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Cams & Pulleys - Early J-H and Lotus Compatibility  Rating:  Rating
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 Posted: 12-26-2007 02:58 am
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Esprit2
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Just dropping in for a quick clarification on some confusion I may have caused before checking out over a year ago.   I had expressed concern that there may be a diffference in keyway position between early Jensen Healey 907's and the later Lotus-spec 907 such that they aren't interchangeable.   Working back through the math for the J-H 115-110MOP pulley and for the 110-100 MOP Lotus pulley suggested that the keyways "had" to be in different places.

Well,  I now know there is no keyway difference and the early & late cams and pulleys,  and they are functionally interchangeable.

My earlier calculations were based upon the published MOP numbers.   However,  I've recently been corresponding with an Engineer at Lotus Cars,  and he mentioned in a sidebar comment that the Lotus 100 MOP is really 97 MOP.   All the others are as advertised,  and he has no idea why the 97 was rounded up to 100.   "It must have been a marketing number".

Running backwards through the numbers using 115/110,  and 110/97,  everything works out perfectly.   The keyway location is the same.

So why did the part numbers change?   In 1979,  Lotus re-drew the part drawings to "lucidate and metricate".   While they were at it,  they assigned new part numbers to match a new number format that would be used going forward.   No significant part changes (some minor ones), and the parts are effectively interchangeable.

The only caution remains with the early J-H pulleys.   They were not hard annodized,  and the raw aluminum pulleys wear out relatively quickly.   For replacement,  the later, annodized pulleys are the way to go.

Regards,
Tim Engel

Last edited on 12-27-2007 06:51 pm by Esprit2

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 Posted: 12-26-2007 11:51 am
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jcdean
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Good information.  I do hope this heralds a return by you to the boards.  I have missed your technical input.

Joey

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 Posted: 12-27-2007 08:55 pm
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Chris E
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 On the subject of pulleys, Does anyone know what the timing is on the pulleys that have no lettering other than Int/Exh and just have a protruding bump to identify each side. It seems to run pretty well with the bump forward on the exhaust & aft on the intake.

Thanks,

Chris

Attachment: JHPulley.jpg (Downloaded 72 times)

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 Posted: 12-28-2007 08:38 pm
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Esprit2
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Chris,

110 red / 100 blue,  except that 100 is rounded up from the true 97.   You have the pulleys installed correctly with the bump foward on the Exhaust and the bump rearward on the Intake.

In your picture,  on the intake pulley,  the dot next to the EX mark should be blue,  and the dot next to the IN mark should be red.   On the exhaust pulley,  the EX dot should be red and the IN dot blue.

Turn a blind eye to the blue dots and time by aligning the red ones...  110/110 MOP.   An engine with original cams will run better with 110/110 timing.

Regards,
Tim Engel

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 Posted: 12-28-2007 09:29 pm
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Chris E
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 Thanks for the info.

 

Chris

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 Posted: 01-09-2008 05:55 pm
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Gary Martin JH 15371
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A quick question on Cam gears. My spare engine (3277) has the gears that only say IN and EX. The gears say IN on one side and EX on the other side. They only have one line scribed on each (no 110 or 115 marks). Standing in front of the car looking back at the front of the engine should the IN side of gear go on the Intake cam and EX side of the gear go on the Exhaust cam?  It is possible to put EX forward on the intake cam and IN forward on the exhaust cam which gives different cam timing (and probably bent valves). The manual is not clear on this point and I just want to be sure.

Gary

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 Posted: 01-09-2008 10:45 pm
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Esprit2
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Gary,
 
Some pulleys have multiple sets of timing dots on them,  others have just one set.   A set being and IN mark on one side, and an EX mark on the other side.   On pulleys with just one set of marks,  it's easy.
 
The IN mark should face forward on the INtake pulley.
The EX mark should face forward on the EXhaust pulley.
Always time the cams by the marks on the forward face of the pulleys.
 
With the crank accurately indexed at TDC,  align the timing dots or scribed lines with one another on the imaginary centerline between the shafts.   It's not enough to just align the marks.   They could both be high or both be low and still align.   They must align on the centerline to be correct.

The timing marks can be a little bit off the centerline... a portion of a tooth pitch.   That small error is the result of production tolerances or skimming the head.   But you can only change timing/ screw-up in whole-tooth increments (ie, move the pulley one tooth on the belt), and being off by a whole tooth is not right.   Fix it.
 
Regards,
Tim Engel

Last edited on 01-10-2008 08:04 pm by Esprit2

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