I’m at present within the means of swapping an M20B25 into my Collection 2 E30, that beforehand had an M40 in it. Alongside the way in which we found some attention-grabbing variations within the driveshafts that I’ll element under. I figured this info could also be helpful to individuals, and I haven’t been capable of finding it anyplace else on-line.

There are two facets I’ll concentrate on right here. The primary being the half shafts of the driveshaft, and the second being the centre bearing and mount of the driveshaft.

Driveshaft Half-shafts

Should you’re considering of swapping out your 4 banger for a 6, there’s a number of belongings you’ll want to alter over with a purpose to make the engine swap work. One in every of which, is the shortening of the driveshaft. 6 cylinder E30’s have a shorter driveshaft, resulting from having an extended gearbox. As such, you’ve gotten two choices. Both get your 4 cylinder driveshaft modified and balanced to suit, or discover a 6 cylinder driveshaft. I opted for the latter, and upon inspection found two issues.

• The half-shaft that connects to the diff is definitely the identical for each the 4 cylinder and 6 cylinder driveshaft (each size and thickness with regard to diameter), it’s solely the gearbox aspect half-shaft that differs in size and thickness.
• The half-shaft that differs in size (connecting to the gearbox) is thinner for the 6 cylinder, and the 4 cylinder half-shaft is thicker.

One factor to remember right here, which will probably be mentioned extra intimately after I discuss in regards to the centre bearings, is that the 6 cylinder driveshaft I’ve is from a sequence 1 E30, and the 4 Cylinder is from a sequence 2. Additionally whereas the half-shaft for the 4 cylinder could look thicker and stronger, the shaft is hole and will presumably be weaker. Exterior seems will not be at all times a superb indication of power. Greatest off utilizing a 6 cylinder driveshaft with a 6 cylinder, and a 4 with a 4 respectively. The photographs evaluating these could be seen under.

Driveshaft Centre bearings and mounting brackets

So the variations proceed. As we tried to mount the 6 cylinder driveshaft within the transmission tunnel, we seen that it wouldn’t match for two causes.

• The highest of the bearing casing was hitting the transmission tunnel
• The mounting holes didn’t line up and the slopes have been too steep on both aspect inflicting the bracket to rub in opposition to the aspect of the tunnel

My E30 is a sequence 2 physique, and as such it appeared that the centre bearing mounting unit from the sequence 1 driveshaft didn’t match, so we proceeded to take away every centre bearing from the driveshafts and swap them round. I took photographs for comparability, and as you may see the sequence 1 bracket is wider and taller and has the holes within the flawed spot for a sequence 2 E30, so hold this in thoughts if you’re attempting to interchange it or switching it over. The brackets/mounting items/centre bearings are straight interchangeable nonetheless, so you may at all times swap them throughout driveshafts if you have already got one which works.

We’ve had many points with compatibility between sequence 1 and sequence 2 components all through this swap, and 4 cylinder vs 6 cylinder points too. The gearbox and shifter linkages are one other difficulty that I’ll write about sooner or later, however to shut up this text, simply hold this info in thoughts if you’re swapping or repairing a driveshaft to your E30.