1. Introduction
Balance shafts are commonly found in inline four cylinder engines such as the Mitsubishi 4G63 which, due to the asymmetry of their design, have an inherent second order vibration (vibrating at twice the engine RPM) which, contrary to popular belief, cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the connecting rods in an inline engine is not symmetrical throughout the crankshaft rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertial force twice in each revolution whose intensity increases quadratically with RPM, no matter how closely the components are matched for weight.
The 4G63 found in the Mitsubishi/DSM turbo Eclipse & Eagle Talon are equipped with 2 balance shafts. The left balance shaft that's directly connected to the oil pump driven gear and the right balance shaft that's driven by the balance shaft belt over the oil pump sprocket. Two balance shafts rotate in opposite directions at twice engine speed. Equally sized eccentric weights on these shafts are sized and phased so that the inertial reaction to their counter-rotation cancels out in the horizontal plane, but adds in the vertical plane, giving a net force equal to but 180 degrees out of phase with the undesired second-order vibration of the basic engine, thereby canceling it. The basic problem presented by the concept is adequately supporting and lubricating a part rotating at twice engine speed at the higher RPMs where the second order vibration becomes unacceptable.
So why do it? The main reason for balance shaft elimination should be reliability as power gains are minimal. As you can see it inherits a potent lubrication problem and unlike the name suggests it's job isn't to balance but merely masks off the vibrations. Silent shaft is a more appropriate term but not used as commonly. Although the chances are slim, it's still one less part that can fail.
The good- More HP to the wheels
- Zero chance the balance shaft belt will fail and kill the timing belt
- Zero chance the balance shaft bearings will fail and damage the rest of the motor
- More oil pressure to the rest of the motor
- More vibration is felt in side the car (no more is made, just more is felt)
- More oil pressure to the rest of the motor, which is usually too much. Extra work to get the oil pressure back in spec.
2. Parts Required
| MD098626 | Stub shaft to replace the left balance shaft |
|---|---|
| MD040597 | Right balance shaft front bearing used to block the oil galley1 |
| MD103722 | Right balance shaft rear bearing used to block the oil galley1 |
| MD092785 | Plug to block off the right balance shaft provision on the front case |
| MD128107 | Spacer to replace the crank shaft sprocket B2 |
| MF140022 | 8 x 14 bolt to replace the balancer belt tensioner (any bolt will do) |
*1 You can use your existing bearing if you're able to pull them out without damaging it.
*2 This is optional but recommended.
* Same parts apply to all 6-bolt, 7-bolt, 1G & 2G. Also applicable to the EVO1-3 and Galant VR4.
3. Balance Shaft Removal
Front case removal
Remove the plug bolt located under the 3rd cylinder freeze plug about 2 inches above the oil pan. Inset a Phillips screwdriver with a shank diameter of 8mm (.32 in.) into the plug hole to lock the balance shaft.
Check to be sure that the screwdriver goes in 60 mm (2.36 in.) or more. If the screwdriver will only go in 20 - 25 mm (.79-.98 in.) before striking the counterbalance shaft, turn the sprocket once and check that the screwdriver goes in 60 mm (2.36 in.) or more. This will lock the balance shaft and prevent the oil pump sprocket and driven gear from spinning while loosening the nut/bolt.
Remove the oil pump sprocket.
Remove the castle plug. The special tool isn't much help since it slips off when torque is applied. Just tap the teeth with a blunt end to break it loose.
Remove the underlying o-ring in the front case groove.
Remove the driven gear bolt that secures the oil pump driven gear to the left balance shaft.
Remove all accessories on the front case and remove the front case from the cylinder block.
NOTE : If the front case sticks to the block pry over the M10 bolt where the flange is the thickest. Cover the crank shaft key with a cloth to prevent damage to the oil seal when pulling out the front case.
Right balance shaft oil feed
4. Balance shaft bearing install
Install the bearings flipped 180 degrees at the vertical axis to block off the oil hole. You can see the bearing oil hole is now to the left.
NOTE : Install the rear first. You can use the balance shaft's front end since it has a larger diameter than the rear bearing.
The left balance shaft bearing can be eliminated since the oil is fed through the shaft and not from the block.
5. Stub shaft install
Install the stub shaft to the oil pump driven gear and torque the driven gear bolt to 25-29 ft.lbs.
Use red loctite or equivalent!
Install the oil pump gears so that the timing mark are shown. You can opt to pack the space with petroleum jelly to build oil pressure faster when priming the engine.
Install the oil pump cover and torque to 11-13 ft.lbs. The cover is installed dry without any gasket.
NOTE : Since we're eliminating the balance shaft there's no need to align the timing marks on the pump gears.
6. Front case plug install
Remove the front case oil seal (red arrow) and install the rubber lined plug in it's place.
The black arrow on the front case is where the balance shaft belt tensioner bolts to. The tensioner is replaced with a shorter 8x14 bolt.
NOTE : Most recommend the use of sealant at the plug and bolt flange. At the plug I never had a problem, when reusing an old frontcase I had oil seeping through the bolt. Above and below the bolt is where the oil passages are so I placed a 1" O.D washer under the bolt and it took care of the problem. The washer used in the tensioner arm works great.
Install a new gasket and lube the crank oil seal and temporarily bolt the front case to the block.
Mount the oil filter housing with a new gasket and torque all M8 bolts to 14-16 ft.lbs.
NOTE : The M10 bolt in the red circle should be tightened at a torque of 20-25 ft.lbs
Install the castle plug and torque to 14-20 ft.lbs. Don't forget to install the o-ring on the front case groove, you risk cracking the front case if you torque the castle plug without it.
Install the oil pump sprocket after lubricating the oil seal and torque the nut 36-43 ft.lbs. This should be done before installing the oil pan as there's no easy way to lock the sprocket with the balance shaft gone.
7. Crank shaft sprocket spacer
The spacer also from the Mirage 1.6 DOHC goes in place of the crank shaft sprocket "B" that would have been spinning meaninglessly without the balancer belt. Not really needed, but it weighs 2oz which shaves 8.7oz off the rotating assembly. Not bad for $7.
Put everything back on, time the belt and you're done.
With the added vibration, I strongly suggest you clamp the oil filter to prevent it from coming loose.
8. How to fix the high oil pressure
...
Removing the balance shaft without pulling the motor
- Remove timing belt, downpipe, transfer case and oil pan.
- Remove alternator, power steering pump, cross member, front and left motor mount to drop the engine low enough.
- Remove the front case with the left balance shaft attached. This involves pulling the crank shaft sprocket and everything else over the front case.
- This is all done laying on your back with oil dripping on your face :D
Ebay Balance Shaft Elimination kits
Stay away from the no-name Ebay BSE kits that provide you with a steel non-rubber lined plug and a stub shaft without an oil groove. The Mirage stub shaft and Eclipse balance shaft both have large grooves acting as a pool for proper lubrication.
Another balance shaft elimination using a full shaft instead of the stub shaft
There are vendors that machine off the left balance shaft's counter weights or provide you with a billet shaft so you have a full shaft rotating instead of using the short stub shaft. Theory is, a stub shaft without the support provided by the rear bearing journal allows the oil pump gears to push apart and wear into the aluminum pump. Eventually resulting in the oil pump seizing. There are more than enough DSM & Evo's with a stub shaft to believe this isn't a problem. Don't let the oil pump run dry and you won't have a problem.