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Raven in the Sea of Cortez and British Columbia
Several days work.

Here they are. The homemade replacement grade eight bolts (six required) to mount the flywheel onto the crankshaft. The two black ones are the Mercedes originals that are stretched and failing. The beefier shiny ones are the new bolts that I machined with lots of help and shop-sharing from my neighbor, Don. These are hard steel 10mm x 1.5 pitch bolts that were literally hiding inside some larger 1/2" US bolts. The six flats on the head were milled down from 3/4" to 17mm, one flat at a time, turn 60 degrees, another flat, etc. Threading the hard steel ate up three new threading dies. The new bolts are purposely a bit larger and have about two extra threads to carry a deeper nut, thus spreading the load. There is room for them in the engine configuration.

03/18/2013 | Allan Smith
LOL! You just made me think back to my days as a naval mmachinist and the arguments (some were fierce) about which were stronger, fine threads or course threads, (yeah, we had some spare time on our hands).
Bolt from the blue.

So I was 95% finished with the reassembly of the motor when I mounted the flywheel and while torquing the last six bolts one of them stripped. Arghhhh!!!!!
The torque was right by the book but the bolt was tired. Once I got it out (no fun) I could examine the others. They all were stretched and ready to go. Have to be replaced. The pan and block make it impossible to remove the bolts from the crankshaft flange - thus removing the oil pan. This meant putting the motor back on the assembly stand, rolling it over after removing the newly mounted fuel injection pump, and removing the oil pan once again. This took some work as it had been all sealed down ready to run. Now it was a cleanup problem. Mercedes wants $125 a bolt and nut. That's ONE bolt folks. Thus my machinist buddy and I are making them. This is a pic of a grade 8 (hard steel) US 1/2" bolt on the lathe being turned down to 10mm. Then we have to cut it shorter and thread it. That's a part I'm worried about.

Pump drive adaptor with new pin.

A new 7mm hard steel pin fit with a few modifications. There is the damaged one beside it. The original was not hard steel. That was the problem. The new pin is a mild press fit and has a retaining circlip.

Bad stuff hidden from view.

The raw water cooling pump on the Nanni Mercedes 636 from the 1980s is driven by a steel pin in an adapter attached to a timing gear. The original was almost cut all the way through and would have caused instant overheating had it broken. The pieces could have easily gone back through the timing gears and caused fatal damage. If you you have this Nanni motor, check this out by removing the raw water pump and looking in there to see if the pin is eaten away.

Put a damper on it.

One broken worn out part was the damper plate that attaches the transmission drive shaft to the output of the engine crankshaft. If it had actually quit the running engine could not have turned the propeller. The new one is not based on springs, but rather uses high tech plastic flex materials in between the two steel plates.

A head on its shoulders.

Here you see the block has had the head added and the oil pan installed. The valve rockers are in place on top of the head.

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