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fredeuce

PRP main bearing cradle

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Has anyone had experience in installing one of these ?

https://platinumracingproducts.com/pages/platinum-racing-nissan-rb26-wet-and-dry-sump-engine-cradle

I am curious to learn of other peoples experience with them and their approach to mating up the gearbox and the four lower bolt holes which are now 12mm south of their original location on the engine.

My concern is that welding tabs on the bottom of the gearbox means anytime you want to change the gearbox for any reason then you have to go through that drama of modifying the gearbox.

My thinking is to make up an adapter plate 8mm thick and use 10mm countersunk bolts and bolt that adapter to the gearbox. The adapter  would be patterned from the sandwich plate but have and  have a 12mm longer bottom section to capture the new position of the holes in the sump. It would also have countersunk bolt pointing forward to go through the sump.

The gearbox will now be 8 mm further back in the car compared to the usual installed position.

Some issues:

1. Will the tailshaft accommodate this reduction in length on the CV joints? My observation is that it should be able to accommodate it.

2. The front tailshaft without any modifications appears to result in the shaft being withdrawn 8mm from the transfercase. That may result in the seal on the shaft not properly functioning. An 8mm spacer on the front diff flange would be appropriate.

3. Clutch fork needs to be spaced 8mm forward to restore correct clutch fork orientation.

4. The spigot on the front of the gearbox appears to have a wide contact surface so appears that it would accommodate running 8mm further back.

5. In a similar way the spline on the front shaft will run 8mm further back on the hub of the clutch plate. The clutch is a Nismo twin plate . The spline on the gearbox appear to protrude the front of the hub by about 5mm so would not fully engage the hub by about 3mm. Not ideal but should work.

6. Will there be sufficient clearance to the firewall?

7.Will the gearbox crossmember accommodate  the gearbox being set back 8mm with some slotting of the holes?

Look forward to your experiences with the PRP installation.

 

 

 

 

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Cut the tabs off the bottoms of the sump and weld them back on in the correct position 

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Waaaaay over complicated bloke....

 

Most people just go without the bottom bolts. I've drilled new holes and will probably run 3 lower bolts.

If it doesn't work I'm not fazed. The rest of the bolts will be more than enough. There really isn't much torque applied between the engine and the transmission.  

Just bolt her up and sent it!

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Like Ewan said.

The same practical issue exists in 4wd RB30 conversions because the sump adapter means the sump's bolt holes are 8-10mm off from the gearbox holes

On my original rb30 I got the sump rewelded (tricky as it is cast). Then i replaced the sump as the quick way to deal with a diff failure (apparently diffs need oil, who knew, not the workshop....) Current setup only uses the 4 engine block bolts and with 400awkw the gearbox hasn't fallen off yet (no promise it won't tomorrow though!)

BTW, noting my experience is not with 1000hp drag cars....is an additional brace necessary or is this just non-externally-visible ricing your car? rbs are unusual (but not unique) in that they have a full cast girdle from factory holding the main bearing caps in place. dinosaurs like most v8s (which can also make big power), still run separate main caps and just put 4 or 6 bolts into each instead. Is there are proven issue where the 2 bolt per bearing girdle in RBs have issues with moving in big power applications? 

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13 hours ago, Duncan said:

Like Ewan said.

The same practical issue exists in 4wd RB30 conversions because the sump adapter means the sump's bolt holes are 8-10mm off from the gearbox holes

On my original rb30 I got the sump rewelded (tricky as it is cast). Then i replaced the sump as the quick way to deal with a diff failure (apparently diffs need oil, who knew, not the workshop....) Current setup only uses the 4 engine block bolts and with 400awkw the gearbox hasn't fallen off yet (no promise it won't tomorrow though!)

BTW, noting my experience is not with 1000hp drag cars....is an additional brace necessary or is this just non-externally-visible ricing your car? rbs are unusual (but not unique) in that they have a full cast girdle from factory holding the main bearing caps in place. dinosaurs like most v8s (which can also make big power), still run separate main caps and just put 4 or 6 bolts into each instead. Is there are proven issue where the 2 bolt per bearing girdle in RBs have issues with moving in big power applications? 

I agree Duncan. The RB26 has a strong as fk main cradle. I don't buy into the necessity of really needing a main cradle block brace unless your goal is somewhere north of 1500hp, and therefore completely unnecessary for most applications.

Japs been running low 9s and 1200hp well before this was even considered a thing in the 90s. The cars that have pioneered this are the CRD and Maatooks 6 sec 1/4 cars before going billet blocks. Ask Rob from RIPS in NZ if he is using one ? I am pretty sure that's a no.

Not saying they aren't good or have their place, just think the necessity for one is overhyped.

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After reconsidering the approach to this issue as the PRP plate is already installed on the engine I went ahead and re-drilled the relevant four holes in the sump. Not straight forward with the sump installed but managed to get a reasonable result . My general concern about this is that the span created between the front engine mounts and the gearbox mount is considerable. With only half the bolts in place that is going to load up the top part of the bellhousing and make it more vulnerable to cracking. 

Some pictures of the result. 

IMG_0107.JPG

IMG_0109.JPG

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Good job, nice and neat.  But again, you're reading more into the strength requirement than you need to.  All the bolts have to do is hold the gearbox parallel with the engine.  The amount of twisting torque is negligible.  The dowels and 2 bolts would handle that.  The horizontal force again as per rotational force is minimal.

Find me an example of where a transmission has snapped off the back of an engine and I'll reconsider my opinion that you're freaking out over a complete non-issue!

Send it!

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