We worked on the Mercedes 280 SE, and I found an assembly error that should have been designed out! While reassembling the radiator system (it has two radiators) my Son cross threaded an aluminum fitting. I told him that he should be More careful on reassembly.
The damaged part is welded on to an aluminum sub radiator used to cool engine oil. It is a 22 by 1.5 metric thread, and they want $1068.00 for a replacement part! We found one online for $200, but it looked the same as the one we had.
Time for Dad to get involved:
This is the be sub-radiator commection involved, along with a new threading die to fit. I bought the die because I didn't want to single point a new metric part this big on my engine lathe.
The first step was to clean the old fitting to see if it can be salvaged. This is where I found the design / assembly error! This fitting had to be aluminum in order to weld to the aluminum sub-radiator. This causes a specific risk that should have special treatment. Aluminum is a soft metal, so it should be hard anodized; once it has need welded on.
The second issue is that the threads MUST be perpendicular to the surface of the sub-radiator! These are Not, and That is why my Son cross threaded this part. It was welded at about a ten degree angle off square, on a direction that is impossible to observe!
This, combined with a steel hose fitting; guarantees this problem must occur!
The threads cleaned up:
This made the die a very good purchase! I threaded this myself because of the offset from the factory. We ended up with a 95% thread, which was more than enough; since the seal is on the inside.
I had the brass located for the replacement part, but we got lucky; and got good cleanup!
This assembly has been repaired before:
In the past, a good mechanic had this unit off, and repaired it properly on this drain hole. Since it is alinum, this smaller hole, that shows up in the first picture on the lower right; has been repaired with a helicoil! You can see the trailing edge of the helicoil insert here.
With the touted quality of Mercedes-Benz,this sub-radiator should have been copper! This was designed badly and assembled poorly, which is unusual for a Mercedes-Benz design!!!!
We had the same problem reassembling this system; but I told him no wrenches, and it must be fully tightened first by hand. I ended up doing this part myself, because I knew the incorrect angle on the assembly! It screwed all the way to the bottom, then I torqued it about a third turn for final sealing.