496 Grooved Idler Pulley
 

While rebuilding my raw water pump I figured I'd replace the idler pulleys as well. The 2 smooth surface pulleys were easy to find - same diameter, bolted right on. The grooved pulley, which rides on the top of the bracket that gets removed while pulling the raw water pump, I cannot seem to find. I've worked with 3 different boat parts suppliers and 3 auto parts suppliers, no luck. When I, and everyone else, look it up through the engine VIN I get a grooved pulley that is 3.5" dia (pn = 865444T). It seems that I have the only 496 with a 3.25" dia. I cannot find this pulley for the life of me. The 3.5" dia pulley will not fit with the OEM belt. The bearing feels solid and I even pulled the seal to inspect and re-grease, however, the pulley grooves look tired. The only ID on the pulley is DAYCO 00076, which yields zero results. Any guidance would be appreciated!

Try this guide with your dimensions

https://www.daycoaftermarket.com/wp-...2019_GUIDE.pdf

Also, don’t quote me but I believe it cross references to Sierra p/n 18-6457

Where are you measuring the 3.25? Overall or on top of the grooves? I'm not sure what Mercury calls 3.5. I'll pull one off the shelf and measure in the AM

we went to our shelves and found one that is about 3.25 overall and 3 over the grooves.

https://www.mercruiserparts.com/807757t-pulley-idler

Which is the same as Sierra 18-6457