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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.

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  • Photos would really help here.
    – zipzit
    Sep 17, 2020 at 20:25
  • Lifters then Cam first for sure, then You have to use special spring compressor and valve keeper installation tools
    – Moab
    Sep 17, 2020 at 20:51
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    Listen to @Moab as it sounds like he's done this before. I have no experience with flathead engines, and as such was going to suggest doing the valves first. I'd definitely pre-assemble the valves though, to ensure you've got everything in the right place and you've got all the parts. Plus, you'll want to lap your valves prior to final assembly. That's going to be more easily done before the lifters and cam goes in.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Sep 17, 2020 at 21:02
  • Rebuilt a few of them in the day
    – Moab
    Sep 17, 2020 at 21:10
  • Since from a "pile of parts" you might not even know which valve came from which cylinder, lap the valves before you do anything else!
    – alephzero
    Sep 17, 2020 at 21:14

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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.

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  • Spring compressor : luxury! I used a ring spanner and dropped the collets in ...
    – Solar Mike
    Sep 17, 2020 at 21:21

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