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Rb30 Question - Re Main Girdle

2LV8ETR

By 2LV8ETR,
in Engines & Forced Induction

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2LV8ETR Mentor

2LV8ETR

Posted
Posted

I have started my first of two RB30 conversions this afternoon and came across an interesting scenario.

I am building two side by side, one 400hp for the street, and the other, an 800hp for competition.

Both engines have been pulled down and one block and crank sent off for the usual machining. I didn't take any notice of what came out of either engine and just put everything up on shelves as I broke it down. Fortunately, one set of stock internals is easily discernable from the other as one engine was full of sludge and burned oil which discoloured the components, and here's why.

When I went to fit the main girdle, the crank locked to the point where it wouldn't spin. I thought that there was an issue somewhere with the bearings being put in incorrect packaging, but measurements dictated otherwise. Just for the hell of it, I cleaned up the girdle that came out of the block I sent off first (the sludgy one), fitted it and torqued it down, and lo and behold, everything spun beautifully.

To put it simply, the main girdle off one engine was slightly shorter that the one on the other engine. The girdle went on the other engine without issue, but they had to be fitted to the block of origin.

This is my first 30 build (I've done 26's and 20's) and it's a first for me. I have had a look around to see if there have been other instances of this but I came up short of an answer as most builds are done singly, not side by side.

Maybe there's a workshop or builder out there who can provide an answer to this wierd little teaser?

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https://www.sau.com.au/forums/topic/378808-rb30-question-re-main-girdle/
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GTRsean Grand Master

GTRsean

Posted
Posted

That's why I'd never mix and match girdles. If I had to use a different one due to damage etc, it would get measured and tunnel bored to suit for sure.

You may luck out with one that might work fine....

zebra Grand Master

zebra

Posted
Posted

ye, all engines are differnt due to core shift in the casting posess.

the block and girdle are machined together, and usually stamped with the clearences from factory on the girdle.

Which is why the girdle from another block caused the crank to jam.

Duncan Grand Master

Duncan

Posted
Posted

+1, I had the wrong girdle fitted to a block, after all the final measuring was done. fortunately in this case we could hear straight away it wasn't right and pulled it down again before damaging anything except bearings.

They must always either be a pair, or be tunnel bored.

bubba Grand Master

bubba

Posted
Posted

That's very odd Al, mixing and matching girdles is a no-no.. are you 100% sure you didn't mix them up?

Even if the other girdle torqued down and everything spun fine.. I still wouldn't be running it like that. I would be inclined to get the main tunnel line bored so you know it's all good.

  • 2 months later...
GTRNUR Grand Master

GTRNUR

Posted
Posted

Despite which girdle was used, what he is saying is that the tunnel wasn't measured with a micromoter before and after test fitting the main bearings. So therefore you have no idea what your main bearing clearences are.

While you might get away with this for a low power street engine. That the crank spins means there has to be a few thou (or more) clearence in there.

With the "competition" engine you need to have the cradle shaved a thou, install the main studs and then have it tunnel bored until the ID of the bearings measure to create at least a 3 thou oil clearence to the crank you are using.

Tunnel boring ensures alignment of the main bearing saddles and allows the propper clearences to be set and matched to the crank.

Tunnel boring after installing a main stud kit ensures the bearing saddles are round, as torquing the main studs distorts the bearing saddles. Imagine main bearing saddles made out of marshmellow. Steel moves the same when torquing forces are applied, just a lot less. All it takes is 1-2 thou and you have bearing damage, a spun bearing, or a crank that won't turn at all.

  • 2 weeks later...
r33_racer Grand Master

r33_racer

Posted
Posted

You can only go so far when tunnel boring to modify the main bearing clearances though. There is a limit on how relaxed you let the crush go when doing this. From memory I believe you can only pick up a few tenths, otherwise its grind or polish to achieve anything else.

  • 2 months later...
2LV8ETR Mentor

2LV8ETR

Posted
  • Author
Posted

Sorry for not getting back to this topic, for some reason I'm not being notified on the forums when a topic I have subscribed to is replied. So I was under the impression that there were no responses.

Anyway, yes, the issue was with myself mistakingly assuming that the girdles would fit between blocks, I just chose the cleaner of the two to start with. I have SNAFU'd somewhere along the way in my thinking.

It's all good now and the engine should be in the car soon as I am presently port matching the RB20DET intake to the 25DE manifold. There's a little bit of difference in size between the two and I just wanted to facilitate an even flow.

Thanks for the replie guys, and Bubba, I'll be hitting you up for some gear soon. I still have your number.

2LV8ETR Mentor

2LV8ETR

Posted
  • Author
Posted

I'll take the latter thanks ;)

But yeah cool, I should probably organise another NIStune group buy for teh Westralians!

I'm at the stage where I'll be dropping in the injectors on the manifold over the weekend, so the resistor pack will be needed fairly soon. PM me if you need my number because I'd like to get hold of one ASAP and I'm more than happy to prepay if needed.

bubba Grand Master

bubba

Posted
Posted

How handy are you with a soldering iron? I'm mucho busy at the moment but more than happy to guide you in its' creation :)

Are you just planning to splice in the resistor box to the power feeds? What engine loom are you using? I found with the RB20 loom the injector layout was confusing (went past, to the water temp senders, then doubled back so it was like 6-5-4 .... 1-2-3)

Suggest having a really good think about how you want to do your wiring :thumbsup:

Once I got my loom apart I found it easier to consolidate it all somewhat, traced the injector power feed and the injector earths back and made a whole new injector harness with brand new plugs.

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