VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Piston rods

Hi all, after taking Dad's '27 out for a spin, after 10 mins down the street, at 30mph, it developed a loud knocking/thumping sound! As I turned the corner it lost power and eventually died. Would start again but not stay running. We towed it home and I took the valve cover off and used the crank to turn it over. No weird sounds, nothing unusual to me! Took the oil pan off and fearing the worst, found no loose parts, no damaged pistons or rods.
But I did notice where the rods connect to the crank, #1 is nice and tight while #2,#3 and #4 do have some play, not much, but can move the rods back and forth alittle!
Should they all be as tight as #1? Please help!!

It is "normal" to be able to move the rods back and forth.
The rods are adjusted to proper clearence by removing shims that are between the rod and cap. Shims are removed until the rod can not be moved back and forth by hand but will move with a tap of a small hammer. Then after broken-in they wil move back and forth by hand.
So the rods that move back and forth MAY be OK or may be loose.I would worry about the one that doesn't move.
All bearing surfaces should be inspected.

There are typically three places to look for a clunk sound source. Center main bearing including thrust surfaces, wrist pin/bushing, piston to cylinder bore. The center main bearing is fairly common source.

Does it clunk under load? Accelerating? Decelerating? low speed? higher speed? same at all speeds? Maximum at one particular speed?

Often the source can be found by listening with stethoscope, pipe, long screwdriver, rod or similar device placed in different places on a running engine. The type sound will also be a clue. Thud, whir, click, tick, tap, bang, clunk, clank, etc. might indicate the problem.

Chev Gene/Chipper, Thanks for the replys, Will look at all that and keep you posted!!