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Jensen Interceptor MK1

Updated: Sep 16, 2023

The MK1 Jenson Interceptor
The mk1 Jenson Interceptor

This lovely looking mk1 is the 6.3 (383 cubic inch) Chrysler v8 auto model. Sporting nice chrome throughout, new wheels and a nice recent coat of paint, this one is quite a head turner. All in working order and very solid unlike the vast majority which are in various states of restoration.

Mk1 Jenson Interceptor side view
The timeless classic profile


Mk1 jenson interceptor interior
Stunning original red interior

Along with the exterior the interior has done remarkably well over the decades with barely a mark on the upholstery, needless to say the owner has looked after this one.


Unfortunately like all customer cars they enter the workshop for a reason. The problem with this one was an overheating issue which after performing a chemical CO2 test confirmed that combustion gasses were entering the cooling system. Generally speaking it's usually the head gasket that is at fault in this situation so that's where we start.

Jenson interceptor rotor arm
Rotor arm checked for tdc

Before removing the heads the timing is set at top dead center. This is done quite simply by aligning the timing mark on the crank pulley with the mark in the timing cover and making sure the rotor arm on the distributor is pointing at the number 1 firing h.t lead.

With the timing set the engine strip down can begin.

Jenson interceptor exhaust manifold
Exhaust manifold

The position of the exhaust manifolds in relation to the steering rack and inner wing-bulkhead ( arrowed) made it impossible to remove the manifold and heads with the engine where it was.

In order to remove the manifolds I had to first remove the engine mounting bolts and lift the engine until the manifold was clear and free to move.

Jenson interceptor engine
Inlet system and heads removed

With the engine slightly raised the heads were able to be removed.


Jenson interceptor engine block check
Checking the block for warping

This is a simple check to see if the block is flat. The block is first cleaned with a scotch pad. A flat edge is then placed across the block in 3 horizontal positions and then diagonally from corner to corner. A light is then shined along the block and flat edge. If any light passes between the two surfaces the gap must be messured. If it's out of tolerance the block or head must be machined flat.

Jenson interceptor mk1 engine block
Imperfection in the head

The driver cylinder head revealed a gap between the two center combustion chambers.

Jenson interceptor head work
Measuring the head distortion

After measuring the gap with several different sized feeler guages the head must be

re-faced. Note that the flat edge used to check for flatness must be a machined flat surface it's self or the check will not be true. A ruler won't do.

All the necessary parts removed for cylinder head machining.


Cylinder heads were skimmed flat to insure a tight seal across the whole face when the new gaskets are installed.

New gasket set includes everything needed for the rebuild and is still readily available to buy.

A more modern fan was fitted to the front side of the radiator and wired into a new thermo switch to insure the car doesn't overheat again.


While the heads are off a few other jobs need attention. First up is a lick of satin black paint. Various areas of the engine bay were left in red oxide primer for some reason. A quick aerosol can tidy's it up.


A small hole was found in the inlet manifold. This will have introduced a vacume leak which would affect the fuel-air mixture resulting in poor running. This was sealed simply with chemical metal.



One of the exhaust rear box heat shields was rattling during driving. One of the bolts holding it in place had corroded and broken off.

To fix the problem I had to remove the rear seats, grind the captive nut off and replace with a new locking nut and bolt. The repair area was given a small coat of rust proofing at the same time.

Rear discs and pads don't look to bad. The discs are a little pitted but not so badly that the need replacing at this time. The pads also look nearly new.

The paintwork is also in good enough order but in one or two areas there wasover-spray present. Presumably from the recent paint work. The is was easy enough to take care of with the polishing mop.


All finished and now back with its owner and more crucially not overheating.



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