I aquired a really nice remington 742 last year.The smith I purchased it from suggested that I use bullet weights 150 grains or less as anything heavier would cause harm to the action.Any comments?

I think the damage can be done by using heavy bullets and slow powder. If chamber pressure stays high after the bullet has passed the gas port the case will be extremely difficult to extract. That leads to a broken extractor. That means that somebody has to remove the barrel to remove the bolt to replace an $8 item.
I replaced one for a friend, no charge, a few years ago. 740/742 Remingtons are not allowed in my shop, anymore.
A rusty, pitted chamber can also cause difficult/no extraction.

Burke--

Factory rifles are made for factory ammunition. There's no factory 30-06 ammo that will harm the 742 but plenty of it may not shoot well. I've never seen a 740 or 742 that didn't operate and shoot the Remington 180 gr CoreLocts pretty well. It was my standard test fire ammo for them for 30 years.
However!! From a gunsmith's point of view,
"Really nice 742" seems to be a serious contridiction in terms and borders on being an oxymoron.

Use nothing but dry lubes in parts above the trigger group. A loose patch with moly or graphite powder on it swabbed through the chamber works absolute wonders on the rattle a matics. One treatment last about 20 rounds.......the average total number of shots fired in American centerfires per year. (look it up. NSSF)

thanks again guys.Thank god I do the majority of my hunting with a custom 25-06.The 742 was bought for a song,and was meant to be a back up.And so it shall remain.Thanks.

Jay is correct. If you use factory ammo, no problems. If you handload 180 or 200 grain bullets, use powders like 4895, 4064, or WW748.....