Will a 4LW start on 1 or 2 cylinders?

[swift1894]

My old Lister JP4 had 4 separate decompressers, which you flicked down one at a time when starting.

My 4LW has one lever for all 4 decompressers so I wondered, if I isolated 2 cylinders by locking down 2 fuel pump levers, it would be easier to start by hand by reducing the total, initial resistance. If so, which would be the best 2 cylinders to start on. Or is this not a good idea?

[RLWP]

That doesn't make sense. On the JP you decompress all of the cylinders to be able to get the engine up to speed, then drop in cylinders by using the levers. Meanwhile the injectors are delivering atomised fuel into the cylinders ready to fire up

What you are suggesting just makes it  harder to start, no fuel going into the cylinders, full compression on every cylinder

Richard

 

Edited October 25, 2017 by RLWP

[swift1894]

19 minutes ago, swift1894 said:

 

Yeah I see what you mean. All 4 cylinders would come under compresssion at once but only 2 would fire up. So the same amount of Kickback at the handle if it didn’t fire up. But with the JP4, you’d only have initial compression resistance with 1 cylinder, then 2, then 3 then all 4, right?

 

[X Alan W]

As Richard says cutting out the pump injection will not reduce the compression on those cylinders & would make the chance of starting 50% less as 2 pots with no fuel have no chance Decompressors of some type are required to aid hand start jf a faster rotation is required

[swift1894]

1 hour ago, X Alan W said:

Decompressors of some type are required to aid hand start jf a faster rotation is required

I don’t understand what you mean.

[X Alan W]

1 hour ago, swift1894 said:

I don’t understand what you mean.

If you are hand starting an internal combustion engine a 4 cylinder for example you will get a position of resistance turning it over 4 times for possibly each rev of the starting handle( dependent on the  gearing) when you come up against compression with one or more decompression levers engaged you will have no compression on that cylinder so all 4 engaged the engine can be turned with out much resistance winding the handle with more & more speed to get the flywheel up to a speed where it will have enough inertia to over come the compression when the lever is disengaged so it should fire on that cylinder doing the same with the other 3 should produce a firing stroke from the other cylinders  a large diesel is very difficult to turn over at a speed enough to overcome compression with  the levers in the run position

[jonesthenuke]

Agree with all the above, shutting off fuel to one or more cylinders will not aid starting.  I suspect an LW would start with fuel shut off to one or more cylinders, Gardner say in the manual that the engine should fire on the first cylinder reaching the compression stroke. However, I have never tried and do not intend to start with a cyinder(s) shut down.

[magpie patrick]

3 hours ago, swift1894 said:

I don’t understand what you mean.

It is the compression which makes it hard to turn the engine

The engine needs to turn fast enough to fire (that's layman's terms - it is more complicated than that)

On my two cylinder engine, knocking the decompressors off makes it easier to turn, which means I can get it turning quickly (in my case with a knackered starter motor), which means that when one cylinder is "turned on" again it will fire. The flywheel will have enough momentum to turn the engine against the resistance of one cylinder and get that to fire, the engine then has the "oomph" to start the second cylinder

Obviously with the decompressor being engaged means that particular cylinder won't fire, but it does make the engine easier to turn. There are other ways of stopping a cylinder firing, such as stopping the fuel supply, but these won't make the engine easier to turn, and thus won't make it easier to start.

 

[swift1894]

My point was that with the JP4 you are only “fighting” against 1 of the 4 cylinders which suddenly comes under full compression, as each cylinder has its own lever, whereas with the 4LW all 4 cylinders come under compression at once, so it the engine doesn’t fire up immediately you can’t continue to turn the handle.

[Machpoint005]

If there was ever a question to which the answer is "suck it and see", then this is it!

[MtB]

On 25/10/2017 at 09:04, swift1894 said:

My 4LW has one lever for all 4 decompressers so I wondered, if I isolated 2 cylinders by locking down 2 fuel pump levers, it would be easier to start by hand by reducing the total, initial resistance.

 

No.

Because it won't reduce the total, initial resistance.

[zenataomm]

Is OP saying that he thinks all 4 cylinders hit tdc on the squeeze stroke at the same time?

[RLWP]

20 minutes ago, zenataomm said:

Is OP saying that he thinks all 4 cylinders hit tdc on the squeeze stroke at the same time?

No, I think they are confusing what the decompressors do and what the pump cut outs on a 4LW do

Richard

[swift1894]

2 hours ago, zenataomm said:

Is OP saying that he thinks all 4 cylinders hit tdc on the squeeze stroke at the same time?

No I’m not. But if the first cylinder doesn’t fire up, then the second one doesn’t etc, then the momentum of the flywheel is stopped and it becomes impossible to turn the handle further, whereas the JP4 allowed the operator to continue turning the handle, as only 1 cylinder would be under compression.

[zenataomm]

I agree with Richard's slant on where the confusion lies having read the thread twice now.

Try looking at it this way.

Decompression levers are not fuel pump levers.

Using a decompression lever opens the exhaust valve, hence there is no compression, but the pump still injects a spray of fuel. With no compression you can turn the handle all day, but it won't start as there is no compression.

Using a fuel pump lever stops fuel being injected but still allows compression. With no fuel you can only turn the handle until your muscles explode. but it won't start as there is no fuel.

A diesel is known as a compression ignition engine because it requires the air in the cylinder to be compressed to a high enough temperature to ignite the fuel when it's sprayed in by the injector.