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Will Dirt Bike Start If Timing Off? Run this test

Cranking and cranking and nothing, what a pain! I hear you. I’m a mechanic and very shortly we’ll check your timing and we’ll be well on the way to figuring out what’s going out with your dirt bike.

When a dirt bike timing is off, you may experience the following symptoms:

  • No start
  • Runs but no power
  • Runs but backfiring
  • The engine won’t crank just clicks
  • Kickstart won’t move

In this post, you’ll learn, why dirt bike timing is important, you’ll learn how to check and reset the timing on both a 2 stroke and 4 stroke motor.

What is Dirt Bike Timing?

Timing is important but you already know that. But what is meant by timing? An engine needs three ingredients in order to run:

  1. Fuel (air and gas mix)
  2. Spark
  3. Compression

When referring to timing on a regular 4 stroke motor we may be referring to ignition timing or valve train timing and we’ll get into that in a little more detail below.

When referring to timing on a 2 stroke we are referring to ignition timing only, since a 2 stroke doesn’t have a valve train there are no valves to time.

Checking and adjusting timing is different depending on what type engine your bike has. Checking and setting the timing on a two stroke as said relates to the ignition timing. If you have a two stroke bike you can jump ahead to checking and adjusting timing here.

Checking timing on a four stroke is a little more work and typically when we refer to timing on a 4 stroke bike we are referring to valve train timing, since ignition timing for most four strokes is not manually adjustable. The timing is advanced and retarded by the CDI/ECU controller only.

Four stroke engines

The purpose of engine timing is to prepare the combustion chamber so that the conditions are perfect for ignition (explosion). If the fuel mix is wrong (too much air or too much gas), if the plug doesn’t spark at the correct moment or the cylinder doesn’t compress, the mixture won’t ignite and the engine won’t start.

Most engines are known as four strokes and this describes the timing of how the three main ingredients are added to the mix, if you like.

4 stroke engine cut away

An engine (4 stroke) may be thought of as unit with two halves, the bottom end, known as the block with the crankshaft being the main component, and the top end known as the cylinder head with the camshaft being the main component.

The two halves must work in harmony in order for your dirt bike to perform. And to do that the two components, the crankshaft, and camshaft must be synchronized.

An assembly known as a timing assembly is employed and charged with the task of synchronizing (timing) both these components. Typically a timing assembly includes sprockets, a chain, guides, and a tensioner.

Let’s take a look at those four strokes (stages) briefly now.

Stroke 1

First stroke – The rotating crankshaft causes the intake valve to open and the piston to fall which in turn draws the air-fuel mix into the cylinder.

stroke 2

Second stroke – The rotating crankshaft causes the intake valve to close sealing the cylinder and allowing the rising piston to squash and compress the air-fuel mix into the top of the cylinder (combustion chamber).

Compressing the mix, heats it through friction making the conditions perfect for combustion.

Stroke 3

Third stroke – The rotating crankshaft passes x° BTDC (Before Top read Center) which triggers the ignition system pickup sensor which in turn fires the spark plug through the CDI and coil.

This is known as the power stroke as the explosion pushes the piston down the cylinder.

Stroke 4

Forth stroke – The rotating crankshaft causes the exhaust valve to open and the piston to rise forcing the spent gases out of cylinder.

And the process starts over at the first stroke.

How To Check 4 Stroke Dirt Bike Timing

Checking the timing is not difficult, all bike engines will have a crankshaft marking engraved which corresponds to a camshaft sprocket marking. Checking timing then is as simple as making sure they align precisely.

Some components may need to be removed in order to access the timing marks, but usually, manufacturers fit removable covers.

I covered the process below, but note all makers will approach this slightly differently, some will be single cam, some twin cam, and some older bikes may not be OHC (Over Head Cam) at all.

Timing check steps as follows:

  • Remove spark plug.
Dirt-bike-timing-inspection-covers
  • Remove the side cover timing inspection cover
  • Remove flywheel fastener access cover
Twin cam ATV engine timing marks
  • Set the engine to TDC by turning crankshaft CCW until mark 1 (flywheel mark) aligns with side cover mark
  • Now check the cam sprocket marks 2 and 3 align

This is a typical see up but your bike may be single cam, but I think you get the general idea.

If your marks don’t align then timing will need to be adjusted. We cover that below, but just before we jump to adjusting timing we should ask why the timing is off in the first place. It may be a warning sign of other issues which I cover below, you can check that out here.

Checking & Adjusting 2 Stroke Dirt Bike Timing

It should be noted not all 2 stroke bike timing is adjustable but this is something you can check in your owners manual before going to the trouble of pulling off a side cover.

Checking 2 stroke timing is usually undertaken in one of two ways. Tools however are required to nail this professionally.

Head cover on – For this process we’ll need a dial gauge to check and adjust the ignition timing. It’s not a difficult task, just a little tedious and you’ll need the specs for your make and model bike. If you don’t have a dial gauge you’ll find one here on the Dirt bike tools page here.

I’ve covered that below, note the side cover will need to be removed also.

Head cover off – If you already have the head off, then a simple timing tool may be used to check and set the piston to the correct ignition timing mark. If you don’t have a timing tool gauge you’ll find one here on the Dirt bike tools page here.

I’ve covered that below, note the side cover will need to be removed also.

Checking timing with head cover off

2-stroke-timing-check-head-off

With the correct timing tool selected for your engine, use the following steps to time your engine:

  • Place the timing tool on the jug and rotate the flywheel CCW until the piston kisses the tool.
  • Now check the timing mark on the flywheel corresponds to the stator base plate.
  • If not, loosen the stator base plate fasteners and rotate so the markings align and tighten again.
  • Job done!

Check timing with the head cover on

This process is very similar but since we don’t have the same access to the piston we’ll need a different tool. For this, we’ll need a dial gauge.

The process is as follows:

Dial-gauge

Remove the spark plug and fit the dial gauge at the appropriate height.

  • Rotate the flywheel CCW to TDC
  • Now zero out the dial gauge
  • Rotate the flywheel CW to the specified measurement
  • Now check the ignition timing mark on the flywheel (orange) corresponds to the stator base plate mark (green)
  • If not, loosen the stator base plate fasteners and rotate so the markings align and tighten again
  • Job done!

The engine is set to the correct ignition timing BTDC.

2-Stroke-timing-adjustment

Some bikes may have three timing marks and that’s super useful for the MacGyver types that like to wing it.

The 3 marks represent the window of adjustment available to us. It’s a case of adjust, test, and readjust until it feels right, who needs a dial gauge tool?

Why does Dirt Bike Timing go Out?

Engine timing is serious business when it’s out a little performance suffers but if timing is out a lot or if timing assembly fails it often ends in disaster for the engine (4 stroke motor). So why does timing move out of sync in the first place?

As with checking and setting timing, why the timing moves out of sync depends on your engine type.

Why 2 Stroke timing goes out

A 2 stroke ignition timing typically needs adjusting after a rebuild and is often forgotten.

Why 4 Stroke timing goes out

The most common reasons a 4 stroke timing moves out of sync include:

  • Worn chains – stretch with age and poor oil quality
  • Worn timing sprocket – wear and tear and poor quality oil
  • Incorrect fitting after rebuild
  • Failed or worn chain tensioner
  • Failed or worn timing chain guide

If you find worn timing components you’ll need to go ahead and replace the tensioner, guides, and the chain. In addition, you’ll need to replace the side gasket together with cam cover gasket.

To replace the chain guides and tensioner we’ll need to do the following:

  • Remove the top side cam (replace gasket)
  • Set timing to TDC
  • Remove tensioner
  • Remove cam caps (star pattern)
  • Remove side cover (replace gasket)
  • Pull flywheel (need flywheel puller) careful of key
  • Remove chain guide and chain

Replace chain and guide and rebuild in reverse order and set timing as per below. Careful to follow correct torque specs in relation to flywheel and cam caps. Replace side cover gasket, cam gasket and tensioner gasket otherwise we’ll be chasing oil leaks.

How To Set 4 Stroke Dirt Bike Timing

Setting the timing isn’t difficult, we’ve already covered how to access and check the timing marks. Setting the timing then requires a few more steps. We’ll need to remove the tank, covers, air box, throttle body/carburetor, etc, wherever else we need to access the cam cover. For the following steps, we’ll assume you have clear access to the cam cover.

They are as follows:

  • Remove spark plug
  • Remove timing covers
  • Remove cam cover
  • Set engine to TDC
  • Note timing marks
Dirt-bike-tensioner
  • Remove tensioner
  • Loosen cam caps (star pattern)
  • Remove or rotate the cam to realign the chain on the cam sprocket mark
  • Refit cam cap and torque to spec (star pattern)

Careful to follow correct torque specs when tightening the cam caps and cam cover. Set the tensioner and fit (fit new gasket) and check tensioner has fired.

You may find the following posts helpful:

Will dirt bike start with low compression?

Signs of bad dirt bike coil

Dirt bike troubleshooting