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Renewing balancer shaft bushes in SAAB B204/234/205 & B235 engines
Applies to SAAB 9000 (from 1993), NG900 , 9-3 (9400) up to 2002 & 9-5 (9600) 4 cylinder petrol engines

A full heavy general overhaul of the 4 cylinder petrol engine must include stripping and inspecting the two balancer shafts and their bearings. If this is not carried out, there is a risk -especially if the engine has sustained a loss of oil pressure- that when reassembled there will be no oil pressure. This happens because the oil feed to the balancer shaft bearing may be cut off. Whereas the balancer shafts can be inspected without special equipment, if the bushes need changing the SAAB Special Tool would be required. Please READ the special warnings in the article before starting work to avoid unnecessary damage.

Balance shaft bearing pull tool is a must for this operation


Background: how balancer shafts work
As many readers will be aware, the SAAB B234 engine was the first SAAB to feature balancer shafts. Traditionally, engineers had shied away from 4 cylinder designs with capacities greater than 2 litres because of the difficulty in achieving the necessary degree of smoothness. This may explain why manufacturers like Audi and Volvo experimented with 5 cylinder designs or V configurations for applications where restricted space or weight considerations ruled out a 6 cylinder arrangement.

The SAAB engine design employs a pair of balance shafts located at different heights within the engine block driven by a thin simplex chain running in the opposite direction to the engine's normal rotation and running at twice the speed of the crankshaft. Readers wondering why such an elaborate arrangement is required find an answer in Physics: the effort exerted upon the piston crown during combustion together with the reciprocating action of pistons and connecting rods together with crankshaft rotation cause inertial forces that result in vibration. Balancer shafts have eccentrically positioned weights specifically designed to cancel out vibration from inertial forces but for them to work as intended, the shafts and the sprockets bolted to them must be timed up in the correct position. Where this is not carried out, a persistent vibration from the engine will be noticeable to a greater or lesser extent, according to engine speed.


Removing the balance shafts

Pre-requisites:
The engine MUST be removed from the car and split from the transmission
The timing cover must be removed & the timing gear removed
The sump should be removed
NOTE: Both these procedures are covered within the procedures archive

Tools:
Hammer, chisel, wooden drift, air supply and blow gun, SAAB Press Tool 83 94 470

Parts:
2x Sealing washers SAAB part # 92 151 501, 2x bushes SAAB part # 91 72 230

Balance shafts should come away easily when the bolt is undone: do NOT lever them! Read text for details

In theory, balancer shaft removal should be simple -undo the single retaining bolt on the front bearing housing and simply lift away but practice has proved that the very opposite is true.

WARNING #1: The shafts should be turned so that the weights point upwards, then withdrawn slowly taking care to avoid damage to the inner support bearing.

WARNING #2: Should the shaft not come away easily, on NO account lever or pry the bearing support within the timing case. Instead, use a hammer and chisel to knock out the large sealing washer (core plug) at the back of the balance shaft chamber. Use pliers to pull out the old plug. Use a suitable blunt piece of wood (an old broom shank, for instance) as a drift and gently tap out the shaft from the back using a hammer.

Inspecting the balance shafts

With the shaft removed from the cylinder block, check for damage to the balancer shaft bearing journal. Slight marks are acceptable but heavy scoring or ridges mean that both the shafts and the bearing MUST be replaced. Do bear in mind that it is quite permissible to use shafts from another engine (the balance shafts are the same irrespective of whether the engine is from a 9000, NG900 or 9-5) so long as new bushes are fitted. If the balancer shafts are OK, the bushes within the block may be left undisturbed so long as the oil supply is checked with a compressed air supply to ensure that the oil feed is clear.

Balancer shafts and bearings seldom wear except where there has been a lubrication failure

Renewing the balancer shaft bushes

The author cannot over stress the need for the correct tool for this job. Whereas some repair operations for which the maker recommends a special tool can be performed with an alternative DIY solution, this job is not one of them. Time and patience will also be required to carry out this operation successfully - don't even think about rushing it!

Alignment of the bush is critical: the author recommends that before using the tool, readers should examine and note the location of the bush -just visible with the cylinder block turned upside down- before starting.

From the flywheel end of the cylinder block, assemble the SAAB press tool and connect the operating rod, washer and nut. The author recommends that a socket is used as a spacer (see photo). Tighten the nut slowly to pull out the old bush. Expect the bush to require considerable effort on the pull rod before it starts moving.

Removing the bearing with the tool is straightforward but it does need locking and a socket used as a spacer is helpful.

Mount the new bush on the recess machined into the pull tool, then install the tool from the back of the cylinder block (i.e. the flywheel end), fitting the large washer and nut. Tighten the nut progressively (it will be tight) until the machined recess in the tool is 5mm from the edge of the housing for the core plug. In practice, we always make a visual check on the bearing position but of course the tool allows the position to be altered quite easily.

The new bearing slides onto the pull tool and is pulled into position. The tool has a red line to advise when the baering is in the correct position but in practise, the bearing should be pulled in until it LOOKS right

This is the correct position for the bush within the block and the bush position should correspond with the position of the original bush, as noted before starting work.

Warning #3 It is essential that compressed air is blown down the drillings from the centre main bearing to establish that the oil feed to the bearing is not blanked off. As a final fail safe, use an oil can to make absolutely sure that oil can run down the drilling into the balance shaft bearing.

It is essential to check the oil supply to the bealancer shaft bearings is clear - used compressed air to make sure!

Finally, fit a new blanking washer (plug) to end of the balancer shaft housing by smearing a bead of Loctite 518 around the washer.

Remove any burrs or rust that might prevent the new plug from fitting easily before tapping the plug into position with a hammer and suitably sized socket. Be sure not to install the plug too far into the housing!

Oil the balancer shaft bearing surfaces and replace the shafts, ensuring the balance weights face upwards to avoid damage. Tighten down the front support bush bolts to finish the job.


How to replace balance shaft bearings in SAAB B204, B234, B205 and B235 engines as fitted to SAAB NG900, 9-3, 9-5 4 cylinder petrol models. Checking balance shafts on SAAB engines. How to inspect or change SAAB balance shaft bearings

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