You may remember I asked your advice about a month ago after a developing an engine clatter on our April Fools Run. Best suggestion seemed to be camshaft end-float letting the cam bang against the timing cover. I rigged a bronze thrust washer to sit on the nut and it seemed to ease the noise but it was still there.
Off came the head. There was oil sitting on #2 piston - could the oil ring have broken up? Out came the piston, rings all fine but as I held the piston horizontal I noticed the con-rod sticking straight out to the side. Seized or very stiff piston pin.
So I pulled the pin and honed the bore till it swung nicely, then checked #1 & #3 - no problem. I wasn't going to wrestle with #4 unnecessarily as the noise was definitely toward the front.
Interesting thing is on last year's April Fools I had the same problem with the open-valve engine, only that seized properly on #1 & #2. Two engines, both nicely run-in (about 3-4000 miles) both std ally pistons, same problem.
Back to just the normal Model T clattering now.
BTW, the lady wife had said 'could it be piston slap?' Nah, said Mr Knowall. Best listen to the Memsahib from now on.
Glad you got it resolved!
Hate to mention this now that you gave it all back together and running good, but... If you had a tight wrist pin, there is a very high chance that you now have a "bent" rod. This is nothing that you can see by eye. I chased an engine problem for a number of years following a wrist pin seizure. After multiple tear downs and much money spent, I finally simply mailed the four rods to Herm Kohnke for inspection. He found issues, corrected them and my motor runs smooth and quiet.
Good point. I did check for any twist on the rod. It was only stiff not totally seized, so it was making the piston slap against the bore. In the other engine they were seized and the pistons got some light damage. Haven't got round to re-assembly of that one yet.