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G8MNY > TECH 07.12.24 15:13l 59 Lines 2763 Bytes #999 (0) @ WW
BID : 21364_GB7CIP
Read: GUEST
Subj: Resistive Ignition Lead Repair
Path: IW8PGT<LU4ECL<K1AJD<VE3CGR<WW4BSA<N3HYM<IW2OHX<GB7CIP
Sent: 241207/1008Z @:GB7CIP.#32.GBR.EURO #:21364 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Dec 22)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
These carbon particle leads are standard on petrol engines with or without
distributors/coil packs, but not found on small magneto ignition engines like
lawnmowers and generators! The advantage is much reduced QRM, but reduced spark
plug power and unfortunately a short lifetime, 10 years? But do check for bad
plugs, as they can fail intermittently too usually when hot.
black outer rubber
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ white inner rubber ³
Carbon dust coated string :::::::::::::::::::::::::::::::::::
Gives about 1k per inch ³ white inner rubber ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
black outer rubber
Lead breakdown is caused due to the current passing through the carbon
particles on a string, heating and oxygen near the exposed surfaces will over
time generating CO2 making the particles smaller and causing bigger gaps
between them and then more sparking and heating etc. Normally the hot Spark
Plug ends are where the failures are, a bit of examination at night looking for
spark light and hearing clicks, or a meter will locate the cause an occasional
missing engine fault. Replacing the lead with new will cure the problem for few
years, but here is a ZERO COST DIY repair...
REPAIR
If spark light is seen at an end (not from on outer to nearby earth) or the
lead is higher resistance than expected, it is usually the hot plug ends that
fail. An internal wire (paperclip) can be inserted along the string once the
spark plug termination clamping the end is removed. This hardest bit is
actually carefully breaking the rubber glue with a small sharp long screwdriver
inserted along the cable outer to free up the plug shield boot.
Boot
========_____
Spark Plug ()²²²ÜÜÜÜÜÜÜÜÜÜÜÜÜÜlead
========~~~~~
Then slide the boot up the lead, carefully bend the metal contact tangs out of
the lead (so they can be reused) abd free the lead. Straighten a paper clip to
leave 1 U fold, and push long piece down centre of lead until U fold is home.
Measure the resistance, it should be a stable resistance now & possibly lower.
Reassemble the metal contact griping the paper clip U & crimp it down on the
lead again. slide boot back & re-glue once all leads retested.
Also see Tech Bul on "Towing & Reversing Bleeper", "Towing Socket for Caravans"
"Vehicle Gutter /P Mast Support" & "Wheel Nuts".
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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