JP2M hi or low compression?

[fittie]

What are peoples thoughts on running JP2M under hi or low compression. One old skipper says always hi and another low?

what is the best for the engine?

[frangar]

I always start on high then run on low. Less stress on the crank and bearings in my opinion. It also keeps the changeover valves free as well. If you always run on high because you are only on canals they might be seized when you go for a long river run and need it to be on low. 

 

No doubt others will say otherwise! 

[RLWP]

59 minutes ago, frangar said:

No doubt others will say otherwise! 

Popular subject of conversation over a pint for JP owners

 

Richard

[RLWP]

I have this:

 

'Modern High Speed Oil Engines, 1949'

 

This is such a successful design that Lister used it in the J series, the FR series then dropped it completely. No-one else adopted it

 

When in 'High' the engine has a pretty straight Ricardo Comet I combustion chamber - very common and highly respected. In 'Low' it has an experimental Lister system

 

You may make your plans accordingly

 

Richard

[MtB]

So from Richards image it seems the high compression setting is intended by lister to be for starting only. 

 

One bit puzzles me. Is the power output of the engine higher on high compression? Not sure how it can be as the fuel charge on each stroke remains the same. Yet petrol engines seem to rise in power with higher compression.  

[RLWP]

21 minutes ago, Mike the Boilerman said:

So from Richards image it seems the high compression setting is intended by lister to be for starting only. 

 

One bit puzzles me. Is the power output of the engine higher on high compression? Not sure how it can be as the fuel charge on each stroke remains the same. Yet petrol engines seem to rise in power with higher compression.  

The governor alters the fuel charge to achieve an engine speed. So, for high and low settings, the governor will be delivering different quantities of fuel for the same speed

 

Richard

[MtB]

56 minutes ago, RLWP said:

The governor alters the fuel charge to achieve an engine speed. So, for high and low settings, the governor will be delivering different quantities of fuel for the same speed

 

Richard

 

Thank you Obvious now you've explained

 

So when running in a boat and driving a propeller, as much fuel is injected as needed to develop whatever power is needed for the engine speed set on the speedwheel.

 

And on high compression this might be less fuel? So fuel economy can be expected to be higher on high compression setting (even though Lister did not intend high compression for normal running)? 

 

[RLWP]

4 minutes ago, Mike the Boilerman said:

 

And on high compression this might be less fuel? So fuel economy can be expected to be higher on high compression setting (even though Lister did not intend high compression for normal running)? 

 

Not according to the article. The theory is that the Lister combustion chamber is an improvement on the Ricardo Comet design because the air chamber increases turbulence, improves mixing and gives better consumption

 

I haven't found information that support this theory, on the other hand the Comet design is widely used

 

Richard

[MtB]

4 minutes ago, RLWP said:

Not according to the article. The theory is that the Lister combustion chamber is an improvement on the Ricardo Comet design because the air chamber increases turbulence, improves mixing and gives better consumption

 

I haven't found information that support this theory, on the other hand the Comet design is widely used

 

Richard

 

Ah yes. I was only reading the article on a phone screen 50mm wide so that bit didn't properly penetrate. 

 

So the answer to the question is for normal running, always on low compression, yes?!

[frangar]

Listed stated that you should start on high compression & run on high if lightly loaded at lower revs. For higher revs & loads use low compression. High compression at low loads should give a cleaner burn and less smoke from exhaust. 

[RLWP]

5 minutes ago, frangar said:

High compression at low loads should give a cleaner burn and less smoke from exhaust. 

Low loads being pretty much any usage for a pleasure boat. I try not to take JPs up to their max operating speeds where they should be working in front of owners - they get scared

Edited June 17, 2018 by RLWP

[frangar]

1 minute ago, RLWP said:

Low loads being pretty much any usage for a pleasure boat

Not if you are punching the trent or Ribble link! My JP is fine on low compression. I think  those that run on high all the time might also be masking other faults such as worn rings/bores/valves which mean that the low compression setting is really low!! 

[RLWP]

57 minutes ago, frangar said:

Not if you are punching the trent or Ribble link!

Out of interest, what engine revs would you be using to do that?

[frangar]

14 minutes ago, RLWP said:

Out of interest, what engine revs would you be using to do that?

I think against the tide on the Ribble we were close on 1000 rpm. The Crowthers prop was starting to cavitate which has never happened before. I decided not to hold it on the stop as decided not to push it harder than needed!  We ran at a little bit less on the trent. Sadly I didn’t have the optical tachometer then to measure it accurately. 

[steamraiser2]

Of course Lister had a change of heart over this and did away with the changeover valves entirely when the JPs were revamped into the JK engines .No change over valves at all. Back in the day, when Lister still did factory training courses, I remember being told that three quarters load at three quarters engine speed was the ideal set up. My company had dozens of them many of them on continuous duty on quarry water pumps. High compression all the time. Leaking changeover valves were always replaced with JK style plugs. I can't imagine that many canal use engines ever get to truly work hard. We recently supplied a JK to a guy for duty on a salvage barge running a large pump. He told me that the old JK ran for weeks at a time under full load and had done that for fifteen years before dying of fair wear and tear. Clearly the lack of  changeover valves did no harm there.

[RLWP]

2 hours ago, frangar said:

I think against the tide on the Ribble we were close on 1000 rpm. The Crowthers prop was starting to cavitate which has never happened before. I decided not to hold it on the stop as decided not to push it harder than needed!  We ran at a little bit less on the trent. Sadly I didn’t have the optical tachometer then to measure it accurately. 

Something around 10-12HP then as opposed to the 22HP it can produce at 1200

 

It's hard to get a JP in a narrowboat to work at capacity. Even harder for a JP3 in a Hudson of course - which makes the OPs question very difficult to answer

 

Richard

[frangar]

5 minutes ago, RLWP said:

Something around 10-12HP then as opposed to the 22HP it can produce at 1200

 

It's hard to get a JP in a narrowboat to work at capacity. Even harder for a JP3 in a Hudson of course - which makes the OPs question very difficult to answer

 

Richard

But I'm also driving a 70 Amp Alternator off the flywheel so theres the loading from that....which does make a difference when you first set off especially if I've been stooped a day or two.

 

Given the age of the engine and the rarity of crankshafts for marine versions I'm quite happy not to have it at maximum power!

[fittie]

The JP is use in a 1936 Northwich with a 2:1 reduction box and a 29" blade.

[RLWP]

1 hour ago, frangar said:

But I'm also driving a 70 Amp Alternator off the flywheel so theres the loading from that....which does make a difference when you first set off especially if I've been stooped a day or two.

 

Given the age of the engine and the rarity of crankshafts for marine versions I'm quite happy not to have it at maximum power!

Which leads me neatly to the answer I usually give, which depends very much on the owner

 

You know what you are doing and like to be involved with your engine, so working the valves makes sense

 

Not true of other JP owners

 

And, as you are technically minded, the forces from combustion on a crankshaft and rods are small compared to the stresses from the rotating masses

 

Richard

[BWM]

2 hours ago, fittie said:

The JP is use in a 1936 Northwich with a 2:1 reduction box and a 29" blade.

29" is a fair sized prop, depending on pitch, I'd imagine that would provide a fair load. I leave my Jp3 on high compression, only time will tell.. As RLWP says, rotation speed will probably have more effect than load - unless you fit a blower!

[fittie]

17" pitch

[RLWP]

1 hour ago, BWM said:

 unless you fit a blower!

Now you are talking! Sounds like a great project

 

I'll arrange a supply of big end bearings

[RLWP]

59 minutes ago, fittie said:

17" pitch

This is your problem:

8 hours ago, frangar said:

Lister stated that you should start on high compression & run on high if lightly loaded at lower revs. For higher revs & loads use low compression. High compression at low loads should give a cleaner burn and less smoke from exhaust. 

Notice Lister don't explain what 'light loads' or 'heavy loads' are

 

Steamraiser2 (from Marine Power Services) and me are of the opinion that it is hard to get a JP in a narrowboat to work at 'high loads' so you're probably better leaving the valves alone. They'll hopefully start out sealed, and if not soot will soon seal them up. As MPS point out, the JK dispensed with the valves so they are probably not necessary

 

On the other hand, I like obscure bits of technology. So starting the engine on high until warm, then switching to low appeals to me. It has a weird ritual to it that is only appropriate to JP and FR engines. If it were my engine, I'd start on high and run on low because I could

 

So there you are - do as you please, it probably doesn't matter

 

Richard

[billh]

10 hours ago, RLWP said:

 

On the other hand, I like obscure bits of technology. So starting the engine on high until warm, then switching to low appeals to me. It has a weird ritual to it that is only appropriate to JP and FR engines. If it were my engine, I'd start on high and run on low because I could

 

So there you are - do as you please, it probably doesn't matter

 

Richard

The Ailsa Craig RF series diesels have a curious way of increasing compression for starting- The rocker shaft is  on eccentric bearings , and the decompression lever on the end of it has 3 positions , decompressed( exhaust valves are opened), normal running,  and high compression for starting. The engine should not be run in high , return to normal as soon as it starts. Ah, we're  talking Listers, I digress, as usual. Long time ago we ran a JP2 , couldn't tell the difference between HC and LC ,it  was a tad worn though.

[Capella247]

On the odd occasion when I've been on a river I ve dialled the valves out on my JP.  But then thought better of it because when dialling out there is a lot of soot and smoke. Once all the way out they don't leak, but when out Ive also noticed sparks from the drilled hole in the valves?  Is that normal or a sign that something is up that needs sorting? Cheers Tom