Paging the older buggers

"Mungo \"Two Sheds\" Toadfoot" gurgled happily, sounding much like they were saying:

Is that a solenoid to the LHS?

No, the condensor.

Si

If you look at where the main shaft is, the casting above this is rather thick and has what looks like a bush between in and the points arm.

No chance the bush is actually the end of a pushrod driven off the main shaft, is there, and this is broken?

Is the only logical explanation I can come up given the parts shown in the picture.

HTH

I do believe that *is* the only way the points could be lifted. I have, however, just mullered it seeing if I could gently ease it out! The pushrod is made of something fibrous, not metal, and half of it just broke off. Still doesn't move though. Bugger.

Si

Yes, well... I suspect you're not going to fix whatever it is until you get access to the innards behind the casing, as in the part of the shaft that's hitting the pushrod, and the pushrod itself.

"Mungo \"Two Sheds\" Toadfoot" gurgled happily, sounding much like they were saying:

With a return spring on it, at the opposite end to the pivot?

I'm sure that I recognise that system - come across it on Briggs and Strtatton engines. There's a little Tufnell (spelling?) pushrod that is operated by a cam or lobe on the crank. In almost all cases they stick in place if the engine has been standing for a fair while. Chances are you'll have to hoik it out somehow (maybe with a sharp scriber) and turn up a new one from a phenolic or Tufnell rod?

Julian.

Could the pivot the points arm is attached to not be a pivot but instead go right through and be driven by some sort of kicker off the main shaft?

I'm assuming the 'Landmaster' in the title of the image refers to the rotavator, not the Landrover competitor? It isn't a Chevy 360 cu.in V8 engine is it?

You're not wrong and the pushrod *is* stuck solid. I've soaked it in WD40 so hopefully it'll come out tomorrow.

Ta,

Si

That was what I thought when I first saw the photo too. There must be a cam on the main shaft that pushes a pin through that bit at 12 oclock. The actual part that touches the points lever appears to be rubber (might be wrong, but possibility). Could that rubber be what the pin/pushrod is made from and perished or broken. If the can on the right is a condenser then it is in the right place and wired correctly. You can just see the white wire going off to the ignition coil. I can only presume the pin in the middle of the presumed condenser is adjustable to set the points gap or perhaps move the whole condenser position inside it's bracket. The bolt securing it looks well worn as if it has been used for that. Interesting.

Mark

Yes, operated by the stuck pushrod. You adjust the points gap by loosening the clamp screw on the condensor and sliding it about. You might well find that the pushrod is worn out. Can't help with the points gap or exactly when (timing wise) it should open. Dave

The arrangement seems straightforward enough although it's not one I've seen before. There will be a cam on the main shaft below the lifting pin at 12 o'clock and the points gap will be adjustable by loosening the clamp screw on the condenser and moving it up or down. The cam will be part of the steel shaft and lubricated by engine oil and is most unlikely to have worn away so the lifting pin must be broken. I'll guess the top part is seized and the bottom part has broken or worn away.

You'll have to remove all traces of the old lifting pin, maybe ream the hole lightly back to size if it's corroded in there and fit a new pin. The points wire is also broken so you'll need a new one of those.

Spot on. Once you have freed the pushrod off you will have to reset the points gap (with the cam on its highest point to either 16 thou or 25 thou (can't remember which). One setting it will run like a pig (or not at all), on the other like a dream.

The wire from the points appears intact to me. To my eye the white wire is not cut or broken but disappears into a grommet and then through greeze on the outside. If you carefully trace it's path, you can see it follow a line out of the grease and along a recess in the cast casing.

Mark

"Greeze" ? "it's path" ? The white wire isn't the points wire, it's the condenser wire. The points wire can be seen at the right with a frayed end. Electrickery needs a route in as well as a route out of summat doncha know.

Points systems work by breaking the current to the coil primary windings at which time the secondary winding discharges. Electrickery flows into the fixed contact, through that into the moving contact and out to the coil. Both the fixed and moving contacts need to be isolated from the casing so they are mounted on non-conductive materials. That's why the lifting pin will be plastic or tufnol. The pivot at the back of the points arm will therefore also be resting in a non-conductive fulcrum of some sort. The points wire does however just appear to be bare wire strands which is odd unless there's some subtlety at work here I can't immediately spot. Maybe when the wire was broken the insulation was also removed.

Finally, given that the cam is mounted on the crankshaft this is either a 2 stroke motor or has a wasted spark system, neither of which really affect its modus operandi.

The white wire is the points wire. Yup, points ground one side of the coil and induce the high voltage in the secondary of the coil as they open, which is what is happening here. Don't talk down to me, I know far more about electricity and electronics than you could ever imagine. Have another think. I can clearly see the white wire leaving the casing. It's covered in grease on the outside where it was not protected, but you can see it if you look carefully enough. I'm not even sure this old mover needs a condenser (hate calling them that) and anyway it wouldn't do much good more than a few inches from the points due to the inductance of the wire. That is why they were always mounted so close to the points.

You are dreaming about both the fixed and moving side of the points needing to be insulated from ground. The fixed side needs to be connected to ground as in this case. How else can it draw current through the primary of the coil when the points close and then switch off the current through the primary when they open to induce the high EMF into the secondary. Some types may have switched the 12V feed to the coil instead of the ground side which would need both sides of the points floating, but I've never seen any.

Mark

Total rubbish. That end of the points is grounded through the casing.

Boy that's technical.

The fixed contact is at ground -ve potential. I presume you are talking about electron flow rather than conventional flow of current if you are talking about current flowing from the -ve side of the battery. BTW, nothing flows "into" the contact, it flows through it. Anyway, you are basically correct, even if you have got it a bit arse about face. Good enough for a car mechanic to get by though.

Incorrect. Only one side is fixed and grounded.

That's why the lifting pin

Only because it touches the moving side of the points.

Those strands look like a bit of crap left in there. It is certainly not a broken wire to the coil. That post next to the spring is at permanent ground -ve potential and little point connecting that to the coil if you want it to work.

Mark

The above is not true for this case. We have a magneto ignition. Both ends of the primary are grounded, and current is induced via the flywheel permanent magnet. At roughly the point of maximum current flow the points open and current flow halts - this created the high voltage output from the secondary.

There is no 12V feed for a magneto, it is a self contained unit.

In this case the moving points contact is grounded, and the stationary points contact is connected to one side of the primary windings. (and condenser)

Julian.

My apologies. Looking at the photo again you're correct. Normally in a car system the fixed contact is grounded to the distributer backplate and the moving contact is insulated with the condenser being separate but on this arrangement it appears the fixed contact is insulated being part of the condenser and the moving contact is grounded so the frayed wire is just an earth with the end broken off. It probably went to a casing screw but might not be needed if the fulcrum end of the contact is grounded.