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How To Replace the V4 Balance Shaft Gear
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How-To:  Replace The V4 Balance Shaft Gear

    This little darling is the bane of SAAB V4 owners the world over.  Anyone who has driven a V4 SAAB beyond 100K miles has experienced (or will soon experience) this failure.  I have included some information on identifying and repairing the problem below.  Corrections and additions are welcomed.

Chris Rogers, VSAAB

Symptoms

1)  Overheating while driving
2) Alternator light ON
3) Engine shudders, out-of-balance
4) Cooling fan not spinning but moves easily by hand

Effect

   The fiber (common) or nylon (rare) timing gear which drives the balance shaft has been stripped of its teeth.  When this occurs, the balance shaft pulley no longer spins.  This pulley is responsible for driving the cooling fan, alternator and water pump via the fan belt.  Without coolant being pumped through the block, the engine quickly overheats.  Obviously, the best way to avoid catastrophic damage to the engine is to shut it down immediately.  

Cause

   This is almost always caused by worn balance shaft bearings.  While these bearings may seem to have an unusually short lifespan, it should be pointed out that the bearings are often placed under excessive strain by over-tightening the fan belt.

Avoidance

   The best way to increase the longevity of the balance shaft gear is by keeping the fan belt adjusted as loosely as possible while still avoiding belt squeal.  This will prevent undue strain on the balance shaft bearings.  Of course, regular and frequent oil changes will extend the life of all the bearings in the engine.  It should be noted that in the USA, "factory" air conditioning was installed at the dealer.  Part of the factory-recommended installation procedure was to replace the fiber gear with a steel version.  It has been found that this part of the procedure was often ignored by dealer mechanics, leading to an exceedingly short balance shaft gear lifespan due to the inordinate stress the A/C compressor places on the gear when in operation.  However, if you come across a car with air conditioning installed, the steel gear may be in there -- a big selling point.

Repair

   Unless the mileage on the engine is unusually low, the failure of the balance shaft gear is a pretty good indicator of general engine health.   One can assume that if the balance shaft bearings are badly worn -- the others are probably not far behind.  If a complete engine refresh is out of the question, it is possible to replace the balance shaft gear alone.  However, if the balance shaft bearings are worn to an obvious extent, i.e. the balance shaft can be vertically moved even slightly by hand, it is not worth the time and effort to replace only the gear.

With that said, the next decision is whether to remove the engine to replace the gear, or attempt to replace it in situ.  While it *is* possible to replace the gear without completely removing the engine, it is not advised.  Here's why:

a) When the balance shaft gear fails, it's remnants drop into the oil pan.  It is impossible to completely remove all of those remnants simply by draining the oil.
b) The oil pan cannot be removed for cleaning with the engine in the car.   There is a cross-member that covers the rear-most pan bolts, making it virtually impossible to completely remove the pan.

Yes, but...

   What's that?  You still want to replace just the gear AND you simply must do it without removing the engine?  Good luck, here's what you need:

Before

1 Timing cover-to-block gasket
2 Blue silicone gasket cement or equivalent (oil-resistant)
3 Antifreeze
4 Timing cover oil seal for balance shaft
5 Replacement balance shaft gear, nylon if available
6 Oil and filters (enough for three or four oil changes)


During

1 Disconnect positive battery terminal
2 Disconnect windsheild washer hose from bottle
3 Remove hood
4 Loosen bleeder valve from heat exchanger, near firewall
5 Remove caps from radiator and coolant capture bottle
6 Drain radiator
7 Disconnect headlight wires & hood release cable
8 Remove grill assembly
9 Label all coil and alternator leads
10 Disconnect all leads from coil and remove coil
11 Disconnect all alternator leads and remove alternator and fan belt
12 Remove lower alternator bracket
13 Loosen hose clamp at upper radiator hose/manifold
14 Remove hose from manifold
15 Loosen hose clamp at lower radiator hose/radiator
16 Remove bolts on lower radiator mounting brackets, L/R
17 Remove radiator, extracting from lower radiator hose (messy)
18 Remove retaining bolt from balance shaft pulley
19 Remove balance shaft pulley GENTLY  (a 5" gear puller helps a lot!!)
20 Remove all bolts around timing cover (1/2" socket)
21 Remove 5 forward bolts from oilpan and all bolts from left and right side, leaving rear bolts in place (they're virtually inaccessible anyway)
22 Loosen hose clamp on upper water pump inlet hose at water pump
23 Loosen hose clamp from head-bound water pump outlet hose and remove hose from pump
24 Gently and carefully pull the timing cover away from the block, complete with water pump and fan.  A putty knife slipped between cover and gaskets can help to facilitate removal of the timing cover. The idea is to sacrifice the timing cover-to-block gasket, but desperately try to preserve the oil pan gasket. If it gets destroyed, you're in trouble. Hopefully the oil pan gasket will come away cleanly from the timing cover and remain intact on the lip of the oil pan.

NOTE:

     The remains of the balance shaft gear will probably clear the lip of the oil pan for removal, however, installing the new one will require that the oil pan be levered down for clearance. Again, take care not to damage the oil pan gasket or bend the oilpan excessively. This is the part of the job where you are clearly in Mickey Mouse territory. However, if luck is with you, it's also the part where a 24 hour job becomes a 6 hour one.

25 Using the 5" gear puller if necessary, remove the remains of the old balance shaft gear.
26 Oil the contact area of the balance shaft liberally with fresh motor oil.
27 Using a large screwdriver or pry bar, *gently* lever the oil pan down far enough to allow installation of the new balance shaft gear. It must move less than 1/2 an inch and if it is done carefully it will not harm the pan or the pan gasket. When levered down sufficiently, use small wooden shims between the oil pan and the block to hold the pan down far enough for the new gear to clear the oil pan lip while it is pressed onto the shaft.
28 Before installing the new balance shaft gear, you must align the dot on the face of the crank gear (the big one) with the #2 dot on the face of the cam gear (small one).  This will properly align the first dot on the cam gear which must align with the dot on your new balance shaft gear.  It sounds confusing, but at this point, simply know that both dots on the cam gear *MUST* be aligned with matching dots on *BOTH* the crank gear and the balance shaft gear.
29 To align the crank gear dot with the cam gear dot, set the emergency brake and shift to neutral. With a large ratchet (preferably 3/8" drive and socket, *slowly* turn the crank gear clockwise (left-to-right) until the dots line up. The  other dot on the cam gear should now be facing the balance shaft.
30 Smear fresh motor oil on the contact surface of the new balance shaft gear.
31

Carefully align the dot on the balance shaft gear with the dot on the cam gear and press the new gear in place on the balance shaft.  It will not simply slip on and a rubber mallet will be a big help in getting the new gear on. However, take your time.  This is not the time to work out your frustrations -- tap, don't bang. Here's why:

a) The gear must rotate slightly as it's teeth mesh with those on the cam gear.
b) There is a freeze plug on the other side of the balance shaft.  If you bash the gear onto the shaft, you're likely to send the balance shaft back through the engine enough to dislodge the freeze plug.   :-P
c) You're already dealing with questionable balance shaft bearings.  Banging on the shaft will not improve that situation.

32 Once the gear is in place and it's face is flush with the other gears, go wash your hands and grab a cold beer.
33 Before reassembly, the oil seal on the timing cover must be replaced.  If at all possible, this process should be done using the proper drift.  Digging the old seal out with a screwdriver will likely damage the inner surface of the seal channel.
34 As they say, "installation is the reverse of removal."  Clean sealing surfaces well and use a reasonable amount of gasket cement on the timing cover and oilpan.  The oilpan gasket will probably leak somewhat after reassembly -- the price you pay for a quick job.

After

 Keep in mind that you have now have a bunch of fiber bits in the pan that you won't be getting out until you actually remove the pan.  The best you can hope for is to remove the small bits that get sucked into the sump and trapped in the oil filter.  Prior to starting the engine, change the oil and filter.   Run the engine to operating temperature and change the oil and filter again.   Take a short drive around the block and change it again.

Is this excessive?  Perhaps.  But each time you take a turn or hit a good-sized bump, those bits will have another opportunity to run through your engine and/or clog the sump.  To me, every oil change improves the odds against a major problem.  If you have an oil pressure gauge, glue an eyeball to it -- and start saving your pennies for the overhaul you know that engine needs...

Chris Rogers, (5/98)


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Last modified: February 29, 2016