View single post by Mark Rosenbaum
 Posted: 01-01-2007 11:22 pm
PM Quote Reply Full Topic
Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
I will again note that the measurements I posted earlier weren't all that accurate -- any or all of the readings I took could easily have been 0.005" or 0.010" off.  Consequently, without proof to the contrary, I'd be inclined to think that your cams are actually Type C's.  Regardless, unless your cams have the groove at the front, they're not real Type D's. 

It's my understanding that as far as anyone has ever been able to document, all JHs came from the factory with Type C cams.  I will note that there's a long-standing rumor that a very few Home Market (UK) cars built early in 1974 had the same Type D cams used in Lotus cars that year, due to an alleged shipping error by Lotus that no one caught until after the cars were sold.  I've never come across any actual proof that this might be true.  However, I do think it's conceivable that Lotus would have deliberately made such an 'error', regardless of contractual obligations to Jensen, if it would have saved them a few bucks in manufacturing costs through not having to custom build a few engines.  In those days, it was often said that when dealing with Colin Chapman, one was always very well advised to count their fingers and their pocket change after shaking hands with the man.

It is also possible that a previous owner installed reground cams at some point in the car's history.  A significant decrease in base circle diameter would be a very good indication of this.  If so, then without some sort of documentation, all you can do is to measure lift versus rotation at many points and compare that information against similar data from possible candidates.  That would be a challenging task.