Timing Chain Rattle..
Posted: Sat Dec 19, 2015 3:16 pm
Noticed that my timing chain rattle is getting to be an issue on startup..and it will rattle for a while until it builds up oil pressure (I have a TR oil pump ) Went looking for advice on the net and found this interesting item. Mainly to do with the TR pumps with the hydraulic tensioner, which were popular in performance rebuilds , but it makes for interesting reading.
Mitsubishi 2.6 TR / TS
Timing Component & Oil Pump Assy
The Mitsubishi Magna 2.6 TR & TS models were fitted with a revised design of the timing and balance shaft chain assembly, in conjunction with an updated oil pump. This revision included a hydraulic tensioner unit for the balance shaft drive chain, and a ratchet mechanism incorporated to the oil pump/tensioner plunger. This ratchet mechanism was designed to maintain tension on the timing chain at initial start up, until oil pressure was sufficient to support the plunger under normal operating conditions.
Frequently these engines are being submitted for timing assembly replacement, due to severe timing noise being present. After all the timing components have been replaced, it is not uncommon for the vehicle to be back in the workshop again after only a short time in operation (normally between 3000 to 16,000 km’s) exhibiting the same timing assembly noise symptoms.
Investigations have revealed the root cause of this condition lies primarily with the amount of wear of the hole in the oil pump, which houses the timing chain tensioner plunger. The pump is constructed with alloy, whilst the tensioner plunger shaft is manufactured from steel.
The wear in the oil pump housing appears to be caused by a number of contributing factors. When the engine is new, the tensioner plunger sits almost completely into the oil pump housing, providing a large surface supporting area. As the timing component progressively wear under normal operating conditions, the tensioner plunger extends to remove timing chain slack, as it is designed to perform. This leads to less support (shorter surface contact area) between the oil pump hole and the tensioner plunger.
Now during cold start up (remembering the ratchet unit is holding the plunger at extension) when oil pressure support is minimal, the chain vibration places high lateral load on the tensioner plunger, and due to its’ extended state, wear of the alloy oil pump hole commences. Following repeated instances of this occurrence, the oil pump hole wears to a point where the tensioner plunger has too much lateral movement for the incorporated ratchet assembly to maintain its’ grip (the ratchet teeth are fairly fine). The tensioner plunger and ratchet mating teeth may then ride across the top of each other’s surface, wearing the mating teeth. The combination of the worn ratchet mating teeth and the worn oil pump tensioner housing, render the tensioning system ineffective.
As a result, the timing chain (operating in a loose state), whips off the camshaft sprocket and bounces along the straight chain guide. The chain in due course wears through this chain guide, resulting in the severe timing noise. In addition, extensive wear may be noted on the tensioner pad, and curved chain guide.
At this time when new timing components are fitted, it is imperative to check and replace the oil pump. **
If the oil pump is not replaced, and new timing components are fitted, it is common (as mention earlier) that the engine will operate correctly for a limited period of time. This is due to the fact that all the timing components are new again, and the tensioner plunger is set almost fully back into the oil pump housing, at a zone of the hole which does not have any significant wear. As the timing components begin to settle under operating conditions and the tensioner extends, it reaches the worn section of the oil pump hole, and the same timing component failure is experienced.
Subsequent replacement of the timing components (without replacing the oil pump) will result in failure at shorter intervals, as the wear in the oil pump housing becomes more extensive.
The options to repair the oil pump/timing assembly are limited, as the problem with the oil pump must be addressed. As the OEM oil pump for this application is quite expensive, many mechanics and engine reconditioners, are opting to retrofit the engine to the earlier model (TM,TN,TP) oil pump/timing assembly setup. This is achieved by purchasing timing kit number AMBTK3, along with a new TM-TP oil pump, part number AM4G54* (the price of the aftermarket AM4G54 oil pump is significantly lower than the OEM TR,TS series oil pump).
Mitsubishi 2.6 TR / TS
Timing Component & Oil Pump Assy
The Mitsubishi Magna 2.6 TR & TS models were fitted with a revised design of the timing and balance shaft chain assembly, in conjunction with an updated oil pump. This revision included a hydraulic tensioner unit for the balance shaft drive chain, and a ratchet mechanism incorporated to the oil pump/tensioner plunger. This ratchet mechanism was designed to maintain tension on the timing chain at initial start up, until oil pressure was sufficient to support the plunger under normal operating conditions.
Frequently these engines are being submitted for timing assembly replacement, due to severe timing noise being present. After all the timing components have been replaced, it is not uncommon for the vehicle to be back in the workshop again after only a short time in operation (normally between 3000 to 16,000 km’s) exhibiting the same timing assembly noise symptoms.
Investigations have revealed the root cause of this condition lies primarily with the amount of wear of the hole in the oil pump, which houses the timing chain tensioner plunger. The pump is constructed with alloy, whilst the tensioner plunger shaft is manufactured from steel.
The wear in the oil pump housing appears to be caused by a number of contributing factors. When the engine is new, the tensioner plunger sits almost completely into the oil pump housing, providing a large surface supporting area. As the timing component progressively wear under normal operating conditions, the tensioner plunger extends to remove timing chain slack, as it is designed to perform. This leads to less support (shorter surface contact area) between the oil pump hole and the tensioner plunger.
Now during cold start up (remembering the ratchet unit is holding the plunger at extension) when oil pressure support is minimal, the chain vibration places high lateral load on the tensioner plunger, and due to its’ extended state, wear of the alloy oil pump hole commences. Following repeated instances of this occurrence, the oil pump hole wears to a point where the tensioner plunger has too much lateral movement for the incorporated ratchet assembly to maintain its’ grip (the ratchet teeth are fairly fine). The tensioner plunger and ratchet mating teeth may then ride across the top of each other’s surface, wearing the mating teeth. The combination of the worn ratchet mating teeth and the worn oil pump tensioner housing, render the tensioning system ineffective.
As a result, the timing chain (operating in a loose state), whips off the camshaft sprocket and bounces along the straight chain guide. The chain in due course wears through this chain guide, resulting in the severe timing noise. In addition, extensive wear may be noted on the tensioner pad, and curved chain guide.
At this time when new timing components are fitted, it is imperative to check and replace the oil pump. **
If the oil pump is not replaced, and new timing components are fitted, it is common (as mention earlier) that the engine will operate correctly for a limited period of time. This is due to the fact that all the timing components are new again, and the tensioner plunger is set almost fully back into the oil pump housing, at a zone of the hole which does not have any significant wear. As the timing components begin to settle under operating conditions and the tensioner extends, it reaches the worn section of the oil pump hole, and the same timing component failure is experienced.
Subsequent replacement of the timing components (without replacing the oil pump) will result in failure at shorter intervals, as the wear in the oil pump housing becomes more extensive.
The options to repair the oil pump/timing assembly are limited, as the problem with the oil pump must be addressed. As the OEM oil pump for this application is quite expensive, many mechanics and engine reconditioners, are opting to retrofit the engine to the earlier model (TM,TN,TP) oil pump/timing assembly setup. This is achieved by purchasing timing kit number AMBTK3, along with a new TM-TP oil pump, part number AM4G54* (the price of the aftermarket AM4G54 oil pump is significantly lower than the OEM TR,TS series oil pump).