Hey everyone. Whats a good way to tell your motor mounts are bad?  I've always had a grinding noise when I really get on the throttle in first gear and torque the engine up. Tonight I took the hood off...and floored it in first gear. My engine flexed quite a bit, and it sounded like the grinding noise is coming from the front of the engine near the fan. The alternator looked like it jumped up about 4-6 inches.  Is this normal?

I got under the car and checked out the mounts. From visual inspection, nothing looks wrong. All bolts installed and torqued...bushings look a little worn...and the welds between the frame and mounts looks good.

Shane, the engine will move when you hit the throttle, but 4-6 inches movement on the alternator isn't normal. It sounds like your fan is hitting the shroud, which would leave a mark. It also appears to me that you do have a bad mount. Hopefully Joel will offer more expertise on this. Mounts aren't that hard to replace. 

Shane here is a link that might help you:  http://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Replacing_Your_Engine_Mounts.aspx

Shane, you also need to check your transmission mount.

My left motor mount broke and raised the engine enough for the alternator bracket to hit AND crack the hood. I have a spider crack about the size of a golf ball - it kills me every time I look at it.

  Make sure you get the correct motor mounts for a 350 Corvette and not a 305 Corvette. A few people have received the wrong mounts only to find out there are two different mounts for a 63-82 Vette.
Good Luck and post if you have any problems!

if there's nothing hitting the shroud, it could be a water pump or other belt driven component starting to wipe a bearing...LukesVette2009-01-11 13:55:01

Yeah...after closer inspection...motor mounts are BOTH shot
I'm looking at the polyurethane bushings from Jegs (Energy Suspension part #355-3-1114G).  They measure 2-5/8'' Width x 1-3/4''Height. Does this sound about right to you guys? I would take mine off now to measure, however the "Red Dragon" needs to roll under its own power to a buddy's house to put on the hooker headers and side pipes tomorrow .

I was gonna go with solid mounts...but with a fiberglass body...I didn't want to run the risk of torquing the frame and cracking something.

Shane, I went with these from Summit Racing. They worked fine....  http://store.summitracing.com/partdetail.asp?part=ENS%2D3%2D1120G&FROM=MG

Corvette440hp:  Thanks. I just ordered the kit. I've figured out how to get the motor mounts in with the floor jack and block of wood (thanks again for the link)...any helpful tips for the tranny mount?