MX5 crankshaft differences - are there any?

[NMX516]

Hi folks,

Can anyone confirm for me whether the crank in an NB8B would be the same as in NB8A's or even NA8's?

Thanks in advance

[orx626]

Hi Gerard, I just checked and the part number is the same...just revised once...went from BP06-11-300C to BP06-11-300D. So they are interchangeable.

So all is good! See you in the morning.

Cheers,
Danny

[NMX516]

Good news! Thanks Danny.

It will be late morning before I can get there, but will see you then.

[manga_blue]

I put an NB8B crank, pulley boss and rods straight into an NA8 block. The cranks appear to be identical but there was a rumour somewhere that the NB8B wwas a better metal.

[NMX516]

hmm, thanks manga_blue. Interesting that the metals could be different.

[manga_blue]

Yh, don't quote me on that. It was a metallurgy thing ... something about the higher compression or power in the NB8B demanding better heat treatment in the bottom end.

[NMX516]

Oh well that's not too bad then, I could always get an earlier one nitrided or tuftrided depending on the metal used if necessary. Might do that anyway, no harm in increasing the strength of a crank.

[manga_blue]

Oh well that's not too bad then, I could always get an earlier one nitrided or tuftrided depending on the metal used if necessary. Might do that anyway, no harm in increasing the strength of a crank.

I asked about that too and got the answer that the rods break long before the crank does. I ended up getting all mine balanced as a set, i.e. standard crank, pulleys, rods, pistons, flywheel and clutch housing. It's only an N/A NA8 motor pushing out about 78rwkw. After losing 5th gear I was holding it on a 7,500 redline in 4th for 17 secs up PI's main straight over about 50 laps with no problems.