Hello Hauser,
I have done the conversion many times both ways (auto to std. or std to auto). A good donor car is a big help in time and money. W108 sedans have the most donor parts unless you have a W113 parts car.
First you need to understand the differences in the W113 engines. The 230-SL has a counter balanced crankshaft. This means that there are throws or massive areas on the crankshaft. The crankshaft is made "out of balance". By adding mass to areas of the flywheel and front vibration dampner that counter the mass on the crankshaft, the entire assembly is brought into balance. Each separate part is out of balance! It is the same concept as adding weights to a wheel to balance tires!
The four main bearing engine in the 230-SL lends itself to this counter balanced design. As far as donor cars you would need a four main bearing sedan like a 220 or 230 series finback (W111) or coupe etc.
The crankshafts, flywheels, vibration dampners in the automatic or standard version of these four main bearing engines are different and interchanging could cause major balancing problems unless the flywheels and dampners are balanced to match the units they are replacing.
Then along came the W129 (250-SL) and W130 (280-SL) engines. These engines (except for the earliest 250-SE engines) had "balanced" crankshfts. These new seven main bearing engines had cranshafts, flywheels, and vibration dampners which were balanced separately. Each part was balanced. With these engines, flywheels auto or standard could be interchanged without much danger of major out of balance problems.
To summarize when converting a 230-SL the flywheel will need to be matched to the original so it will counterbalance correctly.
Swapping flywheels on the 250-SL or 280-SL engines will normally not cause vibration problems.
Now that you understand the basic concept there is a lot of other thing to consider. You will need a pedal assembly with the hydraulic master cylinder, slave cylinder, reseviour, metal line, rubber line clips etc. Surprisingly even the pedals are sedan parts!
Next the front half of the driveshafts are different. You will have to have one made or will have to order a W113. The shifter and linkages will need to be switched (bits and pieces are sedan others are strictly W113.
The flywheels themselves would need to be changed with compatable sedan or W113. If you are going to automatic you will need to remove the centering bearing and dust cover in the back end of the crankshaft. If you are going to standard you will need to add these. the crankshaft/flywheel boilts are different lengths for an automatic or standard. Of coarse a clutch disc, pressure plate, and throw out bearing is needed for a standard. Lastly and most obviously a transmission is needed. Sedan top shift units work fine but they have a stump pulling low first gear depending on what sedan your donor is. All Mercedes final drives (4th) are 1:1 in any standard or automatic except the 5 speed which is an overdrive in most cases. Review the BBB or Tech data manual for gearing on all the transmissions of the era.
The speedometer cableis different in the automatics and sticks.
There are some minor electrical interfaces which have to be dealt with also. Back-up lights, nuetral safety features, kickdown wiring, and possibly some engine idling interfaces may have to be dealt with.
I am sure I have forgotten a couple minor items also, but this is the bulk of it.
It may be cheaper and easier to just buy an SL with what you want on it or learn to love it as it is!
Joe Alexander
Blacklick, Ohio
