DKW Auto-Union Project: English Translation of the Austrian DKW F91 Repair Manual

Motor removal

Depending on the scope of the required maintenance work, in the DKW special class either the engine itself or the engine-transmission unit can be completely removed. In any case, the front of the car must be lifted, with the supports necessary for jacking it up under the wishbone beams or under the frame. After removing the front wheels, loosen the radiator grille and unscrew the water hoses (it goes without saying that the radiator water and transmission oil must be drained off first). The earth cable is to be loosened on the battery, the sensor of the remote thermometer in the upper water hose is to be removed and the hose itself to be detached from the cylinder head. Unscrew the lower cooling water connection on the right (as seen from the front), then loosen the radiator fastening screws, loosen the heater control rod and the strap for the rubber body on the heater box. If the engine is being removed by yourself, it is sufficient to tip the radiator backwards a little, otherwise it may be carefully removed by lifting upwards.

After removing the air intake silencer, the carburetor is covered, the Bowden cable of the starter carburetor, the fuel line on the pump and the accelerator control are disconnected. The wing nut of the clutch adjustment is removed and the exhaust manifold is unscrewed from the exhaust pipe after removing the heat conducting plate. If the motor is being removed alone, it is advisable to remove the light metal bracket in which the breaker plate is mounted and to hang it sideways with all the cables. The best thing to do is to support the gearbox with a jack so that it cannot sag down after loosening the 6 flange screws.

Whether removing the engine alone or the engine-gearbox unit, the starter must be flanged off and the cables on the alternator completely removed. Now the fastening bolts of the front engine mounting can be removed, followed by those at the rear. The rear engine mount mounting bolts are the last remaining part of the engine to be removed. Now the motor can be removed diagonally forwards by just two men, using the fan belt to provide grip.

However, if the transmission is still to be removed, the cables for the freewheel and the clutch must also be removed and the shift linkage between the transmission lever and the selector cable loosened, and finally the odometer cable unscrewed. After removing the upper bolts for the swivel bearing suspension on the front spring, the joint sleeve on the gearbox must be released. Then the spoon joints are rotated in the gear so that they go out through the rectangular opening in the oil baffle and thus both inner cardan shafts can be pulled out by pushing the pivot bearing away to the side.

Danger! Make sure that the rubber caps are not damaged when you remove them! At least the left pivot bearing must be supported in such a way that the brake hose in front of the semi-axle is not unnecessarily stressed. At the rear end of the cylinder block there is a support screw to which the lifting rope is to be attached in order to lift the unit with a rod. This way there is no need to remove the hood.

Installation
When installing the motor-gearbox unit, the main thing is to correctly adjust the gearshift rods, while the other steps must be carried out in the reverse order to the removal instruction. It can be useful to remove the rear engine mounting and the rubber mount before reinstalling it and then to put it on the gearbox. By twisting the rubber mounts, the mount can then be pushed into the frame relatively easily.

Dismantling the engine
After removing the cylinder head, including the fan shaft and fan, the carburettor with intake manifold, fuel pump, clutch and flywheel must be removed. In doing so, it is essential to ensure that the clutch pressure levers are supported by placing U-brackets underneath before loosening the fastening screws so that the clutch plate does not warp when the screws are loosened. The clutch spring pressure of 420 kg makes the clutch unusable if it is not thought of!

Then you place the engine on the cylinder head bolts so that you can easily loosen the 14 screws that connect the lower part of the crankcase to the cylinder block (which is also the upper part of the housing). You will notice that the lower part, including the screws is over-moulded with an insulating compound about 5 mm thick, which should be retained if possible. After removing the lower part of the housing (lightly tapping with a rubber hammer), the crankshaft and the pistons can be removed. The fan pulley, which is connected to the crankshaft end can of course also be removed.

The following must be observed during reassembly: When exchanging connecting rod bushings, the shaft must be inserted into the cylinder block with the connecting rod facing up, and new bushings must be fitted with a clearance of approx. 0.03 mm. For this purpose, rubbing devices with intermediate angles (DKW special tool) are to be used. Under no circumstances should connecting rods be straightened.

Piston pin
These are fitted in a floating manner (18 mm (/)) and secured with spring wire rings. Piston 1 (flywheel side) is a mirror image of pistons 2 and 3 (overflow ducts-cylinder 1) rotated by 180 ° with respect to cylinders 2 and 3. Arrows on pistons must point to the exhaust. When reinserting the shaft with the piston attached, it is advisable to use special piston ring clamping bands. Two skilled mechanics, one of whom has to hold the shaft, can carry out the installation without this aid, as there is a corresponding chamfer at the beginning of the cylinder liner, which makes it easier to insert the piston rings. When inserting the shaft, make sure that the two joints of the ring seals on the coupling side do not come into the plane of the housing separation surfaces. Before placing the lower part of the housing, the belt pulley with the two sealing rings must first be inserted. Later attachment without special tape causes difficulties. The rings should have a side clearance of 0.1 mm. The joint dimension is the same as for the coupling-side sealing rings, i.e. 0.2 mm. The interfaces between the upper and lower part of the housing must be thoroughly cleaned before assembly and kept clean. The separating surfaces are to be coated with thin sealing compound. The screws are to be tightened with the prescribed torque of 4.5 m / kg from the inside to the outside crosswise. The installation of the remaining part is to be carried out with due attention and care with regard to tightness and does not cause any particular difficulties. (The instructions under the relevant heading provide information on setting the ignition.)

When installing the clutch, make sure that the clutch disc is centered using a special mandrel.

Note: the fan shaft, like the alternator, has permanent internal lubrication and generally does not require any maintenance.

Ignition timing
After releasing the pawl behind the second decorative rib, open the hood from above and remove the front dummy radiator screen (there are 2 quick-release fasteners). After removing the interrupter housing cover, first set the contact spacing on all 3 interrupters at the highest cam position to 0.4 mm. Insert the ignition setting gauge in the middle cylinder (No. 2) and bring the piston to 5 mm before top dead center (by turning the fan belt), control lamp on the associated breaker, which is the lowest, and connect to ground. Switch on the ignition and fully eject the flyweight by turning the breaker cam to the right. The lamp should just light up when the flyweights are fully ejected. If there are deviations:- after loosening the clamping screw, turn the interrupter mounting plate accordingly and clamp it again. Then repeat the same process on cylinder No 1 (on the flywheel) and the associated breaker at the top right. Any slight deviations that may exist must be compensated for by small changes in the contact distance. Exactly the same applies to cylinder No 3. The interrupters in the corners of the stop blocks should be lubricated with special grease (Bosch FT 1 V4) every 6000 km. The lubricating felt cartridge in the hollow interrupter cam must be replaced every 12,000 km.

Transmission

As long as the engine and gearbox have been removed, there is naturally no problem in flanging the 3 or 4-speed gearbox on the workbench. The first step is to look at the clutch pressure. Clutch thrust bearings, which can be retrofitted to the transverse shaft with little or no rework, have recently been used. We would like to say in advance that the dismantling or assembly of this gear unit cannot be carried out properly without a few special tools or specialist knowledge, or they must be mechanics above average who are able to help themselves, i.e. Carry out a pending repair in an emergency without or with self-made special tools. We want to identify the possible consequences of wear and tear in advance. Check for wear on the 2nd and 3rd gear synchronizer rings after extended use. Experience shows that even after several 100,000 km the remaining gears of the gearbox and differential gear do not give any reason to change with only reasonable care and lubrication of the built-in roller bearings.

To dismantle the gear unit, the drive shaft must first be pulled out of the inner part of the freewheel after removing the freewheel mechanism and the two slotted screws of the sealing flange or knocked out carefully beforehand. You have to remove the large differential cover beforehand (provided with 2 pressure bores) and let the differential cage fall out completely. Also remove the small differential cover and knock the bevel gear with the bearing out of the housing. When doing so, prevent inner parts of the spoon joints from falling out on both sides by pushing over the metal sleeves (piston ring tightening straps). Then you can pull out the inner body of the freewheel with its 6 rollers (if a ring is still attached to the freewheel bell, it should be removed beforehand and not reassembled later. Proper work is only possible using a special tool to hold the individual parts. Then remove the two small needle roller bearings from the main gear shaft. Here, proper activation of the freewheel of the DKW special class should only take place when the clutch is depressed. For further dismantling, the rear gear cover and the large cover of the change gear must be removed. It is imperative that all seals and washers remain in place or be replaced by ones of the same thickness.

Now, after switching on 2 gears (reverse and 3rd gear - use 2 screwdrivers), loosen the nuts on the main and drive gear shafts, remove the wire locks of the locking screws on the shift rods and loosen them. Pull out the shift rods on the spacer sleeve (shift travel limitation) carefully. Now remove the small sealing ring from the main shaft using a 45 ° cranked, outwardly clamping pliers and pull the freewheeling bell off the spline of the main shaft using a special puller. Then remove the large sealing ring behind the output bevel gear and push out the shaft together with the roller bearing behind the small bevel gear or knock it out carefully. The wheelset is taken out one at a time. Make sure, however, that the wedge bushing described later is not removed from the shaft. Otherwise you have a salad of balls and feathers. It is advisable to make a quick sketch so that you later know how the parts are put together.

Now the angular contact bearing of the main shaft can be carefully knocked out or pressed shut. The bushing for these bearings should remain in the housing if possible. As a result of the bearing greatest load, there is a high probability that the synchronous bronze ring for 2nd gear will wear out first after a long period of operation, and therefore this gear can no longer be switched silently.

We assume that the mode of operation of normal synchronization is known. What is new is that two locking bars only allow the axial movement of the shift sleeve when the speeds of the gears or shafts involved in the shifting process are completely synchronized. The brass synchronizer rings will need to be renewed if the screwed-in oil grooves are worn through or the compression springs are slack. When synchronizing the 2nd gear (in the four-speed gearbox) it should be noted that the short springs must be inserted into the through holes of the synchro-hub with one ball inside and one outside, and the long springs with one ball outside (a total of 6 pieces). The holding pressure of the synchronization, which can possibly be checked by placing weights on it, is around 8 kg. Conversely, from the neutral position of the gearshift sleeve up to the engagement of the cone on the sonic wheel (2nd gear) or gearshift sleeve (3rd and 4th gear) in the respective synchronizer ring, at least 0.3, but not more than 1½ mm of air. Of course, the condition of the locking bar and the run-up curves on the synchronizer bodies must also be paid attention to.

If nothing is to be examined on the parts of the output shaft, the installation of the main shaft can be carried out again after assembling the synchronization, whereby the correct position of the individual parts must be ensured, by placing the main shaft with the roller bearing and the spacer behind it simultaneous insertion of the individual parts of the wheel set gradually pushes in from the differential side. In doing so, it is essential to ensure that all the disks come back to their designated place, otherwise the setting of the differential is no longer correct. The setting itself can only be made using a measuring device. To remove the output shaft, first pull off the freewheeling bell using a special puller, if not already done, and then remove the ball bearing on the rear side of the gearbox with a special puller. Then the roller bearing on the differential side can be knocked out using a driving mandrel and the shaft can be completely removed. The synchronization parts are checked as already described. Particular care must be taken to ensure that the parts are assembled in the correct position of the sliding sleeve. In the top view, the ratchet teeth must each be located behind the locking bolt that is guided from the front. Namely, it is easily possible to put the locking mechanism out of action by turning it through 90 °, which would then make it necessary to dismantle it again. The synchronization pressure, caused by 4 equally sized springs with a total of 6 balls, should be 7 kg. If the compression springs are slack, there is not enough time during the switching process to bring about complete synchronization of the wheels involved, which is noticeable by ratcheting during operation.

The assembly is done in reverse order. First, the drive shaft with all parts must be inserted. The freewheeling bell is pressed open with the same device that is used to pull it off during dismantling. After replacing differential ball bearings, the backlash of the teeth, which should be 0.15-0.20 mm, must be measured and, if necessary, adjusted by replacing the shims or differential cover seals under the bearings.

Front axle
The dismantling of the swivel bearing bodies for replacement of ball bearings and the like does not cause any difficulties after the brake drum has been pressed off. The pulling in of the outer cardan shafts during assembly is best done using a special device. It is recommended to lightly grind the hubs onto the cone of the outer cardan shaft. The storage of the lower wishbones in silent blocks is practically unlimited. Adjustment of toe-in is by means of the adjustable tie rod on the right. Adjustment of the steering axially is by means of adjusting screws and engagement of the pinion by means of an eccentric bearing bush, adjustable steering brake.

Rear axle
The complete rear axle can be removed after pressing the trailing arm away from its attachment to the frame, removing the left spring fastening screw, the right screw with sliding sleeve, removing the brake hoses and unhooking the handbrake and shock absorber arms. The rear spring can be removed sideways after loosening the clamp nuts.

Electrical system

Replace the lubricating felt in the hollow breaker cam every 12,000 km, grease the breaker lever in the corners of the fibre blocks with Bosch grease. Spark plug gap must be 0.5 mm.

The original instructions in German - https://dkwautounionproject.blogspot.com/2020/12/dkw-f89p-and-f91-repair-instructions.html