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RB25/30 build using S1 RB30 - tensioner mounting point

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We've been running an RB25/30 R33 track car for 3-4 years, putting out around 300 RWKW. All was good, until it wasn't - a funny noise & a locked engine, and we found part of a rod on the track. The engine was built with stock rods & pistons.


Haven't pulled the motor out yet, and can't even see where the hole is, but it's clearly terminal. We've sourced another RB30 block, but couldn't see until we started stripping it that it doesn't have the flat surface on the front for the relocated tensioner. Apparenty very early RB30's were like this.

A bit of research shows that Platinum Racing Products sell a converter - it looks like a shaped plate that somehow attached to the front of the block to allow the tensioner to be fitted. I can't find anyone who's used one, nor much other info about them. Does anyone here know anything about this? The plate is https://platinumracingproducts.com/products/rb30-s1-block-converter

Not sure whether to continue with this block, or ditch it and find another one. It does have the turbo oil & water ports on th eexhaut side. The new build will include forged rods & pistons, to try and avoid a repeat problem.

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11 hours ago, GTSBoy said:

Would it not be possible to simply put the engine into a milling machine and duplicate the machined surface?

No, this area on the early blocks needs to have material added, not removed:


8 hours ago, Rusty Nuts said:

Page 7 of this PDF.

I can't see anything on page 7 that helps me - can you expand? To be clear, my problem is mounting the idler/tensioner where the top photo on page 7 shows "RB25 Idler". The pic above shows the same location without the idler. On later blocks this area is filled to the same level as the area on the left hand side of the pic.

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Personally I would get a the correct block rather than use the adaptor. You should only use adaptors if you really have to, and considering there are still blocks around, and you haven’t done any work to this one , makes sense to change now. 

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It'll be fine.  Get a small section milled out of the block and then fit a spacer in that milled section to achieve the desired height for the pulley to mount to. Mine is done this way. Can't remember if I've got photos anywhere....

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1 hour ago, Shoota_77 said:

Here we go, not a great photo but hopefully you can get the idea. 

Thanks for that - massive help. I assume the spacer is just sitting between the block & idler - not welded / JB welded or anything? 


1 hour ago, Ben C34 said:

Personally I would get a the correct block rather than use the adaptor

Yeah - I'm on the fence at the moment. There is a suggestion that the S1 block is somehow stronger, and I've got it. OTOH it was cheap, and maybe the newer block is the better option. I was hoping to find someone who has used the PRP plate - I can always ask them but will they tell me if it's not a good solution?

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3 hours ago, GeeDog said:

Thanks for that - massive help. I assume the spacer is just sitting between the block & idler - not welded / 

Yes mate, its just an alloy spacer. 

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On 10/19/2020 at 10:44 AM, Rusty Nuts said:

Or even easier

Thanks - lots of options there. I had considered the last option, and decided that if it was that easy everyone would be doing it, so didn't think anymore about it.

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