1997 250 hp SSII Bangs in gear w/ new prop.... ??

I am helping a friend troubleshoot a problem. 1997 250 hp Saltwater Series II OX66 engine. He ran a 14-1/4 x 19 prop without any issues. Recently he bought an Apollo 15-1/4 x 19 prop (new) and upon the first test run noticed a significant "clunk" when placed in gear. At cruising speed (4000 rpm) there are no odd noises or vibrations.

I drained out the lower unit oil, no water, no metal. I verified that the thrust washer was installed properly, as was the prop nut and washer. Hub spacing appears correct as well. I do notice some end play in the horizontal propeller shaft.

I put the original prop back on and the "clunking" goes away.

The propeller shop told him it has nothing to do with the propeller.

Any thoughts?

Thanks

It is just a bigger, heavier prop so the inertial loading in more dramatic when the clutch engages. Not to worry though. They can do that seemingly forever with no ill effects.