What is side clearance on a piston and how is it checked?
How can you tell the difference between a inlet and exhaust vavle and why?
What sort of tempatures do the inlet and exhaust valves get upto?
What temperatures and speeds must the piston be able to cope with?
Why do we have piston ring end gap clearance ?
What could the result be if the piston ring end gap is too small?
Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the cylinder head surface ?
What is meant by the terms S.I and C.I in a four stroke engine?
7/4/11 What is the purpose of the margin on the valve
The taper and ovality of the bore is the curvature of the bore and how worn the cylinder is from wear and tear. To check these you take dimensions of the bore. To do this you take dimensions across 'A' and 'B' of the bore. you repeat this 3 times at the top, middle and bottom of the bore. To check ovality subtract 'A' measurement form 'B'. To work out the taper of the bore subtract the measurements you took from the top of the bore from the ones you took from the bottom.
The side clearance on a piston is gap between the piston ring and the ring groove on the piston. To check this gap you need feeler gauge. Use the feeler gauge on a smaller dimension and slip it in between the groove and ring. Continue to try this with bigger gauges until you cant fit one in and record the size you fit last.
The difference between the exhaust and inlet valves are the size. The inlet valves are generally bigger. This is because when the inlet and exhaust valves are open together bad things could happen. The fresh mixture and air may enter through the inlet valve and simply exit through the exhaust valve. The cylinder will be unfilled and produces a gas called Carbon-monoxide (Co1). This is a very harmful gas and may be fatal to your health if dose is high enough. The piston crown is generally at normal operating temp of 300 Degrees but is brought down with use of coolant. An interesting note is that forced induction engines have a operating temp of 600 Degrees at the piston crown.
The ring end gap is very important for the operation of the piston. As with all metals the ring expands when it gets hot. So the gap left at the end of the ring is to allow for the expansion of the ring. If this gap wasn't left as the ring expands it would have no where to go and distort and buckle and may cause seizure of the piston.
We use a steel shim between the valve spring and aluminium head as aluminium is a soft metal. When under heat and higher tension the spring may cause galling on the head. The steel shim prevents this added wear on the head as it is a harder metal and the bigger surface area on the head spreads the pressure.
On a slightly different note we check the alignment of conrods today. I think the one below may be a little bend. But you would have to check to be sure. I think not.
this is good
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