splitfire

Hello.

I try to connect piston and conrod. Here is the problem:




Conrod small end width is 23mm and distance between pin bosses is about 21mm. Pin bosses are tapered toward the top of piston (31mm-20mm):



How to do correctly, should I remove excessive material of pin bosses or slightly taper small ends of conrods?

KAT-PWR

i would take it to an experienced machine shop.

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splitfire

Not an option.

KAT-PWR

then i'd become an experienced machinist.

Really though... its not like it would be hard to ship those to a machinist.

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cotbu

You shouldn't have to do any of that, unless you bought the pistons, pins, and rods separately? If you did? You've known why and what machine shop you were going to use. Are you lubing up these parts prior to assembly? Do you have manufacturer specs? Is this normal for the products to be modified in this fashion?

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splitfire

Yes I bought everything separately. Conrods are Carrillo Pro-SA, pistons and pins are stock SR02VET(oversized 0.2mm)

The nearest trustworthy machine shop is 1550 miles away.
If I were sure, that it's normal to modify parts in this fashion, then I'd modify them without questions

jr_ss

Not sure why you're running factory pistons with aftermarket rods. I'd forge the entire bottom end and be done with it. The correct way to do this, buy forged Pistons to compliment the forged rods.

With that said, I'd modify the rod before the factory piston. Factory pistons are cast and removing material around the rod pin is asking for future problems.

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daryl337

It would require a taper filing of the wrist pin hole of the rod - followed by a proper deburr and possible ream of the wrist pin hole again.

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splitfire

Same problem somewhere in Nihon

Unfortunately Google translation is a bit vague, but seems like machining a piston was OK

DJ 21o3

It isn't that it can or can't be done, it just isn't recommended. But good find.

splitfire

I followed your advice...

Kingtal0n

It seems a shame all the work and money and only for a cast piston. Why not just run an un-opened OEM block or rebuild an OEM block? The Con-rod uprade isn't going to raise the capacity of the OEM piston any, your still stuck with the same fear of pinching rings, shattered pistons, you know cast problems.

splitfire

Why not just try to push stock pistons to it's limit?
Excepting conrods, bottom end is stock. Conrods were upgraded because I want to rev up to 9k

jr_ss

Because the limit has already been found... It's also a waste of money. You'll have ringland issues without a doubt. If you had just thrown forged slugs in you'd have a much more reliable setup and possibly a motor that can handle quite a bit of power.

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splitfire

ALL THIS tuning shit is just a waste of money, from an Average Joe's point of view.

P.S. What's the limit of OEM cast pistons?

KAT-PWR

I'm going to say around 400hp is where things really start getting sketchy. Nissan cast pistons ka/sr have always been the weak points. I'm going to guess SR/KA pistons and rods are made via the same processes. The pistons tend to give out well before the rods do. Weak ringlands break especially with mediocre tuning.
I would upgrade pistons before I upgraded the rods.
I know ka rods are larger than sr's rods but I'd bet the power handling capabilities are similar.
Rs-enthalpy has advised me to not take stock rods over 450WTQ and at that point you'd be really stressing the pistons. Which is why I say upgrade pistons before rods.
For example in my current set up I made 400whp but only 340WTQ, forged pistons on the stock rods. I am about 100wtq shy of the advised 450wtq cut off. I'd probably be making in the mid 500's by the time i hit 450wtq, which is not going to happen with stock pistons.*
*Yes there are examples of people making more numbers on stock motors but those are the few. I am speaking generally.

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Kingtal0n

very well said. I completely agree and do not take stock pistons on my OWN sr engine past 400bhp. If I wanted more I would step up to a V8 or 2J, forget opening the sr20 IMO.

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