automotive engines
*Short BlockShort block is an automotive term describing an engine sub-assembly.
A short block is the portion of the engine block below the head gasket but above the oil pan. An in-block cam engine will also include the camshaft and timing gear. The overhead cam style of engine will not include the aforementioned parts on the short block. A shortblock is usually purchased to upgrade the water jacket, piston size or bore. Assemblies typically include the crankshaft installed and balanced along with the main bearing.
Experiment
Tools Used
- 10mm and 14mm socket
- Feeler Gauges - For measuring clearances
- Valve spring compressor - To allow valves to be removed
- Straight Edge - For measuring how much springs are out of alignment
- Micometer - for measuring taper and ovalitiy
- Ball Gauge
- Square Edge
- Callipers
When examining the pistons and bores I was looking for different types of ware including scuffing and scoring. This is caused by the piston rubbing on the bore when the temperature rises until melting point then particles of metal begin to weld together causing scratching on the surface of the piston or on the surface of the bore. This can be caused by restrictions in the water jacket causing hot spots on the cylinder wall, Incorrect oil pressure, or the connecting rod being misaligned.
To repair this requires the piston rings being replaced if only minimal damage occurred. or the bore re-honed if there was more extensive damage. The engine I was working on did not require this as it was in good order
Pistons Measurement of Pistons
This was done with a micrometer by putting it around the piston skirt and the taking a reading from it. This is done to check if the piston has collapsed due to poor lubrication, Excessive RPM, or a defective piston.
Tested Pistons were all within manufactures specification and no further work was needed. If there was a collapsed piston problem can be rectified by replacing the piston.
Pistons in place in correct cylinders and facing
correct way with dots to front of enginePiston Rings
This was measured by removing the piston rings from all 4 pistons one at a time and then setting them in there bores and measuring the gap in the rings to check if they are the correct size for the bore. If there is no gap the ring will break causing scuffing to the cylinder bore or the rings will not seal properly causing loss of compression on compression stroke, or loss of gas pressure during power stroke. Effecting engine performance.
On the engine I checked there were some rings which were the incorrect size because the gap was to large and they would need replacing if the engine was going to work efficiently.
Camshaft Inspection and Measurements Taken
- Inlet and Exhaust cam lobes: Using a micrometer 5 cam lobes were measured in 2 places to obtain the lift of each lobe
- Shaft ware (out of round and taper): Also measured using the micrometer in 2 directions of the journals horizontally and vertically. journals had to be within 0.05mm
- Cam shaft run out - Using a Dial test indicator the amount of ware on the bearings was measured it had to be within 0.03mm according to manufactures specification
- Oil Clearance - Using a Plasti-gauge the small amount of clearance needed for the oil to move around was measured with the bolts torqued up to manufactures specification a result of 0.050mm was shown which was within specification of 0.035 - 0.081mm
Reason for Measuring Head
Measurements are required to make sure the head is in good order. If these measurments are out they can cause problems like;
- loss of power
- a blown head gasket
- valve seating faults
- A loss of compression
- Coolant leaks
These problems can be rectified by replacing warn parts or resurfacing excessively warn areas to correct specification.
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Short Block Re-assembly
ProcessLubricate all bearing caps to prevent excessive damage on first start up.
Place Crankshaft back into place on block and re-screw bolts to 50% of there torque specifications. With main end bearings in place make sure that correct main bearing caps are on correct bearing on crankshaft if not crankshaft will not rotate.
Re-attach water pump and oil pump make sure that alignment marks on oil pump gear and pump its self are aligned correctly with each other so that pump is working at correct time during operation.
Return each piston to there correct cylinders via labelling on con-rod so that pistons are fitting into the correct bore and compression isn't lost or further damage is caused to bore. Pistons will need taping into place while they are held closed by ring compression tool.
Tighten end caps of con-rods to correct torque specifications and check amount of oil clearance there is in between bearing cap and crankshaft end bearing, using plasti-gauge. Make sure alignment is correct and crankshaft still turns freely.
Bolt on sump to bottom of crankcase.______________________________________________________________________________
Valve timing
In a piston engine, the valve timing is the precise timing of the opening and closing of the valves.In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine operation by the relatively new technology of variable valve timing. It is also affected by the adjustment of the valve mechanism, and particularly by the tappet clearance. However, this variation is normally unwanted.
Importance of valve timing
Correct valve timing is very important because if it is wrong the engine power is greatly reduced as valves will be open at incorrect times or open too long or not long enough affecting the air fuel mixture, drawing mixture out at the wrong time leaving it unused affecting economy, allowing the mixture to burn to cold and taking power if exhaust gasses cannot be removed in time.
How it can be improved
if belt is out of alignment it can be re timed to improve valve operation and cams can also be aligned as well while belt is off. This will correct the timing.
ELECTRICAL COMPONENT SENSORS
