Gearbox Confusion

[170sport]

Hi

I'm doing an engine swap from an M40 to an M20B25. This isn't the problem the problem is the gearbox, I'm gonna whip off the Getrag 260 unit which came with the M20B25 and fit the 240 but....

I've read through the wiki 54 times and it seems to contradict itself... On the link documenting about fitting an M20 engine it mentions that fitting an M40's gearbox is not recommended as the bolt patterns and selectors etc etc are way off which is fine because I'm not fitting an M40 gearbox anyway.

The wiki does actually suggest fitting a '240' from an M20B20 over the 260 but and here's where I'm confused, the page from the wiki which has the little table that indents the different manual gearboxes fitted to e30's stats that the 318is also has a 240 gearbox fitted, (yet that's an M42 engine which has the same pattern as the M40 engine) from which obviously and as earlier mentioned any gearbox from an M40 won't fit an M20...

"Look at the letters" I hear you cry, well yeah but unfortunately I can't seem to find on the wiki what letters should be on an M20B20 Getrag 240 gearbox...?

Essentially the gearbox I want to fit and the part number I've been given from it is a 240.0.01309 but from what the wiki says, 240 gearboxes were fitted to both M42 and M20 engines, how do I tell with this part number what engine it was fitted to? As obviously I don't want to buy it if came from an M42 engine cuz it won't fit.

Many thanks.

[jmc330i]

There are two versions of the Getrag 240, one with the M40/M42 bellhousing and one with the M20 bellhousing for the 320i.
People fit the 320i G240 box because it has ratios closer to the 325i Sport G260 box when compared to the standard 325i G260 and the G240 will be cheaper than a G260.
I doubt the ratios will make that much of a difference and I'd rather have the stronger G260 box fitted.

[170sport]

I see, Well yes I was going to keep the 260 box but, (I've got a 1991 318i) and unfortunately a 318i propshaft won't mate with a 260 gearbox but it will mate with a 240 so I either needed to change the gearbox or the propshaft, and I can't find a 325i manual propshaft anywhere but oddly I have located a 240 gearbox.

So how do I tell (from the part numbers) if the box I'm being sold came off an M40/42 or an M20 engine? Assuming the seller doesn't know of course.

[170sport]

Also as well just out of curiosity why won't an M40 propshaft fit onto a 260 gearbox? (As the wiki claims) is it just because of the length of the shaft?

M20 with its typical 260 box = (1483mm propshaft)

M40 with its typical 240 box = (1480mm propshaft)

Yeah, "BMW made different length shafts for a reason" but just from a manufacturing point of view 3mm is a tiny distance on something that's naturally adjustable anyway. Just curious.

Thanks

[jmc330i]

I would think it's a miss type in the wiki. The M40 prop is definitely longer than a 325i prop, it's also a tad longer than the M42 prop.

[170sport]

Yeah I did think that aswell it did seem odd a physically smaller engine (standard M40 setup) having a shorter propshaft than a physically longer engine (standard M20 setup). You'd think I would be the other way round.

Still like to know tho why a 260 gearbox won't fit onto an M40 propshaft but a 240 will. The only thing I can think of is that the 260 box is that much longer than a 240 which is why a shorter prop is required?

[Brianmoooore]

The only thing I can think of is that the 260 box is that much longer than a 240 which is why a shorter prop is required?

And you will be correct!

[170sport]

The only thing I can think of is that the 260 box is that much longer than a 240 which is why a shorter prop is required?

And you will be correct!

Splendid! So it appears the Wiki wants minor adjustment on the propshaft length then, no pun intended

That clears that one up then thanks!

[Grrrmachine]

If anyone's got the correct lengths for the propshafts, and the letter codes for the M20 Getrag G240 box, then let me know and I'll change the Wiki asap.

[170sport]

I'm still hunting and checking the correct bits I need for my conversion, so if I come across what may be them I'll forward the details on.

Thanks for your help! a‘aaa»

[daimlerman]

If anyone's got the correct lengths for the propshafts, and the letter codes for the M20 Getrag G240 box, then let me know and I'll change the Wiki asap.

I think you will find a photo of randomdave's somewhere here;

http://www.e30zone.net/modules.php?name ... pic&t=6676

..giving prop lengths.

All rear sections are the same,but front bits vary with model...

M50/52 with M40/42 'box needs a 320i front section!

This is due to M50 type engines having the same basic dimensions as M20,so a similar setup will be the same...

[Grrrmachine]

Cheers for the link Malc, but since it's 10 years old all the original pics have long since disappeared, and still no mention of sizes.

[Andyboy]

M20, M40 and M50 all have the same bellhousing bolt pattern - but the gearbox sits at a slightly different angle on the M20. Why would anyone want to replace the unbreakable 260 Getrag gearbox with the 240?

Rear prop section lengths differ slightly depending on what diff it has - small case for 316, 316i, 318i and 320i and medium case for everything else. However there is enough length in the splines to take account of this.

[pacerpete]

Excellent 325 manual prop available here !

[170sport]

Why would anyone want to replace the unbreakable 260 Getrag gearbox with the 240?

Because the 240 box has similar ratios as the 260 box fitted in the sports. Assuming one can't locate a sport gearbox...

[daimlerman]

Why would anyone want to replace the unbreakable 260 Getrag gearbox with the 240?

Because the 240 box has similar ratios as the 260 box fitted in the sports. Assuming one can't locate a sport gearbox...

I have been using a 240 'box with my 2.7 for more than nine years!

(and I'm still using the clutch that came with the 'box and M20B20 engine)

[Grrrmachine]

Same here. Got the original 240 box (26 years old now) mated to a 2.5 lump with no issues whatsoever.