Need A Little Help

[nissan200sx.dk]

Hi all.

Its these ACL bearings I have looked at:

http://www.aclperformance.com.au/NissanRB30ETBearings.htm The 0.025" oversize. (0.635mm)

I am bit confused with this so hoping for a clear answer. I am building a RB25/30DET engine. The crank has 0.045mm run-out. Measured with front and rear bearing mounted and then measuring on the middle mainbearing on crank. So i want to get it regrounded. But im confused on how much to take off the crank and how much to take of the blocks mains.. If I understand this correct I can take 0.06mm of the crank so there is no run-out, and then grind the rest down to same size. 54.90mm on crank on all mains, and all main will then run with each other. A straight crank. This wont take that much material off, and I will hopefully still have a layer of nitrided on the crank. Then I still have 0.575 back from the 0.635 oversize bearings. The rest will then be taken from the blocks mains. I then get the blocks main bearings line-honed up to to 59.225mm, 0.575mm over the std size of the block mains.. Then in total its the 0.635mm these bearings are oversize from were I am right now in my actual parts measurements.

This is my actual measurements as the parts are right now down below. Front bearing first.

Main Bearing number: 1 2 3 4 5 6 7

54.945 54.940 54.955 54.960 54.960 54.960 54.960

Block main bearing: 1 2 3 4 5 6 7

58.655 58.655 58.656 58.660 58.650 58.660 58.655

Should I split the total oversize, so there is taken half of the 0.635mm off on crank, and the other half on block, or is it okay to split it up as have been thinking off?

I hope this is explained properly by me here. Im not that good in english. Hope someone will take the time to help me here, as I have never done this before using oversize bearings and getting a crank reground.

The actual machining will be done by a company here in Denmark, but need to know what measurements it should be. And also want to understand it better.

Thank you very much! Love this site. Its my bibel. hehe

[SteveL]

The crank has 0.045mm run-out.

I don't have any data for RB30, but for an RB26 the max specified run-out is 0.05mm (0.002"). I'd say RB30 is likely to be the same, so you are within acceptable limits for factory specs (a full race engine should actually have these specs 'tightened' a little). I'm assuming here you've (correctly) taken half of the full needle deflection on your dial gauge as the run-out measurement for your crank.....

Also, you have a fundamental mis-understanding of the relationship between run-out and main bearing sizes (hint - think about what would happen to run-out if you grind the same amount of each main journal). Suffice it to say that run-out is a measure of how bent a crank is. If it's outside spec you either toss it and get another one, or get it straightened by a specialist. Once it's straightened (there will always be some run-out), you measure the journals and determine the mains size required (ignoring the run-out). Actually I'd just get the specialist to do the whole lot.

Stock Nissan cranks are not nitrided.

Edited May 20, 2009 by SteveL

[nissan200sx.dk]

It is a specialist that will do the job. I am just trying to figure it all out.

There will not be taken the same amout of each journal, but they will be grinded to the same size.

How about my "calculation" of bearings, og how much there should be taken of in total.? Am I way off there too?

Thanks for the reply

[SteveL]

In the interest of international co-operation I dug out my old RB30 specs manual. It turns out that the acceptable run-out for an RB30 crank is 0.1mm (0.004"), so your crank is fine.

In terms of mains sizing, Nissan specify a main bearing clearance of 0.020-0.047mm (0.0008-0.0019") with a max wear limit of 0.090mm (0.0035").

Unless you have access to accurate bore gauges, I'd suggest you take the block and crank to a engine machining specialist, along with the under-size bearings you are planning to use. They will (or should) assemble the bearings to the block with the caps torqued up to spec, and then accurately measure the internal diameter of each main bearing. Once they have also accurately measured the crank journals, it's a simple calculation to work out how much needs to be ground from each journal to achieve the correct running clearance (see above).

Ditto for the con-rod bearings, although the clearance in that case is 0.011-0.035mm (0.0004-0.0014") with the wear limit the same as the mains.

[nissan200sx.dk]

The thing is, I want to take as little as possible of the crank, only taking off so its straight, and then the rest in the block. Is this possible? Or is all basicly taken from journals to fit oversize bearings? I dont know how far in the material is hardend on crank journals, and want to keep the hardended surface.

I am not building a std RB30, so I really want the crank to be as straight as possible. Im hoping for around 800hp at engine when Im done.

I have measured with precise tools. (0.001mm accuracy @ 20 degress, freshly calibrated from work)

By the way, the run-out i said earlier in my post was total gauge needle deflection. Which was 0.045mm. So my run-out is only half of that?

Thanks alot for your answer sir.

Regards

Ronni

[nissan200sx.dk]

My concern is now. How far in is the crank journals hardended??

Have had a long talk with the company that will be doing the job. They explained. hehe. Learned something today.

They will mount the bearings in the block, measure, and grind of the crank journals so there is the correct tolerance. Only "problem" is my concern if it will take of the hardend part of the journals.

[SteveL]

The thing is, I want to take as little as possible of the crank, only taking off so its straight, and then the rest in the block. Is this possible? Or is all basicly taken from journals to fit oversize bearings? I dont know how far in the material is hardend on crank journals, and want to keep the hardended surface.

There's still a misunderstanding here.....a crank isn't straightened by grinding the journals. It's straightened by, quite literally, belting the crap out of it using a heavy hammer and a (very) blunt chisel-like tool at specific locations. It sounds crude....and it is....but it still has to be done by a specialist, with a lot of experience. Once the crank is straight, the journals are ground to size. If the crank journals are close to standard size and not badly scored or out-of-round then it should not be necessary to go further than one size under standard.

These cranks are induction hardened and the case is quite deep. Assuming the worst case and you have go to the second undersize, there still will be no problem in terms of case depth.

Actually, if this is to be a high performance engine you should use a new crank......the journal grinding process actually reduces the fatigue life of the crank by about 50% (generally speaking)......but don't get too concerned, these components have a high design safety factor.

In terms of the block mains tunnel, for a performance engine these should be checked for alignment, size and ovality.

I am not building a std RB30, so I really want the crank to be as straight as possible. Im hoping for around 800hp at engine when Im done.

All of what I have described is pretty much standard procedure for a performance engine and, really, an engine specialist shouldn't need to be told.

By the way, the run-out i said earlier in my post was total gauge needle deflection. Which was 0.045mm. So my run-out is only half of that?

Run-out is half of the full scale deflection taken at the centre main. Yours is pretty good in that case.

[nissan200sx.dk]

Thanks alot for your help and replys. Have ordered the bearings .025 undersize. And will take the block, crank bearings to the company than will peforms the grinding.

I just wanted to understand the part when grinding crank / undersize bearings.

I have built a few engines, but have never tryed to get a crank regrounded, and using undersize bearings. The engines I have built I could use std size nissan bearings. But this one I cant. Have to learn somehow.

When the crank is reground, should the R2 fillet be moved also?

[Duncan]

excellent explaination, thanks Steve

[SteveL]

When the crank is reground, should the R2 fillet be moved also?

Not sure what you mean by 'move'.....RB crank journals have generous radii and should be left as they are. Ideally the radii should be polished (not linished, but actually polished), however most places don't have the capability. Polishing reduces the potential for crack initiation.

For a performance engine there are a couple of other things that should be done IMHO:

- the crank should be properly crack tested. When I say 'properly' I mean by an organisation certified by a National authority for the purpose. In Australia the recognised authority is the Australian Institute for Non-destructive Testing (AINDT) or, for aviation, (non-military) the Civil Aviation Safety Authority (CASA). [for the sake of completeness, in terms of military NDT, the controlling authority is NDTSL at Amberley AFB in Qld]. Most automotive engine specialist in Australia will do crack testing, but generally aren't certified for the purpose, which means that they basically just grab a can of red dye penetrant and go from there. OTOH, anyone undertaking work on aviation components is required to be certified and regularly checked for compliance inc there equipment. That's why I recommend anyone having critical engine components inspected should have the work done by an aviation NDT specialist (I use a firm out at Moorabbin airport in Melbourne; places like Bankstown in Sydney would have similar). Components like crankshafts and rods should be checked using a magnetic particle bench (MPI in NDT speak). Even new components should be inspected, AFAIC. Unfortunately I can't help with contacts in Denmark.

- When the block mains are being measured as I've described above, that should be done using all the components you plan to use at final assembly. That is, the caps should be torqued to spec using the mains bolts or studs you are going to use. Same for the rods. Again, your engine builder should be aware.

Personally I would also consider having the crank nitrided, but not essential. On the plus side, nitriding assists with wear and crack initiation resistance, but the downside is that it inevitably introduces distoration (bending) due to the combination of high surface stresses and the complex crankshaft shape, which can be difficult and expensive to remove (it's a common process, I know, but I'm just saying it can be expensive to get it right.....the last crank I had done cost $800 just for the nitriding and that was fair few years ago now).

[nissan200sx.dk]

When the journal is regrounded, its gets smaller, and the R2 radi goes from journal and up the side. If the diameter gets smaller the radi doesnt go from journal and up, because journal has been grinded smaller... hope you understand, im not that good in english.

The place I work do magnaflux crack testing. Which they are certified to do.. Have you heard of that?

Thanks alot for your replys! Has helped me alot!

[SteveL]

When the journal is regrounded, its gets smaller, and the R2 radi goes from journal and up the side. If the diameter gets smaller the radi doesnt go from journal and up, because journal has been grinded smaller... hope you understand, im not that good in english.

From memory, the design of the journal on RB's is such that the radius is maintained during grinding (for factory undersize bearings). In any event, the amount removed is relatively small but if your concerned you should specify that the original radius is maintained.

The place I work do magnaflux crack testing. Which they are certified to do.. Have you heard of that?

Magnaflux is actually a proprietary name of a company that manufactures NDT equipment, which also includes mag particle. Experience is a big part of successful NDI, so if your company has done lot's of crankshafts that's fine, otherwise I'd find someone that has.