent Z cars. Could the indent be to accommodate  the bigger valve? Just a wild guess. . . 

Where's the head?  Is it a stock camshaft?  Regrind, aftermarket?  Has it had work done?

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IDK. . . I'm starting to come up with a plan. Just got it apart. Looks stock and unmodified but I've been wrong before. Head is E88 and the valves are 42mm and 33mm. Previous owner raced SCCA years ago and wasn't sure what had been done to this engine. Pistons made me wonder if any other work had been done. I think I'm gonna go with a  ZStory race sport exhaust system as original exhaust fell apart in my hands and am having ZTherapy do their thing on the carbs. I've got a 5 speed and questionable L-26 still in the car.  I ordered a spring compressor and will have valves out in next couple days. Trying to get a recommendation on a knowledgable machine shop in my area (West L.A.). It's gonna be a daily driver and I've no interest in the the track but I'm not adverse to having it be really quick. Will probably do some head work and welcome suggestions as I don't know what the hell I'm doing.    Andy

Head01.jpg

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2 hours ago, 240260280 said:

I have not seen valve reliefs in stock L24 pistons so those may be for high valve lift applications. (i.e. from NISMO catalogue part)

:facepalm:

Sometimes it's like people just don't want to understand what they are looking at.

They are H2716 'Pop-Up' pistons, designed to 'pop up' above the block surface and protrude into a large, recessed combustion chamber in an effort to mitigate the effects of other (non ideal) circumstances. They have valve relief cut-outs because they - by their very nature - impinge on valve stroke territory at certain parts of the 4-stroke cycle.

They were a Nissan service part. Nothing to do with high performance per se, although they could be used in a clever way to utilise certain aspects of their design for a non-stock build. Which is what I would guess we are looking at here...     

 

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Wow!! That's awesome! . . . how can you tell they are oversized and not H2711? Are there advantages / disadvantages to this design change. Sounds like it was more emissions friendly. . . . Compression didn't change but a better burn?  Thanks again. . . 

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21 hours ago, HS30-H said:

 

AMPCO was/is a majority Nissan-owned affiliate company, making parts for use on Nissan vehicles.

Whilst the H2716 'Pop-up' pistons were not OEM on any S30-series Z, they were supplied by Nissan as a service replacement part on Nissan L-series engines. They are not 'aftermarket' or custom.

I’ve been trying to get info on these pistons for a while. I built an L24 engine with 1mm oversized Nissan pistons (with these valve reliefs) some time back and noticed these pistons were about .7mm above deck. I had installed the early E88 Head. They were no problem and worked fine, but my guess is with the stock gasket, they were close to being “too close” to the early head. They worked fine, no contact issues even at high rpm, but I see where 240260280 shows the service bulletin from Nissan saying they were “NOT interchangeable with the earlier cars”. I would imagine if too much metal was taken to “true” the block, there could be a contact issue. Any experience with these pistons being used with the early heads, and if someone was concerned with these pistons being too close, would having a machine shop shave the piston top say .5mm solve the problem? In other words, how much could you machine off of these pistons without affecting the piston?

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These are NOS (new old stock) 240z  original L24 pistons, they have no indents..    these are 1 mm oversize

IMG-20150724-WA0016.jpg

Later on i red that they also fit L26 blocks..

IMG-20150724-WA0014.jpg

(New pistonset.. in stock still. just 30+ years of dust and some lube on them..)  I also have a 1973 complete engine, so i could measure the diff. between those orig. and 1973 pistons, there should be a difference of 0.7 mm! 

 

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7 minutes ago, Diseazd said:

I’ve been trying to get info on these pistons for a while. I built an L24 engine with 1mm oversized Nissan pistons (with these valve reliefs) some time back and noticed these pistons were about .7mm above deck. I had installed the early E88 Head. They were no problem and worked fine, but my guess is with the stock gasket, they were close to being “too close” to the early head. They worked fine, no contact issues even at high rpm, but I see where 240260280 shows the service bulletin from Nissan saying they were “NOT interchangeable with the earlier cars”. I would imagine if too much metal was taken to “true” the block, there could be a contact issue. Any experience with these pistons being used with the early heads, and if someone was concerned with these pistons being too close, would having a machine shop shave the piston top say .5mm solve the problem? In other words, how much could you machine off of these pistons without affecting the piston?

We posted at the same time.. both talking about the 0.7 mm diff..  haha..

I once put a E30  (No not E31)  A E30 head on my L24.. That gives you some compression hahaha long time ago but i remember the starter had trouble starting it!   Did'nt drive very well.. few days later i blew the gasket out haha.. still learning hey...

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5 minutes ago, dutchzcarguy said:

These are NOS (new old stock) 240z  original L24 pistons, they have no indents..    these are 1 mm oversize

IMG-20150724-WA0016.jpg

Later on i red that they also fit L26 blocks..

IMG-20150724-WA0014.jpg

(New pistonset.. in stock still. just 30+ years of dust and some lube on them..)  I also have a 1973 complete engine, so i could measure the diff. between those orig. and 1973 pistons, there should be a difference of 0.7 mm! 

 

No need to measure, 240260280’s post shows these pistons are .7mm taller, and I’ve seen that when I used these later pop up pistons. When you order replacement pistons from Nissan, this is what you get.....or got (not sure if still available). With allowable clearance varying from builder to builder ( most want 1 to 1.5 mm clearance), is .8mm clearance enough? It was in my build, but some may argue it’s not. My question is how much can be shaved off the top of the piston to reach a comfort zone of clearance in the early engines? 

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1 hour ago, Diseazd said:

My question is how much can be shaved off the top of the piston to reach a comfort zone of clearance in the early engines? 

You'll have to measure, and make your own decision. Once you start modifying factory parts, that's the deal...

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Agreed.....good advice.....I would leave that up to a good machine shop. The pistons have been no problem with .8mm (.032 inches) of clearance with a stock head gasket in the early L24. 

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I have 0.58 mm clearance in my engine. I originally had 0.56 mm and a piston just kissed the head.

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On 8/29/2020 at 7:00 PM, ToolBoy said:

Hello to all. . .  I just received an L24 engine a few days ago that I was intending to use for backup parts but I'm thinking it might be a better engine than the L26 that's currently still in my series 1 car.

. Previous owner raced Z's in the midwest 15 years ago and he's now getting rid of some stuff. He couldn't say much for sure about this engine so I took my chances and the price was right. Any info is appreciated. Thanks in advance.

If it's a race engine it's good odds that it's high compression.  The guy used the pistons to raise CR instead of shaving the head maybe.  So, if you want to use it you might have to use high octane race fuel, or "detune" it to avoid detonation.  Retarded timing, run it rich, cam timing, etc.  Doesn't really look like a drop it in and go engine.  Measure and calculate combustion chamber volume to start.

Or, since you have it apart, just buy pistons that will give you the CR you want for a street engine.

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24 minutes ago, jonbill said:

I have 0.58 mm clearance in my engine. I originally had 0.56 mm and a piston just kissed the head.

0.70mm is what I used for "squish" in an engine build tool... nice to have a real world limit!  THANKS!

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