The Sprinter Single Mass Flywheel (SMF)

A few of the BenzForce followers also follow my personal page but for those that don’t know, my own w123 has had on going transmission issues and I just don’t have time to tend to everything I need to.  I felt the quickest route to get going was to throw the 716.648 6 speed manual into it.  First off that was a mistake because I needed pedals, a flywheel, etc but at least the time was spent waiting for parts rather laying on the hot Texas pavement.

A long time ago I bought a Sachs 765 clutch cover and disc and figured when the Sprinter SMF kit showed up I would just get it drilled and machined for the new cover but no, not here.  I spent about 4 hours calling every place I could find in Austin, TX and no one is interested in machining a flywheel.  A quick resurface, maybe but no drilling or custom work.  One shop even said, “Well, that’s a queer setup now, isn’t it.  Maybe you can get one of those California queers to do that, but no one here is going to touch that.” That actually made me laugh because it’s a bolt on world now and it’s obvious that thinking outside the box or using some type of creative or analytical skills are outside of the capability of most. 

The personal goals for my car have been shot down in the near term.  I know other providers have solutions but I think there is still room for another one if I get the price points in line with a premium disc and cover like Sachs.  The relationship with Sachs has been in place for some time now but I have never advertised or sold anything; maybe that should change.  In order to make my own SMF, some essential measurements were needed.  These were taken using the Borg & Beck SMF kit and I compared the SMF cover to the Sachs 765 pressure plate/clutch cover.

The SMF Clutch Side

 

What you see in the table below is a code that corresponds to the picture, a description of what I was capturing and where it made sense, I measured multiple times (using the bolt holes as a reference).  After I averaged them out and made notes as necessary.

Code Description A B C D E F Average Notes
C1 Ring width 11.8 12 11.8 11.7 11.8 11.8 11.82
C2 Lip width 20.8 20.8 21 20.6 20.7 20.6 20.75
C3 Lip depth 7.5 7.5 7.5 7.7 7.4 7.2 7.47
C4 Lip to bearing 50.4 50.6 50.5 50.5 50.5 50.6 22.02 Straight edge was 28.5mm
C5 Lip to crank bolt face 61.8 61.7 61.7 61.8 61.5 61.6 33.18 Straight edge was 28.5mm
C6 Lip to ring gear 24.7 24.8 24.7 24.8 24.9 25 24.82
C7 Locating pin diameter 5.8
C8 Bearing OD 27.8 Same for flywheel bearing hole
C9 Bearing ID 16.6
C10 Bearing edge height 19.5
C11 Bearing center height 25.7

 

The SMF Crank Side

Code Description A B C D E F Average Notes
E1 Timing ring width 27.9 28.2 28.2 27.1 27.3 26.8 27.58
E2 Timing ring to ring gear 21.2 21.6 21.4 20.7 20.4 21 21.05
E3 Timing ring to crank 35.1 35 35.2 35 35.1 35.1 6.58 Straight edge was 28.5mm
E4 Timing ring to inset 53.6 53.8 53.3 54 54 56 25.62 Straight edge was 28.5mm
E5 Crank stickout depth 10.1 9.9 9.9 9.5 10.2 10.3 9.98 Too shallow for the om606!!!
E6 Bearing below crank seat 3

 

Other mentions

  • Most will just grind off the stick-out on the crank to make the SMF fit but if I was going to manufacture one, naturally I would have it cast or machined to fit. This effects the bearing structure though it is a trivial amount
  • The clutch mating surface of the Sachs 765 sits below the steel cover case whereas the SMF kit's cover is above it.  This means that lip on the flywheel (C3) needs to be reduced.  My calculated measurement is close to what is online but is not the same.  To me this would matter
  • In the groups online I have yet to hear anyone mention the throw out bearing to finger gap.  If the gap isn't sufficient then the SMF should be thinner and if its too great then either spacers/shims should be made to go behind the bearing or the flywheel increased from the ring hear towards the transmission.  To get this I need to grind the flywheel and install the kit then measure the 716 to compare ... that is for another day
  • The timing gear to ring gear (E2) is different on the om606.  Not much but if any unnecessary material can be removed then we could prevent having a coffee table for a flywheel

Thanks for reading,

Rodney

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