help

[John Orentas]

I'll make a start, it is better to think first of the advantages of a short stroke engine.

 

1. As short stroke means a relatively big bore which in turn means larger better breathing valves can be fitted.

 

2. Dynamic forces are very much lower, piston speeds are lower, connecting rods shorter and engine speeds can therefore be higher and more speed means more power.

 

3. The combustion chamber has more symmetry, so better flame spread and more efficient burning of fuel. The surface area of combustion chamber is smaller so less heat loss.

 

Long stroke engines;

 

1. They have the potential to give higher compression ratio's but not so in practise.

 

2. A longer power stroke with small pistons and combustion chambers can give smoother, slower running and low tick-over speeds though at the cost of reduced overall power.

 

3. Long stroke means long crankshaft throw, high piston speeds and long connecting rods which means more smooth torque is delivered, but heavy flywheel is required.

[Sir Nibble]

Sorry Alec, but much of that is simply untrue. If the "mixture" explodes, that is detonation and it is destructive to the engine. The rate of expansion of the burning charge will be the same regardless of bore/stroke dimensions given the same conditions for combustion (air/fuel ratio, compression etc). At 1000 rpm the cylinder volume will expand from minimum to maximum in 0.06 seconds. If the swept volume and compression ratio are the same, then the rate of expansion is the same, and the charge has 60ms to complete its combustion in either case.

I suspect you misunderstand my earlier post, I am not so much asking for enlightenment regarding an established fact, as calling recieved wisdom into question. I do not believe there is and torque advantage to be gained by a longer stroke, in fact I could argue the other way!

[Alec Gatherer]

My Riley (80.5x120mm) begs to differ. Pull the side off a house would that. Might not be the same with boats though.

[Sir Nibble]

Don't make the mistake of confusing torque with flywheel effect.

[Guest]

http://www.bath.ac.uk/~ccsshb/12cyl/

http://www.bankspower.com/Tech_somuchtorque.cfm

http://auto.howstuffworks.com/question381.htm

A bit of reading.

Edited February 20, 2006 by Guest

[John Orentas]

Quote from 'How Stuff Works'.

 

"A large diesel engine usually cannot get above 2,000 RPM, but has huge torque because of the long stroke. The torque is what lets your engine pull a huge load up a hill".

 

That's nonsense even knowledgeable people fall for this, it is power and gearing that pulls a load up a hill, torque is only one element of the equation and if your car won't 'pull a house down' it is only because you are in the wrong gear.

 

The smoothest, most progressive and quietest engine is an electric motor but as far as torque goes they are rubbish. Of course a big vintage engine pushing you along feels fantastic but that is not because the engine produces lots of torque (which it does) it is because it sounds nice, it's an illusion.

 

They fit large diesel engines in trucks because they are fuel efficient, long lasting and reliable, if fact the torque and rev range on modern lorries is not that good thats why they have about 30 gears.

 

And now one or two of you will be calling me opinionated and arrogant again, tough.

Edited February 20, 2006 by John Orentas

[Guest]

Quote from 'How Stuff Works'.

 

"A large diesel engine usually cannot get above 2,000 RPM, but has huge torque because of the long stroke. The torque is what lets your engine pull a huge load up a hill".

 

That's nonsense even knowledgeable people fall for this, it is power and gearing that pulls a load up a hill, torque is only one element of the equation and if your car won't 'pull a house down' it is only because you are in the wrong gear.

 

The smoothest, most progressive and quietest engine is an electric motor but as far as torque goes they are rubbish. Of course a big vintage engine pushing you along feels fantastic but that is not because the engine produces lots of torque (which it does) it is because it sounds nice, it's an illusion.

 

They fit large diesel engines in trucks because they are fuel efficient, long lasting and reliable, if fact the torque and rev range on modern lorries is not that good thats why they have about 30 gears.

 

And now one or two of you will be calling me opinionated and arrogant again, tough.

Not at all you are entitled to your opinion. My opinion as to why trucks have many gears is that they have to haul 40 odd tons up hills like the Shap up north etc, something we don't encounter on canals too often. In other words they have gears for all occasions. My mates Scania will travel along the M6 fully laden without dropping a gear from Birmingham to Barton Aqueduct Manchester.

As a kid we were involved with diesel shunting engines which whilst quite small could move ridiculously large loads (slowly), where they long or short stroke that the manufacturers had seen fit to install? I'll leave you to decide.

[Amicus]

My post yesterday giving the slip of a propeller was nonsense. The revised figures are below.

To reiterate, a prop with a 14-inch pitch, an engine RPM of 1600 thru a 3:1 reduction box.

Which is 1.166ft pitch and 533.3 shaft RPM

 

 

If this gives 3 MPH or 264ft/min, this equates to 0.495 ft per revolution,

 

0.495ft over 1.166ft (14 inches) is 0.42

 

1.0 would be 100% efficient and 0.42 is 42% efficient,

 

0.42 versed (1 minus 0.42) is 0.58 = 58% slip

 

And 3.1 MPH is 56% slip etc., so

 

3.0 MPH=58%

3.1 MPH=56%

3.2 MPH=55%

3.3 MPG=53%

3.4 MPH=52%

3.5 MPH=51%

3.6 MPH=49%

3.7 MPH=48%

3.8 MPH=46%

3.9 MPH=45%

4.0 MPH=43%

I tink this is now correct, if anybody sees an error please shout, we is all here to larn

 

I apologise for my previous post, especially to Allan, and my thanks to John O for pointing out to me the error.

From now on I'm going to stick to hanging doors, I'm good at that.

[denboy]

totaly lost the plot now QUESTION am i going to win or loose if i swap from my pj3 to a kelvin p4

[John Orentas]

totaly lost the plot now QUESTION am i going to win or loose if i swap from my pj3 to a kelvin p4

 

 

I think everyone's been neglecting you Denis, it is often like that. Do you have any data on the two engines. A lot of people on here would like to have the dilemma you have, in the end it might well come down to the prettiest looking one as I suspect both engines are very suitable.

[DHutch]

My opinion as to why trucks have many gears is that they have to haul 40 odd tons up hills like the Shap up north etc

Also, compair to a car lorrys a relatively "under engined"

- Ie, they have very power power-to-weight ratios, and hence need to keep the engine working flatout at optimum revs.

- To take extreams, a 40ton curtain-sider may well only have a 340bhp engine, where a ferrari weighing a hell of a lot let, may easly have 600+bhp ontap.

 

 

Daniel

[Guest]

Also, compair to a car lorrys a relatively "under engined"

- Ie, they have very power power-to-weight ratios, and hence need to keep the engine working flatout at optimum revs.

- To take extreams, a 40ton curtain-sider may well only have a 340bhp engine, where a ferrari weighing a hell of a lot let, may easly have 600+bhp ontap.

Daniel

Relatively underengined would be an understatement Daniel, but your point is excellent. My mates Scania produces about 400 BHP giving a power to weight ratio of about 9 BHP per ton whereas my car is about 60 BHP per ton. Little wonder that they need splitters on the gearbox to give many ratios. This is why they get upset with us dickhead car drivers when we hog the middle lane-once they lose momentum they have had it.

[alan_fincher]

totaly lost the plot now QUESTION am i going to win or loose if i swap from my pj3 to a kelvin p4

How do you mean "win or lose", exactly ?

 

As you have already identifieed, the PJ3 is the higher horsepower, but, if, as I believe, the Kelvin delivers 20 HP, then that, as has already been said, it more than adequate for any normal narrowboat with room to swing the type of prop these relatively slow revving engines need.

 

Are you disastisfied with the Petter in some way ? Is it in generally good order and reliable, or does it need of some TLC ?

 

Do you just fancy the Kelvin, because it's a Kelvin ?

 

I'm not sure if you have genuine reasons why you need to replace the current motor, or just fancy a change to something with a touch of class ?

 

Personally, if I was in the lucky position of having the right kind of boat, and the right kind of money, I'd go for something slow-revving with just TWO cylinders. That's almost universally what I remember working boats sounding like, and frankly the engines with 3 or more cylinders just don't sound like a good old fashioned canal boat to me, however powerful or silky smooth.

 

THe Petter PD2 was a great sounding engine, but as you almost never see one these days, I assume nothing like as reliable or long-lived as what people seem to put in old working boats now.

[Hairy-Neil]

 

THe Petter PD2 was a great sounding engine, but as you almost never see one these days, I assume nothing like as reliable or long-lived as what people seem to put in old working boats now.

 

I understand that about 14 of the ex Grand Union boats still have the PD2's fitted and the icebreaker, Tycho still retains its PD3.

[Liam]

The first thing I think of is spares, for any problems you may need to sort.. aswell as general maintenance.

 

I'd rather be given the task of finding Petter spares over Kelvin any day.. and I bet my wallet would too.

[Stephen Sugg]

I would agree, our canal society boat, Panther was built in 1929 and fitted with a 15hp Bolinder as she was intended for towing. Had she not been, her engine would have been a 9hp Bolly

 

Regards

 

Tony

 

 

Slightly off topic, but is Panther that red Coventry Canal Society boat that I saw at the Braunston show last year with the unusual looking (to me) bow? I think I've got a nice piccy of it going round the turn......

[denboy]

How do you mean "win or lose", exactly ?

 

As you have already identifieed, the PJ3 is the higher horsepower, but, if, as I believe, the Kelvin delivers 20 HP, then that, as has already been said, it more than adequate for any normal narrowboat with room to swing the type of prop these relatively slow revving engines need.

 

Are you disastisfied with the Petter in some way ? Is it in generally good order and reliable, or does it need of some TLC ?

 

Do you just fancy the Kelvin, because it's a Kelvin ?

 

I'm not sure if you have genuine reasons why you need to replace the current motor, or just fancy a change to something with a touch of class ?

 

Personally, if I was in the lucky position of having the right kind of boat, and the right kind of money, I'd go for something slow-revving with just TWO cylinders. That's almost universally what I remember working boats sounding like, and frankly the engines with 3 or more cylinders just don't sound like a good old fashioned canal boat to me, however powerful or silky smooth.

 

THe Petter PD2 was a great sounding engine, but as you almost never see one these days, I assume nothing like as reliable or long-lived as what people seem to put in old working boats now.

 

 

ive had a night mare with trying to find spares for my pj3W ive replaced pistons liners head gaskets bryce fuel pumps(by the dozens)they keep breaking springs £42 to rebuild these everytime the spring breaks ive got water getting into the sump had a craked head £200 to get it welded i know every nut and bolt on it by name had enough of it now time for a change

[alan_fincher]

ive had a night mare with trying to find spares for my pj3W ive replaced pistons liners head gaskets bryce fuel pumps(by the dozens)they keep breaking springs £42 to rebuild these everytime the spring breaks ive got water getting into the sump had a craked head £200 to get it welded i know every nut and bolt on it by name had enough of it now time for a change

Sounds like you may have answered your own question !

 

I'm no expert, but I'd be surprised if the Kelvin wasn't up to the job, provided, as I keep saying, you have space to swing an appropriate prop.

 

Alan

[DHutch]

I'm no expert, but I'd be surprised if the Kelvin wasn't up to the job, provided, as I keep saying, you have space to swing an appropriate prop.

Or just gear it up bit more.

 

 

Daniel

[David]

Hi

I gave an reply to this thread when it was new with regard to Kelvin J's and K's.

I have since spoken with the man who knows more about Kelvins than most other people in the country, Richard Gobal, he makes a living soley by servicing and looking after the needs of Kelvin owners and has done so for the past 20 years.

He looks after one or two model P's, the great problem with them is spares are almost none existant, they were not made in great numbers unlike the J's and K's nor were they built at the time when Kelvin's were exported to the rest of the old British Empire, so unlike the J and K spares are not still available from old stock or reproduced in India etc.

david

[denboy]

Hi

I gave an reply to this thread when it was new with regard to Kelvin J's and K's.

I have since spoken with the man who knows more about Kelvins than most other people in the country, Richard Gobal, he makes a living soley by servicing and looking after the needs of Kelvin owners and has done so for the past 20 years.

He looks after one or two model P's, the great problem with them is spares are almost none existant, they were not made in great numbers unlike the J's and K's nor were they built at the time when Kelvin's were exported to the rest of the old British Empire, so unlike the J and K spares are not still available from old stock or reproduced in India etc.

david

Thank you mr B that maybe so but i have searched all over the inter net for the last 4 years in search of a spare PJ3W to no avail aircooled by the bucket load but water cooled rarer than unicorn droppings but i keep finding kelvin p2\p4 that i could get for spares thanks for your reply Regards Denis

[vernon]

I hada P4R ina 46ft narrowboat with 25 inch draught. It was a great engine but probably overpowered for the boat as I had to decoke the heads every year.i finally gave up when the gaerbox dis-assembled itself. A 50p piece would stand upright on the rocker cover at normal cuising speed. Used the original Kelvin 20x15 prop.

This was the first engine not designed by walter bergius and so is very different to the earlier models. I have a copy of the Kelvin handbook and parts list which I could copy if helpful. There is a Kelvin owners club rally at Bugsworth Basin on 19 - 21 May.

[denboy]

I hada P4R ina 46ft narrowboat with 25 inch draught. It was a great engine but probably overpowered for the boat as I had to decoke the heads every year.i finally gave up when the gaerbox dis-assembled itself. A 50p piece would stand upright on the rocker cover at normal cuising speed. Used the original Kelvin 20x15 prop.

This was the first engine not designed by walter bergius and so is very different to the earlier models. I have a copy of the Kelvin handbook and parts list which I could copy if helpful. There is a Kelvin owners club rally at Bugsworth Basin on 19 - 21 May.

 

 

Thanks vernon will see how i get on handbook would be most helpful to me ive got to go for it now ive bought it,i think i have a 24 inch prop fitted at the moment will know when i drydock at the end of the month thanks again

Regards Denis

[tony collins]

Slightly off topic, but is Panther that red Coventry Canal Society boat that I saw at the Braunston show last year with the unusual looking (to me) bow? I think I've got a nice piccy of it going round the turn......

 

Surely is! There is always a lot of interest in her bow, various theories are voiced as to why it quite like it is. If you've got a photo, please put in the gallery as we are collecting all the info we can of her. It is sometimes difficult to take a phot whenh you are actually on the boat!

 

Sorry about the late reply, but I busy putting the magazine to bed at the mom, hence forum time is limited.

 

Regards

 

Tony.

 

PS We will be taking her to Crick and Braunston again this year.