Valve Timing

This was done using lawn mower engines. Which allowed you to see when the valves were opening and closing in time with the position of the piston in the cylinder. 

This is read by using a degree wheel which is attached to the crankshaft of the engine. The amount of valve movement is also measured by a dial test indicator.

Results

Inlet opening: 14 degrees before TDC

Inlet Closing: 60 degrees after BDC

Exhaust Opening: 38 degrees before BDC

Exhaust Closing: 18 degrees after TDC

these results were obtained by taking readings off the degree wheel and watching for when the valves begin to open and close 

Piston Travel 

This was also measured using a vernier calliper to measure how far the piston has travelled at various degrees of crankshaft rotation this is also read from the degree wheel attached to the crankshaft.

These results showed that the amount of distance the piston travels increases at each degree of rotation more so when the piston is heading towards BDC as the mm measurements increase as the degrees go up. 

The first measurement at TDC shows 0mm but by the time the piston has reached the bottom of its stroke it has travelled 46.5mm. 

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.   

Head Re-Assembly

Process

1. Refit Valves into seats:This is done using the valve spring compressor when valves are put back in place reinsert springs. Then caps with spring compressed by compressor. refit valve stem seals and shims by holding them in place with grease. release tension slowly. The spring should then return into place and be held in by shims
2. refit valve caps make sure sliding surface of each is lubricated with clean oil.
3. Oil cam shaft bearing surfaces and set cams (Intake and exhaust) in place. With surfaces oiled place bearing caps back onto each bearing and torque to specification make sure the correct cap is on the correct bearing and correct cam. This can be identified on surface of cap, Will be numbered 1 to 5 with correct cam shaft letter either I or E, also direction it should be facing. This is identified by arrow pointing to front of engine. 
4. Bolt head back in place. Insure that bolts are tightened to correct torque of 78Nm (for these engines half was used 38Nm) Tighten each bolt in steps have to be tightened from center out in a clockwise motion. 



Order of bolt tightening on head






Head Bolted in place

5. Re-attach cam gears, Idler gears and belt to front of engine. Make sure each cam gear is on correct cam. Identified by labelling on gear. Attach Idlers, spring and belt. Spring is put in place first. Then the belt needs to be put in place and aligned correctly by tensioning it using cam gears starting from the exhaust side. Belt is put around exhaust cam gear and on inside of idler, then around driving gear that comes off crankshaft, then inside of the intake cam idler, then finally around Intake cam gear.
6. Bolt cam cover in place. Then bolt on last two pulleys then engine will be fully assembled.

       

Fully assembled B5. Shows path of cam belt and correct alignment of gears

Cylinder Head Measuring

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

Head dis-assembled

Valve Inspection and Measurements Taken

• Surface Warpage: Using straight edge across surface of cylinder head I was looking for any bends in its surface measurements were taken in 6 different places across surface with feeler gauge checking gap between surface and straight edge. Maximum warp allowed was 0.15mm
• Valve Stem Measurement: Once valves were removed from head using spring compression tool to close up spring so pin could be removed. Measurements were taken at 3 different areas of valve stem (top, middle and bottom) with micrometer to measure diameter of stem of both intake and exhaust valves.
• Valve Guide Margin: Using feeler gauge width of valve guide was measured according to width of it had to be 0.5mm at most.
• Valve Guide Clearance: Using the ball gauge to measure how much room there is in the valve guide once measurement was taken a micrometer was used to measure the reading from the ball gauge
• Valve Spring Squareness: Measurement was taken to find out how much the springs were out of alignment using a square edge and vernier callipers this can be found out by the amount of space there is in between vertical edge of the square is measured in 2 places and answer is made by minusing the 2 measurements from each other.
• Valve Spring Free length: Measured using Callipers to find length of spring
• Valve Spring Installed Height: Using Callipers again valve is measured in place in head 

Cams and Valves

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

Cam Shaft on blocks so that run out can be measured

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.   

Short Block Re-assembly

Process

1. Lubricate all bearing caps to prevent excessive damage on first start up. 
2. 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.
3. 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. 
4. 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.
5. 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.
6. Bolt on sump to bottom of crankcase.

Crankshaft In place and torqued to correct pressure
 and correct caps on correct bearing

Pistons in place in correct cylinders and facing
correct way with dots to front of engine

Crankshaft and Connecting Rods

Connecting Rod Inspection


This Inspection was done to check if con-rods had any bends or twists. If they were bent or twisted this would cause damage to the cylinder bore causing scoring of the pistons or the cylinders themselves as I explained in a earlier post.

This was done using a connecting rod aligner and a feeler gauge. Connecting Rod was aligned using this so that accurate angles of bend or the amount of twist can be measured with the feeler gauge.

the tested con-rods did have some bend and twist in them The worst one had a Bend of 0.70mm and a twist of 0.63mm. This can be rectified using a hydraulic rod straitening press to bend rods to the correct alignment.

Crankshaft Inspection 

Measurements Taken:

• Bearing Journals
• Main Journals
• Big end Journals
• Crankshaft Deflection

What I was looking for

The main inspection is done on the crankshaft journals using a micrometer to check for the amount of taper and out-of-round. 

Out-of-round is caused during cold starting because there is little or no lubrication in these areas when the engine is first started and if the engine is revved excessively extra ware occurs. 

Tapered ware is caused by the piston con-rods being misaligned causing the bearings to not ware uniformly this also causes ware on piston skirts in turn wearing out the cylinder bore.

This done using the micrometer to check how much the bearing has worn down in 2 areas of the bearing which are horizontally and vertically this measurement should be no more than 0.05 mm away from the manufacturers specification. 

     

Short Block Dis-assembly

Today I began work on the automotive engines unit the first thing I did was begin work on the short block.

Engine that was dismantled a mazda B6 from a 323

Measurement and Inspection of Pistons and Bore


Tools Used

• 12mm and 14mm socket and driver
• spanners
• Feeler Gauges
• Micrometer
• Bore Gauge
• Dial Test Indicator Gauge

Inspection:The inspection I did was of the pistons and bore to see if there was any damage to them. 

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.

Dismantled Block

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. 

Piston 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.  


Bore


The cylinder bore was measured using a bore gauge set to 78mm. To measure the diameter of the bore for each cylinder for ware of the surface of the bore caused by the piston rings rubbing on the surface when dirt has been inducted into the combustion chamber, from the air filter. Causes loss of compression and power. Can be repaired by re-honing the bore. Tested engine bore was in good condition with no serious damage occurring.