Engine Assembly and clearances

Covid 19 has slowed down an engine rebuild Francois and I have going on for a customer of ours. When the shut down hit, our machine shop had just finished cutting valve seats, and installing guides to the heads, and I wanted to fit valves, install springs, and assemble the heads at Francois’ shop, but I also didn’t want to get Francois, an octogenarian, sick if I was exposed. I decided to take the heads to my shop and do some of the work there and remain socially distant until things got better.

A few months later, Francois and I felt it was safe enough for me to come down to Connecticut and start assembling the engine. I would wear a mask when we were working near one another, and we would try to limit contact.

As I installed the main bearings on the engine, I felt contact of one of the crank throws with something inside the block.

On closer inspection, one counter balance on the crankshaft was touching the bottom of the cylinder liner and not allowing the crankshaft to completely rotate in the block. The liners were previously removed, descaled, cleaned, and reinstalled in the same holes they came out of, so it was strange that the clearance had changed significantly enough to interfere with the crankshaft. Our thought was perhaps this particular liner was not cut symmetrically by the factory, and when my machinist reinstalled the liner, it turned enough to allow part of the liner skirt to come in contact with the crank balance weight.

The interference was very slight, but I decided to take the block and crank back to the machine shop to clearance the liner, and have everything else checked again. I guess this is why we check, double check, and then check again all of our work!