Running engine (diesel) with the ignition turned off

[coopec]

I've put Convey on ignore.

 

[convey]

I've put Convey on ignore.

I'll take that as an "I'm sorry, I was wrong".

 

[PaulRainbow]

I'll take that an "I'm sorry, I was wrong".

I took it as "i can't read any more of this nonsense", perhaps i'm wrong.

 

[PaulRainbow]

I get a page "could not be found" error message when I follow that link. Could you post an accurate one for my fan club, please?

Jeez, a few folk are going to get to know the flavour of my excreta here.


I had no idea we were just talking about MD22s. I'm talking in general, and in respect to the screengrab of animation I posted.

OK ... Look, I have no need to use Google to write my posts but I'll quote you, first link taken at random. Malcolm James Nunney from 'Light and Heavy Vehicle Technology' published by Routledge, Jan 2007. Malcolm Nunney CGIA, MSAE, MIMI has published numerous educational books, including those about automotive engineering for the Newnes-Butterworths/Elsevier Science technician series. See notes below*.

Keep reading the book, you'll get there in the end, or perhaps you won't.

 

[RichardS]

He misses a 5th which would be adding material to the combustion chamber (welding & reshaping) it but I guess that is not considered not "practicable" for mechanics but, in essence,

1) is changing the squish height,​

2) is changing the shape of the combustion chamber,​

3) is changing the shape of the piston,​

4) is changing the deck height.​

As pointed out to you.

For those hard of understanding, by writing "preserving the original operating geometry of the valve train, he's underlining that the others CHANGE it.

There are plenty of other links out there about this. Please don't waste our time about what you did or learned as an apprentice.

Of course, there are other ways of correcting it, like altering the base circle of the cams ... but I guess grease monkeys in the marine industry aren't faced with installing high performance cams very often.

Surely there must be someone else who's had a bit of experience in power boat racing who knows this stuff?

Do you agree that piston shapes don't make the compression ratio but their shapes and their match determines the compressed volume and that determines the compression ratio?

Richard

 

[Skylark]

I've only just stumbled across this thread. I've only read that last few pages but it's highly entertaining and qualifies for the Steel Boat and Never Splashed Colvic award for bolox

?

 

[RichardS]

I've only just stumbled across this thread. I've only read that last few pages but it's highly entertaining and qualifies for the Steel Boat and Never Splashed Colvic award for bolox

?

Go on .... read the whole lot. You know you want to.

Richard

 

[convey]

Do you agree that piston shapes don't make the compression ratio but their shapes and their match determines the compressed volume and that determines the compression ratio?

"Shape" is a very poorly defined term but, to my mind, includes every part of their dimensions, from pin and crown heights, to ring positioning, to valve cut outs, etc ALL of which affect the compression ratio. That's partly why my position was such an easy slamdunk. So let's start from the offending claim,

The shape of the piston crown or cylinder head does not affect the compression ratio.

By which, I presumed he meant the shape of the cylinder head combustion chamber (no one would be dumb enough to suggest the outside of the casting would).

Of course it's the "two hands clapping", the shape of the piston and combustion chamber (and deck height and position of first ring etc) combined, that determines the compression ratio. I've never suggested it's not.

Paul asked in his habitually inaccurate and sarcastic manner, "how do you measure the height of a dished piston?". Inaccurate, in that dished pistons do have "heights", however, he was referring to the void in them.

Actually, it was a fair question, if only it had been asked sincerely, relating to how one calculates the compression ratio of any engine with them.

I responded by saying there were two ways and asked if he knew what they were?

Got no answer as usual.

(The third and most obvious way is RTFM, but I'm discounting that as it's not "calculate", and often one comes up against an engine or piston one does not have a FM for, that has been customised in some way, or was not even set up properly in the first place, ie is running at a lower than designed CR).

Keep reading the book, you'll get there in the end, or perhaps you won't.

... A response with as little real substance as ever.

Paul, you look great with that tail between your legs.

 

[Skylark]

Might be helpful to all to define compression ratio.

It's the total swept volume of the cylinder with piston at BDC divided by the compressed volume with the piston at TDC.

 

[RichardS]

Might be helpful to all to define compression ratio.

It's the total swept volume of the cylinder with piston at BDC divided by the compressed volume with the piston at TDC.

Except that that definition, or variations on it, have been quoted many times throughout this thread .... and it hasn't helped one iota.

Richard

 

[VicS]

Might be helpful to all to define compression ratio.

It's the total swept volume of the cylinder with piston at BDC divided by the compressed volume with the piston at TDC.

Its the total volme at BDC (ie the swept volume + the compressed volume), divided by the compressed volume

The mathematical formula was given early in the thread . IIRC by Roger

 

[RichardS]

"Shape" is a very poorly defined term but, to my mind, includes every part of their dimensions, from pin and crown heights, to ring positioning, to valve cut outs, etc ALL of which affect the compression ratio. That's partly why my position was such an easy slamdunk. So let's start from the offending claim,

By which, I presumed he meant the shape of the cylinder head combustion chamber (no one would be dumb enough to suggest the outside of the casting would).

Of course it's the "two hands clapping", the shape of the piston and combustion chamber (and deck height and position of first ring etc) combined, that determines the compression ratio. I've never suggested it's not.

Paul asked in his habitually inaccurate and sarcastic manner, "how do you measure the height of a dished piston?". Inaccurate, in that dished pistons do have "heights", however, he was referring to the void in them.

Actually, it was a fair question, if only it had been asked sincerely, relating to how one calculates the compression ratio of any engine with them.

I responded by saying there were two ways and asked if he knew what they were?

Got no answer as usual.

(The third and most obvious way is RTFM, but I'm discounting that as it's not "calculate", and often one comes up against an engine or piston one does not have a FM for, that has been customised in some way, or was not even set up properly in the first place, ie is running at a lower than designed CR).

... A response with as little real substance as ever.

Paul, you look great with that tail between your legs.

I'm sorry Convey, but you have a very selective memory.

The "offending claim" was entirely your nonsensical claim that "My only criticism of this video is that it shows the cylinderhead to have a hemispherical shape, which would reduce compression, when most diesels would have a flat top piston, meeting a flat cylinderhead, which would increase compression.

Every engineer on this forum has tried to explain to you why this claim is total nonsense.

You subsequently revised your original claim to "Piston shapes don't make the compression ratio but their shapes and their match determines the compressed volume and that determines the compression ratio".

We all agreed that your revised claim is correct.

Which claim are you championing now, your first or your second?

The whole world is watching.

Richard

 

[Beneteau381]

If I say it, you won't believe it because I am clearly exposing deficiencies in your great guru/Christ figure's wisdom ... so here's a very interesting link that discussion basically every way you are wrong in that statement.

If you need help understanding it, I am happy to go through it with you line by line.

Form, Fit & Function – Valvetrain Components Must Work in Harmony by Larry Carley, author of 12 automotive-related books, over 3,500 automotive diagnostic and repair articles, and developer of automotive training software.

The most pertinent comment in it to the sort of engines we might be dealing with here, is related to effects of deeply pocketed valves, either by age/wear, and/or having been recut in the past. That will also upset rocker angles within valvetrain geometry.

Of course, what I get the most from the so called "marine engineering" trade is that they'd prefer to sell you a complete, brand new engine at £5, 6, 7,000 instead of just fix some minor issue and remanufacture the old one ... because it's easier, there's more profit in it, and consumers are easily blinded by FUD.

Hence my question whether some individuals here were just fitters.

Now, good fitting is also a valuable skill, but it doesn't qualify you to refute what we are discussing here.

I was originally a time served fitter, an honorable skill which means that you can repair things by "fitting" them. Think scraping bearings, repairing worn components etc. It is NOT as some people think, a fitter of new parts which I think is what your condescending post implies! You are the one who I think isnt qualified to discuss the issue judging by your ill informed google quoting!

 

[penberth3]

Except that that definition, or variations on it, have been quoted many times throughout this thread .... and it hasn't helped one iota.

Richard

Several days ago I asked the engine expert to confirm the definition. Never had a reply.

 

[penberth3]

Might be helpful to all to define compression ratio.

It's the total swept volume of the cylinder with piston at BDC divided by the compressed volume with the piston at TDC.

VicS has it right a couple of posts down. Delete the word "swept".

 

[Skylark]

VicS has it right a couple of posts down. Delete the word "swept".

I’m happy to leave it unedited for the pedants to enthusiastically correct ?

I’m equally happy to acknowledge the error and that I should have known better. I did a 7 year apprenticeship ending with an honours degree and was chartered for more than 40 years prior to retirement. Even worse, I worked for 20 years as a component supplier to the engine builders within the automotive industry ?

Better to say sorry than to keep digging ?

Point is, CR is dimensionless and is based upon two volumetric parameters.

 

[penberth3]

I’m happy to leave it unedited for the pedants to enthusiastically correct ?…..

...….Point is, CR is dimensionless and is based upon two volumetric parameters.

Me being pedantic - never!

To be fair, for a typical diesel it doesn't make much difference to the figure.

 

[PaulRainbow]

"Shape" is a very poorly defined term but, to my mind, includes every part of their dimensions, from pin and crown heights, to ring positioning, to valve cut outs, etc ALL of which affect the compression ratio. That's partly why my position was such an easy slamdunk. So let's start from the offending claim,

The offending claim was all yours.

Paul asked in his habitually inaccurate and sarcastic manner, "how do you measure the height of a dished piston?". Inaccurate, in that dished pistons do have "heights", however, he was referring to the void in them.

Try and keep up. the "height" question was in response to some of your nonsense comments about deck height and squish. As usual, you didn't answer, strugging to find the answer on Google ?

How do you measure deck height with a dished piston ? Simple enough question.

Paul, you look great with that tail between your legs.

Dream on, i'm busy with work. You're the one that looks a total idiot here.

 

[jbweston]

This thread is like leaving a pub in the evening and passing two drunks at the bar arguing about the diet of voles, and then coming back in at opening time the next day to find they're still there arguing about the same subject.

The original question was what was the potential damage caused by running a diesel engine with the ignition (sic) off. The answer was 'None, unless you have a very old style setup'. Just saying.

 

[Graham376]

Now, good fitting is also a valuable skill, but it doesn't qualify you to refute what we are discussing here.

So you are correct and multiple experienced posters are wrong?

When a head is skimmed, a few thou are taken off it, the angle of the rocker arm in relationship to the valve doesn't change as the rocker shaft is still bolted to the head in the same position. Tappets are adjusted/slackened or shims reduced to allow for the difference in effective length of the push rods. Don't give a damn how much reading you do or obscure articles quoted, get out there and try it for yourself.