Conservation and Restoration
What was the Achilles heel of the Chrysler 383 & 440 engines as fitted to Jensen cars. We take a look at the infamous Chrysler ‘Silent Timing Chain’.
During the 1960s, Chrysler were looking at ways of making their engines run quieter, and to that end, had been developing their ‘Silent Timing Chain’ system. Advances in plastics technology had allowed Chrysler to manufacture and fit a nylon toothed timing sprocket to their range of engines.
This sprocket, cast in aluminium, had nylon teeth, allowing the engine to run more quietly.
More importantly for Chrysler, testing had shown that the nylon toothed sprocket had a guaranteed life in excess of 50,000 miles, which exceeded their warranty of the time.
From at least the middle 1960s, the nylon toothed sprocket (Chrysler part number 2532490), went into Chrysler’s basic range of engines, including the Chrysler 383 engines sold to Jensen Motors.
The only engines Chrysler retained an all metal timing sprocket on, was their high performance engines such as 440 SP, and 426 Hemi. These carried an all metal sprocket with duplex chain.
As with most manufacturers, Chrysler worked on time or mileage restrictions in regard to warranty, and certainly wouldn’t be concerning themselves as to the longer term viability of these nylon toothed sprockets.
The outcome was inevitable. After some decades of extreme heat, combined with cold, along with the stress of use, the nylon teeth would eventually break up. An unpleasant business if the vehicle is operating at speed at that time.
This is exactly what happened to the Museum’s Jensen FF, chassis number 127/248. It was February 1984, and 127/248 was being driven at around 50 mph, when the engine started to play up, eventually coming to a standstill.
An engine strip-down found the problem. The ‘E’ series Chrysler 383 engine had been built in 1969, and the original nylon toothed timing sprocket was still in place.
Once the timing gear was removed and cleaned up, it was clear that half the nylon teeth had broken up.
The car had covered exactly 52,690 miles from new. Just over the mileage Chrysler had originally given as a guaranteed life, but slightly out of their three year time related warranty – the engine now 15 years of age.
Repairing the damage was a simple enough operation, with a new high performance all metal timing sprocket, along with duplex chain being fitted. Needless to say, it was necessary to thoroughly clean out the engine and sump, to make sure all traces of the shed nylon teeth had been removed.
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