Yanmar YS decompressor lever

[garymalmgren]

As mentioned in another post you need three hands to crack/ hold decompression lever/ release decompression lever on a yanmar YS engine.

There is a way out though,
You need a lanyard tied to the lever,
This led astern, through a block and back forward to a reachable position,
There it is held in a quick release cleat.
For a block I used a plastic ring and for a cleat i used a piece of plastic pipe.
To use, you pull the lanyard and cleat it off.
Crank the engine and flick the lanyard out of the cleat.
Timing is important and a bit of practice will help.
Photo 1 the lanyard on the leaver, slack.
Photo 2 the turning ring astern
Photo 3 the cleat.
Photo 4 the lever engaged.
Photo 5 the lanyard tight
Photo 6 the lanyard cleated.

 

[sailorman]

decompression should only be req when hand starting, or is access difficult

 

[garymalmgren]

When I said "crank", I meant handcranking.
That is why I mentioned three hands
Sorry for the mixup.
I posted this in response to another post about this topic.

gary

 

[rotrax]

decompression should only be req when hand starting, or is access difficult

What an ill informed reply.

A compression release lever on a motorcycle, either the type opening a valve or as in the case of a Royal Enfield motorcycle a seperate unit screwed into a threaded hole into the combustion chamber is only required for two reasons.

The first, in the case of motorcycles fitted with magneto's of the rotating armature type is to stop the engine as ignition cut outs are possible to fit but can be unreliable and work when not intended! A decompession device allows the engine to be stopped. It also enable the rider to position the engine in the optimum position for kick starting. Press kick start until it stops on compression, lift the valve or relese compression, press a little further until it passed TDC then return kick start to the top of its stroke. The " Long swinging kick " will - or should - bring it to life. So, on a motorcycle, engine stopper or engine positioner. Very skilled off road riders also use it for controlled decent of loose surfaced hills.

On diesel engines they are invariably a starting aid. We had a canal narrow boat with a Yanmar single cylinder 12 HP fitted with a dynostart. Despite the engine being an easy starter it was VERY difficult to get it to spin fast enough to start without using the decompressor lever. I worked at the time as 2nd I/C at the largest Lucas Service depot in the UK. Trust me, the Dynostart was perfect! As were the batteries. Spin it fast decompressed, release it, bingo. Chuff, chuff, chuff!

We have a steel Hartley 32 in Wellington, NZ. It has a Bukh DV 20. For the first start of the day I decompress it. It might have been weeks or even months since its last start so 15 seconds or so whizzing decompressed gets the oil around the internals before I drop them and it fires up.

Using a decompressor lever aids starting by hand as you say. I would start a Lister air cooled 3 cylinder by applying each decompressor, cranking bloody fast, lifting No. 1 whereupon it would run on that cylinder only. Lift the other two, in turn, it would chuff away on all three. Easy.

It had no starter motor or dynamo/alternator. It powered a huge arc welding set.

I went on a fishing charter once with a lovely guy called Gordon Hook. His vessel could run on four, eight or twelve cylinders. For economy he would use four. Each engine was coupled with a simple dog clutch using a long lever. One time the fishing was good so we stayed over the mark a bit longer. To ensure he got to the bar with enough water he engaged another four cylinders by operating the decompressors on the engine to be started, shut the running one to idle - which was VERY slow - and threw the lever to engage the dog clutch. With the second engine rotating the decompressors were lifted, so starting the now coupled engine.

As you can see, decrompression levers and valves have a multitude of uses.

Our single cylinder Yanmar had the OE bronze foot control pedal with a bowden cable to the lever on the rocker box. This meant it could be decompressed by foot when cranking or electric starting.

Simples......................................

 

[rotrax]

When I said "crank", I meant handcranking.
That is why I mentioned three hands
Sorry for the mixup.
I posted this in response to another post about this topic.

gary

See the last two sentences of post #4.

 

[davidmh]

I used to run the lanyard back onto the floor and stood in it while cranking, when you are up to spped just lift up your foot and away she goes.

David MH