NK Crank question

[Duncan2Turbo]

I believe the NK crank stroke is 71mm is that a forged crank? Are any particular years models forged?

I am just trying to find any 71mm forged crank for a motor Im planning so if you know of one out of anything 318 320 NK that is forged for sure and 71mm stroke please let me know.

I appreciate any help as I have run into dead end after dead end. I have used search so please don't suggest the search function.

Thank you,

Todd

[gracer]

It depends on which engine your talking about. They came in 1500,1600,1800,and 2000 CC's. The 1800 had the stroke of the 2 liter with the bore of the 1600. The 1600, I believe, had the 71 MM stroke and the 84 MM bore. I would have to look in my factory manual to verify. I think that all the NK cranks were forged. G

[Duncan2Turbo]

It depends on which engine your talking about. They came in 1500,1600,1800,and 2000 CC's. The 1800 had the stroke of the 2 liter with the bore of the 1600. The 1600, I believe, had the 71 MM stroke and the 84 MM bore. I would have to look in my factory manual to verify. I think that all the NK cranks were forged. G

Thanks G thats I was under the impression that the NK cranks were forged I just haven't been able to find anything definitive.

I am looking for a forged 71mm stroke crank and if I knew for sure what year/ models had the forged crank it would really help my search. I know the 1.8 in the 320 etc had the 71mm stroke as well as NK 1.5 and 1.6 I am just trying to determine which were forged.

Thanks again

[Duncan2Turbo]

Does anyone know if the Nk Cranks were forged or not? 1.5, 1.6, 1.8 all are 71mm stroke but are any of them forged?

Somebody must have this info. Im about ready to pay for it as I can't find it anywhere.

So if anyone can give me a yes or no answer I would trully appreciate it and happily repay you.

Thanks,

[Guest Anonymous]

Hello.

I believe this part was forged (by the look of it) and then machine turned (are these the correct terms ?).

I am telling you this from the top of my head, as I recently had the part in question in my hands (it fell off my car while I was driving it this summer !).

Also : do you think this info might be in the factory workshop repair manuel (you know, the big blue official rign binder) ?

I'm asking instead of just looking it up, because the binder sits under a huge pile of documents...

By the way, I am selling this binder.

[Guest Anonymous]

Hum... Sorry. Forget what i wrote about the crank falling off while driving. I meant : the pulley.

Obviously !

About the crankshaft, no information in the blue binder.

However, there are pictures of a replacement crankshaft : and you can clearly see the casting marks on the balancing weights.

This is clearly visible, too, on the crank of my 1800 (1964).

ebergerolle@idobs.net

[Duncan2Turbo]

Thanks for the effort NK.

I believe forged cranks have the casting marks as well. They have the casting marks where they're poured into their mold but then they're hammered which makes them forged.

Or this is my understanding which also makes it all but impossible to tell them a part. I was told that the casting marks are closer together on forged cramks.

I wish the blue book had the info its proved very elusive.

Thanks again,

[NK1964]

Hello Duncan2Turbo.

I ackknowledge the fact that the intimate difference between cast and forged steel had escaped me... So I push forward my searches.

I believe I have found the answer to your query !!!

:

I found the confirmation you were looking for in a

French "Revue Technique Automobile", the stuff

independant mechanics used to subscribe to be able

to proceed with repairs on the many European

types.

In on the editions of the year 1971 I have at

home, the RTA published an updated study of the

BMW 4-cylinder types. Including : 1600-2, 600 TI,

2002 and TI, 1800, 2000, Tilux, 2000 C and CS.

For each and every of these 4-cylinder cars, it is

stated that their crankshaft is a "cast steel

crankshaft with an after treatment. Five main

bearings. With counterweights out of the forge,

balanced afterwards (4 on the 1600 and 1800 motors

; 8 on the 2000 motor)."

Here is the original French text, in case I've

made a mistake while translating it...

VILEBREQUIN :

en acier fogé et traité, 5 paliers, contrpoids venus de forge et équilibrés (4 sur moteurs 1600 et 1800 ; 8 sur moteur 2000).

[NK1964]

Just to be sure, I checked on an early study (still by the French "RTA").

In the 1966 study (this time, only for 1500, 1600, 1800 and 2000), the information is equivalent, if not strictly identical.

It reads as follows : "Vilebrequin à 5 paliers, en acier forgé et traité, tourillons de grande dimension. Contrepoids soigneusement équilibrés, venus de forge."

Note : tons of measures follow (including for the repairs and rebore). So, if you need anything, tell me

NOTE : VILEBREQUIN is for crankshaft ; CONTREPOIDS is for counterweights ; ACIER is for steel ; PALIERS is for main bearings.

Any French Canadian friend around to help you translate ??

[mcmil]

I went into the archives and found owners manuals for 1800ti, 2000 and 2000ti.

They all say "forged crankshaft", so I guess they are all forged!

[tjones02]

It is my belief that ALL M10 cranks are forged, that only M20 eta cranks are cast. I have not looked for proof yet, it will take some time.

So, could you explain why you want to use the short stroke crank? It is not fully counter weighted as all the 2-liter ones are. There is a possibility that the short crank in '71 1600's is counterweighted. There are other differences in the cranks as well.

[Duncan2Turbo]

Thanks everyone.

tjones I want the short stroke for the rpms. Short stroke plus lighweight rotating assembly equals high rpms.

I'm building this motor to put a gt35r on which I think will work extremely well with the higher rpms.

The reason I need a forged crank is I plan to run some equally high boost.

As far as the 1800, 2000, 2002 all being forged are they not all 80mm strokes? I believe I read the 1800 had the long stroke with smaller pistons.

Thaks again NK I have no not even remedial French but thanks.

[tjones02]

Yes the early 1800s had long stroke with small pistons, but in I believe 69 or so they went to big bore and short stroke like the E21 1.8s.

Sounds like a very cool project motor there.

[gracer]

I hope that you are aware that the NK cranks are 6 bolt. G

[Duncan2Turbo]

Yeah I know.

I was going with aluminum flywheel anyway just have on made for newer clutch.

Thanks,