crank woes and bearings help - kind of urgent

[stumo]

i do have one questions.. if i have clearances that are too large due to crank and bearing wear, then the crank is ground back and undersized bearings are used of the same undersizing as the grind, before fitting i should be using plastigauge to check the clearances.. what happens if they are not right?
if it's too tight (not likley) i can have a bit more ground but if it's a bit loose then i'm stuffed as the bearings don't get any thicker.

Yes you should plastiguage the ground crank and undersize bearings. If the clearance is too big then unless there is another (bigger) undersize bearing the crank is scrap.

For the bigend bearings Nissan do 3 sizes of undersize bearings, 0.08, 0.12 and 0.25
For the mains there's only one undersize bearing, 0.25
There is only one std size of thrust bearings.

or am i being a numpty and because they are new bearings and a properly ground and polished crank, it's all going to be super tight and bang on anyway?

If the engineer is a good one then that should be the case but he might bot be..........

 

[red reading]

thanks danny.
i am well over panicking about all this but as it's my first go at it i like to work things out 100% before i do something.
been speaking to a number of people today who have proven to me that many a ground crank has gone on to do great things in the gtir engine. i just need to speak to my engineer about it and then i think i'll just go for it.

i do have one questions.. if i have clearances that are too large due to crank and bearing wear, then the crank is ground back and undersized bearings are used of the same undersizing as the grind, before fitting i should be using plastigauge to check the clearances.. what happens if they are not right?
if it's too tight (not likley) i can have a bit more ground but if it's a bit loose then i'm stuffed as the bearings don't get any thicker.

or am i being a numpty and because they are new bearings and a properly ground and polished crank, it's all going to be super tight and bang on anyway?

To get them absolutley spot on you can either buy nissan graded shell's of differant sizes (as they are done from the factory) to get the correct clearence, or if you use acl bearings or similar buy multiple sets and mix and match as i do till it's right.

 

[red reading]

stumo beat me to it and was more precise with his answer

 

[PobodY]

gas nitride hardening is probably a waste of time.
he did day that other processes maybe useful for hardening the surface and are much more cost effective also.

It's probably plasma nitriding; that works best on steels, whereas the gas nitriding needs a clean oil-free surface that the ammonia can react with an permeate. - Can you put nitrogen into a plasma cutter, then use it to work-harden a steel; that's effectively plasma nitriding it?

I doubt they did it in a salt bath because they'd have tons of toxic salts to dispose of by now if that was the case.

Plasma nitriding followed by sputtering (or similar PVD) can give you a hardened surface with increased corrosion resistance.

 

[mikeyp]

they do it in a pressurised furnace and contol the temp and gas content. the nitrogen in the gas reacts with metals in the alloy that makes up the part and slowly this process hardens the metal to a depth of .3-.5mm depending on exact alloys and time in the furnace. at least 30 hours are needed apprarently.
there are other types of nitriding that are less effective apparently.. i'm in no way an expert, just going on what i have learnt from their websites and from a few phone calls.

i think i'm going to drop the idea anyway. a few people have proven to me that a .25 ground crank can take some real perfomance so long as the oil system is up to the job and the clearances are set correctly at the build stage.
i still need to ok my engineer grinding my crank and with any luck it'll come good at -.25mm. if not then i'm still in the hunt for a new crank anyway. providing my engineer isn't still off work on monday, i should have it ground by the end of monday and i'll know if my crank is good to go or not.

are the nissan undersized bearings also graded like the standard size ones? i can't find part numbers for different grades of undersized nissan bearings. think i'll prob just go down the multiple set of bearings route to get the clearances as close to perfect as i can. not a cheap way to go though.

 

[PobodY]

I think plasma nitriding is more effective than cooking the parts in ammonia; you get a proper ionised stream and can get the ferrous components to convert whilst leaving the chromium etc un-touched. - That's how they get the hardening whilst maintaining corrosion resistance.
Plus the plasma is not effected by part cleanliness (because it will just burn the oils off), nor does it cause any distortion and works best on a ground surface.

I'd be really interested to know if you do your own nitriding with a nitrogen plasma; I don't know enough about the technique. All I know about is plasma-source spectroscopy.

 

[vss irvine]

 

[mikeyp]

been doing more reading and plasma seems to be the way people are starting to go, although some of the better gas people have solved most of the problems it used to have 100 years ago.
aircraft and race car cranks are normally done with gas but some manufacturers are switching to plasma now. no idea on the cost difference.

meh i'm prob not going to go for either process now as it seems to be proven that our cranks can take a grind a still perform. if i can keep costs down then i'd like to as these sorts of engine woes never come at a good time do they?

does anyone know the alloy makeup of our cranks?

 

[astarozna]

i have .25 crank in my car. Using acl bearings calico coated. About 1000klm, runing 300+ bhp

 

[mikeyp]

great, thanks. all helping my confidence.

just spoke to my engineer who is now back at work, he going to get grinding as soon as he clears the backlog. he did say to hold fire on buying bearings till after the grind, just in case. knowing how this project has gone so far, i can see it needed more than .25 which would make it scrap.

finger crossed :?

 

[mikeyp]

right well sorry to drag all this up again but here goes..

i don't believe this, i had a feeling this is exactly what would happen and it apears i was right

the original plastigauge readings for the main bearings were this...
this was with the old very worn bearings and worn crank.

1: 0.056mm
2: 0.050mm
3: 0.045mm
4: 0.040mm
5: 0.045mm

with my brand new acl bearings installed (dry so as not to squew the clearances) and a properly ground crank done by southern rebore who came highly recommended. just stuck some more plastigauge in the bearings to make sure all is fine before i finish the build. these were the results.

1: 0.050mm
2: 0.050mm
3: 0.045mm
4: 0.040mm
5: 0.045mm

almost identical to the readings i got with shot wornout bearings and a crank that badly needed a grind. so shave off 0.25mm off the crank and stick 0.25mm thicker bearings in and the gap remains the same.

normally i really lose my rag with stuff like this when it goes wrong but i've just died a little bit inside and given up caring now.

what's going on?
have i done something wrong (i wouldn't be surprised) that has caused me to get these results?
could my torque wrench be under torqing the bolts?

i'll get some pics up in a second but there isn't much to see other than not very squashed plastigauge on a crankshaft.

please help i really need to finish this car by the end of the week and it looks like it's not possible at the moment.
thanks in advance.

 

[stumo]

torque wrenches do go "off" but unless it's massively out you should be crushing the bearings enough to test.

My manuals are at work to find out the correct gaps...

here's some ideas...it's late n i'm tired

the bearings have been missboxed/sized
the crank has been ground to the wrong size
err

i did find with my brand new crank that the std ACL bearings gave a much bigger gap than using the correctly sized OEM (Nissan) bearings, but as there's only 1 std size v several Nissan ones that's no surprise.

 

[pulsarboby]

not having a great deal of luck are you mikey.....

bit crude but try putting a set of vernier calipers on the crank to see if the journals are differing in size....it sounds to me as though hes just took the same amount off each journal
im no engineer but i would have thought that when a cranks ground if done properly all clearances should be exactly the same as it needs to be 0.25 under stock size and the lathe should be set to differences in journal wear in which case some journals may need .18 others may require more or less to make them all the same.

the ones i would be more concerned about is the bigend clearances youll probably get away with the mains

 

[mikeyp]

yeah i have a set of digital calipers so i'll measure the bearings and crank with that and see if i get the same results.


one thought that i had was if the crank had been ground before and standard bearings had been installed, making me think that it hadn't been ground because the bearings in there were just standard sized nissan ones.

i'll plastigauge the big ends too and also use the calipers and see what results i get.
the main problem i have is i'm fast running out of time and funds to keep replacing parts and fault fixing :doh:

cheers guys

 

[stumo]

yeah i have a set of digital calipers so i'll measure the bearings and crank with that and see if i get the same results.


one thought that i had was if the crank had been ground before and standard bearings had been installed, making me think that it hadn't been ground because the bearings in there were just standard sized nissan ones.

i'll plastigauge the big ends too and also use the calipers and see what results i get.
the main problem i have is i'm fast running out of time and funds to keep replacing parts and fault fixing :doh:

cheers guys

The steel backplates on the Nissan bearings all seem have the same "part number" on them so don't go thinking they're std by trying to crossreference back to the FAST disc.

if you had std bearings and a ground crank it'd never make oil pressure and knock like feck.

 

[mikeyp]

 

[mikeyp]

well checked the big ends and they were all exactly the same as each other at around 0.045mm (hard to tell with plasigauge as they were wider than the 0.050mm measurement on the size chart but not as wide as the 0.038mm mark which is the next one.)

so they seem to be just within spec and all the same as each other. the mains are over spec but just below or on the limit for clearance.

is it worth risking it and building this up or am i only setting myself up for another engine out adventure a few hunderd miles down the road?

 

[mikeyp]

well i've just had a got at measuring the crank.

main journals
1: 54.69
2: 54.69
3: 54.67
4: 54.67
5: 54.66

the results vary by 0.03mm but the max clearance in the manual is only 0.022mm.
ok so my results could be out as it's very hard to get a perfect measurement.

big end journals
1: 47.66
2: 47.67
3: 47.65
4: 47.69

again a 0.03mm swing in the results and again i wonder how much of that is me measuring it.

manaul says that the crank mains are from 54.956 - 54.980mm
big ends 47.956 - 47.974mm

so that means my cranks is roughly .3mm ground on the big ends, too much!
and the mains are .27-.29 smaller than stock, again too much!

so it looks like the machine shop has fucked up. perfect. good luck proving that and getting it sorted within the next couple of days. even if i can prove they ground it too much, then getting them to cough up for a new crank is going to be tough.

any ideas? other than buying a new engine and just having done with this one.
hmm on a side note, has anyone got a working standard engine for sale?

 

[pulsarboby]

very hard to say whether it will be ok or not tbh

why dont you phone the engineering company and explain to him what they have done and ask him if he reckons its within tolerance or not, and if it goes pop will he pay for another crank etc etc.

il be removing a good stock lump within next 2 weeks but all ive got is forged engines in at the mo and no time to build you one up either and time isnt your friend

 

[MarkTurbo]

manaul says that the crank mains are from 54.956 - 54.980mm
big ends 47.956 - 47.974mm

Did you give the guy that ground the crank these measurements? He hasn't just taken 0.25 off all the journals on your already worn crank or something stupid like that has he?