Ford Mondeo Diesel Cylinder Head
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Here's another one of those interesting things you get to see from time to time.
The vehicle is a 1993 Ford Mondeo 1.8 Diesel and as you can see from the first photograph the crown of number 2 cylinder exhaust valve has broken off. The damage which can be seen to the inlet valve and piston in the next photo is secondary damage caused by the crown being carried around the cylinder by the fast moving piston.
The level of damaged caused to this engine rendered it a non-economical repair. The car was 12 years old and had excessive mileage and after the workshop checked the normal suppliers of used engines it was clear the repair job would not be economical and the vehicle was scrapped.
The most annoying factor for me is the advice given to the owner of this vehicle by one of the major roadside assistance organisations. The patrolman informed the owner that because the engine failure had occurred at idle speed there would be little or no damage and repair would be relatively cheap. How it is possible to jump to such a conclusion is beyond me especially considering the history of the Ford 1.8 diesel engine. The correct procedure would be to remove the cylinder head and assess the damage. Until humans are equipped with x-ray vision there's no way of making an accurate assessment until the engine has been partly stripped down.
There's a number of causes for this type of event and I'll list the more common ones below:
Metal Fatigue
The valve stem had a structural weakness introduced during manufacture or developed naturally over time which significantly weakened the valve at the point it failed.
Previous Unrepaired Damage
Previous damage had been caused to the valve by a timing belt failure or incorrect valve timing and this damage was not repaired. Over time the valve weakened due to this damage and failed.
Incorrect Injection Pump Timing
Injection pump timing is critical and if it is incorrectly set detonation or pre-ignition can occur in the combustion chamber causing excessive cylinder temperatures and shock waves which over time will weaken the valves.
Injector Leakage
A leaking injector causes excessive fuel to enter the combustion chamber out of phase to the stroke of the engine. This excessive fuel raises the cylinder temperature and can cause unburned fuel to enter the exhaust port where it is then ignited by the hot exhaust gases which will cause a localised hot spot on the valve stem.
Broken Valve Guide or Valve Seat
A broken valve guide or seat will become trapped between the valve and valve seat preventing it from closing properly. Because of the close tolerances between piston and valves in a diesel engine the rising piston will contact the trapped open valve and will cause the valve crown to bend in relation to its stem. This further prevents the valve from closing properly and will cause a valve stem failure.
Leaking Valve Stem Oil Seal or Worn Valve Guide
If the valve stem oil seal is excessively worn oil will travel down the valve stem and will be ignited by the hot exhaust gas. This burnt oil will carbonise and will continue to glow causing a hot spot on the valve stem. A similar situation can occur when wear occurs to the valve guide which will increase the oil flow down the valve stem. A worn valve guide will also cause lateral movement in the stem when it is opening and closing increasing wear to the valve stem oil seal.
Seized Hydraulic Cam Follower
If the cam follower is seized or otherwise fails to operate correctly the valve clearance will be affected and this may result in the valve being open when the piston is at top dead centre causing piston to valve contact.
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Keywords:
Auto | Autos | Automobile | Automobiles | Automotive | Car | Cars | Combustion | Cylinder | Damage | Diesel | Diesel Injection | Economical Repair | Engine | Engine Damage | Ford | Injection Pump | Injection Pump Timing | Maintenance | Metal Fatigue | Mondeo | Repair | Repairs | Used Engines | Valve | Valves | Vehicle | Vehicles | Cylinder Head
The vehicle is a 1993 Ford Mondeo 1.8 Diesel and as you can see from the first photograph the crown of number 2 cylinder exhaust valve has broken off. The damage which can be seen to the inlet valve and piston in the next photo is secondary damage caused by the crown being carried around the cylinder by the fast moving piston.
The level of damaged caused to this engine rendered it a non-economical repair. The car was 12 years old and had excessive mileage and after the workshop checked the normal suppliers of used engines it was clear the repair job would not be economical and the vehicle was scrapped.
The most annoying factor for me is the advice given to the owner of this vehicle by one of the major roadside assistance organisations. The patrolman informed the owner that because the engine failure had occurred at idle speed there would be little or no damage and repair would be relatively cheap. How it is possible to jump to such a conclusion is beyond me especially considering the history of the Ford 1.8 diesel engine. The correct procedure would be to remove the cylinder head and assess the damage. Until humans are equipped with x-ray vision there's no way of making an accurate assessment until the engine has been partly stripped down.
There's a number of causes for this type of event and I'll list the more common ones below:
Metal Fatigue
The valve stem had a structural weakness introduced during manufacture or developed naturally over time which significantly weakened the valve at the point it failed.
Previous Unrepaired Damage
Previous damage had been caused to the valve by a timing belt failure or incorrect valve timing and this damage was not repaired. Over time the valve weakened due to this damage and failed.
Incorrect Injection Pump Timing
Injection pump timing is critical and if it is incorrectly set detonation or pre-ignition can occur in the combustion chamber causing excessive cylinder temperatures and shock waves which over time will weaken the valves.
Injector Leakage
A leaking injector causes excessive fuel to enter the combustion chamber out of phase to the stroke of the engine. This excessive fuel raises the cylinder temperature and can cause unburned fuel to enter the exhaust port where it is then ignited by the hot exhaust gases which will cause a localised hot spot on the valve stem.
Broken Valve Guide or Valve Seat
A broken valve guide or seat will become trapped between the valve and valve seat preventing it from closing properly. Because of the close tolerances between piston and valves in a diesel engine the rising piston will contact the trapped open valve and will cause the valve crown to bend in relation to its stem. This further prevents the valve from closing properly and will cause a valve stem failure.
Leaking Valve Stem Oil Seal or Worn Valve Guide
If the valve stem oil seal is excessively worn oil will travel down the valve stem and will be ignited by the hot exhaust gas. This burnt oil will carbonise and will continue to glow causing a hot spot on the valve stem. A similar situation can occur when wear occurs to the valve guide which will increase the oil flow down the valve stem. A worn valve guide will also cause lateral movement in the stem when it is opening and closing increasing wear to the valve stem oil seal.
Seized Hydraulic Cam Follower
If the cam follower is seized or otherwise fails to operate correctly the valve clearance will be affected and this may result in the valve being open when the piston is at top dead centre causing piston to valve contact.
Get an Online Motor Warranty Quote instantly with Warranty Direct - Unbeatable cover at a price you can afford.
Discovering how much it will cost to protect your car against unforeseen mechanical failure couldn't be simpler.
Warranty Direct not only sells the warranty but handles the claim as well - for a better warranty buy from Warranty Direct!
Keywords:
Auto | Autos | Automobile | Automobiles | Automotive | Car | Cars | Combustion | Cylinder | Damage | Diesel | Diesel Injection | Economical Repair | Engine | Engine Damage | Ford | Injection Pump | Injection Pump Timing | Maintenance | Metal Fatigue | Mondeo | Repair | Repairs | Used Engines | Valve | Valves | Vehicle | Vehicles | Cylinder Head
posted by Jon Fry at 3:21:00 PM
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