Series I engine rebuild

Old technology isn’t necessarily simpler, in fact it demands a lot of old-style thinking, as Ed Evans explains

Crank and pistons: old tech isn’t always simpler

THIS is the most fascinating engine build I’ve been involved in. Maybe that’s because I’ve never built a Series I engine, but then, nor has Britpart’s Steve Grant who is about to assemble this one. Of course, we had the workshop manual, a lot of advice from Series I specialists, Steve’s ingenuity, and the fact that both of us have built plenty of engines in the past. So, based on previous experiences, I was expecting the job to be finished some time after lunch. Later that day, we were quite pleased to have successfully fitted just the crankshaft and pistons.

It was the fitting of the pistons that had us thinking. On most engines it’s simple – you attach the piston to the conrod and feed the conrod into the cylinder from the top, using a ring compressor to hold the piston rings in as the piston passes into the bore.

There are three reasons why this doesn’t work for this 2.0-litre Series I engine. First, the conrod’s big-end bearing journal is too wide to pass down through the cylinder. Second, the top surface of the block is angled and has the hemispherical combustion chamber machined into it so, unlike on a conventional block, the piston ring compressor doesn’t hold the rings in as the piston is entered into the cylinder. The third reason is that it’s impossible to enter the piston upward from underneath because the internal casting shapes prevent the use of the piston ring compressor. The workshop manual has the answer – before fitting the piston to the conrod with the gudgeon pin, push the conrod up from inside to meet the piston being entered from above, and then fit the gudgeon pin to link the two together. That doesn’t address the problem of entering the piston rings into the bore, and we didn’t use that method anyway.