24V Rev Limiter

[101RRS]

I do not know about 12v 101s, but the 24v versions have a rev limiter fitted. It is built into the distributor rotor button.

What revs does it limit the engine too? I assume it is there to limit over reving in the lower gears rather than in hi range 4th :). When driving around normally does it cause any problems - in my limited driving of my 101 it has not shown up even when reving out in any Hi range gears.

How does it work? - I assume that when revs get to the set level, centrifical force pulls the cylinder lead end contact of the rotor button away from the contacts in the cap or centrifical force breaks the circuit where HT comes into the rotor.

In the 24v distributor, can the special rotor be replaced with a "normal" one and are there any issues.

Thanks

Garry

[101 Ron]

Hi Garry
The rev limiter is only there to save the motor from silly drivers .
It was a common fitting to petrol miltiary vehicles.
It normally works with a spring loaded fly weight in the rotor button .
At the preset speed the brass weight moves out to the distributor cap terminals opposite to the working side of the rotor button.
When this happens it causes bad miss firing( like if you crossed over some high tension leads)
The spark goes to the wrong side of the distributor cap.
I would leave the the rotor button alone as in normal driving it will not operate.
It is easy to solder the sliding brass flyweight if you want to and that will disable the thing.
British 4WD has the rotor buttons new.
I purchased one the other week.
I am investigating of a electronic conversion for the 24volt distributor.
Ron

[101RRS]

Thanks Ron - I thought you had converted your 101 to 12v. As a 101 is flat out getting much more than 4000 rpm in 4th high on the flat I assumed it wasn't an issue when driving on the road but was concerned it might strangle the engine when a few revs are needed in low range.

Cheers

Garry

[101 Ron]

My 101 is 12 volt.
I am going to the military distributor because it is waterproof and only if I can convert it to electronic.
The military or normally called 24volt distributor is in fact 12 volt as a resistor set up is used to drop the voltage as is the coil.
I currently find the civilian distributor and coil in the standard 24 volt locations is prone to water failure as any water going down the fan tunnel is picked up by the fan and thrown sideways onto the coil and distributor.
Wet ignition has stopped me a few times now.
Remember my muddy bog hole episode........the motor died and no winch.
With standard gearing I could get the tacho on my 101 to 5000rpm on a flat road in top at something like 80 MPH.
One time trying to pull a water trailer up a muddy hill I gave the old girl a hard time trying to charge the hill and was surprised to see the tacho showing 6000rpm.........I quickly backed off a bit.
101s are tuff.

[101RRS]

In basic terms, the waterproof distributor is the same as the normal one except there is a metal cover that goes over the distrubutor cap (now there is more to it but that is basically it) so converting to an electrionic system should be easy. I might have a look at that as well but much later down the track.

On second thoughts maybe it was for rev heads like yourself that the limiter was brought in.:cool:

Garry

[101 Ron]

The 24volt distributor is totally different in every way.
Check a workshop manual.
Electronic ignition conversion will be difficult .
Note the 24 volt dist uses twin points and not in the usual way.
Most twin point distributors on a V8 motor try to increase dwell time and half the load on the points by using the points in a way that they are working 4 cylinders each.
The military 24 volt doesn't and uses both points operating together in away that one points opens first and the other closes the breaker circuit on all 8 cylinders in turn.
A civie 12 volt electronic dist drops straight in with ordinary HT leads and spark plugs........as the voltage to the so called military 24 volt dist is in fact 12 volt.
I am looking at a Pertronix system and am checking what trigger wheel may fit the 24 volt dist cam from other Pertronix 8 cylinder dist kits.
Getting info and measurements is hard as the kit catalogs don't give points cam dimensions etc.

[101RRS]

Well there you go, you learn something new everyday ;) - I was going on having pulled my spare dissy apart - but it didn't have any points or condenser inside - the dissy looked like any other except the casing had a facilty to bolt on the outer waterproofing casing an a sealing O ring. Can you not put all the internals of a 12v dissy into the 24v housing and so make a water proof 12v dissy.

Garry

[101 Ron]

With my 24 volt distributor someone tried to remove the inner cap from the outer alloy one and removing the small screws which appear to hold it all together.
They managed to separate the two caps slightly and got no further.
I cannot refit or separate the caps as each HT terminal is heavily rubber sealed .
British 4WD has new distributors.
I havent looked at the rest of the distributor to see if it comes out of its housing .

[101RRS]

After the screws are removed the inner cap will come out but it is a very tight fit. However any force will damage the cap. It needs to be gently tapped through the lead holes, tapping just a little in each hole. If the tapping is not equal around the cap it will just jam. Also too much force and you just punch a hole in the cap - and the odds are it will be damaged anyway.

The following thumbnails show the caps - you can see the damage to the HT hole and the edge of the cap caused by too much force.

I did have an old 12v dissy out of a rover and was going to see if the insides would go inside my spare stripped down 24v housing but in a fit of clean up I have thrown it out - it would have been good to see what would fit and what wouldn't.

The first pic is the inner cap, the second it inside the outer cap, the next is them side by side and the last is them together.

Cheers

Garry

[Dave Jump]

What are your thoughts on using the older style electronic ignition which retains the original points as it's trigger? The points never wear out as the're not carrying any load and it would be a straight swap. It's also worth noting the 24v dizzy has no vacum advance so you have a fixed ignition curve. No big problem unless you plan any serious tuning.
cheers
Dave

[101 Ron]

Using points in any shape or form is a problem.
The 24 volt dist with the way its twin points are set up means there would be little wear of the contact faces of the points any how so the electronic switching ignition using the points as a trigger would be of little help.
The problem is the wear of the rubbing block on the cam which changes the point gap and therefore the ignition timing causing the motor not to run at its best and constant need of resetting of the points gap.
Doing away with the points completely fixes this.