5.5 Demonstration Method
5.5.1 Demonstration Method 1
In demonstration method 1 the lecturer, in this case, demonstrated the whole procedure of setting valve timing, while at the same time explaining the instances in which this procedure might be made necessary in a real setting.
Lesson Based on Observation notes of a demonstration lesson in workshop on setting valve timing
Lesson: Valve Timing setting
Lecturer number: SCOT1 Date: 16 February 2016 This was the first demonstration of valve timing setting to class.
Lecturer has moved with the group of 16 students from the workshop into the demonstration workshop which houses two engines. The engine to be used is one that is partially cut away to show clutch assembly, cylinders, camshafts, prop shaft.
Lecturer [to technician]: Please open the tappet cover...bring allen key…number 14.
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The lecturer then turns the two cams at the top of the engine.
Lecturer: Here we have two camshafts. This one if for the exhaust…and this one is for inlet.
Today we are going to learn how to set the valve timing. [He shows the students the timing belt].
Many times when the timing belt is torn, the car will refuse to start.... what many drivers will do is keep starting the car many times hoping it will eventually start. What is happening when you do that from my experience, are the following:
The valves will bend...why? because the camshaft is not turning…when you crank you move the pistons and they hit against the valves which are not in synch. Remember the valves are moved by the camshaft, and the camshaft is moved by the timing belt...
If the valves have been fitted, you now need to set the valve timing.
First determine TDC [top dead centre]. How did we say we do that?... [all quiet] … which pistons should be at the top? ...this is a four-cylinder engine.
Trainee: 1 and 4.
Lecturer: Remember most engines rotate clockwise when you are standing at the front…where I am standing… this way [he demonstrates]. But some engines like the Honda engine rotate anticlockwise.
Lecturer shows them the clutch.
This is the clutch.
He shows them the pressure plate.
This is the pressure plate…... we will come to these later in our training…for now we just identify them.
Lecturer loosens and removes the timing belt.
Trainee: Why don’t we mark it first so that we know we know how it fitted?
Lecturer: Don’t worry… but you are wise…remember I said you would rather be a fool once, than be a fool for the rest of your life. He [referring to trainee] is correct…I want us to assume the timing belt is torn so we will fit with a new one…. But the new one will be this same one that I have just removed.
Now time the engine… let’s put theory into practice…
[Calls two students to come forward].
Bring piston 1 to TDC. Take that wire, and put it in the plug hole for piston 1…and you [referring to other second student] … turn the engine… to the left…now back a bit.
Trainee [holding wire]: We are at TDC.
Lecturer: Let me check [he checks the wire and turns the engine back and forth a bit] ...
yeah it’s at TDC…piston one is at the topmost position.
Now what I do is find this pointer [timing mark] or mark on the crankshaft pulley, and mark against the block where it is pointing using chalk…or tippex.
…But mechanics may grind off the pointer so that other mechanics won’t know what to do…
so that the owner may have to take it back to them [laughs]… in that case what I do…even if
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you have grinded off all the marks... I pick one point on the crankshaft pulley, mark it…then I mark the point it aligns with on the block like here, and here [marks].
Now what do you do? [No answer].
Why do you mark TDC on the crankshaft pulley?
So that you lower the pistons halfway and can now work on the camshaft.
[Trainee who had been holding wire now attempts to turn the camshaft with the hope that the pistons will lower].
No…. you see the valves hit against the pistons.
NOW WATCH ME AGAIN…
Lecturer puts wire into plug hole for piston 1, turns crankshaft pulley until piston 1 is at TDC.
He then marks the two aligning points on the pulley and on the block. He then relaxes the belt on the crankshaft pulley by pulling it backwards a bit, with the result that the timing mark on the pulley is no longer aligned. He then adjusts the camshafts and explains that the valves will not hit against the pistons as he lowered the pistons when he relaxed the belt on the crankshaft pulley. When he adjusts the camshafts, he says they should watch that when the exhaust just about closes, the inlet is opening bringing in the fuel mixture … that it is at induction. At this point, he explains, he has finished with the valves, and needs to now align the timing marks on the crankshaft pulley.
Lecturer: Bring number 13... [and he tightens tensioner].
[After this he now fits the timing belt and tensions it].
[He then explains that using this procedure there is no need to worry if there were timing marks on the pulley or on the timing belt].
Now the valve timing is correct…now we have done valve timing…. we will still have to learn ignition timing…once you have set valve timing, you have to set ignition timing for the car to be able to start.
So you see I want you to be knowledgeable mechanics…good mechanics…a bad mechanic will say he can’t do valve timing because the timing marks were scratched and he can’t see them…but a good mechanic needs no marks.
So you make your first set TDC, then you mark the timing making sure the mark on the crankshaft pulley is aligned with the mark you make on the block …. you then turn the pulley…you actually turn it 90 degrees backwards to lower the pistons…so that the valves don’t hit the pistons when you adjust the valves from camshafts...and as the exhaust opens ...the inlet opens…now you align crankshaft pulley marks into position…you insert timing belt...you tension.
He asks one trainee to do the valve timing, and he watches like the others.
Lecturer [as trainee finally tensions timing belt]: Now fasten…not too tight...this is a demo engine…we do not want to destroy it.
[Lecturer checks belts, alignment of timing marks].
Not bad for a beginner.
One trainee: And out of 10?
Lecturer: One [all laugh]
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Lecturer then asks each trainee to set the valve timing in turn, making sure the timing belt is first removed before each trainee begins.
This lesson supported the desired outcomes as follows:
Table 5.21 Vocational outcomes from Lucas et al, (2012) framework identified in lesson on setting valve timing
Vocational outcome Yes No Example
Routine expertise X
setting piston 1 at TDC; marking point in pulley and block, adjusting
camshaft, fitting timing belt
Resourcefulness X ‘tricks of the trade’ on how to set valve timing when marks are removed
Functional literacies X N/A
Craftsmanship X N/A
Business-like attitudes X N/A
Wider skills for growth X N/A
To achieve the primary outcome of routine expertise on setting a valve timing, the lecturer relied on these methods:
Table 5.22 Methods from Lucas et al. (2012) that lecturer used during lesson on setting valve timing
Method Example
Learning by watching watching lecturer determine TDC, set timing mark, adjust camshaft and set valve timing
Learning by imitating student set valve timing
Practice (trial and error) student tightening timing belt too hard Learning through simulation setting valve timing on model engine
The pedagogic decisions that the lecturer made in conducting this lesson show the following:
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Table 5.23 Analysis of lesson on setting valve timing using Lucas et al.’s (2012) ten-point decision making tool
Element of pedagogy Choice Example
Role of teacher facilitative didactic Teacher demonstrates and learners then do task
Nature of activities authentic contrived Real engine
Means of knowing practice theory Setting valve timing on real engine Attitude to knowledge questioning certain Learning procedure, still to develop
precision Organization of time extended bell-bound No time set
Organization of space workshop classroom Engine in laboratory Approach to tasks group individual Learners to work in turns
Visibility of processes high hidden Actual engine, actual pistons and valves
Proximity of teacher virtual face to face Teacher on ground Role of the learner self-
managing directed Learner follows procedure shown The setting of the valve timing was simulated using a model engine in the workshop and the lecturer selected a demonstration through which learners watched him demonstrate, before they imitated him individually, using practice and learning through simulation.
The lecturer had to rely on his own resourcefulness to enable the learners to relate the simulated demonstration to reality. The snapping of a timing belt could result in a series of other mechanical problems which could be worsened by the actions and ignorance of the driver. Yet the lesson was not only about setting the valve timing; the explanation given by the lecturer aimed to create a broader context that included a setting where this procedure would be carried out. A torn timing belt is only a part of a large chain of events in the operation of a larger system. This is illustrated in Figure 1.
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The students were then required to each repeat the procedure for setting the valve timing, with each of them removing the timing belt at the end of the session while being observed.
They were repeating a procedure that had been demonstrated; for observant learners – in particular those whose turn came later – this created opportunities for greater learning by watching the procedure repeated by peers.