whats the difference between the 621 bellhousing and the 486?

Bearing retainer hole size.
The 486 is the truck housing with a 5 1/8" hole- car is 4 11/16".
You can use it with a spacer(# BR 4 at www.novak-adapt.com) or the oversize bearing retainer (believe from Auto Gear)for the Muncie.

Pay close attention, read carefully.
BOTH bell housings are for the big, 14in diameter, 168 teeth flywheel.
The 621 is a car housing.
The 486 is a truck housing.
The truck housing has a LARGER hole than the car housings, thus, without either an adapter ring to fill the gap between the hole in the truck housing and the front bearing retainer of a car tranny, such as a Muncie, the tranny may not get properly centered in line with the crankshaft.
Here is the 486-621 side by side. The truck (486) housing can be IMMEDIATELY identified by that extra bulge around the bottom.
http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/705561-R1-07-18A.jpg

Here is a truck housing, Muncie front bearing retainer and the required adapter ring.
http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/Truckbelladapterring.jpg

http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/Truckbelladaptringinstld.jpg

I hope you took notes, there will be a test in first hour Mon morning.

thanks alot!!!

not offering advice but in the 40+ years i have been messing around with GM transmissions the size of the bellhousing hole has never been a factor other than we couldn't put a large bearing retainer tranny in a small hole. have put many a small bearing retainer transmission in a large hole and am about to do that in my 66 this week.

Great post Tom!! This should be a sticky post!!!!!

Great post Tom!! This should be a sticky post!!!!!

There is---------or was. You have to go the last 2-3 pages for all the pictures because whan I originally put all of this together, I moved the pictures to a different folder and didn't realize that the original pictures would no longer be posted. So, I did it all over again AFTER I moved the pictures to the different folder. Thus, you simply have to go the the later pages.
http://www.chevelles.com/forums/showthread.php?t=142525&highlight=101+Bellhousings

Ya, now that you mention it, that was a sticky post I think! :confused:

Maybe a moderater while chime in to advise why sticky posts are hard to come by or don't seem to stay sticky here...??