Author Topic: Quick question about M20 flywheel conversion (Read 5223 times)

irish44j · « **on:** November 11, 2012, 11:00:26 PM »

I managed to come by for cheap all the parts for the M20 conversion from someone who was going to do it but then did an engine swap and didn't need to. It includes:

M20 single-mass flywheel
M20 clutch and pressure plate (new)
323i throwout bearing
M20 starter (new)

From what I have seen, there are two ways to do the M20 conversion:

1. use everything as-is, except add a spacer to the flywheel and switch the M20 starter pinion gear to the M42 starter.

or

2. use everything as-is, including the M20 starter, but have the engine side of the flyweel shaved to clear the bottom of the block/oil pan. From what I can tell, with this method no spacer is needed, and I don't need to use any part of the M42 starter.

Are both of those methods correct?

Thx,
J

romkasponka · « **Reply #1 on:** November 11, 2012, 11:56:07 PM »

At the moment I think the best way is:
1. Modify m20 flywheel to accept m42 ring gear.
2. Shave inside of the flywheel.
3. Balance flywheel.
4. Use stock m42 starter motor.

I think best and easiest way.

Warsteiner · « **Reply #2 on:** November 12, 2012, 06:54:41 AM »

romkasponka has the right idea!

~R

romkasponka · « **Reply #3 on:** November 12, 2012, 07:55:08 AM »

And optionally I would go for lightening to ~5kg, resurfacing and would make 1mm more preload for clutch.

irish44j · « **Reply #4 on:** November 12, 2012, 02:59:03 PM »

damn....since my M42 starter is on its last legs and this is a brand-new M20 starter.

This is a rallycross car, so I don't want to lighten the FW that much, since I want to keep the revs up on shifts

romkasponka · « **Reply #5 on:** November 12, 2012, 04:18:50 PM »

Your clutch will not last long i think in this case if you do flat shifts all the time.
http://www.guy-croft.com/viewtopic.php?t=570
http://www.guy-croft.com/viewtopic.php?t=607&highlight=flywheel

http://www.guy-croft.com/viewtopic.php?t=668&highlight=flywheel

Quote

So is a higher or lower MOI a better thing to aim for?

by Guy Croft � Wed Jan 10, 2007 7:42 pm

lower in every case, trust no-one that tells you a heavy fw and high MoI is ever better on a comp engine.

And I do not see any reason why heavy flywheel is better for competition. Every time you accelerate you loose time, because of flywheel inertia.

http://www.zf.com/media/media/document/corporate_2/products_3/motorsports_1/product_range_motorsports/catalogue/sachs-racing/RCS_zf.pdf
Page 11

romkasponka · « **Reply #6 on:** November 12, 2012, 04:24:28 PM »

P.S. For my competition engine I will go for less than 5 kg, that's for sure and will use clutch disc without springs. Just to keep rotating parts weight weight as less as posible. M47 crankshaft will have to do a diet course also

irish44j · « **Reply #7 on:** November 12, 2012, 09:36:23 PM »

Of course you're right. Maybe I'm just cheap and lazy, in reality

And the car currently has an M10 in it, so even with a heavy FW, it will feel like a rocket-ship once I do the M42 swap

That said, clutch life isn't much of a concern for me in rallycross. RX is pretty easy on clutches.

I'll also note that this car drives to the track, long-distance. Heavier FW does improve fuel economy and speed-holding off the gas. For general driveability the heavier FW is there for a reason. For higher-speed track work, lighter is better.

romkasponka · « **Reply #8 on:** November 12, 2012, 11:49:37 PM »

For every day it is better to because it reduce engine vibrations and if you drop the clutch it is not so easy to stall the engine but it is more easy to burn the tires

I was using lightened m20 5,4kg flywheel ~two years and had no any problems in town traffic. If you are looking for performance there is only one way and it is to go as light as possible.

p.s. starter motors you can also use from newer engines
http://bmwfans.info/parts/catalog/12411740379/ looks like it is the same on various engines and it will be more easy to find it later...