FAQ: Why Do 4 Stroke Motors Require Valve Shims?

Why do you have to shim valves?

By using a shim, you create space between the bottom of the cam and top of your engine’s valve bucket. This clearance is necessary for valves which are wearing out, but they too need to be replaced at some stage.

Why does an engine need valve clearance?

Intake valves open and close to let the air-fuel mixture (or just air in some modern engines) enter the cylinders, and the exhaust valves allow exhaust gases to escape. If there’s too little valve clearance, the valves won’t fully close, causing excessive heat, and the engine will lose power.

How do you know when your dirt bike needs a valve adjustment?

The most common signs of a 4 stroke dirt bike that needs valves adjusted are:

  1. Hard to start when cold.
  2. Popping in deceleration.
  3. Loss of power.
  4. Misfire.
  5. Hanging idle.
  6. Lower compression.
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What is the purpose of a valve adjustment?

What is a valve adjustment? The valve mechanism (push rod, lifter, and rocker arm assembly) is adjusted so that the lash has the proper clearance necessary to regulate the opening and closing of the valve. If the lash clearance is too great, it will affect the engine’s airflow and will eventually lead to valve damage.

How many times can you shim valves?

The rule of thumb for most mechanics is to shim the valves twice. After the valves have moved (almost always tighter) twice, it is time to replace them to minimize wear on the seats. 01 Remove all the parts in the way of the valve cover: seat, tank, shrouds and, on some models, the radiators.

Should valve clearance be tight or loose?

The thing is that as the valves and seats wear the clearances get tighter. Tighter valves will not make any new noise. When the intake valves get too tight they will cause hard starting and poor idling.

What happens if valves are too loose?

If the valve clearances get too loose, this will lead to a noisy running engine. Consequently, this will eventually damage the camshaft lobes; rocker arms ( if equipped ) and the tips, of the valves themselves.

What are the symptoms of bad valves?

The symptoms of bad valves include:

  • Cold Engine. A cold engine test will give you a good idea if your valve seal is faulty.
  • Off-Throttle Braking. Engine braking involves employing different means to slow down your car asides from the external braking.
  • Idling.
  • Excessive Oil Consumption.
  • Excessive Smoke.
  • Loss of Engine Power.
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What happens if you don’t do a valve adjustment?

The valves in your engine open and close through a complex, precisely timed system. They open to accept fuel into the cylinder, close to form compression and open again to release exhaust. Without an adjustment, they may not open and close efficiently, reducing your car’s overall performance.

How much does it cost for valve adjustment?

Between $246 and $336 is the average cost of a valve adjustment. The labor costs are between $220 and $278 while the parts cost between $26 and $58.

How often do dirt bike valves need to be adjusted?

Whether you own a dirt bike, ATV, street bike, or any other four-stroke equipped machine, chances are your owner’s manual outlines when your engine’s valve clearances should be checked. Depending on the application, the inspection interval may vary from 15 hours to 15,000 miles.

What are the symptoms of a bad valve adjustment?

Now that we know a little bit about valve clearances, lets talk about the signs your motorcycle will give you when its time to adjust the valves.

  • Pre-ignition.
  • Rattling Noise (Loose Valves)
  • Overheating (Tight Valves)
  • Increased Fuel Consumption.
  • Valve Train Failure.

How long does a valve adjustment take?

Pros bill for half an hour to an hour. If you haven’t done it before it’s going to take you longer than 20/45 minutes. The time going to vary based on how many are out of spec. If you have to adjust all 16 it’s going to take you longer than if you only have to do 2.

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Can valve lash effect compression?

Yes, valve lash can affect compression results. Too tight = valve potentially open all the time. However over time it is VERY unlikely that lash would become too tight.

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