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Used Forged Pistons, Pics - Can I Used Them, Bore Questions

The Mafia

By The Mafia,
in Engines & Forced Induction

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The Mafia Grand Master

The Mafia

Posted
Posted (edited)

Just letting everyone know before you read on that this WASN'T my engine, but an engine that I bought from someone that blew theirs. I got it cheap, and the Head is in excellent condition (ported etc)

Hi everyone, I just pulled down a RB25 that had a bottom end failure (Spun every main bearing, and some big end bearings)

Are these pistons ok? There are a few marks on the skirts. The rest of the pistons look like new.

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Can the skirts be cleaned up?

The bores have these marks on them obviously where the piston skirts have been rubbing. Is this normal? I've seen other engines like this, so I assume so? There are no deep grooves in the bores like there are on the pistons.

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ok, here is the rest of the bits you'll want to see.

Looks at the cradle........ fark..

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Edited by The Mafia
STATUS Grand Master

STATUS

Posted
Posted

looks like a poor rebuild..... all bearings plus the above hey?

i hazzard poor (excessive) piston to bore clearance hence the rocking and scuffing, burns and breaths the oil then does the bottom end.... or was it cooked?

pistons should be ok providing the did not scuff too bad, mic up the skirt then compare it to 3 or 4mm below ring lands, are the ring lands damage free?

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted

actually, engine went for 20,000kms before the car was sold, and the new owner was supposedly doing lots of rev limiter burnouts. (only had the car for 2 weeks before it blew.

He said he found 2l of oil in the catch can.

I assume this was another "all the oil in the head \ catch can and sump starved" oiling issue.

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted (edited)
i'd throw most of it out :)

I am going to, going to keep the head and pistons.

I just want to know if the pistons are ok to use.

Edited by The Mafia
wrxhoon Grand Master

wrxhoon

Posted
Posted
I am going to, going to keep the head and pistons.

I just want to know if the pistons are ok to use.

No toss them out . You can re-use the block as long as you bore it to suit the next oversize pistons . I can sell you a set just like them if you like, you can have them for FREE ....

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted

other than the scrape marks that look normal, I can't see the problem re-using them?

Mind you, there are a couple of grooves.

Wouldn't mind hearing what a few engine builders have got to say.

wrxhoon Grand Master

wrxhoon

Posted
Posted
This doesn't make sense?

The block is buggered. The Bearing cradles are rooted.

The pistons are stuffed too and you cant do anything about that. You can re-bore the block as long as its 76-86.5 mm to the next oversize .

If you have to you can tunnel bore the cradle as well .

sinistaGTR Grand Master

sinistaGTR

Posted
Posted
other than the scrape marks that look normal, I can't see the problem re-using them?

Mind you, there are a couple of grooves.

Wouldn't mind hearing what a few engine builders have got to say.

Yeh i think that would be your best bet mate def ask a few engine builders and see what they have to say.

The Mafia Grand Master

The Mafia

Posted
  • Author
Posted (edited)
you mean bore to accomadate sleeves for the next size bore. otherwise the engine wont last too long.

boring says good bye to cast hardness and for RB's goodbye to nitride hardening.

are you able to explain this in a little more detail?

Edited by The Mafia
Adriano Grand Master

Adriano

Posted
Posted
you mean bore to accomadate sleeves for the next size bore. otherwise the engine wont last too long.

boring says good bye to cast hardness and for RB's goodbye to nitride hardening.

Since when are the blocks hardened or nitrided from the factory?

deant1 Collaborator

deant1

Posted
Posted (edited)

Not sure which part of my post you want me to explain more, but:

Cast iron (cast anything infact) - soft on the inside and hard on the outside. depending on the size of the cast but generally speaking you don't want to bore out a cast block because at least you are making the hard walls thinner.

Nitriding - the cyclinder surface is hardened using nitriding, expensive to get the cylinders re-nitrided. and it is a key reason why the cylinders are so durable in RB engines.

Cast iron and nitriding = very hard and durable surface. depending on the amount of material removed from the walls ( if you get them bored) would decide on how much you degrade this surface.

The practicle way of getting past this is simply boring to a size that allows you to insert cylinder sleeves which come ready hardened!

hope i answered any of the q's you had,

EDIT: i thought the cylinders were nitrided also, but if i'm wrong it doesn't really matter because sleeving is used to combat the problems of boring in to cast. same outcome.

Edited by deant1
wrxhoon Grand Master

wrxhoon

Posted
Posted

Rb blocks can be bored to 87 mm without any issues, of course you would only go to 86.5 mm if the block is 86 mm now .

Sleeving will make it much stronger but its very costly..

There is no way I would re-use these pistons if I was to do a re-build

Even if the pistons were perfect you would have to re-use them in that block , don't forget Nissan pistons are graded so they are different sizes even in stock virgin engines .

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