I have an 85 300d turbo motor with low miles and it came to me without a flywheel on it. I see no witness marks etc. Have no idea where they are or if needed. I am planning a manual 4speed trans conversion.
So I am planning to use a 240d flywheel and have a Chevy flywheel mated to it.
as pictured below.

My 1st question is.. Do I need to zero balance the new 240/Chevy flywheel and if so - Why? I don't mind doing it , I just want to know why. I found many balance it or don't worry about it post's. I am confused.
2nd. Since my flywheel will weigh more does that effect the front balancer?

I am going the bell housing adapter route instead of the trans adapter.

fwiw.. in the second to last pic you can see the chevy holes are larger but close to the benz configuration. I may just try to redrill
a balance Chevy flywheel to benz but can't find one heavy enough. 40 lbs iirc.
These are not pics of my setup but from another conversion done elsewhere. I just want to avoid a big virbrating problem.

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81' 240d 4 spd 140k on the clock