bmwe21.net forums

The last statement says enough, if i rebuild an engine i expect at least a lifetime of 150000 km of it.

I've once again measured the wall thickness of the cilinder walls of my '87 M20B20.
This can be done very easy if the waterpump is removed.
Front of engine to center of the first bore is 57.9mm, this is the same for all M20 engines.

So measure the minimal depth in the waterpump hole from front face of engine to cilinder wall.
In my case this was 12.9 mm

Wall thickness is 57.9 - R_bore - waterpump depth
So 57.9 - 40 - 12.9= 5mm

If you should bore this block to 84 mm the wall thickness reduces to 3mm, and my feelig says thats not enough !!

But now you can measure and calculate your own block with this formula, only need to remove the waterpump.

Hope this helps anyone with ideas of boring a 80mm engine to 84 mm.

Thank you. I'm currently researching all the options and will be publishing some results soon.

One of the ideas is to fit triple Webers to the M20B25. Probably there will be many voices against it due to the fact that EFI is more efficient etc. but I really like the sound of the engine with carburetors and want to have electronics free vehicle (as much as possible).