Decompression Switch on Volvo 2003

[DinoKanuck]

Ahoy from balmy Canada,

Trying to understand a new boat (LM 28) and need to asking what the decompression leaver on a Volvo 2003 does when in the 9 O'clock position.

I know normal operation is in the 3 O'clock position and emergency stop is 12 O'clock (no fuel and no compression).

Is the 9 O'clock position fuel but no compression?

Dino

 

[JohnShannon]

I bet somebody here really knows, but to me it looks like 12 o'clock is no compression so you are able to hand crank. Once you have built up some speed throw it to 9 o'clock for I suppose compression and fuel. Once it is running return it to 3 o'clock for what? still compression and fuel.

Do you have a hand crank with your boat? I have a 2003 as well but pray to sparky god of ignition and so far haven't had a problem, well except once.

 

[DinoKanuck]

Ahoy UTC-9 and John Shannon,

There feels like no compression at 9 o'clock. Someone told me to use the 9 O'clock position when spinning the motor over to remove air at the injectors.

Looking to confirm that use of the 9 O'clock position.

Over from UTC -4,

Dino

 

[sailormanbigd]

2003

my understanding is the decomp. lever works by not allowing the valves to seat and therefore no compression in the cylinders. Nothing to do with fuel. In the 3 o'clock position all the valves will work normally-comp in all three cylinders. In the 12 o'clock position you are getting comp in one cylinder only, might assist in cranking and starting if compression gets strong enough and hot enough to fire the cylinder- might even run but very roughly. The all the way to the left position (9 o'clock) is no compression in any cylinder witch will prevent the motor from starting or running. You can use this non-compression and non-running mode to assist with bleeding air from fuel system, or more comonly to preheat the cylinders and engine/oil to aid in starting. BE ADVISED THOUGH, PROLONGED CRANKING CAN ALLOW RAW COOLING WATER TO BACKFLOW INTO THE CYLINDERS AND RUIN YOUR MOTOR. It is highly reccomended that you first close the raw water inlet valve BEFORE doing any prolonged cranking.

 

[DinoKanuck]

Ahoy SailorManBigD:

Since 12 O'clock is "emergency stop", ( see photo from operator's manual) wouldn't compression in one cylinder defeat that "emergency stop" feature?


That advice on water in the cylinders has got my attention, Thanks

Dino K

 

[sailormanbigd]

emergency stop?

yes, that has me perplexed. I will have to dig out my 2003 service manual and try and sort it out. I will post my results but am very busy at this time. It has been awhile since i read it and I thought I had it all figured out?

 

[alexco38]

"emergency stop"

I wouldn't use the de-compression level as "emergency stop". It's bad for the engine as the sudden lost of the valve cam and the piston still compressing. The rockers on the cylinder head are moving at quite a fast speed.

All you need to do to stop a diesel engine is to put something to cover over the air intake.