I bought a used Shimano Sienna 4000 FD spinning reel a while back. Yesterday while fishing I noticed that after casting and turning the handle to engage the reel,occasionally the reel handle where was very hard to turn. Sometimes the reel engaged quickly and smoothly as it should,but when it didn't it was really noticeable. Anyone have an idea what's causing this?

Using the handle to shut the bail on a spinning reel isn't a good idea. Use your hand to shut it just like you did to open it.

Always open and close the bail on a spinning reel by hand. Turning the handle to close a bail will often time induce line twist. Now go cast it a bunch manually opening and closing the bail by hand. Pay attention and see if you experience the issue you were speaking of. I know I have heard some people complaining their SHimano Symetre reels are binding up.  If you experience the  problem again then go get the reel professionally cleaned and serviced.  That would be your best option. 

I gotta be honest here. I've been using spinning reels since the first Garcia Mitchell reels came out and this is the first time I've ever heard this. It makes perfect sense!  I've been using Spirex reels for so long and never had any issues with engaging the reel and this Sienna just threw me a curveball.

Always great to learn something new!

Thanks to pawpaw and fishnkamp!

Closing the bail by hand is good practice. Make sure the line roller is right on top if you want the bail trip to work smoothly. What's likely happening is the trip lever is too close to the ramp and binds a bit initially 

48 minutes ago, Delaware Valley Tackle said:

Closing the bail by hand is good practice. Make sure the line roller is right on top if you want the bail trip to work smoothly. What's likely happening is the trip lever is too close to the ramp and binds a bit initially 

I did notice that when the line roller was to one side or another that's when I had trouble. Thank you for the feedback.

3 hours ago, fishnkamp said:

Always open and close the bail on a spinning reel by hand. Turning the handle to close a bail will often time induce line twist. 

Please explain how turning the handle to close the bail will twist the line. 

The reason line twist is induced is the bail rotates almost a half of a rotation while the line is"loosely" coming off the spool ( remember at this point the lure is slowing down from being at the end of your cast and also from the resistance of the water. This is sorta like reeling while a fish is pulling line out against the drag.  Years ago a Lake Erie fishing guide brought that to my attention. His solution, since we were fishing deep, was to slow the line a bit with my finger, then allow the line to pull off as the lure sunk and manually close the bail. I raise my rod up just a bit at the same time to be sure the line is tight on the reel before I turn the reel handle. It is a smooth motion and it just happens now that I have been doing it this way for maybe 15 years

Line twist is also much less of an issue with braided lines when compared to mono/fluoro. 

As mentioned get into the practice of closing it by hand. 

Closing the bail by hand will NOT prevent line twist. It will prevent formation of loose loops in the spool.

 You bought a used $29.99 reel?  Why?  Go to Walmart and buy a new Shimano Sienna 4000 FD spinning reel.  

I'm really surprised no one mentioned lube.  You have a used reel and no idea of whether it has ever been lubed.  Put a drop or two of good oil on every moving point on the reel (roller, bail pivots, grips, and into the hole where the handle goes, both sides)  .

Then try to get into the habit of closing it by hand.