diagnosing rod knock (ahhh I struck coal!)

[DMedal]

I think this is one of those things I knew once and am not now so sure of, so I'll ask. I've got a 16HP older briggs (1 cyl) which is quite loud. I think part of it may be rod knock and I'm thinking I should diagnose that before the rod and crank start to move independently. Do I remember right that I can check it by taking head off and putting piston in mid-stroke, then turning flywheel back and forth, looking for an amount of rotation which doesn't move the piston? If I have to open the crank case up then it isn't going to get done soon. Head on and off I could do fairly easily/quickly. Thanks for any tips- Don

[Willy]

It could be carbon build up on the head and top of the piston. Pulling the head will determine that also. I hope it's carbon , it allot cheaper to scrape then to overhaul.:D

[D-17_Dave]

Just keep running it. The noise will stop sooner or later.:OB):o)

[firefoxz1]

I concur with Willy, could be the piston slapping into carbon build-up. To check it your way will tell if it has a loose wrist pin, rod journal or both. To determine which would require getting into the crankcase.

[DMedal]

thanks, guys. I hope it is carbon too! Head comes off tomorrow and I'll let you know.

[DMedal]

carbon it was! nice call, Willy! even a mark where you could see piston carbon hitting head carbon. I haven't heard it run yet but am very optimistic. No detectable piston play at all. I (carefully) scraped about 3 tablespoons of carbon flakes out of the head, then hand brushed it. looks better anyway. Whew