Some random thoughts:

A general machine shop's rate is about $ 150 hr , it could be worth having them use a measuring arm ( Faro or similar ) to just measure and make a print.

Modifying a steel aftermarket bell housing is easier then an aluminum one. With the dims from the machine shop print, have them drill new holes. If there are any interfering areas, weld on some plate or a round slug to get bolts past the OD of the bell housing.


If measuring at home, in addition to transfer punches there are hole spotters. These come in threaded and non threaded and are used for blind holes.

To measure hole angles using the crank as the center, make a fixture to hold a digital protractor ( the two arms on a pivot not a digital level ) to the crank then move the arm until it contacts a bolt / pin. Be sure to take 1/2 the bolt diameter into account. Cutting up a digital caliper and outfitting it with a cone would give angle and crank to hole all in one shot.

To make your own template, drill a hole on 0.090 aluminum sheet that fits over the crank ( either the flywheel register or the OD of the crank ) install hole spotters, lay this on the back of block and hammer the plate to make marks. Do the same on the engine from the donor trans. Drill holes in the donor pattern you just made and bolt the plate to the donor trans. You can now mark / weld in slugs / drill the donor trans bell housing.

If the crank is above or below the crank pilot you are using, make a large hole in the 0.090 al plate , a smaller plate that fits the crank and some square stock to offset it from the main plate.

Here are some pics of the M119 bolted up to the 420G by means of a partial adapter.

Attached Thumbnails

         

I am still waiting on the ARP bolts for the flywheel so I can not bolt that on the crank yet. It looks like I will need to shave off about .050" of the sensor holder to get it centered on the trigger ring.

I also took some measurements and with this larger pressure plate it looks like the throw-out bearing is in the correct spot. Of course I wont know for sure until I get the flywheel bolted to the crank and the pressure plate to the flywheel, but so far it looks like the time spent thinking about how to go about this was worth the wait.

Because the BMW crank trigger ring is larger then the MB one, the sensor will be sticking out of the bell housing. That may or may not be a problem for the application.

BMW uses a larger tooth pitch ring gear so I ordered a BMW starter. Of course BMW put the starter on the opposite side from MB, but I am thinking that I should be able to either swap the starter drives or the nose cones to make a hybrid starter. I don't like to have "custom" parts that are expected to be replaced, but any starter re-builder should be able to duplicate the combination if it works. The pic with the starter is the MB starter.

All in all I am pleased with how this is turning out.

Attached Thumbnails

 

Nice progress. Good idea on the cut block!

About 10 years ago I found a place in CT that would do this service. At the time they had a sample of a bell housing on their web sight. I'm not sure if this is the place but its in the same area and definitely has the capability.

I have no idea what this kind of service would cost especially if its done by people in the aerospace industry.

https://www.boltonworks.com/reverse-engineering/

__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo

All the parts I make are made to print so they can be reproduced.

On occasion when the budget afforded it, I have had parts laser measured for other projects I have worked on. In fact when we were on the path to cast a M117/119/420G bell housing, I had some a place quote scanning the mock up.

not cheap by any stretch.

There's a scout program at the Sikorsky factory in CT every year. I got to go this fall for the 1st time and while the kids were in awe of the helos, I got to closely question the engineers in the model shop about their tools and techniques for rapid prototyping. It's nothing short of space-age, literally, when they are building prototypes of parts and assembly tools going from an ah-ha moment in the morning to a viable test of the design in the afternoon.

-CTH

__________________
- cth350@gmail.com
http://www.111lakeside.com/

Yes I worked at Sikorsky for 25 years. They don't know how to do anything for less than $100,000.00 especially the model shop. But yes they do have the capability to give you measurements down to the millionth of an inch and temperature corrected to standard atmosphere.

__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo

Take a look at 7:40 in this video. EV West has a bell housing laser scanner setup in their shop. Maybe someone out there in SoCal can wander in with a bell housing and offer a few hundred bucks to see if they could do a scan for you.


https://youtu.be/mOx5uCufB2Q

And the burnouts at 21:10+ to the end of the video are worth watching too.

__________________
Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,

That's awesome. So how did you do it accurately? Just drilled through the plate into the block and reamed it? Then knocked a dowel pin in?

Sent from my SM-J737A using Tapatalk

__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com

The BMW starter came in and although BMW has it mounted on the driver’s side of the engine, it seems to look a home here.

CTH, I question if the starter you found would work on the passenger side as if it is the same as this one, the relay will be straight up at (12:00) which will hit the head.

The actual starter motor and relay are both Bosch and identical, so the MB starter cone could be put on the BMW starter motor, or the MB starter drive replaced with the BMW one. That being said, the MB starter uses 10mm mounting bolts and the BWM starter uses 8mm bolts so if the MB nose cone was to be used, the bolt holes in the bell housing would have to be opened up for the 10 mm bolts. This mod would have to be done with care as BMW uses the bolts as apposed to the dowel pin to locate the starter. My goal is to provide CTH with a kit that that is bolt on and does not require any machining skills. The only area that would have to be modified is the cut out in the bell housing for the cranks sensor.

One other difference between the two is the installed depth of the drive. I only had the MB starter when I was laying out where the starter ring/flywheel needed to be, and took a guess that since the BMW starter is also the same Bosch starter motor, that the locations would be close enough that any differences could be shimmed, which is a common thing to have to do. The gamble was that any differences would have to be shimmed away from the trans and not toward it. Looks like I won that bet lol.

The BMW starter drive is set in a little deeper then the MB drive which means I would either have to move the flywheel further back (away from the engine), or move the BMW starter forward (away from the trans). Based on my initial (not very exact) measurements, the current location of the flywheel (which is based on the shallower MB starter drive location) looks to be about right when I tried to get in there and measure where the pressure plate spring fingers are in relation to where the through out bearing and yoke need to me.

Until I figure out otherwise, I don't think I want to move the flywheel away from the engine much more. It looks like if it was moved away from the engine about .050" (ish) it would line the crank trigger sensor up better (something I did not really worry about because I was planning on having to make a new sensor holder, but it looks like the stock one will work fine). The BMW starter is set in about .300" (ish) more then the MB starter so the flywheel would have to be set back a lot more then what the sensor needs and I think that would also cause a problem with the yoke geometry.

My current thinking is to change the flywheel crank adapter design to move the flywheel away from the engine enough to line up the trigger ring with the sensor, eliminating the need to modify the sensor holder. Then make a starter spacer to line up the BWM starter drive to the ring gear.

The deciding question is, is there anything on the chassis that would be in conflict with the solenoid on the bottom, and is there a problem getting the wires down to it?

It makes no difference to me which starter or combination is preferred.

Attached Thumbnails

 

Steering being in the way comes to mind. Being that close to the ground means exposure to road hazards too. Wiring itself shouldn't be a problem since they can travel from the starter to an intermediate block for distribution.

The 10mm openings for the bolts can't be bushed to handle 8mm bolts?

-CTH

__________________
- cth350@gmail.com
http://www.111lakeside.com/

I think you are thinking about it backwards. The diameter of the BMW starter bold holes are sized for 8mm shank bolts, where as the MB starter uses 10mm bolts.

In order for the MB nose cone to be bolted up to the 420G bell housing, either the 420G bell housing starter bolt holes will need to be opened up for 10mm shank bolts, or the 10mm threads in the MB nose cone need to be shrunk to 8mm threads.

Again, I do not know for sure that the right hand drive starter you found places the solenoid at 12:00, it may be at a 10:00 or 11:00 position. It is just pricey to find out.

I tired to bolt the BMW starter up on the driver's side of the trans and the solenoid hit the block which made it impossible to bolt it up. Silly me, I did not try to install the BMW starter (backwards) on the other side to see if the solenoid hit the block there as well. I will do that today and see if there are any conflicts.

The BMW starter will not plug in with the solenoid above the starter center line. the solenoid hits the block.

I question if the Right Hand Drive BMW starter is not the mirror of the one I have now, which if so, will not work for this application. A lot of the time the pictures used in the listings are generic, but the pictures of the ones I have seen all are mirrors of the Left Hand Drive starter, which has the solenoid at the 12:00 position.

There is a chance that one of the L6 BMW engines has a starter with the solenoid clocked where we need it, but that would have a less powerful motor but we could swap the nose cone so 8mm bolts could be used.

The key visual is the upper starter bolt hole location in relation to the solenoid center line. The BMW V8 starter has the upper bolt in line with the solenoid center line. We want a nose cone where the upper bolt is off set from the solenoid center line.

I am finishing up the reverse engineering of the parts that have to be related to each other and creating drawings. Lots of detail work and checking.

Once the 420G adapter is done, the SBC adapter should be cake lol.

{Sigh of relief}

Today all the reverse engineering of the crank bolt and pin locations, the BMW crank trigger ring orientation in relation to the pressure plate bolts, and the flywheel to crank adapter bolt and pin locations were tested as i drilled the adapter bolt and pin holes in the flywheel.

As part of the measurement and check process, I removed the crank sensor from the holder and made a gauge pin that I used to clock the crank which I then locked in place. In theory, if I correctly related all the various holes that I had measured the locations of, the BMW trigger ring would be at 0 (same as the MB trigger wheel) when the pin lash is taken up in the retarded direction. (I took into account the slight lash from the crank pin to adapter pin hole which is needed to allow for the manufacturing tolerances of the crank and adapter.)

It is on the money at 0 which confirms the measurements and relations are good. The pic is of the gauge pin and BMW trigger ring after the adapter bolt and pin holes were drilled.

If you look close you can see the right side of the large window is on the edge of the gauge pin where it should be.

I am still waiting on the ARP bolts. Very frustrating, but this was the last major hurtle to clear.

Attached Thumbnails