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Summary
  • A flywheel with hot spots on it can cause the clutch to chatter, vibrate, and fail prematurely. It can be dangerous to drive around in these conditions, so it’s best to get your flywheel resurfaced as soon as possible. 
  • Resurfacing a flywheel requires using a brake lathe machine or a block grinding machine. Brake lathes typically can’t cut hard spots on the flywheel, which is why block grinding machines result in a better finish. 
  • Excessive runout, dishing, and hard spots are signs that mean it’s time to resurface your flywheel.

In a manual transmission, the flywheel is a thick metal disc that provides mass for rotational inertia to help keep the engine balanced while it’s running. The torque converter performs this function by default on automatic transmission-equipped powertrains.

Like the flex plate on an automatic transmission equipped powertrain, the flywheel is bolted to the crankshaft in the center with six or eight bolts. 

The clutch is bolted to the flywheel. The clutch disk splines to the transmission input shaft and the clutch cover (pressure plate) is bolted at its outer edges to the flywheel with six or eight bolts that are smaller than the bolts holding the flywheel to the crankshaft.

While most flywheels are typically made of durable cast iron, or steel, some are aluminum or Chromoly. If the clutch lining becomes contaminated or begins to slip a lot for any reason, hot spots can be created on the flywheel that will necessitate replacement or resurfacing the flywheel.

If the clutch lining becomes contaminated or begins to slip a lot for any reason, hot spots can be created on the flywheel that will necessitate replacement or resurfacing the flywheel.

– Richard McCuistian, ASE Certified Master Automobile Technician

Oil leakage from the rear main crankshaft seal is on the front side of the flywheel and away from the clutch lining, but the transmission front input shaft seal can leak and potentially damage it. Of course, if you have a leak as bad as all this, you’ve got bigger problems than hot spots on the flywheel!

See also  Slipping Clutch: Symptoms, Replacement Cost, How to Fix

Why You Should Resurface Your Flywheel

When hot spots form on the flywheel, the clutch can chatter, vibrate, and fail prematurely. In some cases, the crooked flywheel can also prevent the clutch from releasing. This can make the transmission unpredictable, so it’s not exactly an issue you can just ignore. Sooner or later, you’ll have to either replace or resurface the flywheel.

Replacing the entire flywheel assembly can be expensive, which is why some people turn to flywheel resurfacing instead. It offers a cost-effective solution that can help improve clutch performance, extend clutch life, and reduce noise and vibration.

How To Resurface a Flywheel

Resurfacing a flywheel by yourself can be difficult, mostly because you’ll need heavy equipment to do so. Here are two common ways of flywheel resurfacing:

Brake Lathe Machine

A brake lathe machine is a large tool used to correct a brake rotor’s uneven thickness, which is usually caused by uneven contact of the brake pad on the rotor surface or corrosion. It can also be used to resurface a flywheel, but this still depends on the size of the flywheels and the accessories of the brake lathe machine.

If you ask your fellow car owners about this, you’ll likely get mixed opinions. While some claim brake lathes are great for cutting flywheels, others believe they aren’t worth it. Brake lathes typically can’t cut hard spots on the flywheel, and you might find it hard to find an auto repair shop that still has a brake lathe machine.

See also  Flex Plate vs Flywheel: What’s the Difference?

Block Grinding Machine

Some auto repair shops have block grinding machines instead of a brake lathe. Also known as a flywheel grinder, this machine can recondition flywheels, clutch friction plates, pressure plates, and other circular pieces like discs, rings, and flanges. It grinds the surface of the flywheel using a type of stone.

Different machines will have different specifications, including the maximum grinding diameter. In most cases, however, using a block grinding machine will give you a better finish than a brake lathe.

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When To Resurface Your Flywheel

If the clutch is worn or needs replacing, then you probably have to resurface or replace your flywheel as well. Here are other signs that you should get your flywheel resurfaced:

Excessive Runout

Excessive runout typically occurs due to poor resurfacing methods or when the flywheel has been exposed to excessive thermal overload. This causes the flywheel to wear faster due to its uneven surface.

Dishing

While it isn’t typically common with cast iron flywheels, dishing still occurs in steel flywheels, where a deep hole or pocket forms on the surface. These small cracks might not seem like a big deal at first, but they can get worse over time.

Hard Spots and Discoloration

Excessive clutch slippage can cause carbide hard spots to form on the flywheel. Because the surface becomes uneven, the new disc won’t fit properly, causing the clutch to slip and fail. You’ll need to resurface the flywheel to get rid of these spots.

Grooves

If you touch the flywheel and find grooves along its surface, then it’s best to either resurface the flywheel or replace it entirely. Grooves along the mating surface of the clutch disc mean the clutch has less contact area with the flywheel, causing it to slip or create hot spots.

Ring Gear Wear

A ring gear around the flywheel engages with the starter motor’s pinion, cranking the engine upon starting. If the ring gear around your flywheel is worn, then this means the flywheel’s weight is uneven. This slight imbalance can throw off the engine, preventing it from running smoothly.

See also  Clutch Replacement: Bad Clutch Symptoms, Costs, and FAQs

Can You Resurface a Dual Mass Flywheel?

A dual mass flywheel, or DMF for short, consists of two flywheels that rotate independently, with one attached to the clutch while the other is attached to the engine. This design is meant to stop engine vibration from reaching the transmission and driveshaft.

DMFs come with dowel pins that can’t be machined or removed, which is why most manufacturers strongly advise against reconditioning DMFs. If your vehicle has a DMF, it’s better to replace it with a new one.

What To Consider When Replacing the Flywheel

If you’re lucky, you might get away with simply resurfacing the flywheel or replacing it on its own. In some cases, however, you might have to replace the clutch as well, especially if your vehicle has a DMF. When replacing a DMF, you typically have to replace the clutch and other components and consumables as well. This includes the throwout bearing, pressure plate, slave cylinder, clutch fluid, and transmission fluid.

How Much Does Flywheel Resurfacing Cost?

The exact price will depend on several factors, such as the auto repair shop you choose and your vehicle’s year, make, and model. On average, however, you can expect to spend anywhere from $20 to $50. In some cases, however, resurfacing won’t be an option, so you’ll need to replace the flywheel, which can cost anywhere from $40 to $1640.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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