Biturbo Maintenance

Valve Clearance Adjustment
Cam Belt Replacement
Setting Timing
Oil and Filter Change
Differential Lube Replacement

The valve clearances are checked with the engine completely cold. The photos show the heads removed from the engine, but this is not necessary to adjust or check the clearances. The clearance specifications should be located in the owner's manual and on a metal plate on the front of the engine compartment near the radiator.

The clearance check begins with the removal of the cambox covers to measure the clearances with a set of feeler gauges. It helps if the feeler gauges are of the bent variety since they'll fit easier into the cambox.

Rotate the engine with a ratchet on the crankshaft pulley in the direction of engine rotation in order to position the cams. (The engine rotates in the direction of the firing order indicated by the distributor rotor). After each rotation, you can measure two valve clearances on each side of the engine. Record the clearances between the camshaft and the cam bucket.

Adjusting the clearances requires the removal of the camboxes in order to replace the valve shims. The cambox removal procedure is not hard, but it takes time.

When lifting the camboxes off the heads, you need to make sure the cam buckets don't fall out of their bores, because they shouldn't be mixed up. What I do is hold the buckets in with my fingers as shown in the photo, and loop my thumbs around the other side to hold the cambox. The factory service manual says you should tilt the camboxes off the heads, but I found that the buckets will fall out anyways if they're not held in.

Try not to knock the shims off the valve stems when removing the camboxes. I haven't had this happen to me, but it appears that they can fall down into the oil sump through the oil return holes. You can remove the valve shims with a magnetic pickup tool before you actually remove the cam boxes. Keep the valve shims in order after removing them. Measure the thickness of the shims using a micrometer.

The difference in height between the two intake valves with the valve shims installed must not be greater than 0.02 mm, according to the factory service manual. (There is another place in the manual where it says the difference must not be greater than 0.2 mm, but I use the smaller measurement because the valve shims come in steps which allow adjustment to the smaller figure).

I bought a deck height gauge stand from Goodson Tools and put it on top of a flat piece of metal, and then drilled a hole in the metal for the dial gauge extension. This improvised tool works pretty well for measuring the difference in height between the intake valves (see rear of photo).

My improvised tool doesn't work with the heads on the engine because the air injection manifold interferes with it. However I found that I could lay a short machinist's straight-edge on top of the head above the intake valves, and insert feeler gauges between the intake valves and the straight-edge.

MIE sells a similar tool for this purpose (foreground of photo) except that the hole won't fit the stem of a standard 3/8" dial gauge; its diameter is 8mm.

Using the measurements of the valve clearances, the thickness of the shims, and the difference in height between the two intake valves with the shims installed, you can calculate the necessary thicknesses of the new valve shims you will need. After installing your new shims (old ones can be reused), again measure the difference in height between the intake valves.

While you have the camboxes off, you might consider replacing the cambox oil seals and O-rings. Leaking oil seals can cause engine oil to get onto the cam belt, which can cause the belt to strip and leads to serious engine damage. Replacing the seals is easily done with the camboxes removed, and the seals are relatively inexpensive.

Using a new cambox gasket, install the cambox onto the head, making sure that the cam pulley is oriented the same approximate way as when the cambox was removed. (Because the engine is an interference design, you may not be able to rotate the camshaft all the way around without piston/valve contact). Torque down the cambox bolts and measure the valve clearances to be sure you got them correct. If you need to adjust the shims again, don't reuse the cambox gasket.

Be careful when installing the cambox bolts because they can easily force the gasket into the bolt holes. Sometimes it helps to lift the cambox up very slightly when installing the bolts.

Replacement of the cam belt requires removal of the radiator, the air injection equipment and pipes in front of the timing belt cover (if equipped), the front timing belt cover, the accessory belts, and the crankshaft pulley. Leaving the lower radiator hose connected to the radiator makes it easier to re-install the radiator, and it won't require raising the car during the job. The battery should be disconnected and removed.

With the timing belt cover removed, rotate the crankshaft until the #1 piston reaches TDC and the timing mark holes on the cam sprockets are aligned with their corresponding timing mark indicators on the camboxes. A dial gauge with extension can be inserted into the #1 cylinder and attached to the accelerator cable bracket to hold it steady. Another way to check for TDC is to look at the timing marks on the flywheel underneath the car. When the mark "PMS" is aligned with the indicator mark at the bottom of the bell housing, then the #1 piston is at TDC. (Note at this point the #1 piston will be on the *exhaust* stroke, not the intake stroke, and so the rotor won't be pointing at the #1 cylinder. This confuses a lot of people).

When the cam belt is removed in this position, the driver's side cam sprocket will want to rotate CCW (as seen from the driver's seat), often in a violent fashion, so the service manual recommends using the factory tool AG 20390 to lock the cam sprocket in place. I couldn't get the tool to fit correctly onto the sprocket, so I jammed it in sideways (see photo). The two fingers (red arrows) are supposed to fit into the cam sprocket. You could also gently rotate the cam sprocket to its "resting position" after the belt is removed (about 45 degrees CCW, seen from the driver's seat).

With the front timing belt cover removed, the cam belt tensioner assembly should be visible. (There is an older type of tensioner assembly, not shown, which can be upgraded to the newer kind shown). The allen head bolt holding the tensioner is unscrewed (red arrow) and a factory tool, AG 20690, is recommended in the service manual for compressing the tensioner spring. With the spring compressed, the belt can be slipped off the two cam sprockets. The tool is basically a set of vice-grips whose tips are designed to fit onto the tensioner spring assembly.

Rather than using the factory tool, the spring can be compressed using a suitable device and held in by tightening the allen head bolt. Then when the belt is installed, the allen head bolt is loosened and the tensioner will act on the belt.

The crankshaft pulley can be removed by wedging a piece of 1/4" square metal stock between the flywheel and the bottom of bell housing. This will hold the pulley in place so the pulley nut can be removed and the timing belt can be slipped off the crankshaft sprocket.

The tensioner pulley has a replaceable bearing, which is available from MIE. The bearing should turn freely and without uneven resistance. If in doubt, replace it. It is cheap insurance to replace it at every belt change. A machine shop can press out the old bearing and install the new one. The bearing can be installed the wrong way on the pulley. It should be installed as shown in the factory service manual.

With the timing marks on the cam sprockets still aligned to the indicators on the cam housings, install the new timing belt. Then the tensioner spring should be released so it acts on the belt. Then give the crankshaft a few turns in the direction of engine rotation, and measure the distance between the two spring pads. If within specification (25mm for 2.5L and 2.8L 3/valve engines), tighten the tensioner bolt. If not, adjust the number of washer shims between the tensioner support bracket and the pad.

Make sure that both cam timing marks align when the #1 piston is at TDC before re-assembling everything. It is very easy to get the marks off by a notch, and the car won't start or will run very poorly as a result. (Don't ask me how I know).

Many people I've talked to have never used any of the factory tools to change the belt, but I have found the spring compressor to be helpful. There is a third tool mentioned in the service manual, the pulley-stretcher, but I did not find it at all necessary to change the belt.

Each of the cam sprockets has a hole in it for setting timing. When the #1 piston is at TDC, these holes should line up with the raised markers on the camboxes. Use a dial gauge inserted into the #1 cylinder to find TDC. (You could use a timing wheel, but a dial gauge should work OK). Be careful when inserting objects into the cylinders that you do not have the valves try to open on them. The #1 cylinder is in the front of the car, on the passenger side (LHD).

When the #1 piston is at TDC and the cam marks are aligned, the #1 piston will be on the exhaust stroke. (If you don't believe me, remove the cambox cover and look at the orientation of the cam). I would not recommend rotating the engine with the timing belt removed and the camboxes installed, since piston/valve interference is a possibility. Rotate the engine first, and then install the camboxes and the timing belt (see above) if they are not already installed. Always have the timing belt tensioned when rotating the engine, and always turn the engine by the crankshaft, never by the cam sprockets.

With the #1 piston at TDC and the cam marks aligned, rotate the engine a full 360 degrees in the direction of engine rotation, so that the #1 cylinder is now on the firing (intake) stroke. At this point the cam marks will be 180 degrees out of alignment with the indicators on the camboxes.

The timing marks are located underneath the car on the flywheel. The timing specification should be located on a plate in the engine compartment or in your owner's manual. If you need to install the distributor, rotate the engine in direction opposite of the engine rotation in the amount specified by the timing specification (usually BTDC), then install the distributor such that the rotor points to the small notched mark on the distributor housing. This notched mark indicates the #1 cylinder. The rotor will want to rotate when you install the distributor, so keep that into account when you line up the rotor and reference mark. Tighten the distributor hold-down bolt. You can reach it from the rear using a 13mm flex socket. Start the car and check the final timing underneath the car (!).

Remove the engine oil drain plug using a 17mm hex socket. (Baum Tools carries one of these). Be sure to catch the copper crush washer on the plug. In order to remove the oil filter, you will need to push the radiator up a few inches. Remove the hex bolt holding the radiator bracket and gently push up on the radiator while snaking the filter out between the radiator and the front swaybar. The engine takes a UFI 23.171.00 oil filter. Re-install the filter and drain plug with a new crush washer and refill with synthetic oil through the valve covers.

I have seen recommendations that during every other oil filter change, the oil sump should be dropped and cleaned out, to remove any coked oil from the turbo- chargers.

Remove the differential fill plug first before removing the drain plug. If the fill plug is stuck and you drain the oil out, then you'll be in a heap of trouble. On the SensiTork differential, the fill plug takes a 1/2" double square (female) socket, and the drain plug uses a 1/2" pipe plug (male) socket. These can be obtained from Snap-On tools. The Snap-On part numbers for the fill and drain plug are SW416 and PPM516, respectively.

If the fill plug is distorted or otherwise damaged, a 9/16" double square socket might fit well enough to remove the plug. These sockets are available from the Sears catalog.

Be sure to use the correct differential oil type, according to the requirements in your owner's manual. In my owner's manual for my '86 425, it's GL-5. If the oil type does not exactly match your requirements, then do not use it!