Old flathead engine: Valves first or cam first?

Question

I'm reassembling an old inline-4 flathead engine... the kind with valves in the block (not the head).   I did not disassemble it; I got a huge pile of parts I'm trying to turn back into an engine.
The lifters have buttons on the "cam side", which means the lifters must be installed prior to the cam.   However with the lifters and cam in, inserting the valve springs is more difficult.
What sequence is required to assemble it?  Can I install the valve springs then lifters then cam? (that would make it easier to install the valve springs).  Or will installing the valve springs and lifters make it impossible for the cam to go in?  The middle and back cam bearings are larger than the cam lobes, obviously, so I'm concerned they wouldn't be able to get past a valve that is shut.

alephzero · Answer

You need a valve spring compressor to assemble the springs onto the valves and guides and fit the retaining clips (or whatever they are on your engine). This step is actually easier than on an overhead engine, because you don't have to assemble the valves and springs from opposite sides of the head. Find some way to clamp the spring compressor onto your bench, so you don't need more than two hands to hold everything.
The assembly sequence is camshaft (and make sure the timing is correct if it is a direct gear drive and not a timing belt or chain), then lifters, then valves. You will probably need to improvise something to hold each valve in place while you fit its retaining clip. You can rotate the camshaft to give the least compression of the spring when you fit each individual valve, of course.
There are some flat-four and flat-six aero engines still being manufactured (e.g. the D-motor company in Belgium). You might be able to find some maintenance documentation for them to use as a general guide.

Old flathead engine: Valves first or cam first?

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