All cars with a manual transmission come with a mechanical device known as a flywheel. The flywheel serves three purposes. First, it maintains a rotating mass (inertia) that helps the engine rotation and allows a more consistent transmission of torque during running. Second, the flywheel has a ring gear where the starter motor can engage on. Lastly, it provides one of the driving friction surfaces for a friction disc. There will come a time when resurfacing flywheels is needed. It is typically when the clutch is replaced.
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Normal clutch operation produces plenty of heat and friction. The flywheel’s mass absorbs and dispels the heat. When the clutch begins to slip, more heat is produced. The additional thermal stress can result in warpage, heat cracks and the buildup of hard spots in the flywheel’s surface. Upon removal of the old clutch, the flywheel should also be thoroughly inspected to check its condition. The inspection will include: using a straightedge and feeler gauge to measure the flywheel’s flatness, checking the surface for cracks, and checking for grooving or hard spots which refer to discolored areas that are slightly lifted above the surrounding surface.
If the surface is flat and without defects, there is no need for resurfacing flywheels. But if it no longer is in a condition like when it was new, then it needs to be resurfaced prior to installing the new clutch. Failure to resurface a worn flywheel will cause premature wear of the newly installed clutch and most clutch suppliers won’t honor a warranty claim if the flywheel was not resurfaced or was resurfaced improperly upon installation of the clutch.
What does resurfacing a flywheel mean?
As mentioned previously, eventually, the surface of the flywheel gets damaged due to friction and heat. It gets too hard or in some cases, it develops cracks and blisters called “hot spots” on the surface. Hot spots happen due to uneven application of heat. As a result, the hardened areas are not evenly distributed across the surface. This is why manufacturers also recommend resurfacing flywheels when the throwout bearing, pressure plate or disk is replaced. So what does it mean to resurface a flywheel?
Resurfacing flywheels refer to the process when the part is fixed to a machine that is able to cut a very thin layer of metal off the surface. Doing so will expose fresh metal to the disk, and gives a slight roughening of the surface which will enhance the grip over the previously polished surface. The amount of metal cut off during resurfacing flywheels depend on the depth of the hot spots.
It is highly recommended for you to stop using your car when the clutch begins to slip, and have it fixed immediately. When too much metal has to be taken off during the resurface, the part will be too thin, and will fail to meet the specifications of the manufacturer for proper operation, weight and safety.
Because the flywheel is connected to the crankshaft of the engine, the transmission and the engine should be separated to remove the flywheel for a resurface. In many cars, it means the engine must be removed and reinstalled to perform this job.
How long does it take to resurface a flywheel?
There are two methods being used in resurfacing flywheels: through cutting or grinding. Most prefer the grinding method for resurfacing most flywheels. A grinder removes the hard spots, leaving a smooth and homogenous surface. It usually takes 3 to four minutes to grind a flywheel’s surface.
There is actually a dedicated flywheel grinder, but grinding can also be done using a head and block grinding machine. However, a head and block grinding equipment can only handle flat flywheels and consumes more time to set up than a dedicated flywheel grinder. A dedicated grinder should be used for a stepped or recessed flywheel which needs to be ground.
When a stepped flywheel is used such as in Honda and Volkswagen, same amounts of metal must be removed or shaved off on both surfaces to maintain the correct clutch height and pressure. A flywheel depth gauge is needed to measure the amount of recess before and after resurfacing.
To achieve the proper surface finish, wet grinding with silicone carbide stones can be done. Another option is dry grinding with CBN stones. The latter are more costly but they last longer. Softer stones are ideal for grinding forged steel flywheels. Hard stones, on the other hand, are recommended for cast iron flywheels. It is also important to use the correct coolant for good cutting action and long stone life. Water-based coolants must have a rust inhibitor to avoid rust spots from building up on a resurfaced flywheel.
The other method of resurfacing is by cutting. It is typically done on a brake lathe. Setting up a flywheel on a lathe takes time. It should also be done carefully to ensure that the flywheel turns true on the lathe. One disadvantage of this method is that a lathe bit has the tendency to miss hard spots, leaving uneven areas. The other option is to shave off more amount of metal but it can negatively affect the installed clutch height. The release bearing on cars with hydraulic linkages may have limited travel. When too much metal is shaved off from the flywheel, the clutch may not be able to completely release when the hydraulic linkage is at the limit of its travel.
How much is it to resurface a flywheel?
It is always best to resurface your flywheel each time you have your clutch serviced. Several clutch clutch manufacturers do not accept warranty claims when you fail to have your flywheel resurfaced, but it may or may not be related to your driving needs and habits. There are some indications for you and your mechanic should check to determine if the flywheel needs to be resurfaced or replaced. Worn or badly damaged flywheels usually need expensive clutch repairs. On the other hand, if there is glazing or discoloration, then your flywheel only needs to be resurfaced. You won’t have to spend more than $50 for resurfacing a flywheel. Doing so will help prevent clutch slipping or abnormal wear due to glazing and discoloration.
Resurfacing flywheels are a lot cheaper than replacing one. The cost of replacing a flywheel depends on the make and model of your car. If you are lucky enough, you may find a new flywheel at $40 or so. But some flywheels can cost up to $400 or more. These are those that are made from stronger and lighter materials than steel. Dual mass flywheels or other complex implementations are pricier. Aside from the cost of the parts, you also have to spend money on the cost of the labor. Unlike resurfacing, replacing a flywheel takes hours. A mechanic may spend near 4 to 5 hours to replace your flywheel. For example, their rate per hour is $100, that means you’ll have to spend $400 to $500 for labor cost alone. That would make overall total costs in the range of $400 to $1500, depending on the vehicle.
How do I know if my flywheel is bad?
Like any other parts of your car, a flywheel will show signs when it becomes too worn or damaged. Here are some of them:
- Slipping Gears – If you notice your engine speed increasing a lot faster than your ground speed when shifting to a new gear, you are having slipping gears. When lubricants like oil or grease get onto the friction surface of the flywheel, it would negatively affect the ability of the clutch to engage with the flywheel and hold it without slipping. Slipping gears will definitely have an adverse impact on your driving ability and eventually damage the clutch.
- Not being Able to Change Gears – Sometimes you will experience the opposite issue with your gears, that is, instead of slipping, you are unable to change gears at all. For this to happen, your flywheel would have to be in pretty worst condition, and other transmission parts may be bad as well. Since you cannot change gears, you can’t also drive your car at all.
- Burning Smell – Another sign of a bad flywheel is a burning odor inside the passenger cabin (although this could also be a sign of other issues). A burning smell can be produced by a bad flywheel because of all the heat created from the friction in the clutch. Using your clutch unnecessarily can also cause flywheel problems.
- Clutch Vibrations – If you notice much vibrations in your clutch pedal, chances are your flywheel is going bad. The vibrations will eventually get worse and you will experience vibrations on the floor instead of just from the clutch pedal. The flywheel may end up with too much runout over time when driving. This will leave the surface feeling warped when the clutch is engaged. Overheating your flywheel will cause damage to it because of too much heat or metal on metal wear. Worn down clutches will also damage the flywheel. You may notice a bluish color on a damaged flywheel since the metal is exposed to a heat beyond its operating temperature. You will also notice some hairline cracks on the surface. You may even see some smears of metal on the surface due to the heated and cooled flywheel. Some flywheels have springs like dual mass flywheels. If your car has one of these, the springs of the flywheel may be the reason for the vibrations. Dual mass flywheels will likely need to be replaced since they cannot be resurfaced.
- Inconsistent starts or Not Starting At All – If the flywheel’s teeth are damaged, the flywheel may have difficulty engaging with the starter motor, making it hard or impossible to start the car. You may also check your starter if you are having issues starting your car.
- Engine Stalling – When your flywheel is too light for the car or for you, the driver, it will likely stall the vehicle and give you a rough idle. This often happens with an aftermarket flywheel. You may even experience engine stalling just by pushing the clutch in when you have very light flywheels. This is due to the fact that the engine speed plummets too fast for the ECU to add more air and fuel to compensate.
- Engine Vibrations When Clutch is Engaged – Unbalanced flywheel may cause vibrations on the whole powertrain even when the clutch is engaged. Make sure to torque all bolts to specifications and apply thread locker if it is stated in the factory service manual after replacing the clutch, flywheel or pressure plate. A loose or disintegrated flywheel when driving is very dangerous due to the large amount of stored energy in the flywheel. The flywheel is very heavy and can shake the car a lot if everything is not lined up properly and balanced.
Conclusion
If you are having issues with your flywheel and upon inspection the part only looks worn with no major cracks or damage, then the problem can be solved by resurfacing. Resurfacing flywheels is the process where the flywheel is run through a machine to make the flywheel’s surface smooth and remove any indentations that could cause problems with how it should operate. It is highly recommended to have your flywheel inspected every time you have your clutch serviced. It is also important to have your flywheel resurfaced when you get a new clutch so it won’t be a reason that your warranty claim will get denied.
Resurfacing a flywheel is a lot cheaper than replacing a flywheel. But if the flywheel has damage on it and is cracked, you have no other choice but to replace it with a new one. Replacement of a flywheel requires the removal of the transmission. The transmission should also be opened to access the flywheel assembly. It is a complicated job that requires the expertise of an experienced mechanic. Whether your flywheel needs resurfacing or replacement, it is important to fix the issue right away to prevent bigger and more expensive headaches in the future.