View single post by Esprit2
 Posted: 02-02-2020 12:48 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 497
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discogodfather wrote:
Since none of the factory marks seem to be present I always just marked the relative positions of the cam pulleys and distributor pulley in the past when I replaced the cam belt.If you didn't do the intitial installation, and set the adjustable pulleys yourself, and if you don't even know which cams are installed, then you are putting a heck of a lot of blind faith in whomever did the work. Marking the pulleys, then putting them back where you found them may simply be replicating someone else's mistakes.
discogodfather wrote:
(Snip)... a cam grind by Elgin (no idea what the specs are though)...:-/ As a first step, you need to figure out what the cam specs are. Without that, you're just groping in the dark and wasting time.

Call Elgin Cams, and talk with Dema Elgin. Ask him where to find an identifying mark on the cams, then find the marks on both cams separately (don't presume they're the same), and report back to Dema. With the cam IDs, Dema should be able to give you the specs. Unfortunately, he usually quotes the timing specs in a format that is more confusing than helpful. Well... to me anyway. Good luck with that.

Failing that, get a degree wheel and two dial indicators... one on the #1 piston to find TDC, and one on the tappet (perpendicular to it). Don't try to follow the cam lobe... follow the TAPPET. Of course, valve clearance will mess with that reading, so first shim the clearance to a slightly negative value. Then carefully/ accurately determine the following:

. . . . . . . . . . . . . . Intake . . . Exhaust
Lift (inch) . . . . . . . 0.???" . . . 0.???"
Int. Opens, BTDC . . ??° . . . . . ??°
Int. Closes, ABDC . . ??° . . . . . ??°
Exh Opens BBDC. . . ??° . . . . . ??°
Exh Closes ATDC. . . ??° . . . . . ??°
Overlap . . . . . . . . . ??° . . . . . ??°, calculate as follows:
Duration. . . . . . . . ???°. . . . . ???°, calculate as follows:
MOP. . . . . . . . . . . ???°. . . . . ???°, calculate as follows:

Overlap = Int Opens + Exhaust Closes

Int. Duration = Int. Opens + 180° + Int. Closes
Ext Duration = Exh Opens + 180° + Exh Closes

MOP = [(Int. Opens, BTDC + Int. Closes, ABDC + 180°)/2] - Int Opens, BTDC
MOP = [(Exh Opens, BBDC + Exh Closes, ATDC + 180°)/2] - Exh Closes, ATDC

LOTUS Cam ID. . . . . C. . . . . . . D . . . . . . . E . . . . . . . 107. . . . . 104 . . . . . Elgin something or other
Int. Opens, BTDC . . 26° . . . . . 25° . . . . . 27.5° . . . . . 22° . . . . . 32° . . . . . ??°
Int. Closes, ABDC . . 66° . . . . . 65° . . . . . 52.5° . . . . . 50° . . . . . 60° . . . . . ??°
Exh Opens BBDC. . . 66° . . . . . 65° . . . . . 52.5° . . . . . 50° . . . . . 60° . . . . . ??°
Exh Closes ATDC. . . 26° . . . . . 25° . . . . . 27.5° . . . . . 22° . . . . . 32° . . . . . ??°
Overlap . . . . . . . . . 52° . . . . . 50° . . . . . 55°. . . . . . . 44° . . . . . 64° . . . . . ??°
Duration. . . . . . . . 272° . . . . 270° . . . . 260°. . . . . . 252°. . . . . 272°. . . . . ???°
MOP. . . . . . . . . . . 110° . . . . 110° . . . . 102.5°. . . . . 104° . . . . 104°. . . . . ???°

The MOP is different for each grind profile, depending upon the opening and closing events. That's not debatable. Then the correct pulley for that cam must have the keyway cut in the bore at an angular location that supports that MOP. Adjustable pulleys allow you to buy a generic part, and set it to the correct MOP... ie, it's universal. It only becomes a "tuning" tool if you seriously know what the heck you're doing. Failing that, stick with the default values as calculated above. All the Lotus values follow those calculations.
discogodfather wrote:
(Snip)... I noticed in the factory service manual it says that the distributor pulley mark should face downwards and the rotor should be facing in "the upward position from vertical".The Auxiliary Pulley timing dot is 'roughly' across the pulley from the two cam timing marks. If you don't see it on the front of your Aux pulley, then look on the back side. If you see it there, then the pulley is on backwards. You can still time the distributor, but you'll have to wing it instead of following the book.

Do you have a non-emissions distributor WITHOUT an external vacuum retard capsule, or an emissions distributor WITH one?

Functionally, the distributor doesn't care how the auxiliary pulley is timed, or which way the rotor is pointing. You can loosen the clamp and rotate the distributor body as required to align it with the rotor at the desired Static Timing (14°-15° BTDC). But in the real world, there are practical factors. In some orientations, one clip that holds the distributor cap on might end up facing the engine block, in which case it may be difficult to impossible to release. OR, the emissions vacuum capsule will only fit in the gap between the oil filter and the bottom of the front carb. The Aux timing dot is simply a 'safe' location were all the bits fit without interfering with anything else.

With that in mind, if you need help timing the ignition, let us know.

Regards,
Tim Engel

Last edited on 02-02-2020 02:07 am by Esprit2