Category: Miscellaneous

The article documents replacement of the engine on a Deutscher 650 Chipper Shredder. The original engine was a Briggs & Stratton Intek 206 single cylinder four stroke petrol engine which has accumulated 200 hours over 10 years use.

During that time, it had regular oil changes, air filter changes, new carburetor seat and air filter gasket, as well as frequent cleaning with compressed air to ensure the air cooling was fully effective. It passed a leak down test of valves and rings at 200h, then valve clearances were checked and were spot on… no adjustment needed. (Note that the engine was never run on Ethanol fuel.)

Additionally there is ongoing belt maintenance (adjustment and replacement) and blade sharpening / balancing.

Replacement parts were expensive, the seat alone from eBay was over $20, spark plug over $20, the air filter gasket was over $40. Air filter sets were quite cheap on Aliexpress.

It gave good service, and was reliable. Approaching 200h, a decision was made to replace the engine with a Chonda to minimise the risk of failures (like plastic camshaft gears, lobes, compression relief).

Basic fit up

Above is the Deutsher 650 Chipper Shredder. Continue reading Re-engine of Deutscher 650 chipper shredder

Karen purchased a Victa lawnmower many years ago, and it has expired.

Victa was Australian, but now owned by Briggs & Stratton. The engine is different to most two stroke small engines, the notable differences are:

• Victa’s G4 plastic carburettor; and
• the engine is built “upside down”, the flywheel is underneath (ie on the PTO end), and there is no main crankshaft bearing above the big end, the crankshaft is supported by two bearings below the big end.

This article describes the service work to get the mower into good working order.

First checks / observations

The handle bolts and handwheels don’t work, someone has replaced a cup head bolt with a screw and it does not locate in the tube, so a screwdriver is needed to tighten the handle. The lower bolts are loose and need tightening.

The mower takes a lot of effort to push, the wheels are jammed up with string and stuff binding the bearings.

The blades are beyond service life, chipped and blunt, and the blade carrier and mower base are caked with wet decaying grass clippings.

Fuel tank contaminated with solids and water.

This is an air cooled engine, and the cooling fins and cooling fan were caked with oily grass / dust residue. This leads to higher operating temperature, shorter engine life, and performance problems.

Above, the air filter is filthy and will cause rich running which results in carbon build up in the combustion chamber and blocked muffler. Continue reading Karen’s Victa

A recent episode where the 170l gas storage hot water service relieved itself through the pressure / temperature relief valve sent me on a quest to understand the problem.

At the time, a ‘full rate’ discharge of 95° water was holding the valve open, and even with the gas turned off, the flow continued for some time until I closed the water isolation valve to let the system cool down.

So, was this simply a thermostat failure, temporary or permanent, or perhaps the result of ‘stacking’.

Stacking is caused by repeated very short draws of hot water, which cool the bottom of the tank near the thermostat, triggering heat input which can cause the top of the tank to reach temperatures considerably higher than the set point of the thermostat.

Another question that was of interest in choosing a replacement if needed, was how much heat is lost from the heater, what is the running cost of heat leakage alone.

Heat leakage

The heater was allowed to reach ‘normal’ operating temperature and stabilise, and the gas valve was closed which would allow the unit to cool.

A variation on my IoT water tank telemetry project was configured to use a type K thermocouple and 4-20mA converter to provide a temperature logger, a type K thermocouple was inserted between the insulation blanket and tank at the top of the tank. The 4-20mA converter does not incorporate cold junction compensation, but the logger incorporates an ambient temperature measurement facility which will be used for approximate compensation.

Above is the improvised data logger setup. Continue reading Hot water woes

I purchased a Holzforma G372XT chainsaw, it is a Chinese clone of the now discontinued Husqvarna 372XP X-TORQ. It is a relatively new technology carburetted engine without introducing electronic auto tune, a 20 year old design.

There are plenty of online discussions about the 372XP X-TORQ overheating, hot seizures, and pics of blued big ends, scored pistons and bores etc, so whilst the design achieves quite high power output for 71cc, one is warned to pay attention to mixture, fuel quality, and lubrication. This might be an engine that should not be used with other than full synthetic two stroke oil. Continue reading Holzforma / Farmertec G372XT chainsaw – initial evaluation

I have a Toro ride-on mower which ran out of fuel when it was just a couple of years old, perhaps 50 hours on it. Okay, so that is going to happen with failure to check fuel level before starting… but the problem was that when the tank was filled, it would not start, the petrol pump would not self prime even though the suction head was very small with a full fuel tank.

Mindful that long cranking is very hard on batteries, I used the starter sparingly in short bursts with cooling off time. Nevertheless, the battery went open circuit.

So I replaced the battery and primed the pump by hand… and all has gone well for some years… until last week, I ran it out of fuel, duh!

Same problem, when the tank was filled, the pump would not self prime.

The machine has a problem that needs to be fixed.

The inline filter was checked, and fuel flowed though it quite well by gravity. This time, I primed it by hand early in the process and got on with mowing. This was probably not a vapor lock problem, everything was quite cool by the time I fueled the machine. Continue reading The mower appears affected by Ethanol

I have a chipper / shredder that has a Briggs and Stratton 6.5hp (~5kW) Intek I/C 206cc engine on it.

On a recent routing maintenance inspection, I dropped the carburettor bowl to look for signs of Ethanol damage (mainly corrosion). During that inspection I noted that the bowl gasket was hardened even though the engine is only 13 years old, and that a stain on the mulcher body hinted a fuel leak even though the bowl exterior seemed dry on test..

The machine is usually stored with the petrol cock off, so the opportunity for a needle / seat leak would be during a day’s yard work where the petrol cock is on for hours but the machine is run for a lesser time.

A pressure test might provide a firm diagnosis.

A piece of silicone tube was connected to the carburettor in place of the normal fuel hose, a little petrol added to the hose with a pipette, and then a sphygmamometer used to pressurise the hose.

Above, the test in progress. The fuel level in the hose can be seen about 30mm from the end. The pressure is leaking down quite slowly, the leak is not fast enough to upset engine operation (by flooding or even an over rich mixture) but it might well result in dilution of the crankcase oil when the engine is left standing. It needs repair. Continue reading The mulcher appears affected by Ethanol

When we moved to this place in 2009, I could see the utility of a ‘aborist chainsaw’, or ‘top handle chainsaw’.

I bought a cheap Chinese 25cc jobbie, in fact it was so good I bought a second for spares.

SX25#1

This saw had seen off 6 chains by 2021 and forced by some reliability issues, I decided to replace it with the spare and repair it at my leisure (parts from China are real slow). It has had a good life, usually warmed up before being gunned up to WOT to avoid cold seizure. Continue reading Chinese chainsaw review – SX25 #1

I have a 6kVA genset that uses a Honda 8kW GX390 OHV engine that was due for maintenance.

I dragged it out, fueled it (it had been stored dry) and tried to start it for a test run… but no such luck. Continue reading Honda GX390 6kVA genset maintenance

This article explores the physics of fuel metering in a typical small diaphragm carburettor (carburetor to some) as used on small 2-stroke chainsaws, leaf blowers, brushcutters etc.

The discussion following is in terms of absolute pressure, and it is assumed that atmospheric pressure is 100kPa. ALL pressures are absolute unless stated otherwise, to find gauge pressure, subtract 100kPa.

Above from Zama is a cross section view of the metering chamber of a typical butterfly carburettor. The metering lever pivots on an axle (1), the distance from the axle to the needle (2) is 3.5mm, to the spring (3) is 3.5mm, and to the contact to the metering diaphragm (4) is 8mm. The needle seat is 0.55mm diameter. Continue reading Small 2-stroke engines and popoff pressure