rota arms

[pgc520]

Whatb would cause the rota arm top fail, took the car out for a run and after 40mins it stopped working. FJ recovery identified problem, na d new rota arm fitted, then same problem. would itm be the condenser ?

[RobThomas]

Finger trouble? (Only kidindg!)

Cheapo rotor arms, short/damaged/stuck carbon brush in the centre of the distributor cap, slack spring above the brush, oil contamination...lots of possibles. Losing 2 in a short space of time might suggest that the rotor arm is either not the fault or is just one of several faults. Might be worth replacing the whole shebang and keeping the old ones as spares. The other option might be to buy one of each item and replace them one-by-one when it next dies.

Condensers invariably either work or don't. Not common to have an intermittent one unless the wiring is damaged to it or the grounding screw loose. Have you still got the rotor arm? Got a microscope? Worth looking for a crack or a loose rivet holding the metal bit on. Any sign of electricity leaking away and leaving a small burn mark?

I once worked on an aerobatic aircraft that would lose power during aeros. After lots of expensive component changes it was discovered that a metal teleflex cable was contacting one of the magneto wires when performing high-G aeros. Sometimes it isn't what it first looks like.

[LouiseM]

Is there a low tension lead in the dizzy? (I've only had later Minors rather than series MM's so don't know if the dizzys are similar). If so, that could be the problem as sometimes the braiding gets worn leaving the wiring exposed and causing a short. Fitting the new rotor arm might have moved the LT lead so that it no longer shorted - hence the car running again - but driving the car has shifted it again resulting in a further short. Might be worth taking a look at the LT lead (if there is one).

[RobThomas]

Slightly different. More like this...



Long bolt goes through Phenolic resin bush so no braided wire required. Lack of vac advance means the baseplate is solidly bolted and doesn't need the thin fabric braided earthing lead that always looks shabby on the 25D4.

[mike.perry]

Most DKYH4A dizzys have a long condenser, soldered to the base plate. The condenser is connected to the LT lead terminal by a bar, so no bits of fraid wire.
I have a tin full of old rotor arms plus a couple in my tool box (never go anywhere without the tool box).
I came across a dodgy side entry dizzy cap which wobbled as the rotor arm rotated because it was loose when the spring clips were in place. It had all the Lucas markings but was identifiable because the carbon brush had to be removed to gain access to the coil HT lead clamp screw!

[pgc520]

Any thoughts,

Have now replaced the Rota Arm with Distribution Doctor red type, new Distributor cap, Condenser etc.

Problem is now after engine has warmed up 5 -10 minuters engine cuts out and will then restart but will not rev.

Have checked fuel line, and float ?

Any ideas

Andrew

[MarkyB]

Check the pipe to the jet, silt can find it's way down there and nearly block it.
Dash pot and float chamber lid off, then blow with an air duster down the jet is how I do it.