Crankshaft bearings and seals

Crankshaft bearings ensure that the crankshaft continues to rotate smoothly and runs centrally in the engine block. If they deteriorate, you usually hear it first: more rumbling, extra vibrations and sometimes suddenly faster damage. On this page you can read what you can pay attention to, how to choose the right crankshaft bearings for your scooter, moped or motorcycle and which things really count during installation.

What is a crankshaft bearing and what does it do in the engine?

The crankshaft converts the up and down movement of the piston into a rotating movement. There are bearings on both sides of the crankshaft that support the axle and keep friction low. This keeps everything neatly in line and the engine can do its work even at higher speeds without unnecessarily heating up.

A crankshaft bearing is similar in idea to a wheel bearing, but it is a lot heavier. Heat and high speeds play a role in the crankcase, and in many 2-stroke engines this also involves fuel and oil mist. It is then that the right size, internal clearance and a solid bearing make the difference.

Symptoms of worn or damaged crankshaft bearings

Unusual noises and vibrations

It often starts with a rattling, humming or grinding noise that becomes more noticeable as the speed increases. You may also feel more vibrations in the frame or handlebars, especially when accelerating and also when releasing the accelerator.

Loss of power and irregular walking

If there is play on the crankshaft, an engine often runs less smoothly: the idle is restless, the throttle response is less pleasant and the whole thing simply feels less smooth. With 2-strokes, the sealing of the crankcase can also deteriorate, making adjustment suddenly a lot more difficult and the block can run more erratically.

Oil leakage and increased oil consumption

Crankshaft bearings are often replaced together with seals. If a seal is leaking, you can sometimes see traces of oil on the ignition side or on the vario side. Such a leak can also cause false air, with a poorer mixture and an increased risk of overheating.

Consequences of driving through

Continuing to drive with bad crankshaft bearings can ultimately end in seizure, damaged crankshaft webs, a broken crankcase or damage to cylinder and piston. If you tackle it in time, it usually sticks parts replaced instead of a major repair afterwards.

When should you replace crankshaft bearings?

Lifespan and use

There is no fixed mileage that is always correct. Many short journeys, long high revs, too little lubrication or an engine that is not properly adjusted: it all affects the bearings. If you hear clear bearing noises or feel play, then replacement is usually the wisest step.

When overhauling the engine block

If the block has to be opened for an overhaul, preventive replacement is often logical. Most of the work is in disassembly and assembly; With new bearings and seals you can immediately put it back together tightly and reliably.

For tuning or power upgrades

More power simply means more tax. Better go for an A-brand bearing with the correct clearance and specification for your setup, so that you don't have to start over again after a short time.

Which crankshaft bearings do I need?

Make, model and engine code

Start with the vehicle details: make, model, year of manufacture and engine code. If you are not sure, an OEM number or the exact engine type will help you find the right size and version.

Sizes and specifications

Always check inside diameter, outside diameter and width. In addition, you often see indications for internal play, such as C3. That extra play is useful for many engine blocks, because a bearing expands due to heat. Also choose the correct version (open or sealed), depending on how the bearing in your block is lubricated.

Crankshaft bearing set with seals or loose bearings

A complete crankshaft bearing set with seals is often the safe choice: you grab the most important turning and sealing parts in one go. Loose bearings are especially useful if you only need one bearing, or if you already have new seals ready.

Brands and quality

Brands such as NTN and SKF are known for tight tolerances and a long service life. Performance brands such as Stage6 or BGM are more often found in sports and racing setups. If you drive a lot or ask a lot of the engine, proven quality is usually the best deal (even if it costs a little more).

Frequently asked questions about crankshaft bearings

Can you still drive with worn crankshaft bearings?

Sometimes you can get away for a while, but the risk of sudden (and often expensive) damage is high. As soon as you hear clear bearing noises or notice play, continuing to drive quickly becomes a gamble.

Do you always have to replace both crankshaft bearings?

Usually yes. If one bearing has wear, the other has usually had the same operating hours and load. And if the engine block is open anyway, it's better to do it right the first time.

How do I know if it is really the crankshaft bearings?

Noise that varies with the speed can also come from other bearings. Checking clearance, a stethoscope test and inspection during disassembly provide the most certainty. If you have any doubts, have an experienced technician look at it.

How long do new crankshaft bearings last?

That depends on lubrication, adjustment, driving style and the quality of the parts. With good bearings, correct installation and a healthy block, they usually last for years.

Do you want to quickly find the right crankshaft bearings? Use the filters on the collection page and always check the specifications before ordering.