Aermacchi Ignition - part 1 // Paul Brodie’s Shop 

On the subject of thermal grease, you actually do want to squish out as much as possible. Thermal grease conductivity is much much less than the aluminum, so you want only enough thermal compound to fill the microscopic imperfections between the heat source and heat sink. So don't be afraid to squish it down!

Where does that fit in the garden hose? 🤣

Bradley has the answer to the thermal paste. Technically you only need enough paste too fill the voids, direct contact works better but surface roughness / planarity limit conduction. Trying to use a heat sink on the back side of the board limits what you get for cooling. Board designs that do this typically have a bunch of vias to copper on the back side. A copper plated hole condict better than PCB.. I'd question as to weather the heat sink is really needed. With the right mosfet the power dissipated should be minimal.

Speaking as a Retired TV and Electronics Field Tech....... You would NEVER put thermal paste on a BOARD, and then to a heat sink, it goes on the top face of the chips that produce the heat dude! - then the heat sinks touch the top face of the chips, NEVER the board, never ever - That will never work!

Hi Paul! Stumbled across your page - great to see you're still playing with the 'Macchi. Just rebuilt my engine and refitted today! Been racing mine for 40 years next year!! Greg is still around, but not doing anything bike-wise now. Keep up the good work, Adrian, Christchurch, New Zealand.

Usually the heat sink(s) would be mounted on the other side of the board, directly to the component(s) that creates the heat. Usually a transistor or chip, I can see 4 on that board.

Fun to see the spinner at work. Kudos. Finally saw a portion of the mystery man's lens at one point, he does exist.

Well, you've probably heard all you want about a reluctor but the reason it's called that (relying on way old school sessions) is that the pickup is a coil of wire and one of the two properties of coils is their reluctance to current changes. In fact, the rating of a coil is in values of reluctance. Your spinning reluctance cam alters the reluctance value of the coil as the "cam" lobe spins past the pickup coil so it's called a "reluctor" and times the spark the same as the mechanical lobe of your valve cam times the opening of the cam but with an electronic circuit instead of rods, levers & springs. The electronic circuit (probably) has a balance bridge that swings out of balance when the reluctor cam alters the value of the pickup coil by changing the magnetic mass of the coil core and this change triggers an electronic switch that starts or stops current to the ignition coil. So many coils. I hope this has sparked your interest and not wound you around a pole. The other property of a coil (of a wire, really) is to have induced into it current as a magnetic field passes by. This is how a magneto works so that pickup would be called an inductor but is usually just the primary side of the ignition coil.

@9:20 Peacock sez be sure to cover board recess with epoxy resin

These episodes just put a smile on my face, thank you for doing them! You are awesome!

Another amazingly beautiful part. But Oh No, I didn't know that the Italians used Lucas "Prince of darkness" electrical components.

You make it look like a walk in the park Paul. love ya work mate. Dave Australia

reluctance, is my guess as to why it's called a reluctor wheel

Hi Paul, this is a fantastic channel. I work in a college level educational machine shop. I'm into vintage motorcycles, restored a CBX, and was into mountain biking back in the late 80's early 90's. So much content that I can relate to. Keep up the brilliant work!

Heat sinks are usually in contact with the heat source. That’s how heat sinks work. They transfer heat from the source to the air around it.

Always interesting THANKS

Mr incredibly interesting 🧐🇬🇧🥇 love your channel

You don’t have to use heat transfer grease if you pot the whole board in epoxy within the aluminium heatsink. It will be waterproof.

its no walk in the park Paul.. more a tiptoe through a minefield, stay cool !good work both of you

I guess you'll put in a small groove for the cable tie? Thanks Paul.

I always learn stuff when I watch your channel and I work in engineering, building bikes when not at work. Thanks for sharing your knowledge, a gentleman. 👍

You have an affinity with metal Paul

Thanks for letting us hang out in the shop...always a good time!!!

Hi Paul, magnetic reluctance is basically how easily the magnetic flux pulled and pushed through the pickup windings. Generally with reluctor pickups the interrupter is as wide as the permanent magnet in the center of the pickup. Yours looks a little narrower. It will still work but the waveform will be smaller or more sloped looking at it on an oscilloscope. The ignition circuit will trigger on the zero crossing point of the pulse created. Reluctors have soft iron (high permeability) rotor. Again, I think the cold rolled steel will work but may reduce the signal quality/size. Suck it and see how it works, might be worth bearing in mind if you are experiencing any issues with your ignition. Great video again. Thanks to Mitch too. 👍

As always, Thank you Paul & Mitch!

I have a set of lucas rita ignitions on some Guzzi's and it's interesting as to how they work. Found a paper online explaining that the shape of the reluctor also affects the timing advance as the engine speeds up and it seems that's key to it's function. Would you not have been better off going for a modern setup with more tuneability using a toothed plate and position sensor like Yamaha or Honda would have used?

Hey, Paul and Mitch great video! My t-shirt arrived and it was a good fit ;)

as soon as you mentioned the heatsink compund..I paused and had look at the comments....it always seens to bring forth knowledgeable comments..only ever used it under power transistors in mobile radios and the first cellular carphones power modules...we just replicated the amount on the original blown up component...

I so enjoy your videos. Thank you for posting them. I always get nervous when you file/shape and reach around the chuck especially wearing long sleeves!

Your magnetic pickup appears to from a 1970's Chrysler distributor if you need to buy a new one at some point.

I always heard those rubber mounts called ‘Lord Mounts’. Pretty handy

02:55 Reluctor... reluctance is the magnetic equivalent of resistance in an electrical circuit. Higher resistance is less current, higher reluctance is less magnetic flux.

Excellent work, but very strange choice of igntition, why not Electrex world? or other? Dyna?

I’ve always called those rubber bobbins lord mounts.

THANK YOU . REGARDS R .

great job Paul, i like your job :)

A lot of technical jargon about electronics and heat sinks, but we all know it really works on magic.

Lets hope the reluctor is not reluctant to work or recalcitrant in operation.

Thanks for another informative but entertaining show Paul !

A reluctor is a device that is used in electronics, similar to a resistor or inductor. It is used in magnetic devices (electronics and magnetics are directly interrelated via Maxwell's equations). It is a device that specifically breaks up magnetic lines of force. In the case of most electronic ignitions, it breaks up the magnetic lines of force around a winding of wiring around a iron core normally called an inductor (which is one half of a transformer). The electronics of the circuit can "sense" the break up of the magnetic lines of force when the reluctor passes by the winding, and uses it to fire the coil at a precise moment. That is why it is called a reluctor.

Hello Paul, an enjoyable video again thank you and Mitch. The thermal grease has brought quite a few interesting responses. Commonly you come across power IC’s of many types and they use grease between faces. As I understand, the grease helps to fill any slight voids under a component or PCB, which either way, helps any heat transfer away accordingly. A slight clearance around a PCB may be beneficial to allow expansion, slightly slotted holes assist too, this can help maintain the contact surface to a heat sink, which is the primary aim. I am sure that all your meticulous efforts will be rewarded with a beautiful bike, I sometimes wonder how on earth you coped with the theft of your last bike? Thanks again to you both, I look forward to watching part 2. Regards Kevin.

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Very cool Paul, I need to get me a Mill!

I just rewatched this for the wonderful machining. But one question: since the Aermacchi is a single cylinder four stroke, it only needs to fire once per two revolutions of the crank, or once per revolution of the cam shaft. So why does it have two sensor bumps? Does it fire on the dead stroke (between exhaust stroke and intake stroke) like my old BMW did? I would think it only needs one bump to fire between compression and ignition.

A lot of what I have been thinking about the thermal grease has already been said but I think the whole piece needs to be rethought with the heat sink on the component side of the board. The big block would just be a holder. It may be that the only part needing a heat sink is the MOSFET. MOSFETs have a negative thermal coefficient BTW so they can take a lot of heat. You can show a closeup of the board so us electronic egg heads can argue amongst ourselves.

You sure know how to make your lathe and mill work for you, I'm sure it's because you have had lots of practice. 👍

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Not going to be sinking much heat through an FRP PCB! The copper on the board will be doing the majority of the work there.

Hi Paul, Might you run in to a crank balance issue with only having one of the reluctor pegs on the reluctor, might it be better to of had them both, and run a wasted spark ignition to overcome the balance issue. Nice bit of machining though, wish I could do it as good as that. Nice one Paul and Mitch.

Hi Paul, can you give a bit more info about that board ? What I wonder is, did you take the board out of another housing ? Did those black square components have heatsinks on them ? 2 situations can be true. 1 nothing is really going to get hot and you are just making a beautifull housing, in this case you can't go wrong. 2 Some components will get really hot and in that case those black squares need cooling from the top. Cooling is not done from the back of the board (but it does't hurt eighter). Without further info I think 1 is the most probable answer because I doubt an ignition system uses much power = no heat produced. Beautifull crafting like you allways do and Mitch the camera guru ;) .

Not sure why the cam mounted trigger would need 2 reluctance bumps. A single cylinder motor only fires once per rev of the cam. Twin cylinder yes. On a crank mounted trigger, isn't there 1 wasted spark? Don't know the design but is it used to limit dwell / coil heat?

Every computer nerd watching this screams at the screen: You don't need 3 packets of thermal paste!

Hi Paul hopefully it not to late. Use max 1 of these cpu cooler paste!!!! please That stuff is just there to not grind both surfaces. Package looks like thats enough for that piece.

Did you mention your peacock's name the other day? I don't seem to remember it.

Always looks like you could shank your drill bits further when you are using the tail stock to prevent deflection, your comment please?

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Hi

Excellent! How was the original Aermacchi ignition?

Is that a Lambretta cowling on the shelf?

To anyone else I'd say, "hey, just buy a heatsink." The computer industry has them in their thousands. But to you, I'll look forward to all that aluminium/aluminum milling. Hopefully, you bag all the excess swarf up. BTW, Any chance of allowing Paypal?

Dear Paul Brodie, are you sure that is the way the circuit board should be mounted i.e. with the glass fibre circuit board sandwiched between the semiconductor devices and the heat-sink ? I've never seen that done before, much more likely the heat sink would be in direct contact with the semiconductors i.e turn the board over (taking care that nothing will get shorted by the aluminium heat sink). Of course still using a thin film of heat sink grease on the semiconductor encapsulation where it contacts the heat sink. I know nothing of Aermacchi Ignition systems but I've spent a lifetime with electronics and this looks so wrong.

Paul, how come you routinely use a finger to check how effective your de-burring is, without any problem? If I do that just once I get yet another metal splinter.. 😂

Paul, you say “thats a lot of work to save weight on a small piece”, why not make the reluctor from aluminum (saves even more weight) ?????