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Bob UK
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Posted on Tuesday, 30 December, 2014 - 09:22 am:   Edit PostDelete PostView Post/Check IP

Distributors fitted to RR cars 6 and 8 cylinder engines are entirely conventional and are alike many other makes.

Both Lucas and Delco Remy are quality precision distributors of the Kettering design.

Experts will say that diyers cannot rebuild one. This is nonsense.

The precision is more or less built in. The weights can't change wieght. The springs can go wonky, they are cheap. Note often the springs are different from each other this is correct.
All that's left is the bearings which if they have worn and worn the shaft, skim shaft and fit under size bushes. Most don't. End float is controlled by shims 5 thou is ample for most.

Because the Shadow dizzy is upright and well above where adequate engine oil would make it as far as the top dizzy brg, I like to liberally oil the centrifugal advance, this oil then finds its way via gravity to the top brg. Excess drains out of the drain hole.

The cam. Each lobe should be the same. The way to check is set points at 12 thou and check all 8 gaps. Max tolerance is plus or minus 2 thou. If this is wrong then the easier way to fix is to convert to electronic. However it is surprising how well an engine can run with an uneven cam. So if when checked the cam is uneven then try running the engine on it first.

The points gap isn't important but the minimum dwell is. The coil takes time to saturate. The dwell is the amount of angle, and therefore time that the points are closed and the coil is on. The faster The rpm the less time.

4 cylinders use 52 to 56 degrees. This is plenty of time. If the gap was opened up to say 30 degrees of dwell and the ignition timing corrected the engine will run fine. Accept that the points are being opened further in the same amount of time and are moving faster which can causes the points to bounce.
The makers worked out the minimum gap that gives a clean break plus a bit for safety.

8 Cylinders don't have a big margin, because there's only half the time to do the same work.

Dwell meters just clip the leads on and with engine running. Twist long bolt 2BA I think until 26-28. Dwell meters average out the dwell. Rev engine to 1500 the dwell should be the same as the revs go up and down. If the dwell is not steady then most likely the dizzy brgs and or shaft are worn.

Electronic are pretty much the same except it has an air gap instead. Making the air gap smaller will not make sparks stronger.
Magnet type sensors are normally Hall effect. These have two coils with a common terminal. One coil is driven with a constant voltage, usually 5v. The second coil produces a voltage as a magnet passes the powered coil because the magnet upsets the field of the powered coil. The signal has enough volts to work a electronic switch with out an amp. Hall sensors are also used for crankshaft position sensors because the air gap can be wide with out getting a weak signal.

Because the switching can take more than points amp wise. A ignition coil with less primary ohms can be used. This gives a fatter spark. Also it allows the coil to saturate quicker. So good all round.

The ballast, apart from the boosting when starting also protects the coil and other bits from cooking should the ignition be left on for a long time. It limits the current. Also should the coil or something short out the ballast will consume 12 amps if it's 1 ohm. Which is safer than full whack of amps from the battery.

My dizzy is a single point non emission. And therefore has no vacuum module(s).
Vacuum modules can either be advance or retard. To check suck on the module. If the baseplate moves in the same direction as the rotor then it's a retard.

In general most makes are timed with no Vacuum. When the engine tries to start the ignition timing needs to be retarded. When the engine is on idle the timing can advance a bit. Because an engine on a closed throttle has lots of vacuum (21inhg at sea level) this advances the ignition. When the throttle is opened the vac goes and the timing retards, this stops pinking as the engine accelerates. Once at criuse the vac goes up and advance again.

The centrifugal bit relys solely on rpm. This is set by the weights and the springs.

Most cars by 2000 rpm are fully centrifugally advanced.

To check set idle timing disconnect any vac modules and rev engine until no more advance. Then check in specs for angle and revs. If the max is ok and the mechanism is well oiled then one can safely assume the middle is ok. However the more keen can check with a strobe and plot a graph which should be more or less a straight line. The springs can go weak which causes early advance.

If the engine pinks and the timing has to be set retarded to stop it say 0 btdc at idle then suspect weak springs. The springs last a long long time.

Oils to use. Good old engine oil for the weights and for where the base plate swivels. The rest is grease. Not forgetting the little pips what the base plate swivel bit rests on. Also oil for the felt pad on the cam and under the rotor arm. Oil on points is not good it will burn and need to be cleaned off. Also keep away from cap centre brush. The sensor in electronic ones is more or less oil proof.

Vacuums that retard instead. These are fitted to emissions cars. When on idle they retard also a switch is fitted to sometimes advance it. This needs careful attention to supplement U in the manual.

Condensers these last well. If the correct one is not available and it is working then it's not going to fail soon so it is reusable and with care will outlast the engine. Most broken condensers are broken by mechanics.

Because different cars have different ohms of their coil primary windings, condensers are different. So should a new condenser be needed. Then match with one with near farad value. If it does not fit inside it can be fitted outside but the wire length must be short. A get you home bodge.

From a garage mechanics point of view the humble dizzy is a reliable bit of kit that needs a bit of oil and maybe points. Once the dizzy has those the dizzy is not the problem. (A bit of over simplification to press the point. Pun intended.)

(Message approved by david_gore)

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