Yanmar: what does this do?

[joeniver]

This lever is on the top of my yanmar. It has three connections I guess cause it’s three cylinders. My manual does not reference it as far as I can see.

Does Anyone know what it’s purpose is?

Thanks

[maine50]

Possible decompression system.? My 1978 Yanmar 3QM had one but it looked different

[maine50]

didn't realize the picture is 90 degree off- yes it's likely decompression system' Aids when battery is weak.What is the engine?

[GordMay]

Yours appears to be a 3 cylinder. Below is a similar 2 cylinder.

[Boatyarddog]

Originally Posted by joeniver

This lever is on the top of my yanmar. It has three connections I guess cause it’s three cylinders. My manual does not reference it as far as I can see.

Does Anyone know what it’s purpose is?

Thanks

Decompression lever system.
Used to turn engine over without a lot of resistance.
SV Cloud Duster

[belizesailor]

Originally Posted by Boatyarddog

Decompression lever system.

Used to turn engine over without a lot of resistance.

SV Cloud Duster

^ this.

My old Yanmar had fittings on the front pulley to accept a hand crank...a lot easier w compression release thrown!

[blubaju]

Maybe some homebrew design, my yanmar had 3 single decompression levers

[charliehows]

yes its a decompression lever, no its not 'some homebrew design', it's factory fitted. In practice, unless you are a champion powerlifter, it wont help you start the engine with the crank but its very handy for any other procedure that requires turning the engine over - eg, bleeding injectors, setting tappets etc.

[blubaju]

Originally Posted by charliehows

yes its a decompression lever, no its not 'some homebrew design', it's factory fitted. ...

Well, maybe, have a look into this thread:

http://www.cruisersforum.com/forums/f54/yanmar-decompression-levers-165819.html

My 2 3gm30 marine engines, purchased late last Millenium in Asia, delivered by yanmar Singapore had 3 single levers. Handcranking was not possible due to space restriction, flipping them in 1 by 1 never caused any problem. Used when battery was low.

[joeniver]

Wow!

Thanks for all the reply's. This is a great Forum.
The engine is a 3HM. Fresh water cooled, with sea water cooling via heat exchanger.

It was put in new to a 1984 Sparkman and Stephens replica 38' Loki.

Have not had to use the decompression lever yet. Good to know.

Joe

[Differentroads]

I have a 3 cylinder Yanmar (3GM30) with three seperate decompression levers. I've had to use them six or seven times in the seven years I've owned Offbeat forstarting problems, bleeding air from the fuel line (though a pump on the external fuel filter on my engine is better at giving controlled fuel flow) and, twice, for expelling seawater from the cylinders (a design problem in the seawater and exhaust system).
My advice is to throw the lever and see what happens while starting and running the engine. I nearly crapped myself with nerves the first time i threw my decompressors over. But nothing broke and now I know what it sounds like if and when one of my cylinders loses compression or a injector blocks up. Better to get familiar with as much of your engine as you can at the dockside because its hard to climb a steep learning curve out a sea.

[Wotname]

Originally Posted by joeniver

Wow!

Thanks for all the reply's. This is a great Forum.
The engine is a 3HM. .......

Have not had to use the decompression lever yet. Good to know.

Joe

Well you won't be hand cranking your 3HM .

The main benefits of having the de-com levers coupled together like your's is for starting with a half dead battery or for very cold starting.

Step 1 - operate the levers so engine is decompressed.
Step 2 - spin the engine over with the starter motor for say 5 to 10 seconds or until the engine is spinning over at a good rate. It doesn't take much effort or electricity to turn the engine over when decompressed.
Step 3 - release the de com levers and the stored energy in the flywheel etc will take the engine though compression and fire (hopefully ). Keep the starter engaged at this point.

This really works well even if the battery is nearly dead.

Other uses is for an emergency stop. If the engine is not responding to the throttle or engine cut-off lever i.e. in a runaway condition - simply operate the decompression levers and the engine will cease to run (i.e. no compression).

Also handy for making it easy to turn the engine for maintenance.

For those who do have have a hand cranking setup, it is better to have two or three seperate de com levers as you can de compress all the cylinders, and once you have build up some rotational speed with the hand crank, drop one lever to get the engine to fire on one cylinder and then bring the other one (or two) into play.

[Tortuga331]

[QUOTE=Differentroads;3032707]I have a 3 cylinder Yanmar (3GM30) with three seperate decompression levers. I've had to use them six or seven times in the seven years I've owned Offbeat forstarting problems, bleeding air from the fuel line (though a pump on the external fuel filter on my engine is better at giving controlled fuel flow) and, twice, for expelling seawater from the cylinders (a design problem in the seawater and exhaust system).
My advice is to throw the lever and see what happens while starting and running the engine. I nearly crapped myself with nerves the first time i threw my decompressors over. But nothing broke and now I know what it sounds like if and when one of my cylinders loses compression or a injector blocks up. Better to get familiar with as much of your engine as you can at the dockside because its hard to climb a steep learning curve out a sea.[/QUOTE

Is there a know design problem that could cause water to get into the cylinders?

[Boatyarddog]

Originally Posted by Differentroads

I have a 3 cylinder Yanmar (3GM30) with three seperate decompression levers. I've had to use them six or seven times in the seven years I've owned Offbeat forstarting problems, bleeding air from the fuel line (though a pump on the external fuel filter on my engine is better at giving controlled fuel flow) and, twice, for expelling seawater from the cylinders (a design problem in the seawater and exhaust system).
My advice is to throw the lever and see what happens while starting and running the engine. I nearly crapped myself with nerves the first time i threw my decompressors over. But nothing broke and now I know what it sounds like if and when one of my cylinders loses compression or a injector blocks up. Better to get familiar with as much of your engine as you can at the dockside because its hard to climb a steep learning curve out a sea.

A basic mistake in starting a diesel when cold is over cranking, with no starting.
This is how sea water can enter the combustion chamber.
It can be damaging to the engine to have this occur.

The trick that has not been mentioned yet is to shut off your intake to the engine till you get it to start, once it starts turn the intake valve on, and check for flow out the exhaust.

This procedure is nessessary when cranking the engine without starting, as water will back up in the water muffler and into the cylinders.
Important step!
Boatyarddog

[Boatyarddog]

Originally Posted by joeniver

Wow!

Thanks for all the reply's. This is a great Forum.
The engine is a 3HM. Fresh water cooled, with sea water cooling via heat exchanger.

It was put in new to a 1984 Sparkman and Stephens replica 38' Loki.

Have not had to use the decompression lever yet. Good to know.

Joe

Also, see Post 14 by BYD
Applies here.
Boatyarddog