Bellhousing Alignment - Alignment Issues

Written by on July 26, 2006 Few People Are Aware That An Improperly Aligned Bellhousing Can Cause Serious Drivetrain Problems. Thankfully, The Fix Is Easy
Bellhousing Alignment - Alignment Issues View All 12 Photos
Ctrp 0607 01 Z+bellhousing Alignment+ 2/12 An improperly aligned bellhousing can cause premature bearing wear, but it can also cause horsepower-robbing drag. Fortunately, the fix is easy.

For many racers, the bellhousing isn't considered any more often than Christmas in July. Out of sight, out of mind after all. But the bellhousing is more than just the place where the clutch resides. It is also the connection between the engine and the transmission. That's no big deal if you think it only connects the engine block to the transmission housing, but the critical connection is between the crankshaft and the transmission's input shaft.

If the bellhousing isn't properly aligned, that also means there will be a misalignment between the crankshaft and the input shaft on the transmission. In many cases the misalignment is slight, and everything can still be bolted up. Improper alignment can cause serious damage to the engine as well as premature wear to the clutch and tranny bearings.

Ctrp 0607 02 Z+bellhousing Alignment+ 3/12 If everything is aligned correctly, the transmission input shaft should slide into the clutch with relative ease. If you have to shove it in place or use the bolts connecting the transmission to the bellhousing to pull it into place, you are also shoving the crankshaft forward into the face of the thrust bearing.

"If guys aren't careful when they install their bellhousings and their transmissions, it can really cause some problems," explains engine builder Chris Lafferty of Lafferty Performance. "If the alignment isn't correct between the transmission input shaft and clutch, which is bolted to the crank, then the only way to get it in is to force it. When you do that you are also pushing the crank forward against the face of the thrust bearing. Now the crank is constantly rubbing against the face of the thrust bearing, and when that wears down, the shoulders of the mains start getting into all the main bearings, and you've got a lot of trash floating around in the engine. Too often, engine builders get blamed for doing a poor job with the engine, but the real fault lies with whoever bolted the bellhousing in place."

Lafferty also cautions that improper alignment can also lead to early clutch failure as well as bearing problems in the transmission. It also causes drag in the drivetrain that can be quite significant-especially in lower horsepower classes. That's why many of his customers have him install the clutch and the bellhousing when he builds a race engine for them. Of course, many race teams don't have a bellhousing dedicated for each engine in their inventory and must swap housings regularly. Fortunately, the process for checking bellhousing alignment is straightforward and generally requires less than 45 minutes to complete. It also requires one tool most teams will need to add to the toolbox, but the benefits-in terms of longer part life and possibly even better track times-are worth it.

Ctrp 0607 03 Z+bellhousing Alignment+ 4/12 This causes extreme wear on the thrust bearing and can lead to engine failure. In the first photo, the face of the thrust bearing has been worn away as a result of this problem, which Lafferty says the race team initially blamed on the engine builder. The second photo shows how the bearing should look after normal use.

Alignment problems can come from several sources. Core shift is a major culprit. If your engine has been align-honed, the honing process may move the centerline of the crankshaft while correcting alignment issues between all the main bearing housing bores. Finally, there is the simple explanation that few things in life are perfect. Yes, it's a catch-all explanation, but it's still true.

Checking bellhousing alignment is relatively easy. There are different tools available from different manufacturers for this purpose, but they all work on the same principle. Lafferty prefers (and sells) one that uses a dial indicator mated to a shaft that fits in the ID bore of the clutch (where the transmission input shaft goes). Make sure the flywheel's register bore (the hole in the center) is clean and set the dial indicator to ride the ID of that bore. It should be set up so that the dial indicator spins around the bellhousing's register bore when the crank is turned.

Lafferty recommends marking the bore housing in four quadrants-12, 3, 6, and 9 o'clock-and measuring at the four locations. Spin the crank until the dial indicator is pointed at your 12 o'clock mark and set the indicator to 0.050. This is the same thing as calibrating the gauge, but setting it to 0.050 makes it easier to do your math later.

Now spin the crank 180 degrees so the dial indicator points at the 6 o'clock mark. A reading less than 0.050 means the bottom of the register bore is closer to the crank centerline than the top of the bore. To correct this, move the bellhousing down by a distance equal to half the difference between the two readings. For example, if the 12 o'clock reading is 0.050 and the 6 o'clock reading is 0.010, then the bellhousing should be moved down by 0.020 inch. (The difference between 0.050 and 0.010 is 0.040, and half of that is 0.020.) If the number is larger, the bellhousing should be moved up. Everything else in the process remains the same.

Ctrp 0607 04 Z+bellhousing Alignment+ 5/12 The indicator Lafferty uses fits in the ID bore of the clutch and is the only special tool you will need.

Instead of making the change immediately, Lafferty simply writes on the bellhousing how much it must be moved and in which direction. Then, he repeats the process by setting the dial indicator at 0.050 at the 3 o'clock position and measuring the change at the 9 o'clock position. Once that is done you can begin adjusting the bellhousing location. Ideally, you want the register bore on the bellhousing to be centered over the crank centerline within 0.005 inch in both directions. If the necessary change is small, you may be able to simply loosen the bolts holding the bellhousing to the block and give it a few small taps with a dead-blow hammer. If that doesn't work, you can either use a grinder to open the dowel pinholes in the bellhousing or use offset dowel pins, which are available from most bellhousing manufacturers.

Once you have the location you want, torque down the bellhousing bolts, pull the dial indicator, and get on with your life with the assurance that you aren't losing horsepower to something as silly as a misaligned bellhousing. Just remember, if you ever have to pull the bellhousing from the block for any reason, this process should be repeated again.

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