3RZ-FE broken balance shaft chain

After a few days of research on the internet and consultation with mechanics and engineers, I found a large number of cases of balance shaft bearing failures in Ecuador, the US and beyond. My machine shop in Quito has serviced 15 of these in the last two years. This is occurring in the 3RZ engines as well as similar in-line four cylinder engines that suffer from inherent vibration problems, such as those found in Mitsubishi's and KIA/Hyundai's. It is so common in the 3RZ that folks have an acronym for it (Balance Shaft Elimination or BSE) and LC Engineering in Arizona sells a balance shaft elimination kit for helping people correct the problem, as well as for racers who seek BSE as a means of increasing horsepower.

As you may already know, a balance shaft bearing failure can be expensive. Not only did it strand my family (including a two-year old child) and me in the middle of nowhere on the Ecuadorian coast, I have had to remove the engine and machine parts of the block and rebuild my engine (the valves were not affected).

Mechanics and engineers familiar with this technology inform that the balance shafts play no role in decreasing engine vibration. The in-line 4 cylinders inherently suffer from vibration problems. All the balance shafts spin in reverse directions to the camshaft at twice the rate of the engine RPMs, which generates considerable force on the bearings. All they do is dissipate the already generated vibration for rider comfort. They play no particular lubrication function (other than a small jet that sometimes exists at the pinion for lubricating the timing chain; LC Engineering sells a replacement jet).

Yes, you can feel the difference when standing still and revving the engine at 3,000 RPMs, but it quickly disappears once you get started. My All Terrain tires easily generate a greater degree of vibration in the pilot cabin. In addition, driven directly by the camshaft, the balance shafts consume horsepower (between 5-15 hp, depending on how you measure and who you believe). The only potential concern may be increased oil pressure, but no one I communicated with has experienced associated problems.

I would recommend that folks keep an eye on their balance shaft bearings (how without removal of the engine, I don't know!), but keep your ears open for the earlier described marbles... By removing the oil pan, you can reach the balance shafts which lie just above and to either side of the camshaft. If you feel any movement in the shafts, you may have a serious problem in the making... In the event of needing to remove your engine for other purposes, I'd recommend a BSE. I'll report if I have any problems down the road, but from the multiple experiences out there, I do not expect any.

If you are interested in obtaining a balance shaft removal kit for the 3RZ engine do a search at LC Engineering in Arizona.