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Old 30th July 2012, 10:33 AM   #1 (permalink)
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Max you can grind an RB26 crank ?

dose anyone know what the standard journal sizes are for the main bearings and the connecting rods , I can`t find it anywhere . I have no manual and can`t find the specs on here or the NET . Gave up after all the searches started to repeat !!

Any help would be good as engine etc is at engineers and we need to know so we can determine if it has been ground to far !!

cheers

RB25 block to be fitted with RB26 crank - rods - pistons
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Old 30th July 2012, 11:20 AM   #2 (permalink)
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Sorry I can't be of much help with your query, but have you checked out the manual here:

Index of /dokument
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Old 30th July 2012, 11:36 AM   #3 (permalink)
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I think a big factor would be your intended power figures when the engine is finished as to if you should use a reground crank or not.
Standard crank jurnal diameter is 54.951mm-54.975mm
Rod journal diameter is 41.961mm - 41.974mm
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Old 30th July 2012, 11:40 AM   #4 (permalink)
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How far you can grind it is dictated by the bearings available to suit the under ground size.

A quick search shows ACL do 0.025, 0.25 and 0.5mm for conrod and main

I personally have had lots of issues with underground cranks in other race engines, I know also Abbey dont use them in there engine builds. Others will come on here and say its fine, but I personally wouldnt want to use one in an Rb26.
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Old 30th July 2012, 05:47 PM   #5 (permalink)
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Got the figures from engineer today

Main journal Std. is 2.164 ... I have 2.144 = -0.020

ConR journal Std. is 1.888 ... I have 1.868 = -0.020
These figure equate to 0.5 ground off


With HSK forged Pistons ..
Uprated Con-Rod`s
Steel turbo
550 injectors

I was looking for a minimum of 400BHP running up to!! 2BAR

Not sure what to do now as I`m not made of money and seems that everyone is on the make with my cash ! + I have no idea where I am going to get hte cash to find another crank - seen N1`s advertised in the USA for £585 but hen there is shipping and import tax ( UK customs bastards stitch you for tax ON THE SHIPPING COST TOO !!!! as well as the cost of item = THEN PARCEL FORCE STINGS YOU TO DELIVER AND HANDLE !! )

Are there any fake N1 cranks that I should look for ?

thanks for the replys .
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Old 6th August 2012, 10:59 AM   #6 (permalink)
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RB Motorsport will not use ground cranks either, they've tried them in the past & found they don't last.
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Old 6th August 2012, 11:33 AM   #7 (permalink)
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Dont waste your time and money on a reground crank.....once reground they loose there strength.

If its going back in a standard car and funds are stupidly tight then it would be considered at your own risk.....but regrinding a crank and then expecting it to run big power with no issues is a gamble.....and unfortunately will be an expensive one!

Just buy a good used crank and off you go.
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Old 6th August 2012, 11:59 AM   #8 (permalink)
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not the answers i wanted to hear , but , i am of the same way of thinking , CHEERS all
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Old 6th August 2012, 12:20 PM   #9 (permalink)
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The "N1" versions you've seen in America are actually std R33/34 cranks

Quote:
Originally Posted by rasored View Post
Got the figures from engineer today

Main journal Std. is 2.164 ... I have 2.144 = -0.020

ConR journal Std. is 1.888 ... I have 1.868 = -0.020
These figure equate to 0.5 ground off


With HSK forged Pistons ..
Uprated Con-Rod`s
Steel turbo
550 injectors

I was looking for a minimum of 400BHP running up to!! 2BAR

Not sure what to do now as I`m not made of money and seems that everyone is on the make with my cash ! + I have no idea where I am going to get hte cash to find another crank - seen N1`s advertised in the USA for £585 but hen there is shipping and import tax ( UK customs bastards stitch you for tax ON THE SHIPPING COST TOO !!!! as well as the cost of item = THEN PARCEL FORCE STINGS YOU TO DELIVER AND HANDLE !! )

Are there any fake N1 cranks that I should look for ?

thanks for the replys .
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Old 6th August 2012, 12:22 PM   #10 (permalink)
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Quote:
Originally Posted by davew View Post
The "N1" versions you've seen in America are actually std R33/34 cranks

Outch !
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Old 24th August 2012, 08:05 PM   #11 (permalink)
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Quote:
Originally Posted by David View Post
How far you can grind it is dictated by the bearings available to suit the under ground size.

A quick search shows ACL do 0.025, 0.25 and 0.5mm for conrod and main

I personally have had lots of issues with underground cranks in other race engines, I know also Abbey dont use them in there engine builds. Others will come on here and say its fine, but I personally wouldnt want to use one in an Rb26.
This is like efi systems.
Some spend money on motec or haltech.
I use a HKS F-con that cost me 300 bucks and I'm probably pushing more power.
It's knowledge.
Don't have it?
Buy new stuff.
Plain and simple.
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Old 25th August 2012, 11:00 AM   #12 (permalink)
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Quote:
Originally Posted by actionbstard View Post
This is like efi systems.
Some spend money on motec or haltech.
I use a HKS F-con that cost me 300 bucks and I'm probably pushing more power.
It's knowledge.
Don't have it?
Buy new stuff.
Plain and simple.
I did say others will disagree with me and it's quite possible your underground crank has survived a few dyno pulls, I'll only be impressed when you tell me you've done 10,000 miles or a couple of track days with no issues.

Loads of people on here have tried under grinding and a few hundred miles later have spun another big end.

If there is some "knowledge" that has meant your successful where many others have failed. Why not join the community spirit and share that knowledge?

My experience I am quite happy to share comes from under grinding mini cranks for use in all out race engines and a close friend who builds many of the leading engines in the locost series, both of us have tried many times and found underground cranks just are not robust.
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Old 25th August 2012, 08:51 PM   #13 (permalink)
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Wink

Bro my finger nails have grease.
I actually build this motors and have been since you registered to this forums.
My car has been running the same 0.5 as this guy for 4 yrs.
Now before you go out and tell me I pamper my car.
It's my daily driver.
So yes it has way more then 10k miles on it.
It's a lose engine and rev limiter is set for 9k.
Every one who knows me knows my car have seen it spit fire.
And it's not on a stand still only.
No I don't use synthetic oil nor do I use race gas.
My maps are for 26psi only and on 93 octane pump gas.
I don't have a .7 bar map nor anything below the 500 foot pounds of torque it's making since I built her.
Not a race car?
It's doesn't have a cage if that's what you mean?
But I'm a proud member of NASA and I run hpde open events all the time.
Like I said if you don't know you just don't.
Plain and simple.
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Old 26th August 2012, 09:25 AM   #14 (permalink)
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As the crankshaft comes ground in the 1st place, I think it's fair to assume that is it is done correctly, with all the stress relievers in place it will be fine.

Nissan sell -.5 bearings, so the induction hardness should be at least that deep otherwise would they sell them?

It's very easy to get 'grinding abuse' when grinding anything. The wrong wheels, dirty coolant, the incorrect coolant velocity(very common), poor setup, loose machine etc.
This can lead to surface cracking, loss of surface hardening, out of round, bent crankshaft, incorrect corner radius. Nissan ensure there cranks are the best possible, with lots of quality assurance. Does the bloke 'round the corner'.

The 50mm diameter is no magic number, just a common number for nissan. Reducing it by .5 doesn't suddenly ruin everything.

V8 drag engine use the smallest size bearing. They grind the crank down, chrome plate it, then grind the bearing surface on it. They go quite a bit under the original size. But, if done correctly, there is no ill effect.

From a material point of view, there is no issue re-grinding. But it must be done correctly. Some people would rather get a new crank because someone else has checked it, like the manufacturer.
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Old 26th August 2012, 10:24 AM   #15 (permalink)
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mine runs a .25 grind on the big ends std mains, done the ring in 9mins and three trackdays no issue, 600bhp @ the fly on twins.. its how they are ground thats important. mins on std prepped rods arp rod bolts, wiseco pistons with remachined rb26 std wrist pins and grex oil pump, std ported head and 2860,s no problem so far lol
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Old 26th August 2012, 03:06 PM   #16 (permalink)
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To me the hole N1 thing is a waste.
A in between for those on a budget.
You mod your standard crankshaft with a jun crank collar and you have your self a N1.Basically tho
Lol
There is no in between in what You most do.
Either full counter weight or oem.
I have used N1 oil pumps.
Same thing oem with a higher pressure spring.

So thank god for jun collar drives and reimax oil gears lol

But when most look into the engine bays of their competitors I look at the sump.
It's just a say
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Old 25th July 2013, 02:52 PM   #17 (permalink)
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interesting this - the crank going under my R32 has been ground - 0.025"

i find it difficult to believe that this is the sole factor for a crank dying a death... 0.025 THOUSANDS of an INCH?! out of a solid chunk of metal?

I would put money on it the ones that did fail will be down to someone having the "yay new engine build time to spank the RPM limit forever" mentality.
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Old 7th September 2013, 04:51 PM   #18 (permalink)
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I don't agree with the opinion that a ground crank is weak or going to give up in a few hundred K. First off I have a new R34 crank and my engine builder takes it and grinds it to first under right out of the box because he says the factory pins vary to much and he can get better , more consistent clearances if he does that. Second I bugged my engine due to my own lack of attention (ie. put oil in the engine cause they need a little of that) . I now have it ground to the max and 6,600 km on it and it has not given me any problems. And I flog the crap out of it every day with 643 hp at the wheels. Like the guys before said, it has to be done right and even when you pay someone to do it right sometimes it wasn't and you will never know until you get it running and flog it, then it breaks. You then assume it was the under ground crank but it was the job performed on it and the fitment. It could even be a flaw in the metal that was ok full sized but is now over stressed ground down. In which case it could have still let go when full sized, but just later down the road.
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Old 26th September 2013, 04:57 AM   #19 (permalink)
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Quote:
Originally Posted by Monster GT-R View Post
I don't agree with the opinion that a ground crank is weak or going to give up in a few hundred K. First off I have a new R34 crank and my engine builder takes it and grinds it to first under right out of the box because he says the factory pins vary to much and he can get better , more consistent clearances if he does that. .
So your engine builder doesnt know about or understand GRADED bearings?
Nissan has been using graded bearings for many years.
Is he going to re-nitride the journals?

Ive been down the "ground crank" path before..... it didnt end well
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Old 26th September 2013, 05:11 AM   #20 (permalink)
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Oh he knows of the graded bearings and we both think it is crap, CRAP and CRAP. That is just a way for allowing for production line errors and to compensate for them by haveing different sized bearing shells to fix the sloppy production line errors. Cut the crap out and just go to the first over and get some standard bearings from ACL or Clevite where they are all the same size. No fuss and done right the first time. Or until you forget to check the oil and still have the small pan, then expensive noise, ouch ! Don't get to fancy with the Nitriding. You only really want it in the radius of the pins. He builds 1300 hp RB30's and 1500 hp 2JZ's and more thousands of HP, dragster engines, I think he knows what he is doing.
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