Chevy Bellhousing - Dialed To Perfection

Bellhousing Alignment Is Critical-And Here's How To Do It Correctly

Mike Petralia Aug 1, 2001 0 Comment(s)
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Remember that most indicators count up when pressed in and count backwards when extending out. So if the reading at 90 degrees was 0.017 and the 270-degree reading was 0.077, that means the bellhousing needs to be moved to the center of these two readings. The math goes like this: first, 0.077 is 0.023 away from 0.000, and since it's "less than" 0.000, in this case we need to add that amount to 0.017 to find its center (0.017 + 0.023 = 0.040/2 = 0.020). The bellhousing must be moved 0.003 inch so that the 90-degree reading indicates our new figure, 0.020 and the 270-degree reading would indicate 0.080, or 0.020 away from 0.000. After you've done this several times for both the horizontal and vertical axes, you can re-zero the indicator at the top, and it should read very close to 0.000 the whole way around.

Our hero slides through the final bend in the roadway. Ahead lies the longest stretch of open pavement he's ever seen. His machine screams for more, and he flattens the go-pedal, offering an extra ration of fuel and air to the hungry beast. The engine revs in a heartbeat as his right foot relaxes from the accelerator while his left tickles the clutch in one single, fluid motion. His grip on the shifter tightens in preparation of completing another well-practiced shift. The shift gate releases as the trans easily slips out of Second gear. Suddenly, the engine screams in protest, popping and banging past its redline as Third gear is locked out, but his right foot instinctively smashes the gas pedal before his brain comprehends the severity of his mistake. His $10,000 engine accelerates towards oblivion in a nano-second with no hope of restraining it as the shifter sticks in neutral. Not responding fast enough, our hero is now the fool who has paid the ultimate price for not properly aligning his bellhousing.

Okay, we've gone over the edge just a little with this scenario, but it can-and does-happen. The problem is usually the result of installing a new transmission/bellhousing combo and not properly locating it in relationship to the crankshaft's centerline. With the bellhousing misaligned by as little as 0.010 inch, the gearbox will be difficult to shift under power, can pop out of gear, and eventually may fail completely. Factory bellhousings and transmissions rarely experience this problem because of the loose tolerances purposely built into those units. But install an aftermarket scattersheild and/or a performance transmission without realigning them, and trouble is just around the bend.

Luckily, properly locating your car's bellhousing doesn't require any high-zoot equipment or fancy know-how. All you'll need is a few hand tools, magnetic-base dial indicator, and some offset dowel pins to realign the bellhousing to the engine.

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To show you just how simple this task is, we procured a scattershield and a set of offset dowel pins from Lakewood and went about aligning it to our Camaro's Rat motor using a dial indicator (and magnetic mount) from Powerhouse Products. While this check can be performed in the car, it's much easier to do with the engine on a stand. Unfortunately, a normal engine stand won't let you hang a bellhousing off the back, so you'll need another way to work on it. We found the perfect solution to this and our shop's tight engine storage problems with a new product called Moto Feet (see photo).

Properly locating the bellhousing will take some time and a whole lot of patience because it involves some confusing, but not too difficult, math calculations. The Lakewood scattershield comes with instructions showing how to properly align it, but we've added some extra touches to ensure your car's bellhousing never gets out of whack. It's also easier to do this check by yourself if you have a harmonic damper that's marked off every 90 degrees like one from Fluidampr. Have a notepad and calculator handy, and don't give up just because this stuff is a little tough to read. It'll all make sense when you're actually doing the work. And the transmission you save could be your own.

Bolt the flywheel to the crankshaft and the bellhousing on the block with the stock dowel pins still in place. Turn the crank so the harmonic damper indicates TDC, or "0" degrees, then mount the dial indicator on the flywheel perpendicular to the bellhousing bore and slightly off center of the crank so it will make a complete circle as you turn it. Zero the indicator, pointing straight up. To check the bellhousing turn the crank clockwise, reading the indicator every 90 degrees, starting at 90 degrees on the right, 180 degrees on the bottom, then 270 degrees on the left. Turn the crank over two full revolutions to see if the indicator returns to zero at the top and that the readings duplicate on each revolution.

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Remove the bellhousing and knock out the factory dowel pins from behind using a brass or aluminum punch. Don't use a steel punch, especially on the driver's side pin, which is particularly difficult to knock out, because the steel punch will damage the dowel pin bore. The new Lakewood dowels are machined with an offset that relocates the bellhousing as they are turned with a screwdriver.

To keep the new dowel pins from rotating in their bores once everything's done, we drilled and tapped holes for two 10-32 x 1/4-inch long setscrews we picked up from the hardware store. Lubricate and install the new dowel pins with their slots aligned. When making adjustments, loosen the bellhousing bolts just enough to allow the dowel pins to turn, and keep track of how much the indicator needle moves as you loosen the bolts-take that movement into consideration when figuring the change needed. After you've correctly located the bellhousing, lock the setscrews in place with some thread-locking compound.

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Here's a tip we've learned the hard way: Lakewood supplies some Allen-headed bolts for the bottom holes of the bellhousing. But you can't get an Allen wrench on the bolt once the trans is in the car, so we switched all six bellhousing bolts to 12-point fasteners from ARP. Now we can use a 3/8-inch, 12-point flexible socket or the box end of a 3/8-inch wrench on the bolt in the car. You can also see the adjustable Lakewood dowel pin that's been turned so many times it's pretty chewed up, but that doesn't matter once it's locked in place.

From all the markings on our diagram you can tell it took several tries to get this bellhousing right. It needed the 0.021-inch offset dowels and indicated within 0.001-inch when finished. Anything over 0.005 inch is bad news.

Perfecting the bellhousing alignment cannot be done on an ordinary engine stand. We used these Moto Feet.

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Lakewood offers offset dowels in three sizes, .007, 0.014, and 0.021 inch. These can cure misalignments up to 0.052 inch; anything more and you'll need to have custom dowels made.

In case you're wondering how we got the indicator to fit inside the bellhousing bore; here's our secret. We removed the second arm from the magnetic mount and clamped the indicator in its place.

Sources

Powerhouse Products
Memphis, TN 38118
800-872-7223
http://www.powerhouseproducts.com
Lakewood Industries
Cleveland, OH 44144
216-688-8300
http://www.lakewoodindustries.com
Jim Grubbs Motorsports (Moto Feet)
Valencia, CA 91355
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