For my config, I chose a knee with an 81mm rise – we can find it in ETA engine blocks, as well as in the diesel m21b24. The diesel elbow is forged, unlike the ETA, and many have expressed the opinion that it is better to put it on – more reliable and all that. But I still chose the crankshaft from the ETA engine – it is much easier to find, and also the guys from Metric Mechanic, which builds strokers based on the M20, wrote that the diesel knee can burst.
Let me remind you – the m20b27 engine was installed on the e28 and e30 – we are looking for it there.
The beginning – as usual – mine:
We are taking it to the turner and we hope that something can still be done with this piece of metal. All necks are inspected for scoring, measured with a micrometer, the knee is placed on the stand and checked for runout. After this, a verdict is issued – throw it away or sharpen it to the repair size.
In my case, they sharpened in the first repair (+0.25) both the main and connecting rod journals.
It is highly desirable to also grind the surfaces where the front and rear oil seals will be located (again, you need to look to see if we get out of the tolerances). All the crankshafts that I saw had grooves in these places. Of course, you can not bother and, when pressing, just move the seals a little to one side or the other from the groove, but this is not my option.
In order for everything to be absolutely perfect, it would be necessary to balance the crankshaft assembly with the flywheel and damper (front pulley) that will be installed on this engine. But in my city they can’t do this anywhere, and they didn’t manage to take it to neighboring Voronezh, and later, after talking with people about balancing, I decided to abandon this idea. Maybe in vain.
After turning and polishing the knee, we wash it again. And also ALWAYS clean the oil channels, even if the turner swore that he had already done it! It will be unpleasant to screw up the engine due to chips or abrasive left there.
We also change the bearing on the flywheel side.
Here is another small step in the construction of the engine.