I'm running my spare (1926) engine cos I still haven't sorted the original after the piston pins seized on last year's April Fools Run.

So what happens on this year's Run? A clatter from the front of the engine. Not a worn timing gear, it's got a new fibre one. Not a loose crank pulley. Quiet when you open or close the throttle, loud on a light throttle, quieter when you retard the spark. What should I go looking for?

Upper fan pulley?

Just how new is the fiber timing gear? I'm no mechanical expert by any means, but I've heard nothing good about them. So maybe it IS the gear?

Jem, this doesn't answer the question, but even if the fiber timing gear isn't the problem I would sure get rid of it. Bronze, aluminum, nylon, original, anything but fiber.

Is the nose on the pan tight in the spring/engine mount at the front?

Allan from down under.

Your description sounds like a loose connecting rod to crankshaft bearing. Remove the inspection plate and check the bearings. You should have no more than 2 thousandths inch clearance. If you adjust them adjust to 0.0015"
Norm

Did you check camshaft end play when you changed the gear ? Before going over my T last fall there was a similar light rattle, not a deeper con-rod knock. (Fiber gear in my T ran over 15k mi. in 12 years I'm told. By then the web was warped and the lock nut was loose, there was excessive end play. I replaced it with an aluminum gear and used a shim kit from Chaffin's. )

I'm with Mr. Kling.
Took a wrong turn once in 1958and ended up in a very steep hill. Low started slipping and glazed the band, but i also got a rod knock. Had to drive home alternating throttle position between wide open and closed. Any part throttle position caused severe knocking. Took all the pistons out and had the big ends of the rods repoured with fresh babbit.

See if the camshaft rocks up,down and around when you grab the timer roller with a rag.
For some reason,in my experience,some 26-7 engines have the i.d. of the front camshaft hole a little too big,eventually causing an erattic clatter that varies strangely.Also could just be worn front cam bearing.And,of course,what others suggest.

I think cam end float is the problem. No sideways movement but I can move the shaft maybe .030 back and forth with a audible clunk. Nothing loose in the bottom end.

And Mr Jelf is right about the fibre gear. One tooth is starting to break up so I'm going to an ally one.

I shall shim out the cam nut and see if that quiets it for a while, the engine will come out later in the year as the mag coil is shorted. Thanks tor your help gentlemen.

Jem,l wonder if your fibre cam gear might be loose,rocking around on the pins.
A new gear is definately in order.Those new fibre gears like to loosen up for me.
I had an A that the modern repo gear would loosen up on,because the flat nut that held it on had a raised spot on it that would bed into the gear,and then gradually loosen up.Drove me to distraction until finally solved.