M20 engine. Gearbox options, m52 5 speed?

Fri Jun 12, 2015 5:09 pm

First post so be gentle. Planning an engine build for a project. Probably a 2.8 stroker, rowlands inlet manifolds, and Jenvey throttle bodies, along with Emerald management. Used this combination before and it's worked brilliantly. Anyway, my question is this: will the 5 speed off an E46 M52 engine fit the M20? I've got a few gearboxes lying around, but I don't want to use them for this project. Thanks in advance.

Sat Jun 13, 2015 1:30 am

Thanks for that. The engine I have didn't come with a gearbox. The gearboxes I have are the "dog leg's", which I don't want to use. I have a thing about Getrag 262's etc. many thanks for the info though.

Sat Jun 13, 2015 10:15 am

Don't forget that the choice between these two gearboxes will also affect the choice of diff. ratio, since the E30 box is an overdrive version and the E46 one is a direct top gear. Depending on what diffs. you have available, and what you may need to source, buying a G260 might be the cheaper option.

Tue Jun 16, 2015 8:59 pm

Thanks for the reply. Direct top is ok, prefer it anyway. As a matter of interest, as the angle of the gearbox is about 10 degrees off from the engine, which way would the engine have to go to "level" the gearbox? Would it be more canted over or less? Thanks.

Tue Jun 16, 2015 9:00 pm

Thanks for the reply. Direct top is ok, prefer it anyway. As a matter of interest, as the angle of the gearbox is about 10 degrees off from the engine, which way would the engine have to go to "level" the gearbox? Would it be more canted over or less? Thanks.

Thu Jun 18, 2015 9:18 am

You can fit a dogleg box to the M20 - you just need the right bellhousing to suit...

Thu Jun 18, 2015 12:35 pm

For what its worth, I have my M20 mated up to the G250 from a 323 M52 lump.

All goes together just fine, you need to use the clutch fork mod or taller bearing like the M20 flywheel onto M5x conversion, the box will also need an E36/46 slave cylinder not your current E30 one.

I used the 323 prop and a Z3 diff with the centre bearing reversed to cope with the offset of the gearbox output to the left, gives a nice straight shot to the bearing and a decent offset to the diff for the UJs.
(e36 prop has the joints both on the rear half so front needs to be a straight shot).

The linkage is an easy fix, just twist an e30 linkage.

You will want an E36 compact or Z3 diff or similar ratio from an E28 etc, easy to solve.

So far it has been ok for the last 4k miles. Cars semi off the road for some bodywork at the moment.

Thu Jun 18, 2015 12:49 pm

Is that the E36 centre bearing/mount?

Thu Jun 18, 2015 1:02 pm

Nope E30 one.

The E30 one is a touch offset to one side. With the E36 box on the output is moved to the left.
With the e30 bearing in normal way I found the prop was pushed to an angle, stressing either the guibo or the centre bearing.
E36 props need good alignment of the front half.

I looked at the E36 centre bearing but the mount is massive and no way going to fit the E30.

With that said the advice about turning it around for an M50 engine is crazy, it will make the misalignment even worse.

Sat Jun 20, 2015 6:30 pm

Thanks for that. Just what I needed to know. I've got a couple of doglegs that go straight on the M20 engine,
(Integral bellhousing) and a couple with detachable bell housings. I don't want to use them, saving them for other projects. I've also got an S14 engine that is destined for another project, so that accounts for one of the doglegs.
It would still help to know which way the 10% would send the engine when the gearbox is fitted. Further canted over, or more upright. Thanks again.

Sun Jun 21, 2015 1:12 am

Think I've got my head round it now. If I've got it right, the engine would in effect be more vertical than canted?
That actually works well, for where I'm putting the engine. Thanks for that, great help.

Sun Jun 21, 2015 1:19 am

I should add, my previous project using an M20 engine was a road legal replica of a maserati 250f. Current project will be an M20 powered mgb gt sebring replica. ( narrow engine bay) hence my previous questions on "straightening" the engine. Once this is done, I'm going to finally build a "maserati birdcage". That's what I'm saving the S14 for.

Sun Jun 21, 2015 8:24 pm

Thanks for that. Although my E30 days (temporarily) ended with the selling of my beloved M3, ( worst decision I ever made), I'm still a BM' man. E46 325i shooting brake as the daily. Other half has an E53 X5. Still in the planning phase with the sebring project, but not far off. My plan is to use as much BMW running gear as possible, to build a reliable long distance tourer, but keep the look as "original" looking as possible.

Mon Jun 22, 2015 11:12 am

Sorry guys, the engine would be more tipped over. An M5x with M20 box would be more upright but this is vice versa.

I think the m20 sits at 15 degree slant and the M5x engine is 25 degree slant clockwise from driver perspective.
The engines lean towards the front right wheel.

The M5x engine is tilted more to the RHS of the car for clearance on the twin cam head.

To put the M5x box at the right angle the M20 engine would be 10 degrees more slanted to the right.
To put the engine at the right angle the box needs to rotate anti-clockwise or to the left.

To do mine I have used a mini exhaust mount rubber on the left and an E36 gearbox mount with 4 washers on the right (need to make a custom x-member but the welder was AWOL when I did it).

I know the MG engine bay (used to work at a vintage place) and they are tight, luckly the M20 does not have anything but the exhaust on the RHS which it is tilted to.

Mon Jun 22, 2015 5:00 pm

Looks like plan B then, which may involve a large hammer.

Tue Jun 23, 2015 1:24 pm

Your M5x engine and M20 box though right?
In which case you would be tall mount on left.

To do the (slightly more backwards?) M20 engine and M5x box the tilt will be the other way.

I brought the E30 to work today so could have a check but I am pretty sure its an anti clockwise rotation of the box when m5x box is fitted to the M20.

Thu Oct 22, 2015 9:48 pm

Sticking to the topic with slight change, Could anybody reccomend some companies who perhaps make internal replacement parts for Getrag gearboxes? Any options welcome. As i have carbed m20b20 project going and after mods i will need something more reliable and perhaps more fun to be replaced/moded to work

Thanks

Thu Oct 22, 2015 11:24 pm

What kind of power are you expecting? The G240 that the 320 uses is the same internally as the G240 fitted to the 318, many of which now live bolted to M50s and M52B28s so they can take some welly. I know of one that was fitted to an M20B25 that had the crap kicked out of it for 5 years and was only retired to use a 1:1 5th gear box.

Fri Oct 23, 2015 7:02 am

HairyScreech wrote:What kind of power are you expecting? The G240 that the 320 uses is the same internally as the G240 fitted to the 318, many of which now live bolted to M50s and M52B28s so they can take some welly. I know of one that was fitted to an M20B25 that had the crap kicked out of it for 5 years and was only retired to use a 1:1 5th gear box.

Ok it is not about the power but making gearbox getting refurb. Is it bmw officials who could sell synchro rings and such? My mechanic said something that it is possible to buy kits for getrags which can deliver crisper smoother gear changes. Pardon my lack of technical knowledge and dictionary

Fri Oct 23, 2015 9:04 am

http://bmwfans.info/parts-catalog/E30-2 ... nsmission/