I made a discovery today that might save some of you engine assemblers a little (or maybe a lot) of grief- - - -or maybe I'm just not as smart as I've always thought! The latter is a distinct possibility, BTW! John and I started reinstalling the reworked cylinder head on the 261 engine in Charlie today, and things were going quite well, at least once a couple of his neighbor guys gave us some much-needed assistance lifting that HEAVY cylinder head back into place. A couple of long 1/2-13 bolts with the heads cut off and a screwdriver slot hacksawed into the top keep the head gasket aligned and also guide the head into the proper place on the block with no damage to the gasket.
Now, here's the "Eureka" moment- - - - -a stovebolt can definitely be an "interference" engine under the right circumstances! The rehabbed head got a slight mill job to be sure the blown head gasket was not the result of a warped head, and all new valves. Once the rocker arms and pushrods were installed, I stated doing a preliminary valve adjustment- - - -get a piston close to top dead center, snug the adjuster screw down gently, back off 1/4 turn, and lock the jam nut down. Move on to the next cylinder in the firing order by turning the fan. WAIT A COTTON-PICKIN' MINUTE- - - - -THE ENGINE LOCKS UP! This happened repeatedly. After a lot of head scratching, and a few choice quotations from the "Old Mechanic's Book Of Words And Phrases" we finally discovered the cause of the problem. Those aforementioned brand new intake valves must be slightly longer than the ones we removed, and unless the rocker arm adjusting screws were backed up several turns, the pistons and intake valves were getting together at the top of the exhaust stroke as the intake began to open. I had no idea that a stovebolt engine could do that! Exhaust valves aren't a problem- - - - -due to the angle they're mounted into the head, there's no way for piston/valve contact to happen, no matter how far the valve is opened.
Fortunately, I didn't use my normal method of adjusting valves- - - - -move the starter linkage to spin the engine to the next cylinder in the firing order. Just one time doing that would have resulted in one or more bent valves or pushrods, or maybe a broken rocker arm. We will be putting the finishing touches on the job in a couple of days, and I'm planning to do a bit of research- - - - -get a piston to top dead center on the exhaust stroke, and use a dial indicator and a pry bar to measure the clearance between the opening valve and the top of the piston. I have a sneaky feeling that it's going to be a lot closer than I thought! Stay tuned for more information!
Jerry
