Timing Question.

Hello John/Ont.
That was just a remark not a resentment on my part. If you have any questions about engines I will do my best to help you. My e-mail is open.... feel free to contact me off the board.
Guido.

Engine timing originates at the cranckshaft.

Guido.

I would agree that timing starts with the crankshaft since it's installed first in the block then you install the cam or other gears to match up with the crankshaft.

Either way as long as everything is in time it really doesn't matter where it starts. It's all predetermined by the mfg.

In a multiple cylinder engine - the only absolute and constant is the position of each piston individually relative to the valves, time of ignition or fuel delivery, etc. - not a general reference mark from either end of the crankshaft.

If you are teaching students that such a crank reference mark is the absolute - and they believe it -they will be lacking a few mental diagnostic tools.

Hello jdmaris.
The cranckshat positions the piston in the bore at the proper time/height before T.D.C.
Guido.

A few examples why that is not always true.

Take an engine that has the reference mark on the flywheel and/or front pulley/balancer reading TDC.
That is supposed to indicate that one of the cylinders is at top-dead-center. Now, suppose that cyinder has a broken rod. That mark is then in error- period. It it telling you the piston is at TDC and it is not.

Take an engine that has the front, or back of the crank snapped right off - and I've seen a few. Again, the marks mean nothing.

A mulitiple cylinder engine is basically many engines tied together with a common crankshaft (in most cases). When all is as it should be - yes - the crank has perfect throws and good reference marks - but not always. Each cylinder depends on the pistons relationship to the cylinder it sits in, the valves, etc.

Engine timing does not originate at the crankshaft- heck, firing order does not even originate at the crankshaft. Take a look at small block fords- 289-302-351W firing order is established by the cam- you can put a 351 cam in a 289, but you need to change the firing order (and I think one could say that firing order is the essence of timing!).
The crank doesn't even dictate rotation- camshaft does. Look at Marine BBChevies- or even the reverse grind cams that used to let you change direction of Corvair motors to stick them into VWs without having to flip the ring gear in the trans.

not really...in a 4cycle engine, how many times is the piston at TDC? How many times does it fire? When you refer to timing, I would imagine you are refering to ignition timing- and TDC may or may not be the firing point- could be exhaust stoke!

Only when all is correct with that crankshaft. At this point - I'm getting kind of lost as to exactly what you are claiming. Yes - the crank will determine piston placement respective of the cylinder it sits in - as long as the rod is hooked up - be it wrong or correct. If a rod is broken - no. If a rod or piston wrist pin is loose - no. If a piston is broken in half- no. The crank is not the standard reference for determining/verifying if each piston is where it ought to be as it relates to valve operation and igntion timing. Suppose you've got a multiple cylinder crankshaft with one throw for one cylinder out of wack? Then what? As I mentioned earlier, we had to fix a bunch of new Deere diesels that had exactly that problem. With those engines - the TDC Deere timing mark was wrong for one of the cylinders since it was reading from the flwheel bolted to the crank. We discovered the problem after pulling the head, mounting a dial indicator on each piston, one by one, and finding out not all were where they were supposed to be - when they were supposed to be (in relation to the valves and time of fuel injection) . Deere had a run of bad crankshafts in that case.

Your idea is reliant on a perfect crankshaft with every throw for every cylinder being exactly where it ought to be. That does not always happen. Your idea also - in most practical applications - also relies NOT on the crank - but reference marks stamped onto the front damper-pulley, or the flywheel which adds more room for error. If you want, I can list many examples of when and how it happens.

If you are teaching students with the attempt to teach problem-solving and diagnosis - timing goes beyond the idea of general crankshaft reference marks.

As I said before - several times. "Timing" is a vague reference that can mean many things. I certainly wasn't referring to just ignition timing, and Guido never clarified his very vague question. In fact - he never said anything about this being a four-stroke-cycle engine, a two-stroke-cycle engine, or something else.

If you are asking me how many TDCs occur in an Otto Cycle engine for every power stroke - that's a pretty easy one. You are throwing in a bunch of specific details that have noting to do with Guido's vague timing declaration.

We could talk all day about piston-travel timing, valve timing as it relates to the pistons, valve timing as it relates to the crank, fuel injection timing as it relates to injector opening pressure, ignition timing as it relates to piston position, etc. &c. But, that has not been the issue here.

This vague reference to "timing" sounds like basic text-book teaching without the discussion of reality in the engine world.

And - yeah -with Corvair engines - I stuck special cams in several to make them run backwards to run Volkswagen Beetles That doesn't have much to do with any of this.

Good Point!!

sure it does...timing- what is it? so little to do with the crank- so much to do with the cam!
A simple point- if the crank is the legs of the engine, the cam is the brain!

The word "timing" is useless if not put into specific context. An internal combustion engine requires the proper timing of many things.

If you don't buy gas in "time" the engine dies.

If your engine overheats and you don't turn it off in "time", you lose your engine.

If the engine blows to pieces, it might be "time" to buy a new one.

If a mechanic says your engine is not running correctly because it's out of "time" what does that mean? Not much without more specificity.

If you are an engine-design engineer and wish to convey proper valve timing - it has to be expressed in direct relation to something else.

If you wish to express ignition timing - you need to specify ignition where? - at the source or at the target. Not so important with spark-ignition travelling at the speed of light, but VERY important with compression-igntion with liquid fuel travelling slowly though injector lines or passages. Ignition timing also needs to be expressed in relation to what other part of the engine?

So, I ask . . . if to you - the crank is the "legs" of the engine, and the "cam" the brain - what is the piston?

Your "brain" idea has some big problems - especially since many engines don't have cams or valves.

This is getting a little silly. Maybe I ought to fire up my "brainless" chainsaw and go cut some wood. Amazing it runs at all without that central control center.

WHAT is the problem? Nearly all times refer to piston position - relative to Top Dead Centre (TDC)or sometimes easier to quote BDC (bottom dead centre. That has to be in the direction of normal running.

Timing simply refers to when an event occurs in relation to another. TDC is not the same crank position for both ways of rotation. Full stop.

So timing is relative to the piston position. Diesel injection is often measured as distance of piston before TDC when the injection cycle commences. It happens to be 2.26mm + or - not a lot before the piston is at top dead centre position on my little Peugeot.

Degree markings are simple men's working marks and are close enough for nearly all mechanical operations (provided they, the mechanics, can remember to turn the engine in the right direction!). Proper Engineers measure distances. They are the fellows who designed the engine and a few others who might just want to get it exactly 'as design'

RAB

I've been reading this thinking it's funny! It is getting deeper and deeper. I could see someone lighting up a "J" and saying "yeah man, that's deep!" The relationship between man and machine! "Far out!"
What does it all mean?

the whole topic starts to sound like a clip from the Seinfeld tv show

Hello Rob.
If timing is relative to piston "POSITION" isn't the crank (POSITIONING) the piston?
GUIDO.

Hello jose bagge.
The first step of timing an engine is to turn the CRANCKSHAFT to position the piston in the cylinder used for that particular engine.
Not all engines are timed to #1.
Firing order is not established by the cam, firing sequence is! The camshaft is timed to the CRANCKSHAFT to do that. Engine rotation is just that, engine rotation.
Guido.

Not if the rod is broken,not if the crank throw for that cylinder is out of wack, not if a wrist pin is loose, not if a piston is broken, etc., &c. The piston is an absolute and its connection to the crank is a variable.

Hello Guido

In reply to : Hello John/Ont.
That was just a remark not a resentment on my part. If you have any questions about engines I will do my best to help you. My e-mail is open.... feel free to contact me off the board.
Guido.

I will return the favour should you ever be in the same position

Thanks
John/Ont

Explain the difference between firing order and firing sequence?

Hello jose bagge
The camshaft firing sequence, fallows the cranckshat positioning of the cylinder on the firing/compression stroke. In order for the camshaft to open or close the valves on the cylinder ready for that event, it has to be TIMED to the CRANCKSHAFT.
Firing order is controlled by the cranckshaft which positions the cylynder in the firing positon.
Guido.