View single post by Esprit2
 Posted: 09-11-2017 08:21 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 343
If you have read my previous post already, read it again. What made sense in the wee hours of the morning read a little weird after a few hours of sleep. I've edited the whole thing. Sorry about any confusion.

Tony, I suppose I could have just answered your questions.
tonyhawker wrote:
Is it possible to reverse the intake and exhaust cams and/or reverse the cam towers on reassembly?Yes. The cam carriers themselves are identical and will bolt-on to either side of the head. The stock cams are the same, so they will also swap sides with no complaints.

However the two identical cam pulleys are installed reversed... ie, flipped front to back between the intake and exhaust. That's a very significant point of difference with regards to cam timing, but one that's easily overlooked. Since the cam carriers will bolt on to either side of the head, there is no 'one way' fail-safe feature to prevent you from making a mistake. You need to know what you're doing with regard to pulley orientation, and pay attention.

tonyhawker wrote:
If there has been a reversing of the cams has the engine been trashed?  It turns over very freely.Maybe, maybe not... read the long version. But yes, the cam timing is wrong when the cam carriers are swapped (pulleys are backwards), and depending on which timing marks were used, the pistons may have hit the valves. In that case, the entire engine is not trashed, but the head will require a rebuild. New valves for sure. Maybe new guides and seats as well. Not inexpensive.

On the upside, it's possible the timing was off just far enough to kill compression without the pistons hitting valves. In that case, correcting any cam timing errors should be all that's required to 'fix' the engine.

tonyhawker wrote:
Are the cams identical or marked as to their location?The stock cams are identical, and not marked per their location... intake or exhaust. Look at the exposed bit of cam that's visible between the front of the cam carrier and the back of the pulley.

If it's clean with no machined or stamped markings, it's the J-H 907's stock C-Cam. It was also the stock cam in all Lotus 'Federal' 907s. Requires 110, red-dot pulleys for design-correct timing. J-H early emissions timing set the MOP to 115 on both cams. Later emissions timing used 100 MOP Intake and 110 MOP Exhaust.

One groove machined all the way around indicates the D-Cam. It was the Lotus 907's early stock 'non-Federal' cam, and it was never used in any stock J-H 907. Requires 110 MOP, red-dot pulleys.

Two grooves indicates the later (? 1978-ish intro) Lotus 'non-Federal' E-Cam. Requires 102.5 MOP, yellow-dot pulleys.

7777777.... stamped all around the shaft indicates the 107 cam that is popular with some J-H owners. Requires 104 MOP, green-dot pulleys.

4444444.... indicates Lotus' street-performance 104 cam. Requires 104 MOP, green-dot pulleys. The "104" as used in both the cam and pulley names refer to different things. It's purely coincidental that a 104 cam requires a 104 MOP pulley... don't get hung-up on that... there's no numerical meaning/ relevance.

If the cams have been reground to some other profile, then you're at the mercy of whoever did the regrind to add appropriate markings. I have two reground, unmarked cams I can't identify.

For more details, read my previous message, #3 above.

Regards & Good luck,
Tim Engel

Last edited on 10-08-2017 04:26 am by Esprit2