2000StreetRod
Moderator Emeritus
- Joined
- May 26, 2009
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- City, State
- Greenville, SC
- Year, Model & Trim Level
- 00 Sport FI, 03 Ltd V8
Background
The SOHC V6 timing chain related components can fail as early as 45,000 miles and as late as 250,000 miles depending on component improvements incorporated in the year of manufacture, vehicle maintenance, driving habits, and just luck. Various years and models of Explorers, Mountaineers, Rangers, Mustangs and Discovery III vehicles were produced with Ford's SOHC V6. Ford recognized a few years after the first 1997 SOHC V6 model was sold that there were problems with the durability of the original tensioners and guides. Various upgrades were incorporated between 1997 and 2002. The 3 leaf spring primary (crankshaft to jackshaft) timing chain tensioner was replaced with a larger base, 6 leaf spring unit. The wear resistance of the various guides was improved. The left guide assembly was reinforced with metal on the chain traction and slack sides. The right guide assembly was reinforced with metal on the chain slack side. The left and right spring/hydraulic tensioners were improved.
Failure of the primary timing chain tensioner or guide normally does not result in engine damage. It only affects camshaft timing relative to the crankshaft due to slack in the primary chain. However, if both the tensioner and guide are failed, it is possible that the chain could slip enough that the pistons and valves on both banks could collide.
Failure of the camshaft timing chain guide assembly can result in the chain slipping. When it slips, it frequently slips enough that the exhaust valves collide with the pistons on that bank as shown in the photo below by cjmedina.
It is difficult to identify by sound which timing chain related components have failed. The dreaded timing chain rattle echoes within the engine making isolation uncertain even when using a mechanic's stethoscope. Timing chain rattle can occur at engine start, at mid-range engine speeds, or may start and stop seemingly at random. The rattle could be due to weak or broken spring or hydraulic tensioners, broken or excessively worn plastic guides, worn chains or worn sprockets. Normally, the chains and sprockets are functional significantly longer than the tensioners and guides.
The only reliable method of determining the source of timing chain rattle is visual inspection. The upper sections of the left and right guide assemblies can be inspected after removal of the valve covers (requires removal of the upper intake manifold). The primary tensioner and guide and the lower section of the left guide assembly can be inspected after removal of the front timing cover.
Since the right guide assembly can only be replaced by removing the engine (or the transmission) I recommend checking it first. If broken, you may decide to replace (rather than repair) the engine. There's no point finding what else may be wrong if it's not going to be repaired. Next, the left valve cover should be removed and the left guide assembly inspected. If it's broken then the front timing cover will have to be removed to replace it. If it's not broken then the timing chain rattle is coming from under the timing cover. The original style primary tensioner frequently fails before the left guide assembly.
The SOHC V6 timing chain related components can fail as early as 45,000 miles and as late as 250,000 miles depending on component improvements incorporated in the year of manufacture, vehicle maintenance, driving habits, and just luck. Various years and models of Explorers, Mountaineers, Rangers, Mustangs and Discovery III vehicles were produced with Ford's SOHC V6. Ford recognized a few years after the first 1997 SOHC V6 model was sold that there were problems with the durability of the original tensioners and guides. Various upgrades were incorporated between 1997 and 2002. The 3 leaf spring primary (crankshaft to jackshaft) timing chain tensioner was replaced with a larger base, 6 leaf spring unit. The wear resistance of the various guides was improved. The left guide assembly was reinforced with metal on the chain traction and slack sides. The right guide assembly was reinforced with metal on the chain slack side. The left and right spring/hydraulic tensioners were improved.
Failure of the primary timing chain tensioner or guide normally does not result in engine damage. It only affects camshaft timing relative to the crankshaft due to slack in the primary chain. However, if both the tensioner and guide are failed, it is possible that the chain could slip enough that the pistons and valves on both banks could collide.
Failure of the camshaft timing chain guide assembly can result in the chain slipping. When it slips, it frequently slips enough that the exhaust valves collide with the pistons on that bank as shown in the photo below by cjmedina.
It is difficult to identify by sound which timing chain related components have failed. The dreaded timing chain rattle echoes within the engine making isolation uncertain even when using a mechanic's stethoscope. Timing chain rattle can occur at engine start, at mid-range engine speeds, or may start and stop seemingly at random. The rattle could be due to weak or broken spring or hydraulic tensioners, broken or excessively worn plastic guides, worn chains or worn sprockets. Normally, the chains and sprockets are functional significantly longer than the tensioners and guides.
The only reliable method of determining the source of timing chain rattle is visual inspection. The upper sections of the left and right guide assemblies can be inspected after removal of the valve covers (requires removal of the upper intake manifold). The primary tensioner and guide and the lower section of the left guide assembly can be inspected after removal of the front timing cover.
Since the right guide assembly can only be replaced by removing the engine (or the transmission) I recommend checking it first. If broken, you may decide to replace (rather than repair) the engine. There's no point finding what else may be wrong if it's not going to be repaired. Next, the left valve cover should be removed and the left guide assembly inspected. If it's broken then the front timing cover will have to be removed to replace it. If it's not broken then the timing chain rattle is coming from under the timing cover. The original style primary tensioner frequently fails before the left guide assembly.