Running engine (diesel) with the ignition turned off

[PaulRainbow]

Valvetrain geometry, exhaust and carb manifold issues, engine mounting etc, eg the angles between the valves/rockers/pushrods/cams.

Please accept that given the variety of valvetrain designs, eg chain, belt, desmodromic etc I can't included every variable in every post but, yes, similar issues exist.

Possibly the biggest load of drivel you have typed in this thread, hard to be sure, you have typed so much utter garbage.

how the hell does skimming head change "the angles between the valves/rockers/pushrods/cams." and all of the other nonsense you just typed ?

 

[PaulRainbow]

By skimming a head you, in essence, lengthen the pushrods. The pushrods then tilt (or rotate) the rocker arms down (round) more on the valve tips, changing the position on which they push on the valves. If you're pushing on one side of the tip rather than the centre, the valve will then be pushing onto the other side of the valve seat, encouraging wear on the guides and seats (they'll start to cut into one side). In short, all the angles (geometry) change slightly requiring management in someway, eg using adjustable pushrods or shorter custom fixed pushrods, to match how ever much you took off the heads. In extremis, they might even start tapping on parts of the engine.

Wear on the guides will then lead to other problems.

It's all about clearances and tolerances. An engine and its components will be design to operate within a range of tolerances, even with self-adjusting hydraulic systems (they can only adjust so much). So a light skim to level a face or after a weld might remain within tolerances, but a heavy skim for the sake of performance will.

Of course, if your valves are chain or belt drive it's a different scenario.

Why not just unscrew the tappet adjuster a turn or two ?

This is just getting more and more ridiculous, which i didn't think possible.

 

[PaulRainbow]

Kinell, we thought Brent was deranged ?

 

[convey]

Why not just unscrew the tappet adjuster a turn or two ?

Because not all rocker arms have tappet adjusters and, again, you'll have limited ranges of adjustablility. Unless you are using something like elephant foot adjusters, you'll still (eventually) start to have problems with angles.

As I wrote, it's impossible to include every variable in every post.

As my comment was in response to one of your idiotic "deck height" and "squish" remarks, it's pretty obvious what i meant.

The problem isn't my accuracy, it's your lack of knowledge and understanding. What did people like you do before Google ?

Are you really unable to make a single post without lacing it with sarcasm and insults?

Only an aggressively condescending twat, trying to hide his own weaknesses would. There was no Google in the 1970s.


No, you are not being clear and specific enough at all, you are flailing around in the wind trying to cover yourself behind a barage of bluster.

BTW, have you conceded that piston shape, combustion chamber shape and deck height do actually combine together to determine the compression ratio yet?​

(I'll have to read back to find out what you are now claiming is 'idiot", can you remind me?)

 

[pvb]

Kinell, we though Brent was deranged ?

He only joined a month ago, but has since made over 400 posts, mainly contentious. So perhaps you should ask what his previous username was.

 

[black mercury]

By skimming a head you, in essence, lengthen the pushrods. The pushrods then tilt (or rotate) the rocker arms down (round) more on the valve tips, changing the position on which they push on the valves. If you're pushing on one side of the tip rather than the centre, the valve faces will then be pushing onto the other side of the valve seat, encouraging wear on the guides and seats (they'll start to cut into one side, pocket and not seal so well). In short, all the angles (geometry) change slightly requiring management in someway, eg using adjustable pushrods or shorter custom fixed pushrods, to match how ever much you took off the heads. In extremis, they might even start tapping on parts of the engine.

Wear on the guides and seats will then lead to other problems.

It's all about clearances and tolerances. An engine and its components will be design to operate within a range of tolerances, even with self-adjusting hydraulic systems (they can only adjust so much). So a light skim to level a face or after a weld might remain within tolerances, but a heavy skim for the sake of performance will.

Of course, if your valves are chain or belt drive such as with overhead cams, it's a different scenario.

When skimming a head you are taking material away measured in thou. You don't remove 1/4 of an inch.
Wouldn't matter to valve timing on modern overhead cam engines most now have floating pulleys, so valve timing isn't affected.

 

[RichardS]

Why not just unscrew the tappet adjuster a turn or two ?

This is just getting more and more ridiculous, which i didn't think possible.

Indeed. All the skimmed heads I have dealt with, as a means of removing distortion, have all been compensated for within the existing tappet adjuster. When the head has been seriously re-worked in order to increase compression ratio, I have seen the tappets run out of adjustment but the solution then is to fit shorter pushrods. I guess that the rocker supports could be shimmed higher if shorter pushrods were not available but I have no experience of such shimming.

Richard

 

[penberth3]

…..If there is anything you don't understand, ask a specific question and I will explain it to you...….

I don't think you've answered one of mine yet, unless I've missed the reply. I was interested to know about your engineering education.

 

[black mercury]

I don't think you've answered one of mine yet, unless I've missed the reply. I was interested to know about your engineering education.

Hasn't answered mine either. Maybe doing some research.

 

[convey]

how the hell does skimming head change "the angles between the valves/rockers/pushrods/cams." and all of the other nonsense you just typed ?

I just explained how.

What you are really saying is, "I've never heard this before" and exhibiting how you react to new information, in a primitive manner.

Go speak to an expert if you don't believe me. Take what I wrote and ask them if it makes sense (but what I wrote, not how you tried to distort it).

Perhaps the problem is that you've only ever worked on stock, low performance engines?

Have you conceded that piston nd combustion chamber shape and deck height all determine compression yet, and accept that the engine as illustrated would, therefore, be unlikely to work yet?​

​

I'm waiting for an answer to see if you have any humility and integrity at all.

I'll try for you so all you need to do is copy and paste.

OK, I admit it. I was wrong. Piston and combustion chamber shape and deck height are all factors determining compression ratio

 

[black mercury]

This is hillarious.
You simply adjust either the tappet, the pushrod, the rocker, or shims on the tappet to keep the valve clearances in spec after a head skim, or even replacing a head gasket without a skim. It will even be on the service schedule unless hydraulic tappets or rockers are used. That way all will be in spec.

 

[PaulRainbow]

He only joined a month ago, but has since made over 400 posts, mainly contentious. So perhaps you should ask what his previous username was.

I was thinking just that, one has to wonder, which previous poster (troll) this is.

 

[PaulRainbow]

I just explained how.

What you are really saying is, "I've never heard this before" and exhibiting how you react to new information, in a primitive manner.

Go speak to an expert if you don't believe me. Take what I wrote and ask them if it makes sense (but what I wrote, not how you tried to distort it).

Perhaps the problem is that you've only ever worked on stock, low performance engines?

Have you conceded that piston nd combustion chamber shape and deck height all determine compression yet, and accept that the engine as illustrated would, therefore, be unlikely to work yet?​

​

I'm waiting for an answer to see if you have any humility and integrity at all.

I'll try for you so all you need to do is copy and paste.

Never mind all f the drivel, answer the question (would be a first for you);

So, answer the question, where do you take the measurements for deck height and squish with a dished piston ?

 

[coopec]

I'm always wary of people posting for the first time and asking "I want to start up a business repairing outboards. Can anyone tell me what tools I need?" Others get their rocks off by posting a grainy photo of a yacht out on the horizon and asking if anyone can identify the builder/model. And still other first time posters ask " I want to get into yachting: what sort of yacht should I buy"?

Also I'm wary of responding to a person who is posting for a first time. (but of course we must make the effort to respond even if there is an element of doubt) But if they haven't responded to (say) the first three posts by way of thanks to respondents or asking further questions I figure they are probably trolling and we'll never hear from them again.

Has anyone looked at Convoy's previous posts to see if there is a theme to them?

We must not respond to these idiots because that gives them an adrenaline flush and that is what they want.

 

[RichardS]

I'll try for you so all you need to do is copy and paste.

OK, I admit it. I was wrong. Piston and combustion chamber shape and deck height are all factors determining compression ratio

I really don't understand where you're coming from Convey.

You've already explained that "piston shapes don't make the compression, but their shapes and their match determines the compressed volume, that determines the compression ratio" and we all agreed with that statement and thought that you'd finally got it,

You now seem be to saying more or less the same thing again. Why would we admit that we were wrong when we've already agreed with you that piston shapes don't make the compression, but their shapes and their match determines the compressed volume, that determines the compression ratio ..... or are you retracting that earlier statement?

Richard

 

[Beneteau381]

By skimming a head you, in essence, lengthen the pushrods. The pushrods then tilt (or rotate) the rocker arms down (round) more on the valve tips, changing the position on which they push on the valves. If you're pushing on one side of the tip rather than the centre, the valve faces will then be pushing onto the other side of the valve seat, encouraging wear on the guides and seats (they'll start to cut into one side, pocket and not seal so well). In short, all the angles (geometry) change slightly requiring management in someway, eg using adjustable pushrods or shorter custom fixed pushrods, to match how ever much you took off the heads. In extremis, they might even start tapping on parts of the engine.

Wear on the guides and seats will then lead to other problems.

It's all about clearances and tolerances. An engine and its components will be design to operate within a range of tolerances, even with self-adjusting hydraulic systems (they can only adjust so much). So a light skim to level a face or after a weld might remain within tolerances, but a heavy skim for the sake of performance will.

Of course, if your valves are chain or belt drive such as with overhead cams, it's a different scenario.

I would have thought that someone as clever as you would have known that an MD22 is OHC so no effect on "valve train"

 

[Graham376]

This is hillarious.
You simply adjust either the tappet, the pushrod, the rocker, or shims on the tappet to keep the valve clearances in spec after a head skim, or even replacing a head gasket without a skim. It will even be on the service schedule unless hydraulic tappets or rockers are used. That way all will be in spec.

Agreed, I've never heard such a load of rubbish. The rocker is in a fixed position relative to the head and valve. I served my apprenticeship in the motor trade when overheating, warped heads and skimming were regular events. Have lost count of the number of heads we had ported and skimmed when uprating performance on rally cars.

 

[coopec]

Here are Convey's other posts.

https://forums.ybw.com/index.php?search/88923/

 

[convey]

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 would have thought that someone as clever as you would have known that an MD22 is OHC so no effect on "valve train"

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*.


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?

This book is an essential textbook for all students of automotive engineering, particularly on IMI / C&G 4000 series and BTEC courses and provides all the underpinning knowledge required for NVQs to level 3. By bridging the gap between basic and more advanced treatments of the subject, it also acts as a useful source of information for experienced technicians and technically minded motorists, and will help them to improve their knowledge and skills.

This new edition has been brought fully up to date with modern practices and designs, whilst maintaining the information needed to deal with older vehicles.

 

[convey]

Agreed, I've never heard such a load of rubbish. The rocker is in a fixed position relative to the head and valve.

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.