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post #58 of (permalink) Old 03-22-2018, 09:07 AM Thread Starter
Join Date: Aug 2010
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Timing Belt, part II

Part II

In either case, with the timing belt now fully slack, slide it forward off the two cam pulleys, the auxiliary pulley, the tensioner and the crankshaft sprocket.

If the task at hand is to simply install a new timing belt, then start that now. However, if there is other work to be done, then there’s some risk of the crank inadvertently being rotated enough to bring a piston into contact with some valves and possibly bending the valves. The safe thing to do is to turn the crank back to 90 BTDC. That puts all the pistons half way down their bores and well away from the valves.

Tasks to be considered at this point are:

1) Rebuild the Water Pump, or at least, install Allen cap head stainless bolts.

2) Replace the front main seal.

3) Replace the cam seals

4) Replace the Auxiliary shaft seal.

5) Check the valve clearances, and shim the valves if required.

6) Replace the tensioner bearing.

7) Rebuild the semi-automatic tensioner (G-cars)

8) Re-set the “emissions’ cam timing to the design timing, installing new cam pulleys as required.

Install the Timing Belt:
The small toothed sprocket on the crankshaft has a cupped flange washer behind it. Check the sprocket for cracks; remove, wash, examine (often cracks trough the threaded hole area). A raised boss on the back face of the sprocket telescopes through the washer, then the sprocket pinches the washer back against a step on the crankshaft. If the sprocket has been disturbed or removed, then it’s common for the washer to slip off the sprocket’s raised boss, and drop down behind it. Make certain the washer is properly seated. If the old timing belt is not being removed, and the bolt securing the front V-belt pulley was never loosened, then the washer has not been free to move.

The above washer is cupped rather than flat. As it extends out beyond the sprocket’s OD, it also curves back away from the sprocket, forming a funnel-guide for the timing belt. If the washer curves forward over the sprocket, then it’s on backwards. Remove the sprocket and re-position the washer.

If the crank sprocket needs to be removed, it can usually be pried off using two screw drivers, one per side prying simultaneously. If it’s really stuck, there are two M5 tapped holes in the front face that accept bolts from a small puller (ie, steering wheel hub puller).

Both the crank sprocket and the V-belt pulley should be installed with Anti-Seize applied to their bores, keys and the crank journals.

Double check that the crank is at TDC, and that the timing dots on the cam pulleys are adjacent to one another, and aligned on the centerline between the cams. If they are aligned, but above or below the centerline, they are still not properly timed. The dots must be BOTH aligned and on the centerline. Make sure that the pointer (visible in the clutch inspection window), is at the TDC mark on the rim of the fly wheel.

Slip the timing belt onto the small toothed sprocket on the crankshaft. Route the belt up over the tensioner pulley, and generally lay the belt up into position near the upper pulleys.

Grasp the belt with both hands, one on either side of the crank sprocket. Pull upward firmly on the strands to either side of the crank, wiggling back and forth a bit as necessary to fully seat the belt teeth on the crank sprocket. Fish the slack-side strand up around the tensioner pulley and toward the auxiliary pulley. Don't put it on the auxiliary pulley yet, just have it staged there.

Pull the tension-side of the belt up snug toward the exhaust cam pulley. Murphy's Law probably won't allow the belt and pulley teeth to mesh perfectly, but don't pull the belt testosterone-tight when going for a mesh. You cannot stretch the belt (!), and too much force will only rotate the crank... then you'll have to go back and start over.

Instead, pull the belt up taut toward the exhaust cam pulley, put a 17mm wrench on the bolt that retains the cam pulley, and turn the pulley minimally as required for a perfect mesh. Slide the belt back onto the pulley only about 3/8" to 1/2"of its width… just enough to be secure. Use the wrench to turn the pulley back in the tension direction just enough to pull slack out of the belt, but don't try to tension it (pull too hard and you'll turn the crank, and/or loosen the pulley bolt).

Note: The belt is very stiff side to side (in the flat plane). If it is slid all the way back onto one pulley, it will be too stiff to zig-zag back out to start on the forward face of the next pulley. Barely start the back edge of the belt on all three upper pulleys (two cam pulleys and the auxiliary pulley) before sliding it back to fully engage them.

Pull the belt taut over to the intake pulley. Again, use the wrench to turn the intake pulley as required to meet the belt, and slide the belt 3/8" to 1/2" onto the pulley. Turn the pulley back in the tension direction just enough to pull slack out of the belt.

Check the cam timing dots for any obvious mis-alignment at this point... the crank must be at TDC and the pulley dots aligned ON the centerline. Correct any error before proceeding over to the aux pulley.

Engines with crank-triggered ignition (910S, Esprit SE thru S4s) don’t have to worry about the Aux pulley’s position, but engines with distributors do. Turn the Aux pulley to align the dot on the rim with the centerline between the Aux shaft and crankshaft, as noted in the manual, and as an addendum below. Or, if you made your own paint dots as suggested at the beginning, now is the time to count belt teeth from the Intake pulley paint mark to the Aux pulley paint mark. Know which teeth you need to mesh before starting your struggle with the belt.

With the timing belt on the cam pulleys on one side, and over the tensioner roller on the other side, pull all the slack from both sides of the crank pulley up and around toward the Auxiliary pulley.

It can be difficult to fit the belt on the last pulley (Auxiliary pulley). The belt is nearly a net fit on the pulley circuit, and there's no excess slack to make it easy to slide it onto the last pulley. Make sure the tensioner is fully backed off so you have the entire possible belt slack available. A used belt will have stretched a bit during prior use and will be easier to install; but a new, un-stretched belt can be pretty snug. HTD belts are thicker and stiffer than trapezoidal belts, and will fight you more.

If the belt just will not go on the Aux pulley despite your best effort, then try this. Position yourself behind the pulleys, reaching forward to handle the belt. Start the belt onto the Aux pulley from the side facing the intake cam, and barely hooking it over the edge of the pulley. Work it on as far around the pulley as you can before it just won't go any more.

Hold the belt there with your left hand. Then, working from behind the pulley, lay the fingers of your right hand across the top of the pulley and belt, catching the far, forward edge of the belt with your first knuckle joint. Force the edge of the belt down, laying it flat over the front face of the pulley. "On-edge", the belt is stiff, and you can pull it back up, sliding it along the face of the pulley until it's edge "just" clears the rim the rest of the way around. Then rotate the belt back up to horizontal while simultaneously pulling it back onto the pulley. With a little practice, you can make that one fluid motion. Doing it is not as difficult as deciphering what I just wrote.

Now that the belt is started onto all the pulleys, you can slide it back fully onto all three pulleys.

Adjust the tensioner to put some heavy tension on the belt, but don’t worry about an exact amount for now. In the case of the spring loaded, semi-automatic tensioner, that means remove the locking pin, re-install the second mounting bolt and tighten them both, and screw the adjuster inward. When the tensioner pulls the slack out of the belt, sometimes the pulleys move.

Normally, if you kept all the slack out of the system while installing the belt, the pulleys won’t move enough to get out of time. But don't get bummed if the first fitting requires a re-do... it happens. What must not happen is to let it go un-corrected.

Double check that the crank is still at TDC, the cam pulley timing dots are aligned on the centerline, flywheel pointer at TDC and count the number of teeth between the painted teeth on the two pulleys (if you’re using that method). If everything is not perfect, then note which way any pulley has to be moved on the belt, and repeat the process as necessary to get everything installed correctly. Don’t worry about small, partial tooth misalignments, since you can only index the pulley on the belt by whole tooth increments. Get the timing correct under some tension before worrying about setting the tension to spec.

The manual shows an extra dot on the pulley rim that's used for setting the Aux pulley (see the NA Workshop Manual, Section E – Engine, Page 19, or the Turbo Service Notes, Sect EB, page 10). That works okay on an engine stand where you have a good view of the front of the engine, but it's not as convenient when you're working between the engine and the firewall.

That dot/centerline set-up works for the Euro version of the engine. However, the federal engine uses a different ignition timing that often results in the vacuum diaphragm capsule striking either the oil filter or the intake manifold before achieving the spec static timing.

In that case, the aux pulley needs to be timed with the dot a couple of teeth off the center line; however Lotus didn't re-draw the illustration for the Federal engine. If you wish to use the dot/center line method, check (better yet, PHOTOGRAPH) the relationship at TDC before taking everything apart.

Note: One tooth pitch on the pulley = 9° degrees of cam timing (360 divided by 40 teeth on the pulley), = 18° of crank timing

All cam timing is done with the crankshaft set to TDC. Imagine it's welded there. You can't create a scenario or excuse to justify moving the crank off TDC !!

With the crank at TDC, the cam pulley timing dots must align on the imaginary center line between the cams/ pulleys and flywheel pointer has to be on TDC mark. If the dots align, but they're both above or below the center line by a whole tooth increment, then the cams are still not properly timed. The dots must be on the center line. Index both pulleys on the timing belt as required to get their respective dots on the center line.

Having said that, the world isn't always perfect.

On a single pulley, from the tooth with the dot, look to the next tooth over and imagine another dot in the same place on that tooth. That's a whole tooth pitch increment... a gap plus a tooth width. From any point on one tooth to the exact same point on the next adjacent tooth is one whole tooth pitch. You can only move the pulley on the belt in whole tooth pitch increments... there's no way with stock parts to adjust for less error than that.

It's common for the dot/tooth alignment to be less than perfect. Anything that affects the dimension between the crank and cam center lines will cause small variances in dot/tooth alignment. Things like production tolerances, milling the head for flatness, decking the block, etc, will result in extra belt slack. When the tensioner pulls that extra slack up over the cam pulleys to the tensioner side of the engine, it will rotate both pulleys a little in the process... retarding both cams a little.

If the crank is at TDC, and the dots & teeth are very nearly aligned, but off by less than a whole tooth pitch, then there is no adjustment possible with stock parts that will bring them into perfection. You could fix it with aftermarket adjustable vernier pulleys, but that's a completely different discussion.

1) With the crank at TDC (!!), are the pulley timing dots aligned on the center line between the pulleys? ALWAYS EVALUATE TIMING DOT ALIGNMENT WITH THE BELT TENSIONED. It doesn't have to be the "correct" tension, but have some tension... ie, a healthy dose of tension sufficient to pull all existing belt slack over to the tensioner side of the engine... in the belt before checking the timing dot alignment.

2) If they're off, then are they off by a whole tooth pitch? Not just off by some fraction of a pitch. Not just off by a tooth FACE width... but a whole tooth pitch (i.e., will indexing the pulley one tooth on the belt solve the problem?)

...a) If the dots ARE off by a whole tooth pitch (gap+tooth width), slacken the tensioner making sure the belt is fully seated, partially remove/lift the timing belt at the offending pulley and index the pulley on the belt as required to get the timing dot aligned on the imaginary centerline. I t is handy tying belt to the “good” pulley with cable wrap to prevent slipping off.

...b) If the dots are off, but only by a small amount (a fraction of a whole tooth pitch), then there's nothing you can do about it short of installing aftermarket adjustable cam pulleys. That small amount of error is not optimal to a perfectionist, but it will not cause a major problem in the engine's operation. It will not cause a 20 point drop in compression pressure.
If one or both pulleys is off the imaginary centerline by a whole tooth pitch, then that could result in low cylinder pressure.
If a pulley is off by one tooth pitch, that's not enough to cause the valves and pistons to collide. Being off by two tooth pitches could be a bent valve problem... you're getting really close!

NOTES and OBSERVATIONS SE, S4, S4s (no distributor):

-Use small amount of Nikal anti-seize compound on the crankshaft and camshaft ends, sprocket/pulleys bores, miraculous stuff.
-Inspect the crank sprocket for cracks and flange/washer for proper seating/fit over the sprocket flange. Any undetected problems in the sprocket/washer integrity or alignment shall result in very costly engine failure!
-When replacing the tensioner bearing, shop around for Flennor or SKF "Germany" made parts. Never press on any protruding features of the tensioner.

-To break the crank pulley bolt: depress clutch and engage 5-th gear to "lock" the crank. Be sure that rear wheels are on the ground or on the ramps.

-The easiest way (at least for me), to install the new belt was:
Start at the crank sprocket, over exh and int pulley, as described above. Zip tie belt to both pulleys and install tensioner (loose & @ maximum slop setting). Next engage aux. pulley into a belt loop over the tensioner and slide it onto the jack shaft. Do not install pulley bolts until last (after final tweaking and adjustments). If you use Nikal, the pulleys can be moved out with two hardwood pry-sticks, or even by hand.

-Adjusting missed tooth on exh or int pulleys is easy. Mark the pulley/belt teeth where your belt supposed to be after adjustment (on both pulleys), adjust the loop, hold in place (tight to the pulleys), tighten the tensioner.

-Adjusting missed tooth on the crank pulley requires removal of the jack shaft (aux) pulley to allow lateral movement of the belt. Tie wrap the exh & int pulleys to prevent belt jumping at the top whilst you're manipulating belt @ crank pulley.
-REMEMBER to unlock the "5-th gear immobilizer" when you try to rotate the engine (LOL!)
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Last edited by MRDANGERUS; 03-29-2018 at 06:27 AM.
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