Rock the gauge back and forth and take the smallest reading. The smallest reading occurs when the gauge is perpendicular to the cylinder wall. Add the reading to 4.040 to determine the bore size. This gauge reads .0002-inches (two ten-thousandths of an inch), which is commonly referred to as “two-tenths.” That is 15-times thinner than the average human hair!If the cylinder was honed with a torque plate, chances are the bore is out-of-round without the cylinder head torqued in place. Therefore, the best practice is to check the bore size with the torque plate installed. If it is not available, take the measurement near the bottom of the cylinder at the point where the sleeve exits the block core. Cylinder distortion is limited in this area.

Rear wheel bearings on old BMWs are incredibly robust. I’ve only ever had one go bad. It was on a Bavaria that my wife and I took on vacation to Martha’s Vineyard in 1986. We were foolishly driving in near-hurricane conditions and got caught in a tidal surge on the road that runs on the barrier beach between Edgartown and Oak Bluffs and drove through water that was deeper than we expected (as I said, foolish). On the drive home, the right rear wheel bearing began rumbling ominously. At the time, I didn’t own the necessary bearing puller, and had to take the car into the late great Beaconwood Motors who had the back page ad of Roundel for a generation. It was one of a handful of repairs the past 40 years I’ve paid someone else to do.

Measuring tools should also be at room temperature. Keep hand contact with the tools to a minimum. Take a measurement, then set the tool down to record the reading. Body heat from holding the gauge in your hand will move the needle two-tenths. Hand warm the gauge before zeroing and taking measurements as an alternative.

I then jacked up the left front wheel and rocked it at 6 and 12. Yup, play. Then I spun it. Yup, rumbly. No doubt—a bad left wheel bearing. I set the car back down and began to walk back to the computer to order the bearings, vividly recalling how much of a pain in the butt they were to replace in the 528iT wagon ten years ago. I wondered if maybe still having those eight spare bearing bolts had made the whole thing a matter of fate.

And so, just to be certain, to placate my left brain and make sure I didn’t go to all that work unless it was absolutely necessary, I took a 1/2-inch ratchet and a 17mm socket and checked the wheel’s lug nuts.

Average life of wheelbearings

Then I checked the lug nuts on the right front wheel. While none were loose to the point of being free-spinning, all were substantially below the 88 foot-pound torque spec. The rears were fine.

Perhaps the down comforter of soft failures is a bad wheel bearing. Loss of lubrication will cause them to wear, resulting in a rumble that sometimes can be more felt than heard (they may also squeak or squeal), but the failure process is gradual. They’ll get louder as wear and play embrace each other in an ever-widening downward spiral, but you’d have to be an idiot not to hear it and address it, making outright failure rare. Wheel bearings are pretty robust in BMWs. After owning over 70 cars, I’ve only ever seen one wheel bearing that completely self-destructed—a ’67 2000CS I bought came with one that had destroyed the stub axle. I had to replace the entire front strut assembly.

Once all the tools have been acquired, the clearance specification and the measuring point for the piston need to be located. Both of these are provided by the piston manufacturer. Mahle supplies an online version of their application guide via their website.

How many wheelbearingsdoes acarhave

I snugged them down, grabbed the wheel at 6 and 12 and verified that the play was gone, spun it and verified that the noise was gone, let the car down off the jack, and tightened them up with a torque wrench.

Using the Mahle application guide is simple. Locate your application then find the piston part number on the right. Just to the left of the part number are the minimum and maximum clearances and the piston measuring point. Locating the correct measuring point is critical because each piston has a unique profile. Measurements taken above or below the specified point will be incorrect. An incorrect piston measurement will cause the piston to bore clearance calculation to also be incorrect. The dial caliper is set to the proper distance to locate the measuring point (above) and then a Sharpie is used to mark the point on the piston (see below). Be sure to put one mark on each skirt as a reference. It is critical that the micrometer is placed on each skirt at the correct height. The anvil and spindle of the micrometer must be perpendicular to the skirt. If one side is off slightly, you will get an incorrect measurement. Record the piston size.

The dial caliper is set to the proper distance to locate the measuring point (above) and then a Sharpie is used to mark the point on the piston (see below).

In the repair world, there are “hard failures” and “soft failures.” Hard failures are things that instantly drag a car to a stop when they break. Broken ball joint? The worst type of hard failure—the front wheel folds under the fender like a broken ankle and you lose control of the car. Bad fuel pump? Usually a hard failure—it either pumps or it doesn’t. (Okay, there are some exceptions. The one my E39 wigged out on a low tank in hot weather, then recovered. I replaced it anyway.)

Engine assembly requires the measurement of several components to ensure adequate clearances. Piston to cylinder bore clearance is one of those critical areas. Although the clearance is typically set by the machinist during cylinder honing, it is imperative that the assembler knows how to take the measurement to double-check the machinist. Mahle Motorsports has put together this informative how-to video on the process.Specific tools are required to measure piston to bore clearance. The list includes the following: micrometer, dial caliper, and bore gauge. Micrometers have a one-inch range and will be used to measure the piston. Select a micrometer with a range that includes the piston diameter. The dial caliper is used to locate the measuring point on the piston. A zero to six-inch caliper will be sufficient.Finally, the bore gauge will be used to measure the cylinder bore diameter. Like the micrometer, bore gauges cover a certain range. However, the bore gauge comes with a range of extensions and spacers to cover a larger spread such as two to six-inches.Once all the tools have been acquired, the clearance specification and the measuring point for the piston need to be located. Both of these are provided by the piston manufacturer. Mahle supplies an online version of their application guide via their website. Using the Mahle application guide is simple. Locate your application then find the piston part number on the right. Just to the left of the part number are the minimum and maximum clearances and the piston measuring point. Locating the correct measuring point is critical because each piston has a unique profile. Measurements taken above or below the specified point will be incorrect. An incorrect piston measurement will cause the piston to bore clearance calculation to also be incorrect. The dial caliper is set to the proper distance to locate the measuring point (above) and then a Sharpie is used to mark the point on the piston (see below). Be sure to put one mark on each skirt as a reference. It is critical that the micrometer is placed on each skirt at the correct height. The anvil and spindle of the micrometer must be perpendicular to the skirt. If one side is off slightly, you will get an incorrect measurement. Record the piston size. There are a couple of ways to set up the bore gauge. In this example, Mahle set up the bore gauge to measure the actual bore size. The bore gauge reads zero at 4.040-inches. An alternate method is to measure the clearance without having to do any calculations by setting the bore gauge to read zero at the piston measurement. The reading on the bore gauge will be the piston to bore clearance. Rock the gauge back and forth and take the smallest reading. The smallest reading occurs when the gauge is perpendicular to the cylinder wall. Add the reading to 4.040 to determine the bore size. This gauge reads .0002-inches (two ten-thousandths of an inch), which is commonly referred to as “two-tenths.” That is 15-times thinner than the average human hair!If the cylinder was honed with a torque plate, chances are the bore is out-of-round without the cylinder head torqued in place. Therefore, the best practice is to check the bore size with the torque plate installed. If it is not available, take the measurement near the bottom of the cylinder at the point where the sleeve exits the block core. Cylinder distortion is limited in this area. Cylinder bore size minus piston diameter equals piston to bore clearance. Variables That Affect Piston To Cylinder Bore ClearancePrecision measurements like bore size and piston diameter are critical for engine survival. Consider any outside factors that may skew the measurement. Mahle pointed out two common ones.First, temperature will cause the cylinders and pistons to expand and contract. It is imperative that both the cylinder block and the pistons are at room temperature. Small differences in temperature can change measurements considerably considering the micrometer and bore gauge are measuring in one ten-thousandths of an inch increments.Measuring tools should also be at room temperature. Keep hand contact with the tools to a minimum. Take a measurement, then set the tool down to record the reading. Body heat from holding the gauge in your hand will move the needle two-tenths. Hand warm the gauge before zeroing and taking measurements as an alternative.As mentioned earlier, cylinder honing sets the piston to bore clearance. Provide the engine machinist with the pistons so the correct clearance can be obtained. The steps laid forth by Mahle will allow the assembler to double check the machinist work.

On 1970s-era BMWs, there are inner and outer front wheel bearings with each sitting in its own race that’s pressed into the hub. Since the front discs on these cars sit on the inside surface of the hub, and since the bearings lift out of their races and present their greasy private parts to you when you pull the hub off the spindle, the advice is that, if there’s no documentation on how old the bearings are, to replace both sets of bearings on both sides when the front discs are replaced.

On newer BMWs, the front wheel bearings are very different than on the 1970s-era cars. About ten years ago, I owned a ’99 E39 528iT wagon that needed struts, control arms, and other front-end work. The E39’s wheel bearings are part of an assembly that includes the front hub—the wheel bearing assembly bolts to the steering knuckle, and the wheel bolts directly to the bearing assembly.

As mentioned earlier, cylinder honing sets the piston to bore clearance. Provide the engine machinist with the pistons so the correct clearance can be obtained. The steps laid forth by Mahle will allow the assembler to double check the machinist work.

The anvil and spindle of the micrometer must be perpendicular to the skirt. If one side is off slightly, you will get an incorrect measurement. Record the piston size.

Wheel bearing replacement cost

I intentionally jacked up the car at the right front wheel—the one I didn’t think was making the noise—to get a baseline. I grabbed it at 6 and 12, rocked it, verified it was tight, and spun it. As expected, it was quiet.

Car Ball bearingscost

When I arrived home, I pulled the nose of the car right into the garage, then hopped on the laptop to get a set of front wheel bearing on order. I looked on FCP Euro, and was more than a little surprised to find that a front wheel bearing kit with German FAG wheel bearing assemblies now cost $312. Of course, I still had that set of bolts, so I could save myself the $4.29 per bolt right there. I mean thirty-four bucks is thirty-four bucks, right? One FAG bearing was $139. I began entertaining replacing just the left bearing, then price-shopping other manufacturers, when I decided that I should be certain that the wheel bearing was really the problem.

I was driving my 2003 E39 530i up to do some recording in Chelmsford, about 30 miles north of me, when I began to hear and feel a rumbling coming from the left front of the car. It ramped up over several minutes, but then plateaued. If it instead had gotten VERY loud VERY quickly, with obvious metal-smacking-against-metal instead of the more gentle rumble of a worn bearing, that would be the hallmark of loose lug nuts, something you need to pay attention to IMMEDIATELY because you may have only five or ten seconds before the wheel falls off.

First, temperature will cause the cylinders and pistons to expand and contract. It is imperative that both the cylinder block and the pistons are at room temperature. Small differences in temperature can change measurements considerably considering the micrometer and bore gauge are measuring in one ten-thousandths of an inch increments.

Using the Mahle application guide is simple. Locate your application then find the piston part number on the right. Just to the left of the part number are the minimum and maximum clearances and the piston measuring point.

After the recording session ended, I began driving back toward the highway. As I approached a small service station, I debated stopping to have them throw the car up on the lift and check it, but again, since the rumble remained low and constant, I headed home. Still, to err on the literal side of safety, I stayed in the right lane, turned the flashers on, and drove at 50 mph.

And I’m going to have some sort of voodoo ceremony with that bag of Locktite-coated wheel bearing bolts. I can’t tell whether they were bad juju that triggered the problem or a talisman that warded off disaster, but clearly they played some role outside the normal Western vectors of Newtonian mechanics and Cartesian cause and effect. They deserve reverence.

Ball bearings carreplacement

Rob’s newest book, The Best of The Hack Mechanic, is available here on Amazon, as are his seven other books. Signed copies can be ordered directly from Rob here.

Still, to be careful, I pulled into the right lane, slowed down, and listened. The somewhat rapid onset was uncharacteristic of a wheel bearing, but the other symptoms fit. Since I had a recording appointment with a fiddle player, I preferred to keep going, unless of course I couldn’t for safety reasons. The rumbling remained at a constant low level, so I assumed it was a wheel bearing doing the soft failure thing, and continued on.

Why do I have these and why can I lay my hands on them instantly? As Joseph Fiennes said in Shakespeare in Love, “It’s a mystery.”

There are a couple of ways to set up the bore gauge. In this example, Mahle set up the bore gauge to measure the actual bore size. The bore gauge reads zero at 4.040-inches. An alternate method is to measure the clearance without having to do any calculations by setting the bore gauge to read zero at the piston measurement. The reading on the bore gauge will be the piston to bore clearance.

In contrast, soft failures are things that either give you ample warning before they fail completely, or their failure doesn’t immediately drag the car into the breakdown lane. A textbook soft failure is when the alternator or voltage regulator dies. Even though the battery is no longer being charged, the car can continue to run for some amount of time off the battery alone. On a vintage car like a 2002, you can likely drive for hours during daylight before the battery no longer has enough juice to light the spark plugs. On a late-model car loaded with electric motors and control modules, you might have more like fifteen minutes to an hour—enough to get to a rest area, possibly even a repair shop.

Although bearing rumble is usually quite clear, part of testing for a bad wheel bearing is to jack the car up, set it on stands, grab the wheel at the 6:00 and 12:00 positions, and push-pull it. If you’re hands are at 3:00 and 9:00 instead, play in a front wheel can come from anything in the steering mechanism, but 6-and-12 play pretty much has to be coming from the wheel bearing. In an old-school car with adjustable wheel bearings, if there’s no rumble, you can try adjusting the bearing by pulling the cotter pin and moving the castellated nut by one notch, but play plus rumble equals bad.

Front wheel bearing noise symptoms

Locating the correct measuring point is critical because each piston has a unique profile. Measurements taken above or below the specified point will be incorrect. An incorrect piston measurement will cause the piston to bore clearance calculation to also be incorrect.

Be sure to put one mark on each skirt as a reference. It is critical that the micrometer is placed on each skirt at the correct height.

My ever-rational left-brain shot back indignantly. “You can’t be serious,” it sneered. “You actually had a wheel fall off that 1600 back in 1984. And you’ve had two close calls, both more recently than you’d like to admit. You know what loose lug nuts sound like, and this wasn’t it. And you learned your lesson. You conditioned yourself to always tighten lug nuts with a torque wrench. It’s not loose lug nuts. Really. It’s not. It can’t be. You are not that careless.”

To make sure this doesn’t happen again, I’m instituting a new system of checking the lug nuts on all four wheels after I’ve done any work where a car is jacked up for any reason.

How to tell which wheel bearing is bad while driving

Ball bearings carsymptoms

Finally, the bore gauge will be used to measure the cylinder bore diameter. Like the micrometer, bore gauges cover a certain range. However, the bore gauge comes with a range of extensions and spacers to cover a larger spread such as two to six-inches.

Rob Siegel has been writing the column The Hack Mechanic for Roundel Magazine for 35 years, and is the author of eight books available on Amazon. He currently owns thirteen cars. Yes, his wife knows about all of them.

Specific tools are required to measure piston to bore clearance. The list includes the following: micrometer, dial caliper, and bore gauge. Micrometers have a one-inch range and will be used to measure the piston. Select a micrometer with a range that includes the piston diameter. The dial caliper is used to locate the measuring point on the piston. A zero to six-inch caliper will be sufficient.

Precision measurements like bore size and piston diameter are critical for engine survival. Consider any outside factors that may skew the measurement. Mahle pointed out two common ones.

There are a couple of ways to set up the bore gauge. In this example, Mahle set up the bore gauge to measure the actual bore size. The bore gauge reads zero at 4.040-inches. An alternate method is to measure the clearance without having to do any calculations by setting the bore gauge to read zero at the piston measurement. The reading on the bore gauge will be the piston to bore clearance. Rock the gauge back and forth and take the smallest reading. The smallest reading occurs when the gauge is perpendicular to the cylinder wall. Add the reading to 4.040 to determine the bore size. This gauge reads .0002-inches (two ten-thousandths of an inch), which is commonly referred to as “two-tenths.” That is 15-times thinner than the average human hair!If the cylinder was honed with a torque plate, chances are the bore is out-of-round without the cylinder head torqued in place. Therefore, the best practice is to check the bore size with the torque plate installed. If it is not available, take the measurement near the bottom of the cylinder at the point where the sleeve exits the block core. Cylinder distortion is limited in this area. Cylinder bore size minus piston diameter equals piston to bore clearance.

I can only speculate what happened. Due to the space constraints in my garage, when I swap winter/summer wheels, I’ll usually pull one end of the car in, jack it up, swap both wheels, snug the lug nuts with a ratchet, let the car down, torque the nuts, air the tires, then pull the car out, flip it around, and do the other side. I must’ve gotten interrupted. Maybe I received a text I felt that I needed to respond to. Maybe my wife was leaving and I walked outside to kiss her goodbye. Maybe I had back pain and took a break. I don’t know.