Motorcycle: Hardware - Twin Cam 88
Date: Sunday, October 31 @ 14:08:19 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
Twin Cam 88
The Twin Cam was unveiled in 1998 and billed as "the biggest change in engine design since the Knuckle". First seen on the 1999 SuperGlides, DynaGlides, Road Kings, RoadGlide and ElectraGlide, the Twin Cam offers more power and torque in a smoother, more refined package. Yet despite the name, this is still an overhead valve engine — the cams in question are downstairs. Unlike the gear-driven camshafts of previous big twins, these are chain-driven and far less costly to produce. Considerable savings are also made in crankcase machining, which required 37 distinct operations on the Evo but only three on the Twin Cam.
One area which received particular attention was the oil circulation. Surprising though it may seem, as they set out to create the Twin Cam, Milwaukee's engineers had very little idea what the lubricating oil in the Evo engine actually did — except that it didn't always go where it ought and that pressure could fall dangerously under very hot conditions. After 18 months of painstaking work on engines littered with Plexiglass "windows", the engineers believed they had the new engine figured out at last. In fact, the actual hardware — a high-capacity "gerotor" pump and two distinct scavenge systems — is less crucial than the engine's internal detailing. This was simple compared to the project's biggest problem, which had nothing to do with hardware,
but with people. After the lay-offs of the 1980s, Harley simply didn't have a team capable of developing a new engine. One had to be created almost from scratch before work on the Twin Cam could begin. Depending on the state of tune, Harley claims a 14—22 per cent power increase (to 87bhp on the DynaGlides) compared to the previous Evolution design. This is achieved partly through higher compression ratios, improved combustion-chamber shape and induction plumbing, as well as a new ignition pack.
Last but not least is a ten per cent increase in capacity to 88.4cu in (1,449cc), making this the largest stock engine Milwaukee has ever built. To achieve the extra volume, the stroke has decreased from 4 to 4 1/4 in (108 to 101.6mm) while the bore has risen substantially from 3 7/16 to 3 13/16 (88.8 to 95.3mm). Traditionalists may bemoan the departure from the hallowed 88.8 x 108mm (3 7/16 x 4 1/4m) dimensions which have endured since the Shovel.
They will certainly not bemoan, however, the Twin Cams prodigious peak torque: 86lb/ft (116Nm) at a mere 3,500rpm. Riders needing more can take heart: the Twin Cam was designed to allow an increase in displacement as high as 1550cc, adding another six to eight horsepower.
Compared to the bolted-up crankshafts of previous ohv twins, the Twin Cam has a pressed-up crankshaft. With its shorter stroke, it is capable of higher revs. Although the 5,500rpm redline is only 300rpm higher than before, development engines have been safely tested at up to 7,000rpm.
Harley surprised everyone by dropping the
Evo and unveiling the Twin Cam 88B for the year 2000, a unit-construction engine specifically tailored for the Softail range.
It represents another Harley first - twin balance-shafts to smooth out engine vibrations.
Softails will no longer be able to lay claim to being the "judderers" of the range.
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