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Bargain Bin USB-ODB Interface

ODB Adaptor
ODB Adaptor

This is a little bit of kit I got to talk to the Webasto TT-V I salvaged from a scrap Jaguar S-Type, and converts USB-RS232 to the standard car diagnostic ODB connector. (These are a much cheaper option at £4 than the official Webasto diagnostic adaptor & loom which is over £90.

PCB Top
PCB Top

There’s really not much to this adaptor, the only signals that are routed to the ODB connector seem to be the +12v on pin 16, K-Line on Pin 7 & L-Line on pin 15. The main IC here is a CH340 USB-Serial interface, with some glue logic in the form of an LM339 quad comparator.

PCB Reverse
PCB Reverse

The reverse side of the PCB only has the power indicator LED.

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Jaguar S-Type Aux Heater / Webasto Thermo Top V Part 1 – Teardown & Cleaning

Jag Label
Jag Label

Here’s another Diesel-fired heater related project – these Webasto heaters are fitted to Jaguar S-Type cars as auxiliary heaters, since (according to the Jag manual), the modern fuel-efficient diesels produce so little waste heat that extra help is required to run the car’s climate control system. (Although this seems to nullify any fuel efficiency boost, as the fuel saved by not producing so much waste heat in the engine itself is burned in an aux heater to provide heat anyway). The unfortunate part is these units don’t respond to applying +12v to Pin 1 of the ECU to get them to start – they are programmed to respond to CAN Bus & K-Line Bus only, so they require a bit more effort to get going. They also don’t have a built-in water circulation pump unlike the Webasto Thermo Top C heaters – they expect the water flow to be taken care of by the engine’s coolant pump.

Webasto Label
Webasto Label
Water Side
Water Side

The water ports are on the side of this heater instead of the end, the heat exhanger is on the left. These hearers are fitted to the car under the left front wing, behind a splash guard. Pretty easy to get to but they get exposed to all the road dirt, water & salt so corrosion is a little problem. The fuel dosing pump is in a much more difficult spot to get at – it’s under the car next to the fuel tank on the right hand side. Access to the underside with stands is required to get at this.

ECU Side
ECU Side

The ECU side has all the other connections – Combustion air, exhaust, fuel, power & control.

External Connectors
External Connectors

Only two of the external connectors are used on these heaters, the large two pin one is for main power – heavy cable required here as the current draw can climb to ~30A on startup while the glow plug fires. The 8-pin connector on the left is the control connector, where the CAN / K-Line / W-Bus buses live. The fuel dosing pump is also supplied from a pin on this connector. The small 3-pin under that is a blank for a circulation pump where fitted. Pinouts are here:

PinSignal
1Battery Positive
2Battery Negative
Pin NumberSignalNotes
1Telestart / Heater EnableWould usually start the heater with a simple +12v ON signal, but is disabled in these heaters.
2W-Bus / K-LineDiagnostic Serial Bus Or Webasto Type 1533 Programmer / Clock
3External Temp Sensor
4CAN-CAN Bus Low
5Fuel Dosing PumpFuel Pump output. Connect pump to this pin & ground. Polarity unimportant.
6Solenoid ValveFuel cutoff solenoid optionally fitted here.
7CAN+CAN Bus High
8Cabin Heater Fan ControlThis output switches on when heater reaches +50°C to control car heater blower
PinSignalNotes
1??
2Circulation Pump +
3Circulation Pump -
ECU Cover Removed
ECU Cover Removed

Removing the clipped-on plastic cover reveals the other ECU connectors. The large white one feeds the glow plug, & the large multi-pin below brings in the temp & overheat sensor signals.

MC9S12DT128B Microcontroller
MC9S12DT128B Microcontroller

The heart of the ECU is a massive microcontroller, a Freescale MC9S12DT128B, attached to a daughterboard hooked into the ECU power board.

Power Section
Power Section

The high power section is on the board just under the connectors, here all the large semiconductors live for switching the fan motor, glow plug, external loads, etc.

LIN & CAN Bus Transceivers
LIN & CAN Bus Transceivers

The bus transceivers are separate ICs on the control board, a TJA1041 takes care of the CAN bus. There’s also a TJA1020 LIN bus transceiver here, which is confusing since none of the Webasto documentation mentions LIN bus control.

Combustion Fan Motor
Combustion Fan Motor

The combustion fan motor is in the ECU compartment, nicely sealed away from the elements. There is no speed sensor on these blowers, unlike the Eberspacher ones.

Motor Details
Motor Details

The motor is a Buhler, rated at 10.5v.

Water Ports & Combustion Fan Cover
Water Ports & Combustion Fan Cover

Unclipping the cover from the other end reveals the combustion fan, it’s under the black cover. (These are side-channel blowers, to provide the relatively high static pressure required to run the burner).

Sensor Clip
Sensor Clip

The overheat & temperature sensors are on the end of the heat exchanger, retained by a stainless clip.

Temp & Overheat Sensors
Temp & Overheat Sensors

With the clip removed, the sensors can be seen better. There’s some pretty bad corrosion of the aluminium alloy on the end sensor, it’s seized in place.

Burner
Burner

The heater splits in half to reveal the evaporative burner itself. I’ve already cleaned the black crud off with a wire brush here, doesn’t look like this heater has seen much use as it’s pretty clean inside.

Burner Chamber
Burner Chamber

Inside the burner the fuel evaporates & is ignited. There is a brass mesh behind the backplate of the burner to assist with vaporisation.

Glow Plug
Glow Plug

The glow plug is fitted into the side of the burner ceramic here. This is probably a Silicon Carbide device. It also acts as a flame sensor when the heater has fired up. The fuel inlet line is to the left under the clamp.

Heat Exhanger
Heat Exhanger

The hot gases from the burner flow into the heat exchanger here, with many fins to increase the surface area. There’s only a couple of mm coating of carbon here, after 10 years on the car I would have expected it to be much more clogged.

I’m currently waiting on some components to build an interface so I can get the Webasto Thermo Test software to talk to the heater. Once this is done I can see if there are any faults logged that need sorting before I can get this heater running, but from the current state it seems to be pretty good visually. More to come once parts arrive!

The full service manual for these heaters can be grabbed from here, along with the wiring details for the Jaguar implementation & the Thermo Test software for talking to them:

Webasto Thermo Top V Service Manual (344 downloads) Webasto Jaguar Service Info (5893 downloads) Webasto Thermo Test (307 downloads)
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Honda GX35 Clone – Are They Any Good?

In a word, no they aren’t any good. As usual, cheap doesn’t equal good, and in this case the cheapo clones are a total waste of money. Read on for the details!

I’ve been looking into using a cheap Chinese clone Honda GX35 engine to drive an automotive alternator as a portable battery charging & power unit. These engines are available very cheaply on eBay, aimed at the mini-bike/go-kart market.
For those not in the know, the Honda GX25/35 4-strokes are strimmer-type engines that traditionally were always of 2-stroke construction. Honda worked out how to have a wet-sump engine without the need to keep the engine always in the “upright” position. They do not require mixing of oil into the fuel for lubrication as 2-strokes do, so should be much cleaner running.

So far I’ve had two of these cheap engines, as the first one died after only 4 hours run time, having entirely lost compression. At the time the engine was idling, no load, having been started from cold only a few minutes before. Having checked the valve clearances to make sure a valve wasn’t being held partially open, I deduced that the cause was broken piston rings. This engine was replaced by the seller, so I didn’t get a chance to pull it to bits to find out, but I decided to do a full teardown on the replacement to see where the cloners have cut corners.

Oil Return Hose
Oil Return Hose

I’ve already stripped off the ancillary components: exhaust, carburettor, fuel tank, cowlings, as these parts are standard to any strimmer engine. The large black hose here is the oil return feed back to the rocker cover from the crankcase. The oiling system in these engines is rather clever. The main engine block is made of light alloy, probably some permutation of Aluminium. There is much flashing left behind between the cylinder fins from the die-casting process, and not a single engine manufacturer’s logo anywhere. (From what I’ve read, the genuine Honda ones have their logo on the side of the crankcase).

Rocker Box
Rocker Box

Here’s the top of the engine with valves, rockers & camshaft. All the valve gear up here, minus the valves themselves & springs, are manufactured from sintered steel, there are no proper “bearings”, the steel shafts just run in the aluminium castings. The cam gear is of plastic, with the sintered steel cam pressed into place. The cam also has the bearing surface for the pin that the whole assembly rotates on. The timing belt runs in the oil & is supposed to last the life of the engine, and while I’d believe that in the original Honda, I certainly wouldn’t in this engine. The black grommet is the opening of the oil return gallery.

Cam
Cam

Here’s the cam on the back of the plastic pulley. A single cam is used for both intake & exhaust valves for space & simplicity.

Intake Valve Stem Seal
Intake Valve Stem Seal

Just visible under the intake valve spring is a simple stem seal, to hopefully prevent oil being sucked down the valve guide into the cylinder by intake vacuum. Running these cheap engines proves this seal to be ineffective, as they blow about as much blue oil smoke as a 2-stroke when they’re started cold. 😉

Starter Side
Starter Side

The starter side is where the oil sump is located on these engines, along with the dipstick.

Flywheel Side
Flywheel Side

The flywheel end of the engine is the usual fare for small engines. Ignition is provided by a magneto, with a magnet in the flywheel. This is no different from the 2-stroke versions. As these ignitions fire on every revolution of the crankshaft, the spark plug fires both on compression, igniting the fuel for normal operation, and again into the exhaust stroke, where the spark is wasted.
One thing I have noticed about these engines is an almost total lack of cooling air coming through the cowling over the cylinder cooling fins. Plenty was flowing over the exhaust silencer side, I believe bad housing design would be what causes this problem. A lack of cooling certainly wouldn’t help engine longevity!

Engine "Sump"
Engine “Sump”

Separating the bottom of the engine was a little difficult, as there is a significant bead of sealant used instead of a gasket. Inside the sump of the engine are a pair of paddles, which stir up the oil into a mist. As the piston moves in the cylinder, it acts as a pump, creating alternating pulses of pressure & vacuum in the crankcase. Oil mist flows through a drilling in the crank from the sump, into the crankcase where it (hopefully) lubricates the bearings & the cylinder wall. Incidentally, the only main bearings are on the crankcase – the far end of the shaft that carries the oil paddles & timing belt is just flapping in the breeze, the only support being the oil seal in the outer housing. The crank itself isn’t hardened – a file easily removes metal from all parts that I could get at. The big end journal pin might be, but these cranks are pressed together so I can’t access that part.

Lubrication Gallery
Lubrication Gallery

The oil mist feeds into the crankcase through this hollow section of shaft, there’s a drilling next to the timing belt pulley to connect the two spaces together.

Lower Crankcase
Lower Crankcase

The lower crankcase is just a simple die casting, there’s a check valve at the bottom under the crankshaft to transfer oil to the rocker cover, through the rubber tube on the outside of the engine. After the oil reaches the rocker box, it condenses & returns to the sump via the timing belt cavity.

Piston Crown
Piston Crown

Removing the crankshaft from the engine block gives me a look at the piston. The factory couldn’t even be arsed to machine the crown, it’s still got the rough finish from the hot-forging press. This bad finish will pick up much carbon from combustion, and would probably cause detonation once enough had accumulated to become incandescent in the heat of combustion. Only the centre is machined, just enough for them to stamp a number on.

Cylinder Bore
Cylinder Bore

A look up the cylinder bore shows the valves in the cylinder head. These engines, like their 2-stroke cousins have a single casting instead of a separate block & head, so getting at the valves is a little more of a pain. The cylinder bore itself is a cast-in iron liner and it’s totally smooth – like a mirror finish. There’s not a single sign of a crosshatch pattern from honing. If the first engine that died on me was the same – I’d be surprised if it wasn’t, this could easily cause ring breakage. The usual crosshatch pattern the cylinder hone produces holds oil, to better help lubricate the piston & rings. Without sufficient lubrication, the rings will overheat & expand far enough to close the end gap. Once this happens they will break.

Engine Valves
Engine Valves

Finally, here’s the valves with their springs removed from the cylinder. These are the smallest poppet valves I’ve ever seen, a British penny is provided for scale.

In all, these engines share many components with the older 2-stroke versions. The basic crankshaft & connecting rod setup is the same as I’ve seen in many old 2-strokes previous, the addition of the rather ingenious oiling system by Honda is what makes these tiny 4-strokes possible. I definitely won’t be trusting these very cheap copies in any of my projects, reliability is questionable at the least. The apparent lack of cooling air flow over the cylinder from the flywheel fan is concerning, along with the corner-cutting on the cylinder finishing process & piston crown, presumably to reduce factory costs.