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Rb 25 Block Prep Before Assembly.

britz1

By britz1,
in Engines & Forced Induction

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britz1 Enthusiast

britz1

Posted
Posted

as title states guys

i have a RB25 block i have got back from the Machinest it has had all the usual rebuilt work done.

I am just after some info on cleaning up the casting dags ect inside the block. Whats the best way to aproach it?

and what should i not do ?

also i have an RB26 head and i am fitting it on the RB25 block. Using RB 25 crank and pistons. have other people done this sucessfully? how did the compression ratios turn out... as far as i calculated it was somwhere near 8.2 to 1.

cheers guys.

PS im using a 26 head because it was on my last motor and has port work and 272 10.5mm cams fitted. also the 25 block and crank was free.

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https://www.sau.com.au/forums/topic/405240-rb-25-block-prep-before-assembly/
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kitto Mentor

kitto

Posted
Posted

Why not use rb26 crank and pistons to get the proper compression ratio. 8.2:1 is a tad low.

Rb25 and rb26 rods are the same, although rb26 are stronger.

Don't bother cleaning up any casting marks inside the block. Make sure all the oil and water galleries are free of swarf.

Inspect and replace welsh plugs.

What machine work did you have done?

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Rb25 and rb26 rods are the same, although rb26 are stronger.

How can they be the same if the other is stronger? :P

Why not use rb26 crank and pistons to get the proper compression ratio. 8.2:1 is a tad low.

Agreed on the comp ration. 8.2 is quite low nowadays considering the quality of fuels available compared to 10 years ago.

Then add in 272 cams and depending on what port work, it'll be pretty unimpressive anywhere that isn't smack on the boost happy area.

Can use a RB25 crank though, and 26 rods. Not a major issue, just need pistons to suit then.

britz1 Enthusiast

britz1

Posted
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Posted

okies cheers guys i have removed the plugs. and i will fit new ones. i have oil restrictors aswell and a couple of plugs for the vct squirter and one of the oil squirters.

What machine work did you have done?

I got the block bored and torqu plate honed to piston specs

Line honed with cradle torqued with arp mains

Crank polished ballenced with clutch harmonic ballencer and flywheel. also taped the oil bungs in the crank and tapered the oil outlets on the mains and big ends journals.

The machine shop rebuilt the head with new valves jun valve springs and bronze valve guides and skimed the deck.

Machine shop also checked the CP pistons and Argo rods for weight and tollerences ect.

I do need a bit of help in reguards to my compression ratio. I dont understand how to work out the piston height above the deck or the CCs of the piston dome.

Please refer to the spec sheet supplied.

Stats of motor

Combustion Chainbor 69cc (Stock RB26)

RB25 Stroke 71.7mm (stock)

Bore 3.406in

Head Gasket bore 87mm

Head gasket 1.2mm Tomei

6itlr.jpg

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