Rb Wrist/Gudgeon pin to conrod clearance

Hi all.

I have an rb25det that i am rebuilding with help from the courses on here .

I would appreciate advice on the wrist pin to rod end bush clearance .

The first rod I measured ,with a micrometre and dial bore gauge, I'm measuring a clearance of 0.007 to 0.010mm.(0.003mm out of round)

I can't find an rb25det workshop manual but the rb26 manual states 0.005 to 0.017mm clearance. Which i am inside of.

I have the head built up with shimless solid lifters as I want to increase the rpm limit and aiming for 600+ bhp.

The Rods are Bc6239.

The pistons are CP sc7305.

I see others setting this clearance to 1thou .

Is this what I should be aiming for?

Thanks Damien

Hi there,

You're right they do seem a touch on the tight side, maybe within spec for OEM but since you're planning on putting more pressure and heat through there you might want to run a little bit more towards 0.02-0.025mm.

Is there a local machine shop you can speak to confirm your thinking? I'd expect there would be a world of experienced rally engine builders in Ireland honing rod end bushes for various applications that would point you in the right direction.

Or have you been in contact with Brian Crower and CP or referenced the design tolerance in the spec sheets as a sanity check?

Not the most helpful I know but I'm sure another forum member with direct RB experience could share their thoughts

Hi Scott

I appreciate the reply.

You are correct, some great machine shops here , the 1 that i use is excellent but I haven't asked them yet.

I was just asking on here first to see what the majority choose.

The Rods pins and pistons are in tolerance of there spec sheets.

Any experienced Rb guys out there?