How-to: checking bellhousing alignment / runout

[LEEVON]

Well, this is my first manual trans install and I like to be prepared. My preparations led me to understand that bellhousing alignment is critically important for transmission function and longevity. It should always be verified and adjusted (if necessary) when installing a manual transmission. There are a couple of tutorials out there in cyberspace, but none here. I found out this is pretty easy, the hardest part is setting up a dial indicator.

Step 1: Mock-up your dial indicator so it is located roughly in the center bore of the bellhousing. I didn't think a magnetic base would work, so I fabbed (and I use the term loosely) a rigid piece of metal to firmly hold the indicator and provide a little adjustment. Here's a look at what I made, it bolts straight to the crank and there's a slot for the dial indicator, which I fastened with a 2" bolt and three nuts to adjust it. With the slot I made and the bolt it could adjust in both axis. It's important that the indicator be in the same plane as the mounting surface, and it will fit in the bore.

Step 2: Install bellhousing onto the engine block (without flywheel or clutch) and snug up the bolts.

Step 3: Rotate the crank, finding near center and zero out your dial indicator and make a mark at that location.

Step 4: Rotate the engine about 30-45 degrees (pick one, keep it consistent). Make a mark where you stop and note the runout. Rotate again and do the same until you have marked the bellhousing in a complete circle.

Step 5: You are comparing these measurements against each other in planes. If you have a reading of .010 directly opposite of -.006, subtract one from the other and divide by 2 to determine which way the bore is shifted. In this case, you have .004/2 = .002 or "2 thousandths".

Step 6: Runout should not exceed .010. In my case all measurements opposite each other were less than .010 so I'm good to go. However if your runout exceeds .010 you will need to source bellhousing alignment dowels, which I believe are available in increments such as .007, .014, .021.

If I'm off the mark or missed something please feel free to add to this thread.