scottie
Well-known member
And if you grind the valves ?
Running engine (diesel) with the ignition turned off
- Thread starter Robert Wilson
- Start date
- Status
PaulRainbow
Well-known member
RichardS
N/A
The questions in #157 and even #171 are both awaiting your attention. What are you waiting for?
Richard
179580
Active member
Of course deck height or bumping clearace not only is the CR a consideration but also linear expansion and Young's modulus is also compensated for.
rogerthebodger
Well-known member
PaulRainbow
Well-known member
Now you are just taking your drivel to new and even more ridiculous level, grow up.
Neither deck height or squish are adjusted to change compression ratio, they have to be what they have to be and if they materially affected compression ratio the ratio would be adjusted after setting deck height and squish. But neither of these are likely to need modification on a typical boat engine, i'll remind you again, this is PBO. As for Youngs modulus, that's hardly likely to be a consideration here either, same with linear expansion. You're just waffling and bullshitting now, we're not race tuning engines, it's a sailing forum, if you want to get into race tuning willy waving to to a race tuning forum.
PaulRainbow
Well-known member
rogerthebodger
Well-known member
Roger, i wish i could give this post more than one like
Paul are we agreeing on this. I must go any lie down. No just joking.
When I first read Tamarside's post I just shook my head in disbelief.
black mercury
Active member
Perhaps on an engine running on nitrous or running at a far higher rpm than standard.
Ideally an engine piston should be level or slightly above the level of the block at TDC for efficiency and emissions. You really don't want the cool cylinder walls to be in contact with the combustion process.
RichardS
N/A
Good grief Tamarside ..... wheat and chaff? Seriously?
Now I understand why the simple questions in #157 and #171 are my garlic to your vampire.
Richard
scottie
Well-known member
But what effect does it have on compression ratios?Technically known as lapping, best not done with the engine running
rogerthebodger
Well-known member
Unless you recut or have inserts in the valve seat the effect on CR will be very small.
Its when you start reshaping, polishing and balancing the combustion chamber or fit larger valves you start having an effect on the CR.
Stemar
Well-known member
A
If the valves are leaking, it could make a BIG difference to the compression
I'd love to see someone try...Technically known as lapping, best not done with the engine running
Which reminds me of an old joke. Several mature students are studying to become mechanics. For the final exam, they had to rebuild an engine and one was awarded 200%. When he asked the examiner why, he replied, "It worked perfectly afterwards and everything was in tolerance. That was worth 100%, but doing the whole job through the exhaust manifold? That's why I gave the other 100%. What did you do before?" "I was a gynaecologist"
RichardS
N/A
Although it will have no effect on the compression ratio whatsoever.Apedantshitstirrer writes ...
If the valves are leaking, it could make a BIG difference to the compression
Richard
179580
Active member
Thanks for your offer, maybe the same as you will help me with the understanding you perceive.What are you smoking
rogerthebodger
Well-known member
Where I live we can smoke weed and we can have it on us for our own use legally
I don't and have never partaken in any illegal drugs even at university in the late 1960's
If you wish to pop over I can easy arrange at the shop around the corner for you you to get some to bring some sense to your thinking.
convey
N/A
Again, you are spouting utter crap and fudging or distorting what has said to try save some face. Literally the opposite of the truth.
What stuns me is that you don't even seem to realise it, digging your heels in at the limits of your knowledge and comprehension.
Are you really just a fitter, rather than an engineer or even a mechanic?
Your comment, "have to be what they have to be" seems to betray this. As in, you're at the bottom end of just being a slave to the manual, rather than designing the engine, and writing the manual. It's a typical mindset.
You write
You're trying to change the discussion to common practise in maintenance.
What I wrote was "determines".
Again, here, you write
But what I was talking about, were the factors that determine the volume of the combustion chamber at TDC.
Shims, aka decompression plates, are widely used to adjust compression ratios, eg a typical example would be when fitting a turbo chargers. Coincidentally, I have a parts book for a 1970s Volvo Penta diesel right next to me at this moment. Hardly modern or "high tech". It lists several sizes of shims. Strictly speaking they are bodge but that wasn't up for dispute.
You also don't appear to know what race tuning is all about. It's not about "performance". Performance is just a by product of increasing efficiency, maximising combustion, controling the atomising of fuel & mix etc, which are all applicable and beneficial for every day use in many ways, from ease of starting, to fuel economy, to reducing carbon depositing, air pollution etc.
And, indeed, are transfered to every day use.
Fair enough, marine engines are not in a high state of tune as they tend to be low rpm units but that does not deny the principles. Nor the benefits of setting them up well.
convey
N/A
Correct, not at all. It would only have an affect if you had a differently shaped cylnder head, eg a hemi-, a D-shapes or wedge, where you would be reducing the size of the combustion chamber.
The shapes will determine the compression ratio, and what determines the compression ratio.
It also doesn't change the CR very much, and can leading to other issues to resolve, eg relating to the valvetrain geometry and so on.
Last edited:
convey
N/A
Now to go back to where the conversation and your looping out started.
In the non-technical animation, the engine has an approximately hemi-spherical combustion chamber, matched to a dished piston. I criticised it and you kneejerked.
The bottomline is, such a design is highly unlikely to be able produce sufficient compression for a diesel engine. As I wrote and stand by, with diesel engines, the face of the cylinder head is usually flat and the combustion chamber controlled BY THE SHAPE (dimensions etc) of the piston.
I presume you're reading the stuff about deck height and squish at the perimeter off a website ... because it's also crap. Deck height and squish are measurements right across the piston and wherever the face of the head exists.
The problem is this discussion is that you really don't know or can't admit the limitations of your knowledge. And it's going beyond them.
What you're doing is describing stuff beyond the limitations of your knowledge as "wrong", and trying to dumb it down or pull it back to where you know.
Remember, what you wrote was
Whether you can comprehend it or not, what this discussion has proven is the opposite. If you don't trust me, please go and speak to a piston manufacturer or cylinder head expert that you respect and ask them.
Then come back here and tell us what they say.
FWIW ... a flat top is, in essence, the ideal shape for performance, but that's a whole other discussion that I suspect is equally beyond your ken.
Using a piston where the top compression ring is closer to the crown of the piston will also increase the compression ratio by about .5.
In the non-technical animation, the engine has an approximately hemi-spherical combustion chamber, matched to a dished piston. I criticised it and you kneejerked.
The bottomline is, such a design is highly unlikely to be able produce sufficient compression for a diesel engine. As I wrote and stand by, with diesel engines, the face of the cylinder head is usually flat and the combustion chamber controlled BY THE SHAPE (dimensions etc) of the piston.
I presume you're reading the stuff about deck height and squish at the perimeter off a website ... because it's also crap. Deck height and squish are measurements right across the piston and wherever the face of the head exists.
The problem is this discussion is that you really don't know or can't admit the limitations of your knowledge. And it's going beyond them.
What you're doing is describing stuff beyond the limitations of your knowledge as "wrong", and trying to dumb it down or pull it back to where you know.
Remember, what you wrote was
When in fact,
Whether you can comprehend it or not, what this discussion has proven is the opposite. If you don't trust me, please go and speak to a piston manufacturer or cylinder head expert that you respect and ask them.
Then come back here and tell us what they say.
FWIW ... a flat top is, in essence, the ideal shape for performance, but that's a whole other discussion that I suspect is equally beyond your ken.
Using a piston where the top compression ring is closer to the crown of the piston will also increase the compression ratio by about .5.
Last edited:
PaulRainbow
Well-known member
You critisied it because you don't know what you're talking about, you wrote drivel.
Given the illustrations of hundreds of diesel pistons, shaped similar and in some cases identical to the one in the illustration, it's hard to believe you are still trotting this nonsense out.
Seriously ? How do you measure the height of a dished piston ?
Oh, i don't need to read about it off of a website, i leave website quotes to you and your fellow troll.
The level of stupidity now exceeds my willingness to post threshold, i can't even be bothered to read most of the latest, inane drivel.
- Status