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Inductive Hour Counter / Tachometer – Petrol Engines

As one of my current projects involves a small petrol engine – a Honda GX35 clone, I figured an hour counter would be very handy to keep an eye on service intervals. (More to come on the engine itself later on). I found a device that would suit my needs on good old eBay.

Inductive Engine Monitor
Inductive Engine Monitor

These engine monitors are pretty cheap, at about £4. The sensing is done by a single heat-resistant silicone wire, that wraps around the HT lead to the spark plug. The unit can be set for different firing intervals via the buttons. In the case of most single-cylinder 4-stroke engines, the spark plug fires on every revolution – wasted-spark ignition. This simplifies the ignition system greatly, by not requiring the timing signal be driven from 1/2 crankshaft speed. The second “wasted” spark fires into the exhaust stroke, so has no effect.

Internals
Internals

The back cover is lightly glued into place with a drop of cyanoacrylate in opposite corners, but easily pops off. The power is supplied by a soldered-in 3v Lithium cell. The main microcontroller has no number laser etched on to it at all – it appears it skipped the marking machine.

Input Filtering
Input Filtering

The input from the sensing wire comes in through a coupling capacitor & is amplified by a transistor. It’s then fed into a 74HC00D Quad 2-Input NAND gate, before being fed into the microcontroller.

Pickup
Pickup

The pickup wire is simply wound around the spark plug lead. I’ve held it in position here with some heatshrink tubing. Heat in this area shouldn’t be an issue as it’s directly in the airflow from the flywheel fan.

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nb Tanya Louise Drive Coupling Replacement – The Final Install

It’s time for the final part of getting the boat’s engine & drive back together, now I have the new coupling hub. I decided to address one of the issues with the pump mounting while I had everything in bits. When the hydraulic drive was installed, a custom plate was laser cut to fit the pump stack to, as we had no bellhousing with a standard mounting pattern.

Even though this plate is 10mm steel, under full load it actually bends – so to strengthen it along the long edge, I have welded a pair of ribs to the plate.

Pump Mounting Plate
Pump Mounting Plate

The mounting plate as removed from the mounting brackets. The slotted holes at the sides allow for some movement to adjust the position of the pump & flywheel coupling.

Prepared For Welding
Prepared For Welding

I ground off the paint & grease with an abrasive disc, and am replacing one of the pump mounting studs while I’m at it.

Strengthening Ribs
Strengthening Ribs

Here’s the plate after welding. a pair of 10mm bars have been attached along the edges, this will give the mounting significantly more strength on the long axis & prevent any deformation.

Pump On Hoist
Pump On Hoist

Here the plate has been loosely mounted on it’s brackets, & I’ve got the pump stack with it’s associated tangle of hoses on the chain hoist. This unit is very heavy on it’s own – a 2 man job to lift it into place on it’s mounts – with the very stiff hydraulic hoses attached & filled with oil it’s absolutely unmanageable.

Lining Up The Mountings
Lining Up The Mountings

Here the pump is being jostled into place. The central hole in the mounting plate is a very snug fit, if the pump doesn’t go in exactly straight it will jam & cause damage to both parts. The mating hole in the coupling hub can be seen here – it’s not quite lined up yet.

Almost There
Almost There

We’ve got about 10mm to go before the pump is seated. It’s held in place with a pair of large studs & nuts.

Coupling Connected
Coupling Connected

Here the pump is fitted enough to get the main mounting bolts into the coupling. These are torqued down to 150ft/lbs – a difficult thing to do considering the restricted space in the engine bay.

Flush Mounting
Flush Mounting

The pump has been pulled down onto the plate evenly with the mounting studs, and is now completely flush with the plate. As can be seen, I didn’t bother tidying up the welds with a grinder, they aren’t in any visible place in normal operation, so it didn’t warrant the effort.

Pump Refitted
Pump Refitted

Finally, the control cable is reattached to the pump’s control lever & everything is installed! A short test trip proved that everything was stable & no undue movement of the pump or coupling was noticed.

Until next time, 73s!

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nb Tanya Louise Propulsion Rebuild – Part 1

New Coupling Hub
New Coupling Hub

Time to get on with the job now the parts have arrived! Above is the new coupling hub, as can be seen compared to the old one that I previously posted about, this one has it’s full complement of splines.

Rubber Element
Rubber Element

The hub bolts into the centre of this rubber coupling, which itself locates on pins attached to the engine’s flywheel. This part wasn’t damaged so it’s being reused with the new hub.

Hub Installed
Hub Installed

Here’s the hub installed on the input shaft of the main hydraulic pump stack, the pair of holes on the side of the hub are for the grub screws that secure the coupling on the splines. These screws coming loose are what destroyed the old coupling.

Flywheel
Flywheel

Here’s the engine flywheel, where the rubber coupling normally sits. The mounting pins have been greased ready to accept the rest of the coupling.

Doughnut
Doughnut

Here’s the rubber element mounted on the pins – there’s nothing holding it there in normal operation apart from the mating side of the coupling with the pump.

Unfortunately the weather here in Manchester has prevented us from getting any further – more t0 come when the rain stops!

73s for now folks!