Fitting a M20B25 into a M20B20

Post Mon Dec 21, 2015 1:42 pm

Hi,

My M20B20 needs to come out of my '90 cabbie so i can fix the oil leaks, exhaust manifold, get the injectors cleaned and do the belts etc etc.

As its my daily, I need to keep it on the road while carrying out the above work, so plan "a" is to drop a M20B25 in (there's one in the for sale section that fits the bill). However, its is missing the flywheel, clutch or starter.

Am I missing something, or could I simply connect the B25 engine to my B20 gearbox, and use the B20 starter and flywheel, and re-chip my ecu?

I would also need an exhaust system to match the B25.

Any guidance / advice would be gratefully received.

Post Mon Dec 21, 2015 1:59 pm

Flywheel, clutch driven plate, and starter motor are all the same. 320 clutch cover plate uses a lighter spring than than the 325, but is perfectly adequate for normal use, and arguably preferable, since it makes the clutch pedal require less effort.
325 engine fits the 320 gearbox with no problems. Much the same applies at to the clutch - 320 gearbox is weaker than the 325 one, but will give no problems in normal use, and has better ratios.
Exhaust manifold is the same between the two engines, and although the OE exhaust system is slightly smaller, it will work happily in the short term, and if the exhaust has been replaced at any time it's quite probably the same anyway.
ECU is as you say. AFM needs to be the 325i version, so make sure that's included, and don't forget to fit a spigot bearing to the end of the crank, if the replacement engine's from an auto.
Only thing I don't understand is why you'd want to remove the 325 again and refit the 320?
If the 325 engine does end up staying, it'll be a good idea to fit a diff. with a more suitable ratio.

Post Mon Dec 21, 2015 3:15 pm

Brilliant Brian, thank you, better PM the guy selling the 325.

The 320 engine is a good one, apart from the various leaks, with 'only' 109k on it. I imagine you will be right, and once I've driven it with the 325 engine I'll sell the 320 one and use the money to get a better diff.

Thanks again for the quick response.