Odd noise

[Charles P]

Thanks chaps. All good ideas.

Phoenix crank, Barlow rods and a Bonewell blown cam & followers - which isn't particularly high lift. The crank is held at the rear main with floating front bearings. The Barlow rods are a tighter fit than Phoenix and number 3 rod has more thrust face float than the others from the balancing. Not excessive but it does warrant a look again. However surely a rod moving around axially on the pin wouldn't be limited to a trailing throttle?

I had the engine out last week and dived in from the sump. I couldn't see any evidence of rods hitting lobes with my mirror on a stick. I turned it over by hand to try and replicate a collision and drew a blank. Doesn't mean that it isn't it hitting.
The "off throttle " nature of the rattle makes me suspect anything driven by helical gears which leads to cam moving.
I too, have suspected a cam follower problem but why would the noise manifest itself on the trailing throttle, unless the cam is moving (which I didn't think that it was). The tappets were in the previous engine before I destroyed it so shouldn't be soft.

Keep it coming

Charles