Previously, a Timken bearing install required time-consuming machining of the left-side crankcase. A Timken conversion can also be considered for stock 88ci or 96ci engines, so plan accordingly to avoid rolling the dice and losing sleep at night worrying about potential “bottom end blues.” Nevertheless, it is prudent to install a left-side Timken bearing on all ’03 and later Twin Cam engines when doing major performance upgrades or the engine cases are disassembled. Do yourself a favor-don’t follow in their footsteps. Unfortunately, some riders have waited too long and have only considered a Timken conversion after their engine’s straight roller bearing disintegrated. Installing a Timken bearing in a left-side TC case requires disassembling the engine, so this upgrade is best done when doing major performance upgrades such as installing a stroker crank or big-bore cylinders that require crankcase machining. Since the Timken bearing is more tolerant of crankshaft flexing at high speed, it is used in aftermarket Twin Cam crankcases designed for high-performance and racing applications. The fix for the bearing problem is to replace the straight roller bearing with a dual tapered Timken roller bearing. When that happens, broken bearing fragments fall into the flywheel cavity and end up circulating with the engine oil, destroying engine components and sometimes leading to catastrophic engine damage. ![]() Once an engine reaches approximately 100 horsepower or more, normal crankshaft flexing at high speed can fracture the straight roller bearing’s outer race. While the straight roller bearing eliminates the need for setting bearing endplay, which significantly reduces labor costs during assembly, it cannot sufficiently handle the high loads generated by big bore/stroker engines designed for substantial horsepower output. For ’03 and later TC engines, the factory replaced the durable Timken with a straight roller bearing on the left-side sprocket shaft. When set up correctly, the Timken bearing provides trouble-free service for even the largest and most powerful engines. Similar to the Shovelhead and Evolution engines, the ’99 to ’02 Twin Cam engines were shipped with a dual tapered Timken roller bearing on the crankshaft’s left side. ![]() In this discussion, we will focus on replacing the Twin Cam’s left-side crankcase straight roller bearing with a tried-and-true tapered Timken roller bearing. For instance, if you have an ’03 or later Twin Cam, one worthwhile modification is converting the engine’s left-side case roller bearing to a more robust dual bearing setup. Although the Twin Cam engine improved upon many of the Evolution’s shortfalls, there are still several major improvements you can make to the Twin Cam’s lower end that will afford you peace of mind and worry-free performance. ![]() An opinion, nothing more.Building a solid bottom end should be foremost in one’s mind when hopping up any engine. Like I say, if it was mine, I'd only change the pulley, but buy in the other parts, ready to do the full job, if and when the time comes. Would be different if it was the front pulley that had gone, because it would be pulled down anyway to change that, and no point in skimping then. When the belt change ultimately was done, the rear pulley wouldn't be changed a second time, unless it was years down the road, and well knackered again, so I'm thinking there's nothing to be lost by just changing the pulley on its own, for now. Replace the rear pulley, front pulley and belt, all at the same time.Īs the belt doesn't seem to be in imminent danger of failure, my view is just change the rear pulley now, and hold off on the belt change for a while, maybe a long while, rather than do all that invasive surgery, possibly for no benefit. Hope the belt is OK, and run it until it isn't.Ģ. ![]() Fit the rear pulley, and do nothing else. I think Roy is buying a new rear pulley anyway, so the options (as I see it) are:ġ. Yes Kev, I think we may well be at cross purposes here.
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