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JPJH
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Hello JHPS members.

I currently have a MK II car (74) and contemplating a MK I. (Late 72 early 73) I’m trying to better understand what’s ‘really’ different between them.
I know the interior, headlight finishers are different. I think, major systems are the same, but not 100% certain.

I’d appreciate any feedback on major parts and system components to identify differences.

Thanks in advance for any help.

DonBurns
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I'll defer to people more knowledgeable than me, but I have always assumed it coincided with the addition of catalytic converters and federal bumpers (and other minor cosmetic changes) part way through 1974 model year (so production in 1973?). Not all JH's were sold in the US of course - just most of them. Both of my 74's were early 74 with SS bumpers and no cat converters. I don't think rope seals were the distinguishing factor. Only very early Mark I had those.

Correct?

answerman
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Off the top of my head:

Besides the interior and headlight surrounds, I'm pretty sure that the lip seal as opposed to the rope seal for the rear main started with the introduction of the MkII. Also, the rear brakes on the MkI were Girling while the MkII used Lockheed.

The crankcase ventilation was different on the MkI, at least the early ones, with a separator/catch can in the breather line. MkIIs and later vented directly to the airbox.

The bumper changes are complicated: MkI used the SS bumpers, MkII used the same bumpers but with longer standoffs (at least in the rear) until the very end of the MkII run overlapping the start of the JH5 run, which changed to the rubber bumpers. Most of the MkIIs have the earlier SS bumpers.

Esprit2
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DonBurns wrote:
I don't think rope seals were the distinguishing factor. Only very early Mark I had those. Correct?
All Mk I 907s had rope seals, and the Mk II was introduced in Aug 1973

answerman wrote:
The crankcase ventilation was different on the MkI, at least the early ones, with a separator/catch can in the breather line. MkIIs and later vented directly to the airbox.The Mk I 907's crankcase ventilation did not include a built-in oil separator, so a separate oil separator/ catch can was mounted on the firewall. A bottom drain and hose returned oil to the sump as fast as it was collected. An upper hose vented fumes to the carb airbox.

The decision to add the oil filler neck & cap to the catch tank was probably not the best, since the drain hose was small diameter, and it took 'forever' to refill the sump when changing oil.

The Mk II received a 'lip' style rear main seal, mounted in a bolt-on rear cover/ housing. Inboard of that cover, built into the back end of the cylinder block, is a cavity designed to be an internal oil separator. With that added to the engine, the external separator/ catch can on the firewall was deleted, and an oil filler neck & cap were added to the intake cam cover. Being more oil free, crankcase fumes were vented directly to the carb airbox where they were drawn into the engine and burned.

Regards,
Tim Engel

JPJH
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Thank you all for the information. I was scratching my head on the oil separator difference. I ended up acquiring the MK 1, so I’m now trying to see what it really needs apart from brakes, fuel pump rockers and probably the right floor pan.



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