M20b25 gbox from auto to manual engine

Post Sun Oct 26, 2014 3:06 pm

Ok my 1.8 is out I got the b25 engine waiting with a torque converter on it. I found out my 1.8 box won't link up perfectly to it so I'm on a hunt for a getrag 260 and flywheel on payday. Now will any m20 flywheel link up ? Also will the old 1.8 manual prop shaft fit the 260 box, clutch cable the same ? Basically what do I need to order.

Thanks in advance and if u have the box ect ect I will most probably be interested

Post Sun Oct 26, 2014 3:31 pm

You will need a prop that matches the gearbox you use as the gearboxes are different lengths.
The clutch is hydraulic not cable operated. I would suggest changing the slave cylinder before fitting the engine and gearbox as it makes sense/is easier to do with the gearbox out of the car. You should ideally change the master cylinder as well as its best to do them as a pair. You could also renew the clutch hose (if it looks to be past it) before fitting engine and box, as again it will be easier.

Post Sun Oct 26, 2014 3:41 pm

Ok I defo will be fitting new slave with a new clutch kit. Do I need the whole propshaft from the box to the diff ? Also is the slave fitted in the same location as the 1.8 box so it will just connect. This is turning out to be soo much work lol also just read the speedo don't work with the conversion so another thing to sort out.

Cheers jmc mate helped a lot again

Post Sun Oct 26, 2014 3:53 pm

speedo comes from the speed sensor in the diff

Post Sun Oct 26, 2014 4:08 pm

It's only the front section of the prop that differs (all the rear sections are the same) so you could use just the front section but, each prop is balanced so its better to just get a complete original prop from a known source.

As Ross said, the speedo is driven from a sensor in the diff, so that won't be an issue. You will need to swap the diff for a medium case diff though - the small case diff in your 1.8 might not last too long!
You might be confused with the rev counter. You will need to swap the coding plug in the instrument cluster for a 6cyl coding plug otherwise the rev counter will read incorrect and go nuts at high rpm.

Post Mon Oct 27, 2014 9:10 pm

Alright thanks im getting the full prop, gbox, diff and flywheeel (soo hard to find the whole set!)

Also got a small of this subject question about the loom, i have a the whole wiring loom from the engine to a round 16 or 32 pin plug can't exactly remember on the m20b25, now what do i have to convert for it to start run ect ect? Probably been asked a million times, is there some sort of diagram / guide?

so much work for a simple engine conversion

Post Mon Oct 27, 2014 11:06 pm

The most important thing about fitting a manual gearbox to an ex auto engine hasn't been mentioned so far! There is a hole in the end of your crankshaft that needs a bearing pushed into it to support the end of the gearbox input shaft.
Loom has a 20 pin plug on it, and unless your car is some ancient example, it will plug straight into your car, BUT check what is connected to pin 20 on both sides. If there is no wire connected on the engine loom side, then nothing more needs to be done, but if there is a wire on the engine side, check to see if there is a thin brown wire connected on the body side. If there is, it must be cut away from the pin, and cut back so that it can't touch anything.
M20 flywheel needs a matching starter motor, BTW.

Post Tue Oct 28, 2014 10:17 am

What bearing is it how can i get hold
Of it ? Ill get a starter thats not a problem so the 20 pin plug from the m20b25 will plug into my 1.8 looom ?

Post Tue Oct 28, 2014 10:30 am

http://2009.bmwfans.info/parts/catalog/ ... _flywheel/

Part #8 (ignore all the other bits and twin mass stuff). Available from your local dealer, Cotswold, or is also used as the rear drum bearing on several Hotpoint washing machines.
Engine loom plugs into your body loom, BUT CHECK PIN 20.
Fit loom to the engine before fitting engine to car.

Post Tue Oct 28, 2014 12:44 pm

Ok decent mate ill get the loom all connected up seems simple the bearing has to sit on the cs then spacer just before flywheel and then the rest is fairly simple hopefully it will all work nicely.

I have an ecu from an auto i take it i need one from a manual ?

Thanks for all the advice guys id be stuck
For ages if not here

Post Tue Oct 28, 2014 1:25 pm

Bearing just pushes flush into the end of the crank - all the other odds and sods shown in the diagram have long since been deleted. Check that it fits your gearbox input shaft before you fit it, as there are two sizes used by BMW.
The 'spacer' for the flywheel sits under the heads of the flywheel fixing bolts, NOT between the crank and flywheel. It's a 'load spreader' for the bolts.
Your auto ECU will be fine.