[B_man_Al]

My model B 4 cylinder has developed a mysterious knock/rattle at idle or during deceleration but is not there when the engine is rev'd. Its more like a loud rattle rather than a knock, and appears to be coming from the valve or timing gear area, but not sure. The engine runs fine, so I don't think its the distributor drive or a broken valve spring.

The noise doesn't change as each spark plug is sequentially shorted out so I don't think its a connecting rod or wrist pin.

I put an aluminum cam gear in it a few years ago, wonder if one or more of the teeth got screwed up?

Any thoughts before I rip it all apart ? What order to check these things?

Thanks Al