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77 530i motor into a 77 730i ?

Posted: Thu Jan 09, 2020 5:18 pm
by canada karl
How complicated would it be to swap a good motor (bad body) from a 530i into a 730i with a seized motor(good body)? in terms of ECU's and electrical harness's etc. I know it's kind of an odd thing to do but I have a very good M30 motor in the 530i and it would save a nice looking 730i from the wrecker. Any thoughts?

Re: 77 530i motor into a 77 730i ?

Posted: Thu Jan 09, 2020 7:38 pm
by Lock
From what I've read, they are an identical motor and transmission and all the parts including the ECU are the same. There might be small differences but not enough to matter, the 7-series is just a slightly bigger, slightly improved e12 5 series.

I don't know of the 730i being sold in the US, only the 733i and 735i - is this a Euro import, or Canada-spec model? My guess is the only differences regarding that would be emission controls, or lack of. Euro models with higher compression and no cats.

If you wanted to be 100% sure you could swap the ECUs and harness but I'd say if you check the stickers on them, I'd bet they are the same color and part #.

If either is an auto, they're all hydraulic as well with no electronics beyond reverse lights, starter Park/Neutral relay and gearshift indicator, so keep the best of the two transmissions.

Re: 77 530i motor into a 77 730i ?

Posted: Thu Jan 09, 2020 8:41 pm
by canada karl
Thanks for the info. I made a mistake...it is actually a 733i i was talking about.

Re: 77 530i motor into a 77 730i ?

Posted: Fri Jan 10, 2020 3:02 pm
by Lock
No problems, in that case it would be a minor downgrade, 3.3 to 3.0 liter. As I understand the connecting rods are the same length in M30 motors, it's the wrist pin location in the pistons which is moved for the different stroke, but I could be wrong. In case you were thinking of swapping the crankshaft across.

The 3.0 and 3.3 liter blocks are the same 89mm bore, just different stroke 80mm vs 86mm so the external physical dimensions will be the same and in fact will have the same 3.0/3.3 stamped on the side of the block so if you installed it, it will look original at least.

Re: 77 530i motor into a 77 730i ?

Posted: Fri Jan 10, 2020 9:45 pm
by 528i-1981
Lock wrote:
Fri Jan 10, 2020 3:02 pm
in fact will have the same 3.0/3.3 stamped on the side of the block so if you installed it, it will look original at least.
You can see for yourself in Mike (keenh)'s teardown photos.