I read some where that I have to change my distributor gear if my distributor is coming from a non roller cam to a roller cam. How can I tell what gear I have. The dist. is a IV that I bought used so I really dont know what it was originally on.

Before I bought the new 502 crate. I used the dist. on my old 502 that I converted to a roller cam and the gear showed no adnormal wear after over 100 hrs. So should it be ok to use this on my new roller 502? How long does it take to notice if Im using the wrong gear. Is it something that happens right away?

It depends on the cam. Are you running a GM high performance cam such as the ZZ502 cam? If you are you will need to use the "melonized" distributor gear that you can get from GM. On the other hand most hydraulic roller cams from Comp or Crane don't require a special gear.

Best bet is to use the new GM melonized gear made just for roller cams, its PN# 10456413 and is pretty cheap insurance. Thats the gear I used on my old merc distributor when I put the 502 in my Baja.
PS, you should not use the 502/502hp GM cam, its lobe centers are too close and that can cause reversion. I used the Ultradyne cam and am more than happy.

Thanks for the info. I dont know what cam it is other then it is a all stock GM MARINE 502 / 415hp crate. Is there any way of telling what gear is on there?

I went and ordered one from summit just in case for $29.00