Jump to content
SAU Community

Recommended Posts

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.

1.jpg

2.jpg

3.jpg

4.jpg

5.jpg

6.jpg

7.jpg

8.jpg

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.

1.jpg

2.jpg

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

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

1.jpg

2.jpg

3.jpg

4.jpg

5.jpg

6.jpg

7.jpg

8.jpg

9.jpg

10.jpg

11.jpg

12.jpg

Edited by The Mafia

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?

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.

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
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 ....

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.

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 .

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.

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
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?

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

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 .

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • @Haggerty you still haven't answered my question.  Many things you are saying do not make sense for someone who can tune, yet I would not expect someone who cannot tune to be playing with the things in the ECU that you are.  This process would be a lot quicker to figure out if we can remove user error from the equation. 
    • If as it's stalling, the fuel pressure rises, it's saying there's less vacuum in the intake manifold. This is pretty typical of an engine that is slowing down.   While typically is agree it sounds fuel related, it really sounds fuel/air mixture related. Since the whole system has been refurbished, including injectors, pump, etc, it's likely we've altered how well the system is delivering fuel. If someone before you has messed with the IACV because it needed fiddling with as the fuel system was dieing out, we need to readjust it back. Getting things back to factory spec everywhere, is what's going to help the entire system. So if it idles at 400rpm with no IACV, that needs raising. Getting factory air flow back to normal will help us get everything back in spec, and likely help chase down any other issues. Back on IACV, if the base idle (no IACV plugged in) is too far out, it's a lot harder for the ECU to control idle. The IACV duty cycle causes non linear variations in reality. When I've tuned the idle valves in the past, you need to keep it in a relatively narrow window on aftermarket ecus to stop them doing wild dances. It also means if your base idle is too low, the valve needs to open too much, and then the smallest % change ends up being a huge variation.
    • I guess one thing that might be wrong is the manifold pressure.  It is a constant -5.9 and never moves even under 100% throttle and load.  I would expect it to atleast go to 0 correct?  It's doing this with the OEM MAP as well as the ECU vacuum sensor. When trying to tune the base map under load the crosshairs only climb vertically with RPM, but always in the -5.9 column.
    • AHHHH gotchaa, I'll do that once I am home again. I tried doing the harness with the multimeter but it seems the car needed a jump, there was no power when it was in the "ON" position. Not sure if I should use car battery jump starter or if its because the stuff that has been disconnect the car just does send power.
    • As far as I can tell I have everything properly set in the Haltech software for engine size, injector data, all sensors seem to be reporting proper numbers.  If I change any injector details it doesnt run right.    Changing the base map is having the biggest change in response, im not sure how people are saying it doesnt really matter.  I'm guessing under normal conditions the ECU is able to self adjust and keep everything smooth.   Right now my best performance is happening by lowering the base map just enough to where the ECU us doing short term cut of about 45% to reach the target Lambda of 14.7.  That way when I start putting load on it still has high enough fuel map to not be so lean.  After 2500 rpm I raised the base map to what would be really rich at no load, but still helps with the lean spots on load.  I figure I don't have much reason to be above 2500rpm with no load.  When watching other videos it seems their target is reached much faster than mine.  Mine takes forever to adjust and reach the target. My next few days will be spent making sure timing is good, it was running fine before doing the ECU and DBW swap, but want to verify.  I'll also probably swap in the new injectors I bought as well as a walbro 255 pump.  
×
×
  • Create New...