Timing on 1988 Esprit

[nikker99]

I have a 1988 Esprit that the timing was off. The mechanic who worked on the car could only get it to 10 degrees before it would hit an obstruction ( do not know what he called it I'm new to this game) It should be set at 15 degrees. I remeber reading someone with the same problem and had a way around it. Any suggestions would be appreciated.
Thanks,
Larry

[lotusguy]

I have a 1988 Esprit that the timing was off. The mechanic who worked on the car could only get it to 10 degrees before it would hit an obstruction ( do not know what he called it I'm new to this game) It should be set at 15 degrees. I remeber reading someone with the same problem and had a way around it. Any suggestions would be appreciated.
Thanks,
Larry

Hi Larry,

Sorry to hear of your troubles. Since you are self-admittedly not fully knowledgeable about the subject, let me explain in a little greater detail. You may want to print this response to give to your mechanic.

First, a little background. The ignition timing determines where, in the upward travel of the piston, the spark occurs which ignites your fuel mixture. Since the height of the piston is relative to a point of the crankshaft's rotation (which drives the pistons), this point is expressed in degrees of the crankshaft's rotation.

Also, the pistons reach their uppermost travel at 90° intervals. This is because your crankshaft rotates 360° in one revolution and 4 (pistons)/360 = 90°. The #1 piston (closest to the firewall) is at it's uppermost travel at 0° of the crankshaft's circle and is referred to as TDC or Top Dead Center. The other three pistons reach their uppermost travel at 90°, 180° & 270° After Top Dead Center of the #1 piston or ATDC. In order to properly balance the engine, and to reduce excessive vibration, the pistons are set on the crankshaft so that first the #1 piston, then the #3, then #4 and finally the #2 pistons top off in their respective cylinders in turn.

But, you want your spark to occur slightly before this TDC position of each piston in order that sufficient time is allowed for the fuel to combust and expand so that maximum power can be derived from it. So, on nearly all gasoline internal combustion engines, this spark is set to occur BTDC or Before Top Dead Center. At or beyond TDC, and combustion will be incomplete and much potential power from the fuel will not be achieved. There is no specific point the spark can occur and still achieve combustion of the fuel, but rather, a range. The engine designer determines the optimum point the spark should occur, but power may not be the only determination. Controlling emissions or making the engine capable of operating on several grades of gasoline also factor in to where this optimum spark occurs.

Since the spark is electrical, it is controlled by a switch. This switch is your distributor. It has two contacts (well actually 5, but for discussion's sake let's stick to one cylinder). One contact is on the center and the other four are on the perimeter of the distributor cap. The center one leads, via the high tension lead to the coil, a type of storage battery which also has the ability to multiply the voltage supplied to it thousands of times. Each of the other four contacts are attached to the sparkplugs, via high tension leads. A rotor with two contacts, one in it's center and one on an arm which traces the circle of the four electrodes in the distributor cap, lives under the cap. It's center contact remains in contact with the coil electrode, albeit rotating under it. The other contacts each of the other four electrodes of the cap in turn as it rotates in a circle driven by a shaft which is connected to the timing belt and so mimics the rotation of the crankshaft. When the outer electrode on the cap is contacted by the rotor a circuit is closed and the coil can discharge it's current to earth via the engine block by producing a spark which jumps the gap between the sparkplugs electrodes. This is the spark which ignites your fuel.

Since the distributor cap, and it's four electrodes, are fixed to the body of the distributor, rotating the distributor body will change the point at which the contacts meet and close the circuit. In the Esprit, if you rotate the distributor body clockwise the spark will occur sooner (advanced). Conversely, if you rotate the distributor body anti-clockwise, the spark will occur later (retarded).

But, on the Esprit, with it's horizontally mounted distributor, you cannot rotate it a full 360°. This is because a vacuum advance module protrudes from the side of the distributor and will be obstructed by the intake manifold on it's upward rotation and by the oil filter on it's downward rotation. These obstructions limit the maximum rotation of the distributor body to roughly 36°. This translates to about 10°-15° of ignition timing.

The ideal point for the ignition spark must live in this 36° of arc of the distributor body. As mentioned previously, the rotor rotates on a shaft which rotates through the center of the distributor body, which can also rotate. Think of it as a circle within a circle. So, the proper ignition point is achieved by rotating the circles relative to one another until the ideal point lies on this 36° of arc. Since the circle representing the distributor body cannot rotate 360°, the circle which represents the rotor shaft must be rotated to that when the engine is at #1 TDC, the rotor arm lies just before the electrode in the dist. cap for the #1 cylinder. Ideally, this point will exist in the middle of the dist. body's allowable arc of travel so that fine tuning can be made simply by turning the dist. body a few degrees in either direction.

Lotus places a reference point on the aux. shaft timing pulley to allow you to easily find this ideal point. It is a dimple on the rim of the pulley. The shaft must be rotated so that this dimple intersects an imaginary line running through the centers of both the crankshaft and the aux. shaft when the crankshaft is at TDC. If the timing belt has slipped a tooth or the pulley improperly aligned, the distributor will be thrown off by a factor of 18°(each tooth represents 9° of crank rotation and 18° of cam/aux. shaft rotation).

Once this index mark has been properly lined up, and with the engine at TDC and the dist. body rotated so that the vacuum advance module is centered on the available arc of travel of the dist. body, remove the dist. cap and note the position of the rotor arm. Replace the dist. cap and position the #1 sparkplug lead so that it lies just beyond the position of this rotor arm going clockwise. Now, place the #3, #4 and #2 plug wires in a circle clockwise to the #1 wire. Your firing order is 1,3,4,2. This should be sufficient synchronization to allow you to start the car. Once started, using a timing light, rotate the dist. body until the appropriate amount of advance has been achieved. The light will flash and indicate which timing index mark on the flywheel is matching with the fixed pointer when the #1 sparkplug fires. Hope this helps. Sorry for the lengthy reply. Happy Motoring! Jim'85TE

[kylie]

Jim I must say, that is impressive!!! Does that apply to most models?
KS
89 Esp Turbo

[lotusguy]

kylie said: Jim I must say, that is impressive!!! Does that apply to most models?
KS
89 Esp Turbo

Kylie,

You really are too sweet! Thanks for the kind words, but it's not that impressive to understand how it all works. Now, if I had invented it all, that really would be impressive, but, alas, I did not.

To answer your question, no this would apply only to cars which have a distributor, though the info. about the function of engine timing remains the same.

On cars with an ECU, there is no distributor. The distributor's function is relegated to the software governing the ECU. This ECU uses a crank sensor to determine the crankshaft's position and also has the ability to alter the timing dynamically in real time based upon signals it receives from the various sensors on the car. The data it collects from these sensors is compared to a set of pre-programed parameters and the ECU times the spark based upon these instructions. There is no need to ever set the timing yourself. If you wished to do so, you would have to change the code on the chip to either give it new instructions based upon the maps it has stored, or furnish it with a whole new set of maps. Got to be a lot brainier than I to accomplish this. Happy Motoring! Jim'85TE

[jonwat]

Lotusguy wrote:
________________________________________________
Also, the pistons reach their uppermost travel at 90° intervals. This is because your crankshaft rotates 360° in one revolution and 4 (pistons)/360 = 90°. The #1 piston (closest to the firewall) is at it's uppermost travel at 0° of the crankshaft's circle and is referred to as TDC or Top Dead Center. The other three pistons reach their uppermost travel at 90°, 180° & 270° After Top Dead Center of the #1
_________________________________________________

I'm afraid I have to disagree with you there Jim, when number 1 piston is at TDC so is number 4, numbers 2 & 3 are at BDC.

When the crank has turned thru 90 deg all four pistons are level (1 & 4 are half way up, 2 & 3 are half way down).

The ignition timing is at 90 deg intervals but the pistons are at 180 deg intervals & this is achieved by the distributor shaft being driven at half the crank speed, just like the camshafts

Cheers,

John W
'95 S4s

[kmaier]

Yes, I agree that Jim did quite a nice write up and was nice of him to take the time to explain things. Overall, I agree with most of what he wrote, however, paragraph 3 which explains the pistons and crankshaft positions is quite incorrect.

I have yet to see any inline 4-cylinder engines which do not follow the classic arrangement. Jim's descrption implies that the 4-cylinder engine has a 2-plane crank which allows each of the 4 pistons to be staggered 90 degrees from each other (360 degrees for a single rotation of the crank divided by 4 cylinders).

In practice, you must consider the fact that all 4-stroke engines require two full revolutions (720 degrees) to complete one engine cycle. Using 720 divided by 4 cylinders gives you the correct 180 degree stagger between the cylinders. So, you really have a single plane crank. As is the case, the first and fourth cylinder operate as a pair and the second and third cylinders operate as a pair which are 180 degrees apart. The camshafts are driven at a 2:1 reduction ratio from the crankshaft and their respective timing is also staggered at 180 degrees between the paired cylinders allowing one cylinder to be on the compression stroke while it's paired cylinder is on the exhaust stroke, etc. This gives you a power stroke every 180 degrees using 4 cylinders.

Hope this clears things up.

Regards, KM
2000 V8

[lotusguy]

Hi,

OMG, Shame, Horror, Distain, Self-Loathing... I don't know how I didn't catch it, better spend more time proofreading before hitting the Submit Reply button.

John W. and KM, of course you are correct! The pistons are at 180° intervals. Only way it can work on a 4 stroke w/ a single plane crank. My Bad, I knew the correct info, but was trying to do 3 things at once when composing my reply - writing, finishing laundry and making dinner. Guess my multi-tasking skills aren't what they used to be

Still, my error is a good example of the scutiny the info posted here must endure. Not too much incorrect info remains unchallenged on this list. That should be comforting to some of the newer listers.

Thanks JW & KM for pointing out the error and correcting it. I try to assist newer guys, but never want to pass along incorrect info. Happy Motoring!... Jim'85TE

[nikker99]

Thanks to everyone for helping me out. This website is a great asset to everyone and a great bunch of people out there. Fixed the timing problem!! Thanks Jim. It feels like a different car now. It snaps my head back!!
Larry