Club Night Forum – Failures and How to Avoid Them
PART 5 - ELECTRICAL FAILURES
Notes from a technical forum evening of the DA7C hosted by Phil Whitter
Click here for Part 1 - Engine faults
Click here for part 2 - Transmission
Click here for Part 3 - Lubrication
IGNITION FAILURE or MISFIRING
Rotor Arm
* Carry tried and tested spare
* Try to use new old stock whether Lucas or Bosch 009
* Check Lucas for correct rotation as arrow
* Solder wire across Bosch to short out ballast resistor which goes
disconnected on Chinese imports
* Check carbon brush
* If not rotating drive gear may be stripped !
Condenser
* If disconnected gives weak spark and pitted points
* Use old stock as more reliable than Chinese items
* Check for screw loose on clamp
Distributor
* Bob weights can be seized causing engine not to rev as adv/retard not
working
* Need to lubricate adv/retard bob weights
* Need to restrict advance on Bosch with blue crimp sleeve as it is
designed for VW engine
* Lubricate shaft on Bosch as not splash fed like VW engine
* Ensure anti lift screw fitted and tight
* Check cap not cracked
Contact Breaker
* Ignition battery feed wire loose or disconnected
* Loose screw or rivet on base plate
* Loose screw on condenser
* Spring can touch body of distributor
* Smear cam with Vaseline or grease
* Very sparingly lubricate pivot
* Fit Accuspark but not optical system like Lumenition
Coil Weak Spark
* Fit new coil from quality source
* Use Lucas or Bosch from Germany or Brazil
* Ensure reads 6V or 12V at the coil with engine off
* Check polarity correct
Plugs Oiling/Sooting
* Rebore
* Carb jets
* Wrong plugs
* Use Colourtune for mixture
* Champion D16 good with 20 thou gap and 25 for Accuspark
CHARGING
Not Charging
* Brush sticking or worn
* Wire broken off/loose inside or on terminal block
* Commutator dirty
* Field, Output or Half Charge fuse blown
* Cut out not earthed
Intermittent Charging/ Low Output
* Loose connections
* Brushes tight or worn
* 3rd brush in wrong position
* Switch panel problem
* Cut out loose connections/dirty contacts/poor earth
* Commutator dirty or oval from worn bearings
* Field coil breaking down
* A reverse charge shows your ammeter is reversed!
Over Charging
* Third brush in wrong place (Typical full charge is 8-10 amps for later
C35 type dynamo with 6-8 amps for earlier DFL type)
Heavy Discharge
* Points on cut out stuck
A short circuit somewhere? - Flow chart to located on
the Cornwall A7 Club website. Under ‘Technical Articles’, select ‘Charging Fault
Finding’.
LIGHTS
Too Dim
* Upgrade to 12V
* Provide good earths especially from chassis to engine
* Check your battery posts and clamps
* Change to LED
* New reflectors and bulbs Seven Workshop
Too Bright
* Probably LED not properly in focus
TRAFFICATORS
Not Rising
* Provide extra earth
* Lubricate solenoid post and pivots
* Put them out before you brake!
* Only use them to supplement modern indicators
BRAKE LIGHTS
Not Working
* Spring on the switch
* Make sure straight pull and lubricate
* Connectors corroded
WIPER
Not Working
* Try to repair on/off switch
* Use potato on the screen!
* Use Rainex
Not On The Screen
* Renew the spring or bend the arm
STARTER MOTOR
Slow
* Try new battery after checking everything else
* Check brushes and commutator
* Provide good earth to chassis
* Bad switch
* Check cable size and make sure lugs are clean and soldered
A 6V system requires a good battery, heavy gauge leads
and soldered connections. Ideally an earth lead should run from the starter
motor directly back to the battery. With this arrangement, the starter should
turn the engine over quite quickly.
Not Engaging
* Low volts due battery or poor connections/earth
* Bendix dirty
Switch Catching Fire
* Keep switch clean which is directly under oil filler
* For safety have a battery isolator which can be quickly reached
Locking Up
* Bendix jammed – broken spring?
* Badly worn gear starter/flywheel
GENERAL
Did you know that using a late coil (positive earth) in an early car (pre Dec 35) will result in erosion of the plug earth electrode due to reversed spark. Also the coil will not be so efficient in this direction. All coils are marked CB and SW not +ve and -ve as on modern coils. Remedy is to reverse the connections on a late coil if fitted to an early car. Note that all coils are dated on the base.
If removing the dynamo and dynamo casing, this leaves the exposed gear for
debris to fall in. When removing the dynamo casing, cover the hole to stop
debris falling in.If you strip the thread for the long bolt on the dynamo/casing
(into aluminium block), you can use a long stud to reach the lower part of the
thread as the tapped thread is very long in the block. Whitworth thread.
3 brush dynamo: If converted to 2 brush dynamo what do you need to change in the
electrics? - Need to include a compensated voltage regulator but difficult to
find. Maybe electronic (from classic Dynamos) or Morris Minor version maybe. AW
Electrics can do the conversion.
Charging faults
Comparing the performance of the standard Lucas distributor with that of a
Bosch 009. Find a long gradual gradient hill, setting the timing and then
stopping frequently to fine-tune it for best effect. A magneto to coil
conversion made a huge difference on a Chummy. It is recommended to carry a
spare rotor arm. The Bosch distributor has an automatic advance. It is suggested
setting the timing at a fast tickover to 27⁰ before TDC, which equates to six
teeth on the starter ring gear.
CONCLUSION
From this session it is clear there are very real benefits to be had from
perhaps using more modern ignition components but to try and avoid cheap Chinese
copies for items such as points, condensers and rotor arms.
Providing a separate earth connection from a bellhousing bolt to a good chassis
earth is a sound investment in reliability together with checking all screws in
the ignition system. I would always recommend soldering battery lugs and any
other terminals in the electrical system including those dreaded crimp
connectors!
With many thanks to Phil Whitter DA7C