In racing, you want all the power your motor can make to reach the drive wheels. To that end, we commonly use steel motor mounts to replace the factory rubber models on Hobby Stocks or Street Stocks. When the rules for more advanced classes allow it, front and rear motor plates hold the engine rock steady. Any severe driveshaft angles cause a power loss. We can also be sure to dial in the rear pinion angle to keep all of the power coming out of the engine when it's at maximum torque.
There is one more area that can be tweaked to ensure there is no drag on your driveline. Although it involves using a dial indicator, it's not that difficult to accomplish. It might just extend the life of some of your driveline components. If you already dial in your bellhousing, you are probably in the minority of those in racing who take advantage of this simple but effective procedure.
Start with the block plate in place. Add the flywheel, but not the clutch, on a block with
Friction is a big culprit. It works against you in two ways. The first is friction on the driveline, which robs horsepower. Second, friction due to misalignment can cause premature failure of driveline components such as U-joints, driveshafts, clutches, pressure plates, throwout bearings, rear ends, and-worst of all-your expensive transmissions. The basic idea is to make sure the bellhousing you use is perfectly in the center of the crankshaft coming out of the engine, not the center of the block. The rear end of the crank lines up with the input shaft of the tranny. All of the aforementioned components will work off the proper alignment of that input shaft.
Bad alignment of the bellhousing and its related components comes from a number of sources, the most common being core shift, when the block has flexed permanently for a variety of reasons. Most blocks, iron or aluminum, are cast and contain plenty of voids such as the bores, water passages, and even the overall design of the block. They can shift when torque and/or heat are applied from assembly, rebuilds, or engines running at operating temperature. Casting blocks is not an exact science. Some variations are not only tolerated but expected due to the inconsistencies of flowing a liquid metal into a form or mold and then having it cool under a variety of conditions.
Lower the bellhousing into place.
Another culprit is align-boring of the block. Align-honing will do it but to a lesser degree, as less metal is taken off. When align-machining is done, the centerline of the crank is affected. Even if it is slight, that's just enough to throw off the bellhousing. Also consider any other machine operation that may be done to the block. Whenever any material is taken off the block, the core can shift and throw your alignment off.
Even the bellhousing itself can be off. It is, after all, a machined part susceptible to variations. It may start within tolerance but move when attached to a block slightly out of tolerance. Though most bellhousings will be in tolerance, it's good insurance to find out just how the two match up. The transmission centerline is another source of runout that can kill components. If the input shaft or the bearing retainer on the front of the tranny is off, a misalignment of the block and bellhousing can exaggerate the runout.
In a bad-case scenario, a misaligned tranny will start to wear out the input shaft. The front bearing retainer will also wear and cause bad shifts, even to the point of hanging up a shift. If the clutch is thrown out of alignment from the input shaft running out of round, it cannot engage correctly. Add the breaking of transmission cases and/or mounting ears, and you've got a bigger dent in your racing budget. It's no different than any other assembly in that it will work more effectively when in total harmony.
There's another reason to consider dialing in your bellhousing. Once all the components are bolted together, virtually all misalignment will be undetectable. You won't know you may be slowly destroying your drivetrain and components.
Line it up on the dowel pins in the block.
Unfortunately, most factory service manuals are good for theory but don't give the tolerances or instructions for adjusting the housing. Speaking of factory parts, those units won't contain a clutch or flywheel explosion like an SFI-approved bellhousing. Stock units are OK for stock usage, but when racers take their engines up to 9,000 rpm, that's asking for quite a bit of protection from cast aluminum.
If we've scared you enough to consider dialing in, you have only one more hurdle to clear, and that's the alignment pins on the block. They can cause some of the same problems that core shifting causes. They can also be a problem if they have been pressed in with more than the usual 0.001-inch tolerance, but that's manageable, too. They are the main components for aligning your bellhousing, so you'll need to make sure they are in good shape.
Follow this simple procedure and you'll sleep a little better knowing you're not shaking your driveline to death every time you put a lap on it.
Use the block and bellhousing you plan to race. Do this anytime you swap these components. If you're using a block plate, put it on first. (If you're not using a block plate, you're shortchanging your protection. It's a simple 1/8-inch steel plate that's part of the system. It helps contain problems and even keeps the clutch and flywheel clean from track debris.) Install the flywheel and housing you want to use. It's easier to mount it up without the clutch assembly, as you don't need it for this procedure. With the crank in the block, tighten up all the fasteners on the bellhousing. Torque the 3/8-inch bolts to 35-40 pounds. Now check for paint buildup on the inside diameter or register bore of the housing. If any is found, use an emery cloth or a scratch pad to smooth out any high spots. Mount a magnetic dial indicator on the flywheel, making sure it can turn it 360 degrees inside the bore without contact. The indicator's plunger should just touch the inside diameter of the housing. Rotate the flywheel and read the gauge.
If there are high spots of paint inside the register bore, take them off.
As you are measuring a circle, remember misalignment is one half of the indicator reading. It's best to always use the same location spots as you go through measuring and fitting. The Lakewood personnel who showed us how to do it marked the 12:00 and 6:00 locations with their readings. If the reading is within tolerance of 0.005 after checking twice, you're ready to go racing.
If there is an off-center condition, select the offset dowel pins that are closest to your measurement. Lakewood makes them in 0.007-, 0.014-, and 0.021-inch sizes. (If the reading is 0.016, divide by 2 to get 0.008. The closest replacement dowel pin is 0.007 inch.) The first step to put them in is removing the bellhousing.
Removing the stock dowel pins can be accomplished either by driving them out with a drift from the front of the block or using gripper pliers and pulling them out. Once removed, clean out their bores and coat them lightly with a thin lubricant. If the holes are too tight, you may have to ream them to be ready for the 0.001 press-in difference that is needed.
Your bellhousing should look like this with all the proper hardware in place.
Lubricate the new dowel pins and install them into the block. The slot end of the pin should be the one exposed. The direction of the slot indicates the maximum offset. Both pins should always be installed parallel to each other and in pairs (i.e., both 0.007 inch, 0.014 inch, or 0.021 inch). Use two screwdrivers to align the pins with the housing loosely mounted to correct the tolerance discrepancy. Tighten the bellhousing to specs and check for runout. To make any adjustments, you'll need to reposition the dowel pins, still using the slot as a reference. This involves trial and error. Tighten up the bellhousing and check it again. Repeat this procedure until you are within tolerance for best results.
For those who must routinely take their bellhousing on and off the same engine, a weld-on dowel pin kit is available. Just dial them in and then weld them.
The key points to this simple procedure are:
1. Measure the actual pieces you are using.
2. Keep tolerance at 0.005 inch.
3. Divide the dial indicator reading by 2.
Do it like you'd turn a lap-consistently and smoothly-and you'll ensure your driveline has a chance at a long and productive life.
With the dial indicator in place on the flywheel, zero it out on one side.
We sought our information from the folks at Mr. Gasket's Lakewood division. There was an extended line (over 20 models) of SFI-approved, made in the USA bellhousings. These bellhousings are hydroformed using extensive tooling. Hydroforming the steel gives it the same thickness throughout the piece, regardless of any bend or radius. Normally when a stamping is made, the bends thin out
The standing joke is that they test bellhousings by throwing a hand grenade inside and seeing how many pieces come out. It's obviously not true, but it does illustrate how devastating a clutch or flywheel explosion can be. If you're not aware, those situations have been known to harm drivers and spectators, cutting the hands, arms, and legs of drivers and hitting spectators with shrapnel-like pieces. It's a relief to know that the bellhousing will contain the explosion and prevent you and those around you from what used to be your clutch or flywheel.
SFI bellhousings seen in the circle track industry have had a number of refinements added. One version that can help dirt racers has a smaller hole for the clutch fork and offers a tight-fitting rubber cover to keep it cleaner.
Mr. Gasket's Hays brand makes a series of bellhousings/adapters without certification from SFI. These are made the exact same way from the exact same materials (1/4-inch steel) but are not tested. Made for the aftermarket industry, they can be used for transmission swaps. They can make life easier when you're putting a Ford tranny on a Chevy motor or a GM tranny on a Ford motor. They fit Jerico, Muncie, Richmond, Tremec, and other styles. Because they are steel, you can safely weld on brackets you may need for the swap without damaging the adapter.
Hays also has a version that has the lower flange shaved off as close as it can be for optimum ground clearance. If your racing sanction doesn't require SFI-approved bellhousings, you can use these transmission adapters. Always check your rule book.
Measure the other side and note the difference. Check the text to calculate properly.
If you have to adjust the new dowel pins, use two screwdrivers at the same time.
Here's the lineup on bellhousings and adaptors from Lakewood and Hays. The red one is an S