Unofficialbmw.com

[Dwight]

Hello All,

I am brand new to this forum and have a question about swapping a newer 1986 3.5L into a 1981 733i. I am writing for my brother who is completely computer-illiterate.

My brother bought the 81 5-speed 733i with 2 holes in the block of the 3.2L and then bought a 3.5L from a 1986 735i automatic to put in it.

The first problem/opportunity he encountered was the timing mark on the flywheel. He took the automatic off the back of the new engine, as well as the torque converter and flywheel. He didn't know that BMW's timing mark is on the flywheel so he didn't look for identifying marks as to where TDC is to align the flywheel when installing the 5-Speed.

How should he install the flywheel to insure the timing is correct? Are there marks on the flywheel and the crankshaft for alignment for which he should be looking.

Also, if the new engine from 1986 is completely computer controlled, will he need to get the wiring harness and computer from an 86 to make it work in the 81?

Finally, is there anything else regarding this switch that we have yet to consider?

Is this a crazy undertaking or will it work with some modifications?

Thanks for all advice.

Dwight

[edjack]

All the BMW flywheels I know about are indexed onto the crankshaft flange via a collar in one of the bolt holes, and a corresponding recess in the flywheel mounting face.

Does the the '81 engine still have a distributor, or is the timing controlled by the computer? If the latter, you may be able to run the '86 engine with the '81 computer.

This would be much preferable to sourcing all the cables and ECU from an '86, and then installing them.

The first thing to do would be to contact Brett Anderson, at Koala Motorsports, and pay him a consulting fee for some specific instructions as to how to go about this swap, since there could be pitfalls because of the evolution of design from '81 to '86. His fee could very well pay to help you avoid "gotchas".

Too bad there are no longer any shop manuals published on this model.
_________________


Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.

[Dwight]

Thanks Ed,

Unfortunately the 81 has a distributor.

I wasn't on hand when he put the flywheel on so I'll ask him about that.

Unfortunately my brother can sometimes be penny wise and pound foolish, so I don't know the consultant idea will be received. We'll see.

Thanks for the input.