M47 Crankshaft and everything else stock

[Ivan Petrov]

I was wondering if I can use M47 crankshaft without changing anything else? With stock pistons, stock connecting rods... etc.

[hesgone2fast]

It is possible, but the stock pistons are sitting 0,15mm over the deck(they protude 0,15mm). The M47 crank, would make them protude 3,5mm more, so you would have to shave the piston at least 3,6mm.
Having the pistons flush with the block deck (0 deck height) would give you around 1929cc, and 11,7:1 CR, that´s a little too much for stock specs. To be on the safe side, I would go no higher than 11:1 CR. That would mean to have the pistons sitting below deck around 0,6mm. Having to shave a total of 4,15mm off the top of the piston. Now comes the problem with the first ring being too close to the piston deck if you shave that much.
I would go for different pistons or a shorter rod, the M40(Euro 318i) has 5mm shorter rod than the M42 (M40: 135mm rod / M42: 140mm rod) also the US M3 e36 S52 engine(321hp) has a 135mm rod and same bearing size.
I have the following combo: M47 crank, M42 E30 rods, M3 e36 (S52) pistons (86,4mm bore) and pistons are sitting 0,05mm below deck. Final displacement of 2040cc, 11,5:1 CR.

If you need any more advise just let me know. Also please keep in mind this numbers might be wrong, so double check to make sure.

I hope this helped!!

[Ivan Petrov]

Thank you wery much for the info ;)
One more question, do I have to change someting in the block, if I want to install m47 crankshaft? And what will happen if I use m47 crankshaft + m47 connecting rods? I don`t like the idea of boring the block to 86.5... I preffer not to touch the block

[futron.sim]

Thank you wery much for the info ;)
One more question, do I have to change someting in the block, if I want to install m47 crankshaft? And what will happen if I use m47 crankshaft + m47 connecting rods? I don`t like the idea of boring the block to 86.5... I preffer not to touch the block

Hi! Where did you managed to get the M47 crankshaft? Cause I am looking for one.

Thanks!

[Ivan Petrov]

I haven`t get M47 crankshaft yet :)

[hesgone2fast]

It´s not possible to use the M47 rods, they have a much bigger piston pin, something like 30mm instead of the 22mm (maybe 21mm, can´t remember right now...) of the M42.

You don´t have to change anything else on the block, it´s a direct fit.

But also remember that you need to do 2 mods to the crank itself:
- Shave around 0.4mm off the front of the crank (nose radius), where the chain sprocket goes.
- Machine a second woodroof key, using only the stock one is not safe, because it is on the very edge of the sprocket.