Even though the bell housing is out of site out of mind, it is still a very important part of your vehicle. It is the connection between the engine and the transmission, the critical point being the connection between the crankshaft and the transmissions input shaft.
When a bell housing is not properly aligned, the crankshaft and input shaft will also be misaligned. Even if it is only a small difference, and everything is bolted up, the misalignment will still cause serious problems with the clutch and the transmission. (If everything is aligned correctly, the transmission input shaft should slide into the clutch very easily. If you have to force it in, you will also shove the crankshaft forward into the face of the thrust bearing.)
- In order to ensure that your engine crankshaft and input shaft are in as straight a line as possible, there are steps one must take. One way is to bolt up your flywheel to the crankshaft flange (remember that you are only using the flywheel to hold the magnetic-based dial indicator. You do not have to torque the bolts at this time.)
- Once you have the flywheel on, bolt the bell housing to the engine block. (Make sure that it is tight, but there is no need to torque the bolts yet.) Put the base of the magnetic mount dial indicator on the friction contact area of the flywheel, then arrange the indicator arm so that it stays along the inside diameter of the bell housing’s register hole.
- Next, mark the bore housing in four quadrants; 12, 3, 6, and 9 O’ clock. Spin the dial indicator until the dial is pointed to 12 O’ Clock, mark that spot and set the indicator at 0.050. Yes, this is the same as calibrating the gauge, but setting it at 0.050 makes it a little easier when it is time to do the math portion.
- Next, spin the crank 180 degrees so that it points to the 6 O’ Clock mark. A reading less than 0.050 means that your bottom is closer to the crank center line than the top of the bore. To correct that, move the bell housing down by ½ the difference between the two readings. For example, if the 12 O’ Clock reading was 0.060 and the 6 O’ Clock was at 0.020 then you would move the bell housing 0.020 inches. (The difference between 0.060 and 0.020 is 0.040, then divide that by 2 (because you wanted to move it half) and it would equal 0.020) When the number is larger, the bell housing has to be moved up. Everything else stays the same.
5- Then you move to the side to side numbers. (3 and 6 O’clock) and repeat the same steps. Put the dial at 3 O’clock, then move it 180 degrees to 9 O’ clock and see if there is a difference. If there is, use the above mentioned math to move the bell housing as needed.
When you are finished with this process, you want your bore to be centered over the crank center line within .050 inch in both directions. If for any reason you have to remove the bell housing, this process should be repeated.
If when you are finished you discover that your measurements are more than the .005” allowed, you can use offset dowel pins to fix the issue. These pins are specially made in 3 different offsets; .007”, .014”, and .021” to allow for a wide range of alignment adjustments. Dowel Pins are made to align your bell housing to your engine.
“To Install a Dowel Pin
- Remove the bell housing from the motor and remove all original bell housing dowel pins. Once you’ve removed the old dowel pins, make sure the bores are clean and smooth.
- Once side of the new dowel pin has a slot this side goes out toward the transmission while the other side is inserted into the engine block. The dowel pin has a high side and a low side. To find the high side, place the pin on a table with the slot facing up and down. Put pressure on the top, center of the pin and one side should come completely off the table. If it’s not the slot side, turn the pin 180 degrees, if it is, you’ve found the high side.
- Install the dowel pin with the high side of the dowel pin pointed toward the area with the low side mark on the bell housing. Tip: apply a little grease to the pin to make it easier to insert and rotate.
- Install the second dowel pin parallel to the first.
- After the new dowel pins are installed and oriented correctly, re-attach the bell housing and set up the dial indicator once again. Re-measure the alignment as you did the first time, and verify the measurements are within specification.
If not, the dowel pins may need to be rotated slightly to bring the numbers into spec. Repeat until the bell housing meets the .005” requirement.
Once this step is complete, it does not have to be done again, unless you replace the bell housing. As long as you use this bell housing, you can remove and replace it over and over again, without the need to re-measure the alignment.” (Ben DeHaven How To: Dial-In a Bellhousing)