This document provides instructions for setting the base ignition timing on an MGB GT engine. It involves using a timing light to measure the current timing, then loosening the distributor clamp and rotating the distributor clockwise or counterclockwise in small increments to advance or retard the timing as needed. The goal is to adjust it to the desired timing of 31 degrees once the engine has reached an operating temperature of 180 degrees Fahrenheit. Safety precautions are outlined due to the risk of electrical shock when adjusting the distributor with the engine running.

1. Setting the Base Ignition Timing on the
MGB GT
By Joseph Legan
Beginning Notes:
 The timing cover on both engines does not have the correct timing marks. It is from a
different generation of the engine. The correct timing cover is no longer available
commercially at the time this was written.
 This task requires a 5/16” deep socket on a ¼” ratchet, a 7/16” combination wrench, the
jumper battery and a timing light with an advance adjustment feature, and a minimum
of 2 people.
 Follow all lab safety rules at all times.
 The car in its current configuration had a tendency to shock the individual making the
distributor adjustments if the engine was running. For this reason the procedures listed
within should be followed carefully.
 Read all the directions before any work is started.
Tools Required:
All the tools required to do these
procedures. The gloves are
recommended due to the
proximity of ones hands to the hot
engine.

2. Step 1 Hook up timing light to car and battery
Move the car outside. Place the battery cable clamps on their respective battery posts and
place the spark sensor on the #1 cylinder spark plug wire close to the spark plug itself. Be
careful routing the sensor cables to keep them away from the alternator fan.
Pictures shows the correct
way to hook up the timing
light to the battery and to the
#1 cylinder spark plug wire.

3. Step 2 Start engine and build heat
Start and run the engine until the water temperature reaches 180 degrees Fahrenheit. A sure
way to make sure the engine is warm enough is to adjust idle ignition timing is to run the
engine until the radiator cooling fan turns on and back off. This will ensure that engine will idle
properly and the adjustments will be accurate.
Make sure water temp is at
180 as indicated by the water
temp gauge before any timing
adjustments are made.

4. Step 3 Measure and record current timing
This is where the advance feature of the timing light as well as the incorrect front engine cover
come into play. The Top Dead Center (TDC) marks on the crank damper and the front cover
must be used in conjunction with the advance feature to correctly measure the ignition timing.
Reference the pictures for details on the marks. Read the captions for detailed directions.
TDC on front cover as viewed
from above and in front of car .
TDC on crank damper.
With the engine running at a constant 1500
rpm and idling smoothly adjust the advance
dial until the strobe catches the TDC mark on
the crank matching smartly with the TDC
mark of the front cover as pictured above.
Due to the front cover being incorrect, take
the number of degrees indicated and
subtract 22 to calculate the actual ignition
timing. Example: Indicated 55 – 22 = 33
degrees of advance.

5. Step 4 Shut off engine and loosen distributor clamp
Using the 5/16” socket on the ¼” ratchet and the 7/16” wrench reach underneath the
distributor to the base and loosen the clamp bolt.
This is the step that was getting people shocked in the past. The cause is thought to be the
loose fit of the distributor cap allowing it to shift and then the hands become the path of least
resistance for the spark energy.
Distributor base clamp bolt. Best accessed by reaching under
the distributor. Use caution due to the heat of the engine.

6. Step 5 Make adjustment by rotating the distributor
Note that the engine rotates clockwise when viewed from the front of the car and that the
distributor rotates anti-clockwise when viewed from the passenger side of the car.
To advance the timing rotate the distributor clockwise.
To retard the timing rotate the distributor ant-clockwise.
Make small adjustments as it is easy to move too far and miss the desired mark.

7. Step 6 Start engine and measure timing again
Repeat Steps 5 and 6 until the desired setting is achieved.
Note: The current engine as of 2014 made the most power with the timing set at 31 degrees of
advance while the cam was installed per the cam sheet specs.
Step 7 Turn engine off and tighten clamp
With the engine off tighten the distributor base clamp and put away tools.