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L20B piston


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I need 4 L20B rods so to speed the process I cut my L20B pistons off. This will make it easier to press the pins out. Anyway Thought I would post what the piston looks like in cross section.


They are very brittle/hard, the small burr I could remove by rubbing with my thumb. All (or most) pistons are hyper-eutectic, that being, they have silicon mixed with the aluminum and forced beyond the eutectic point where it will naturally mix to it's limit. Silicon is basically glass, so the piston becomes very hard and brittle BUT it also does not expand much from heat. Thus there is virtually no knock on cold start up.




At it's thinnest point it is 0.320" That's almost a third of an inch. I thought they were much thinner.

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I tried heating the rod end and using a vice and a couple of sockets. It popped once and moved 1/16" and that was that. Need a hydraulic press. We have one in our materials testing 'lab' up the street. There's an electric one for crushing 4" diameter concrete samples to their breaking point. There's also an oven.


Sure would like to have floating rods....

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Nissan over sizes the KA rod end, presses in a brass bushing and then reams to size. Someone here said they just ream the small end out to size. Size being about a thou clearance. The manual says the pin should be able to press fit the piston by hand at room temperature so likely the rod would be the same. When I cut the pistons they just slid off the pins. The small end also has to have a small hole drilled in the top side to allow oil in to lube it. 


KA24E rod small end



If the pins were floating I could assemble them myself. I would have to shorten the pin length so that C clips could hold them on the KA pistons.


My KA-E piston and rod set. Pins fit just loose enough to push in by hand. To keep them in the piston and from working themselves sideways against the cylinder walls, C or cir-clips are fitted into grooves in the piston pin holes to hold them in place. The pins seem to be identical to the L20B pins, just shorter.


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I drilled holes on the underside, (3/32 I believe) and honed it till the pin just slid in, .0008 to .0012 clearance. I've been thinking about making a fixture to enable me to cut snap ring grooves in all pistons. Cheaper than buying a rod oven and a press. I've seen a few pistons ruined by pressing pins out.





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I do not know enough but this seems that floating wrist pins or floating pistons means that as cir clip holds the rod pin in instead of a pressed in fit


Is this correct ?

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That's how I see it. Frees up a small amount of power from reduced friction but mostly it's easier to put together.


0.008 to 0.0012 sounds about right. I think my FSM says that for pin to piston clearance. I don't want to pay to have it done, instead maybe buy a hone or ream. Eric where would you get one?

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I tried heating the rod end and using a vice and a couple of sockets. It popped once and moved 1/16" and that was that. Need a hydraulic press. We have one in our materials testing 'lab' up the street. There's an electric one for crushing 4" diameter concrete samples to their breaking point. There's also an oven.


Sure would like to have floating rods....


My LZ has fully floating rods/wrist pins  :ninja:


Be jealous.

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A hone would be Spendy. I have a little Sunnen hone all for doing valve guides and I think it was about $400.00. A simple brake hone doesn't work well. They tend to bell out the ends. You might get it to work by reducing the stroke, I have cleaned them up like that.


When I need a reamer, I either borrow one from work or have my boss order one. He takes it out of my tool money fund, so I usually don't even know how much it cost.


I have better luck with a full on Sunnen hone that I use at a previous employers shop. Your going to want to have the big end checked and possibly resized anyways, so to have them turned around and given a few licks shouldn't cost much.

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I have a few of those, but don't ever use them. You don't have a very big window. It could be done I suppose. Start with an ugly rod to get it set right, then do the real ones. 

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King Rat,


Do you know how large the small end bushing is?  Found the perfect piston for my engine combination, but it has a 23mm wrist pin.  From the pictures it looks like the small end can (barely) be bored out to 23mm without getting into steel, though.

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 I think all the Nissan L, Z, KA piston pins are 21MM.


I went out and measured the width across the bronze bushing in the KA24E rod small end. It's 1/10" or 0.100" or 25.4mm. I'll round to 25.5mm... so it's only 2..25mm thick around. Does that help?

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In my experience, piston pins always float in the rod.  Ones that ONLY float in the rod (but are either pressed or set-screw locked into the piston) are semi-floating- that's how Datsun pistons are.   Full-floating pins float on BOTH the piston and rod. The Allison V1710s I work on use full-floating pins with circlips that keep the pins from sliding out of the piston.


There were engines in the past that floated only in the piston, but that has long gone out of use.

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You know, I was going off the pistons I have in boxes.  Aftermarket pistons.  Sure enough, the FACTORY Datsun setup float in the piston and are pressed into the rods.  Backwards from the aftermarket pistons I have, which are supposed to be pressed into the piston.



Or, at least that's what the manual says.  It contradicts itself by saying the pins are pressed into the rod, but then says the con rod small end is pressure-lubricated.  If the pin was press-fit to the con rod, it wouldn't need lubrication at the small end.  The pin has no way to send oil from the small end to the wrist pin bores in the piston.


I is confuzed.


The pistons have no retainers on either end, so if the pin floated in the piston it could slide out and hit the cylinder wall.

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I haven't torn down many newer engines, but I have only seen 2 variations. Either interference fit in the rods and floating in the pistons. Or full floaters with clips or teflon buttons.


The rods on a press fit aren't pressed together, because it would scrape the hell out of the wrist pin. The rod ends are heated, then assembled while hot. They cool down and shrink around the pin. 

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