cooling

This lesson was a bit short, but sweet.
We learnt what we needed to in the short time given.

We were told that anti-freeze/coolant is there to prevent the water inside the engine from freezing up.
In colder countries water freezes inside the engine and when water freezes it expands cracking the block.


Coolant is used because it does not freeze (hence the other name anti-freeze) that is why it is used in engines cooling systems, aswell as the fact that coolant also helps prevent corrosion in the water jackets and cooling system of the engine.


 
The vehicles radiator system is mainly operated by pressure to help the engine tempurature stay at the best operating tempurature of 108 Degrees Celcius.
The fact that the coolant/water or whichever you have in the radiator is under pressure, it wont evaporate because the "would have been" steam has nowhere to go other than the inside of the radiator.

Cylinder head disassembly.

After my play around with the engine short block, i moved onto the the cylinder head after my partner was done with it.


here, i started by removing the valves (both inlet and exhaust) to prep for measuring. i did this by using the valve spring compressor tool.
i whipped out the valves and measured its margin thickness, valve seat, valve guides etc.
for this i used a micrometer.


after measuring the valves (time consuming *sigh*) i unbolted the camshaft caps and whipped out the camshafts.


i took a micrometer and measured the cam lobes to see if they all lined with even measurements, aswell as other measurments.

later i checked the surface of the cylinder head for any warpage. to find out if there was, i used a steel straight edge and feelergauges to see if there was any spaces for the feelers to get through, if so there was warpage, if not then there was no warpage but in my case, there was none.

 

one of the last things i checked on the head was the torques on the cam journals.
i got some of this thread stuff called plasti-gauge, i put plasti-gauge in cam journals then place the camshaft back onto the head, place the caps back and torque down to spec.
unbolt the caps, remove the camshaft and take the squashed plasti-gauge and measure according to the key measurments on the plasti-gauge packet.


so that was the overall stuff that i had to do with the cylinder head and boy, did that measuring take its time.

robs questions 3

What is the firing order of a four stroke engine?
A:Intake, Compression, Ignition, Exhaust.

What is the difference between a S.I and C.I engine?
A:S.I is spark ignition and C.I is compression ignition.

Is there any difference between a S.I and C.I piston if so what?
A:S.I is used in petrol engines and C.I is used in Diesel engines.

What year was the diesel engine invented and by whom?
A:In 1893 the Diesel engine was invented by Rudolf Diesel.

What is the purpose of the oil jet on the connectng rod, and where does it spray?
A:The purpose of the oil jet is to spray on the walls of the cylinder bore as it travels from TDC to BDC to help lubricate and prevent ceasing Etc.

On the connecting rod where is the big end and little end?
A: Big end connecting to the crankshaft and Little end connecting to the piston.

What is the purpose of the thrust washers on the crankshaft?
A:The thrust washers stop the play of the conrods on the crankshaft, and the crank itself.

On a diesel engine whats the difference between direct injection and a indirect injection type?
A: Direct is injected directly into the combustion chamber while Indirect in injected into a Pre-combustion chamber before being ignited.

Explan the term valve timing?
A:Valve timming is the time a valve opens and closes during the four stroke cycles. Exhaust opening to let out exhaust gases, Inlet opening to let in the Air/fuel mixture and then both of them closing to keep the mixture in for compression.


Why do we have valve clearance?
A:Valve clearance is the gap between the camlobe and the top of the valve. You can damage your engine if you set your clearances too tight causing it to wear and after prolonged wearing it can stop the valves from seating properly.

What is the purpose of a glow plug on a diesel engine?
A:To heat up the combustion chamber to prepare for firing.

Whats the difference between an two stroke and four stroke petrol engine?
A: Two storke engines fire once every 2 cycles. There intake and combustion cycle happen at the same time and there exhaust and compression cycle happen at the same time allowing it to fire every 2 cycles.
The 4 stroke takes 4 cycles to fire once. Intake, compression, combustion and exhaust to fire once. the cycles happen individually.

Rob's Q's 2

What is taper and ovality in the bore, how is it caused how do you check it?
A:Ovality is the wear in the cylinder bore. The ovality is caused by the main friction of the piston's movement up and down the cylinder bore. Though it may seem the piston moves straight up and down, the pull from the conrod going back and forth by the motion of the crank causes the piston to do the same but since the piston follows up and down the bore, it moves up and down.


What is side clearance on a piston and how is it checked?
A:The side clearance is the distance between the piston and the cylinder wall. The piston rings are used to close the gap when under pressure to help contain the compression in the cylinder. To check the side clearance on the piston, place the ring into the piston and use a feeler gauge to measure the clearance in between. 


How can you tell the difference between a inlet and exhaust valve and why?
A:The inlet valve is bigger, it lets in plenty of Air/fuel mixture. The exhaust valve is smaller, it lets out the exhaust gases, not a higher priority.

What sort of tempatures do the inlet and exhaust valves get up to?
A:the inlet valves can get up to round 250 degrees celsius and the exhaust valves can get up to around 750 degrees celsius.

What temperatures and speeds must the piston be able to cope with?
A:Most pistons handle temperatures up to 300 degrees celsius and handle speeds up to 7500rpm which is the common "redline" for most vehicles.
Why do we have piston ring end gap clearance?
A:To allow the ring to expand when pressure gets underneath it to increase the strength of the seal.

What could the result be if the piston ring end gap is too small?
A:Not much pressure would be able to get underneath it and make an adequate seal.

Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the cylinder head surface ?
A:To prevent damage to the head as the head is made by a softer/lighter alloy and after time the spring loses tension, the shim would also bring it back to normal.


What is meant by the terms S.I and C.I in a four stroke engine?
A: SI means spark ignition and CI means Compression ignition



What is the purpose of the margin on the valve?
A:The valve margin is the width of the edge of the valve head between the top of the valve and the edge of the face. It is used to disipate heat. (exhaust valve has a thicker margin as it undertakes more heat than the intake) A too thin a margin results in preignition from a bad seal and the valve being damaged through over-heating.


What is the purpose of a core plug?
A:To prevent the engine block from cracking when the weather is cold enough to freeze the water in the block's water jacket solid. The plugs pop out when the water turns onto ice and expands.

What is end float and run out on a crankshaft, hows is measured?
A:The end float is the allowed play in the crankshaft and the runout is the ovality in the crank journals. These are measured with a DTI gauge.