Rb25 With Rb26 Internals

[B0oStEr]

I'm planning a rebuild of my spare r32 rb25de motor using an rb26 crank, rods and pistons.

I've never had either of these motors apart so it's unfamiliar territory.

I just had a look at the ACL race bearing applications.

The rb26 mains are different to those listed for the rb25 de/t

Apparently the thrust bearing goes in main bearing position no.6 in the rb25 and no.4 in the rb26.

Is the rb25 block and cradle machined to accept the thrust bearing in both positions to suit either crank?

Should I use rb25 or rb26 bearings?

[BezerkR32]

If you are miss matching main caps you will need to get the block line bored and then have bearings to suit.

I'm planning a rebuild of my spare r32 rb25de motor using an rb26 crank and rods.

I've never had either of these motors apart so it's unfamiliar territory.

I just had a look at the ACL race bearing applications.

The rb26 mains are different to those listed for the rb25 de/t

Apart from the extra oil holes in the rb26 main shells they are 20mm wide compared to 19.12mm wide for the rb25.

The bit I'm less sure about is the flange bearing that has the thrust surface.

Apparently it goes in main bearing position no.6 in the rb25 and no.4 in the rb26.

The flange bearing is 26.95mm wide for the rb25 and 27mm wide for the rb26.

To give the correct crank end float it would seem I need to use rb26 mains or doesn't 0.05mm additional end float matter.

Will rb26 mains fit straight into the rb25 block and can the flange bearing fit in position no.4 to suit the rb26 crank?

[B0oStEr]

I'm using the original rb25 cradle so no swapping.

According to previous searches I've done an rb26 crank will bolt straight into an rb25 block so this shouldn't be a major issue.

I had assumed all rb motors had the thrust bearing in position 4

I hope you can just swap the flanged main bearing from pos. 6 to pos. 4

to suit the rb26 crank.

BezerkR32 Shaun rang me. Said the crank looks great Thanks

[BezerkR32]

just make sure the sides of the cap are machined to accept the thrust bearing.

I'm using the original rb25 cradle so no swapping.

According to previous searches I've done an rb26 crank will bolt straight into an rb25 block so this shouldn't be a major issue.

I had assumed all rb motors had the thrust bearing in position 4

I hope you can just swap the flanged main bearing from pos. 6 to pos. 4

to suit the rb26 crank.

BezerkR32 Shaun rang me. Said the crank looks great Thanks

[B0oStEr]

Hey I know some of you guys have done this.

I'm just trying to get the right bits together before I pull my motor down.

[NutR33]

i have an r33 gtst rb25det with an rb 26 crank and rods in it. the crank drops straight in as do the rods and pistons. i clearanced the oil squirter cut outs in the pistons a touch more as the pistons were coming very close to the squirters when i had venolia pistons, but i dont know about the std rb26 pistons.

The thrust bearing is in number 4 main bearing on the rb25det block, i can only assume that it is in the same spot on the rb25de block.

Apart from the crank, rods, pistons, you will also need the harmonic balancer bolt and washer for the rb26 crank as it has a different thread, the rb25 balancer will also fit onto the rb26 crank.

PM me if you need any other info,

NutR33

[Mik]

i have an r33 gtst rb25det with an rb 26 crank and rods in it. the crank drops straight in as do the rods and pistons. i clearanced the oil squirter cut outs in the pistons a touch more as the pistons were coming very close to the squirters when i had venolia pistons, but i dont know about the std rb26 pistons.

The thrust bearing is in number 4 main bearing on the rb25det block, i can only assume that it is in the same spot on the rb25de block.

Apart from the crank, rods, pistons, you will also need the harmonic balancer bolt and washer for the rb26 crank as it has a different thread, the rb25 balancer will also fit onto the rb26 crank.

PM me if you need any other info,

NutR33

RB26 runs 20mm wide main shells and the RB25 runs 3/4 inch. You should be able to use either with the 26 crank.

[B0oStEr]

i have an r33 gtst rb25det with an rb 26 crank and rods in it. the crank drops straight in as do the rods and pistons. i clearanced the oil squirter cut outs in the pistons a touch more as the pistons were coming very close to the squirters when i had venolia pistons, but i dont know about the std rb26 pistons.

The thrust bearing is in number 4 main bearing on the rb25det block, i can only assume that it is in the same spot on the rb25de block.

Apart from the crank, rods, pistons, you will also need the harmonic balancer bolt and washer for the rb26 crank as it has a different thread, the rb25 balancer will also fit onto the rb26 crank.

PM me if you need any other info,

NutR33

I rechecked the acl site and they list the rb25de/det thrust bearing at pos 7 not at 6 as I thought but as you say it's in pos. 4 so I've got nothing to worry about.

The cranks off getting an oil pump collar fitted so I'll have to check the balancer bolt thread when it comes back.

Is there anything special about the bolt eg. a step or nonstandard thread or could I just get a high tensile bolt from a bolt shop?

The balancer that was on the rb25 only has a three rib PS pulley and I need a four rib pulley for my r32 hicas so I hope the rb20 balancer fits.

[NutR33]

the bolt for the rb26 crank is a different thread i believe, i brought a new bolt and washer from nissan

RB26 crankshaft pulley bolt NI-12309-05U00 $7.64

RB26 crankshaft pulley bolt washer NI-12308-05U00 $11.56

both these prices were list price 18 months ago, may have changed slightly.

you will have to try the r32 pulley but my bet is that it will fit as most parts are interchangable.

PS, if you are using the rb26 crank, bolt and washer i strongly surgest that you use the torque setting for the rb26 balancer bolt which is 446 - 466Nm, thats DAM tight, trust me. for that tension you will most likely have to use a special torque wrench, i borrowed a 5ft long one from a truck place and strugled with 2 people to do it up!!!

Have Fun

NutR33

[stav]

Does using the RB26 internals in the RB25 give you the same displacement as an RB26 ? What sort of compression do you end up with as the RB26 has a smaller dome than the 26 ?

[B0oStEr]

Does using the RB26 internals in the RB25 give you the same displacement as an RB26 ? What sort of compression do you end up with as the RB26 has a smaller dome than the 26 ?

Yes 2568cc as both engines have an 86mm bore.

Sorry which head has the smaller dome/chamber?

As far as I know they have the same volume but I've only been told.

I'll have to check it out for myself. On my "to do" list.

I'm hoping to get a CR of 8.5:1

Anyone care to comment on chamber volume r32 rb25de head vs rb26?

NutR33

How did you hold the crank still to get it that tight?

[B0oStEr]

I just did some checking in the rb30/25 thread.

SK states rb26 and rb25de heads have the same size combustion chambers.

They each vary according to casting differences somewhere between 62cc and 64cc.

[cameron]

Used rb25 crank with rb26 rods and rb25 piston in rb25 block

[NutR33]

I waited until the motor was in the car, luckly it was a manual, put it in 4th gear with someone in the car with their foot on the brake.

I quess there would be a tool that would lock the crank in place by holding the flywheel/flex place.

NutR33

[Drift_Mulisha]

Im also interested in buildng up an RB25DE Motor with GTR Crank & rods & some 87mm forged pistons, is there any isses with block height between rb25 & 26? ie: will fitting the gtr crank/rods raise the compression from the pistons coming further up in the bores? does anyone know what thickness head gasket to use to achieve a 9.0 comp ratio? how much more capacity will the 87mm pistons give, is that enough of an increase to call it a 2.7?? or just a "big" 2.6 if that makes any sense.

Cheers.

Edited June 26, 2006 by Drift_Mulisha

[MR331307]

i got a photo of the thrush washer installed on the Rb25 block while i was building a customers motor,

If you need it PM me your email

[B0oStEr]

Im also interested in buildng up an RB25DE Motor with GTR Crank & rods & some 87mm forged pistons, is there any isses with block height between rb25 & 26? ie: will fitting the gtr crank/rods raise the compression from the pistons coming further up in the bores? does anyone know what thickness head gasket to use to achieve a 9.0 comp ratio? how much more capacity will the 87mm pistons give, is that enough of an increase to call it a 2.7?? or just a "big" 2.6 if that makes any sense.

Cheers.

Rb26 and RB25 have the same deck height so no problem.

The gudgeon pin is higher in the rb26 piston to accommodate the longer stroke.

Most forged RB26 pistons seem to aim for about 8.5:1 CR the same as stock.

To get 9:1 CR you will need to deck the block to run minimal piston to head clearance (0.75mm) with a thin gasket or get 9:1 pistons made.

The stock RB26 is 2568cc and an 87mm bore gives 2628cc 86.5 mm gives 2598ccRB26

[Drift_Mulisha]

sweet, cheers man. would going to an 87.5mm bore be getting closer to 2.7? & would a 1.5mm oversize bore be considered dangerous? i noticed most rebuilds seem to be +1mm and the most extreme i have seen is +2mm on an australian gtr.

[B0oStEr]

sweet, cheers man. would going to an 87.5mm bore be getting closer to 2.7? & would a 1.5mm oversize bore be considered dangerous? i noticed most rebuilds seem to be +1mm and the most extreme i have seen is +2mm on an australian gtr.

A lot of people say 2mm o/s is risky in the std block especially for big power.

Without working it out I'd say 87.5mm would give you around 2660cc and 88mm almost 2700cc.

There's an 88mm kit on ebay selling as a 2.7L kit.

[Darius]

A lot of people say 2mm o/s is risky in the std block especially for big power.

Without working it out I'd say 87.5mm would give you around 2660cc and 88mm almost 2700cc.

There's an 88mm kit on ebay selling as a 2.7L kit.

1) I wouldn't go over 1mm overbore because if you blow your motor and need to overbore the cylinders, there's 1mm of material to spare. An extra mm of diameter is not going to give you noticibly increased power anyways. I would err on the side of safety.

2) As far as swapping RB26 internals into an RB25DET is concerned, what brand of bearings are recommended? Also, shouldn't the machine shop measure the crank and rods and determine what bearing thickness is needed from that?

3) I am installing Tomei valve springs with new HKS cams (256 x 8.8mm) and RB26 rods and pistons. What is a reasonable increase in redline with this setup?