Valve clearance adjustment on Chevrolet Spark 0.8 L and 1.0 L S-TEC I4

Hydraulic tappets are a useful and practical thing, but not every engine has received this privilege. Chevrolet Spark with an S-TEC engine, for example, was left without them, and therefore the adjustment of the thermal valve clearance shines on the owners of all 0.8 and 1.0 l S-TEC engines. How to adjust the valves with your own hands, when and what will happen if you drive with unadjusted clearances, let’s understand right now.

Why adjust the valves on the Chevrolet Spark S-TEC

The valves in the cylinder head must seal the combustion chamber during the compression stroke. However, this is not always the case. When at least one of the valves, either the intake or the exhaust, performs its job after its sleeves, the valve lip does not fit tightly on the seat, the gases heated to a huge temperature burst into either the intake or the exhaust manifold.

This threatens at least a loss of compression and deterioration of the cylinder filling with the fuel-air mixture. That in turn causes a drop in power, complicates start-up and has a negative effect on fuel consumption. But this is not all. The heated gases tend to destroy first the valve edge, and then, after the appearance of microcracks, cause complete destruction of the working part of the valve.

If the valve does not open fully, when the thermal clearance is too large, then in addition to poor filling of the cylinder with mixture, there is poor ventilation of the combustion chamber between the compression strokes. This leads to inefficient combustion of the mixture, which also leads to a drop in power and high consumption.

In addition, the gases stimulate the formation of a large amount of carbon on the entire timing mechanism – springs, valve guides, rocker arms, which leads to wear of valve rods and a great disruption of the timing process.

This is why thermal clearances between tappets and valve necks are critical, because all metals expand by a certain amount when heated. This is the value by which we leave the clearances between the valve and the rocker arm.

The manufacturer strongly recommends adjusting the valves on the Chevrolet Spark at least once every 20,000 km. The clearance values are as follows:

1. For the intake valve the clearance is 0.15 mm.
2. For the exhaust valve it is 0.32 mm, because the exhaust valve warms up much more than the inlet valve.

Symptoms of Valves on S-TEC that need adjusting

In addition to the manufacturer’s recommendation that the clearances be adjusted every 20,000 km, there are a series of signs that directly indicate the need for adjustment. Logically, adjustments are needed if the cylinder head has been repaired. There are a number of other symptoms as well:

1. A characteristic ticking, chirping sound from under the hood. An experienced mechanic can easily determine from the sound alone that the valves need adjustment.
2. A gradual drop of power. The thermal clearance is not knocked down instantly. Therefore, it is sometimes difficult to determine the loss of traction and dynamics. However, if the power drops critically against the background of other symptoms, it is possible to speak about the loss of nominal thermal valve clearances.
3. Engine overheating. Because some of the hot gases enter the manifolds, the engine can overheat severely, even at low loads.
4. When revving, there may be noticeable popping in both the intake and exhaust.
5. Incorrect engine operation, hard starting, unstable idle revolutions..

If even these symptoms are present, you should already think about checking the valve clearances.

What you need to adjust the Spark valve clearance

Of the tools you will need a set of bits, sockets, extensions and gimbals, a set of screwdrivers. You also need two 0.15mm and 0.32mm dipsticks. Since the 0.32 mm dipstick is hard to find, you will use two 0.3 and 0.02 mm dipsticks together. If the valve cover is fastened by the factory bolts, a 5 mm hexagon is needed.

By the way, about the valve cover bolts (M6x1, length 35 mm). They are extremely unreliable, and the manufacturer recommends changing them every time the cover is removed. The point is that the hexagonal well often slips when used again. So, if they are on sale, it is better to buy new original ones.

The catalog number of the original bolt is 94500741-GM, their price is about 1 dollar apiece. As a last resort, you can use Dacia or Renault camshaft bed bolts, but using regular hex bolts is highly undesirable.

Many people would be happy to save money on the valve cover gasket as well. It, too, is disposable, even if it still looks decent. The fact is that over the years the gasket shrinks, dries out, loses elasticity.

If there is no particular desire to see oil leaks on the cylinder block, it is better to replace the gasket. Recommended options are:

We will also need a jack and, of course, a wheel wrench. If you have all this at hand, you can start adjusting.

Adjusting the valve clearances of the Chevrolet Spark

The adjustment is carried out on the engine cooled to 20 degrees. If the temperature is higher or lower, it is necessary to adjust the gap value plus or minus one-hundredth of a cent.

First, let’s jack up the car and remove the front right wheel and mudguard, put a stand under the hub and lower the jack.

Open the hood and remove the air filter together with the housing and the entire piping assembly.

Now it’s turn for the ignition module. Disconnect the high-voltage wires and the terminal block on the back of the module. After that, unscrew the three bolts fixing the module and remove it.

Disconnect the vacuum hoses, remove the throttle cable. Now remove the connector from the sensor and the pipe behind it. They will also be in the way.

Remove the breather hose and check its integrity. Especially in the place marked with an arrow. If a crack is formed there, you will get uncontrolled air leakage at the intake.

Let’s remove the timing cover. First unscrew the two far bolts on the right side. To do this, use the propeller shaft and an extension. Then we unscrew the other four. Be careful not to tear the splines. Hexagonal bolts for 5 mm.

Now that the cap is removed, we will set the first cylinder piston to the top dead center of the compression stroke by turning the crankshaft. To do this we use a 17 mm socket, an extension rod and a screwdriver. That’s why we removed the wheel and the mudguard.

It is not necessary to remove the timing belt cover and align the first cylinder at TDC. Although, this method has the right to exist and is considered correct.

However, it is much easier and faster to set the piston of the first cylinder at TDC, guided by the position of the piston and camshaft. To do this, turn the crankshaft clockwise (!) until the piston reaches TDC and the camshaft cam looks straight down.

In this position we will be able to adjust both valves on the first cylinder as well as the intake of the second cylinder and the exhaust of the third cylinder.

First, check the existing clearances with a feeler gauge. The feeler should not pass freely between the valve and the rocker arm, but it should not pass too tightly either. The feeler gauge should slip with a little force.

If there is a need to correct the clearance, take a socket wrench for 12 mm, tear it off the fixing nut. Without removing the wrench, with a flat screwdriver set the desired gap by rotating the rocker arm tappet.

Having achieved the desired clearance, keep the screwdriver in this position and tighten the lock nut. Check the clearance again, and then tighten the nut to 20 N∙m. Do the same with the remaining loose valves.

Now turn the crankshaft 360 degrees. At this time the camshaft will turn 180 degrees. In this position adjust both valves of the fourth cylinder and the exhaust of the second and intake of the third cylinder on the 1-l engine.

After adjustment, tighten the locknuts again and check the clearances on each valve again.

When reassembling, carefully wipe all the fitting surfaces with a rag, and tighten the valve cover crosswise, starting from the center with a torque of 10 N∙m. Reassemble in reverse order.