Small 2-stroke engines and popoff pressure

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

Small engines and green fraud

Recent weeks have seen some catch up work on maintenance of small engine yard equipment. There are 22 engines in all, 6 4-stroke and 16 2-stroke.

For some years, ‘green’ measures implemented by government meant that ordinary unleaded petrol (ULP) was not available retail, one had to use E10 (ULP with 10% Ethanol).

Greens claimed that at such low Ethanol, that the fuel was compatible with all existing and new engine equipment.

Diaphragm carburettors

Most of my 2-stroke small engines use so called diaphragm carburettors. These ‘all position’ carburettors are common on yard equipment like brushcutters, leaf blowers, chainsaws etc.

Above is a Chinese after market clone of a Zama ‘butterfly’ type (note the throttle butterfly) diaphragm carburettor that suits a Stihl BG85 and similar leaf blower. (This cost $15 inc shipping on Aliexpress.) Continue reading Small engines and green fraud

Replacing the crystal in a Seiko V158-0AD0 watch

I have a Seiko V158-0AD0 which works very well, and I recently noticed the crystal was scratched more than the case… so a strong hint that it is an ordinary mineral glass crystal.

Searching the net, I could find that the Seiko part number for the original crystal is 310P03HN0 which indicates a diameter of 31.0mm but it does not have the thickness encoded simply. I could not find any articles giving the thickness of the part… so measurement was needed.

Above, the original crystal measures 1.6mm. A ‘standard’ 1.5mm sapphire crystal should be just fine. Continue reading Replacing the crystal in a Seiko V158-0AD0 watch

Reassembling a certain common chainsaw clutch

I managed to drop a chainsaw clutch and it separated into its component parts.

Thinking there would be a simple trick to this, I consulted Youtube. It turns out that reassembling these has proved a challenge for many people, and their online posts informed as to what approaches don’t work well, describing the many hours spent trying to reassemble. One online expert advised buy another, they are so cheap.

Above is a clutch of the type I will discuss, mine is from a 45-58cc Chinese chainsaw. There are variants, and the technique may be adaptable to them. Continue reading Reassembling a certain common chainsaw clutch

Sydney harbour is a beautiful place

One of the trips I am known to take is to Manly for lunch.

Above is a pic taken whilst waiting for the train home at Circular Quay. On the right is the ferry Freshwater arriving from Manly. The Opera House is just visible on the right north of the ‘toaster’ (one of the eyesores on the harbour).

It was a sparkling day on the harbour (Port Jackson) which bought back memories of many happy days boating and sailing, it is a beautiful waterway.

Manly is about 30min north east, 12km over the water, just on the north side of Sydney heads.

It is challenging to get pics on the ferry as tourists push their phone in front of your face to take videos, 5 to 10 minutes as a time.

Above, the route is from home to Bowral station by car, diesel train (Endeavor railcar) to Central, electric train on the Sydney underground to Circular Quay, and ferry to Manly. The return journey was similar but electric train from Circular Quay to Campbelltown then diesel train to Bowral. The round trip is just on 300km and nearly three hours for each direction of travel.

An interactive zoomable map is available. Zooming in around Sydney and a little south will show track jumps due to underground rail.

The track was captured with a Holux RCV-3000 GPS logger, logs downloaded with BT747 (Chinese firm Holux is defunct and so is their application which is now locked out of its maps provider).

Holux web site missing / offline, Holux ezTour crippled

I have had a couple of Holux GPS loggers for some time, a RCV3000 and GPS245+.

They come with a neat little application called Holux ezTour for Logger.

Over time, the application has been unreliable, mostly knock on effects of Google Maps licencing and Holux’s failure to obtain and distribute the appropriate licence keys. Continue reading Holux web site missing / offline, Holux ezTour crippled

Refurbishing the push button in action cam cases

In my experience, action cam underwater / weatherproof transparent cases have buttons that are quite difficult to use. This seems mostly because they are assembled with no lubricant.

Above, the button in the genuine Sjcam SJ8  has a stainless spring, shaped washer, two 6x2x2mm orings, and a 2.5mm E clip. This pic shows that the thing is assembled dry which makes operating pressure high, and in any event not smooth as the button shaft is not particularly smooth. Continue reading Refurbishing the push button in action cam cases

Garden hose couplers – there has to be a better way

A continuing frustration is garden hose maintenance.

We use reinforced hose that comprises essentially three layers, an inner plastic layer, a braided fibre reinforcing layer and another layer of plastic. Though these layers are bonded in new hose, there is potential for them to separate in service resulting in the reinforcing braid pulling back into the hose length and allowing the hose to expand in diameter at that point (lacking the benefit of the reinforcement). At this point failure of the hose by bursting is inevitable, sooner rather than later.

Some hoses are supplied fitted with factory crimped ferrules, and experience is that they have lasted well except that the fittings are plastic and break if subjected to rough treatment.

User serviceable screw collets fail, either through failure of the collets, or just the outcome of the screw collar loosening and resultant pull-back of the reinforcing braid.

What is needed is a tough and durable coupler with an easily applied ‘permanent’ clamp.

I have conducted a trial of brass fittings modified to remove the screw collar and nylon collet, then used with a stainless steel stepless one ear clamp.

Above at left is the unmodified coupler, and at right the coupler with the collet and screw collar discarded, thread turned off the coupler, and a one ear clamp for installation. Continue reading Garden hose couplers – there has to be a better way

Cheap Chinese wristwatch #1

I bought an inexpensive Chinese manual wind wristwatch for my grandson. It is a skeleton style watch based on the communist Tongji movement.

Above, the watch looking pretty flashy in gold coloured finish. The gold plate wore off the band in just a few days to reveal a brass band tarnishing by the hour. The bezel is probably base metal and will corrode in no time. Continue reading Cheap Chinese wristwatch #1