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In the February issue of Cycle World page 31 in the article MotoGP Refugee it states, "Yet engineers were dissatisfied with the inline-four because it consist of two 180-degree twins set end to end. Each such twin wobbles vigorously about its center, applying a bending moment that flexes and may in time crack the crankcase and cause cylinder base-gasket leakage."
OH Snap! Do I need to carry JB Weld with me? Has anybody ever had their crankcase crack?
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(02-03-2015, 09:10 AM)Novice_imp Wrote: In the February issue of Cycle World page 31 in the article MotoGP Refugee it states, "Yet engineers were dissatisfied with the inline-four because it consist of two 180-degree twins set end to end. Each such twin wobbles vigorously about its center, applying a bending moment that flexes and may in time crack the crankcase and cause cylinder base-gasket leakage."
OH Snap! Do I need to carry JB Weld with me? Has anybody ever had their crankcase crack?
I would toss in some zip ties along with the JB Weld to help hold it until it sets.
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Yup. The cb750 is the same way. Two CB350s taped together and you know how much the 750 wobbled and split apart all the time. Also, mine has cracked twice already, so I know that's right.
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Where do they come up with this stuff? I've never heard of this crankcase cracking issue and I've been riding UJMs for 35 years. Given the huge popularity of inline 4s over the decades, I have doubts that any competent engineer would seriously be concerned about this.
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Agree with Flynrider. There are a LOT of old... er, experienced riders here, and I think, after 45 years, someone would have heard this or knew someone that it happened to, or at the least it would have become known and pointed out by the motorcycle reviewers in the media as a design flaw.
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(02-03-2015, 10:52 AM)Flynrider_imp Wrote: Where do they come up with this stuff? I've never heard of this crankcase cracking issue and I've been riding UJMs for 35 years. Given the huge popularity of inline 4s over the decades, I have doubts that any competent engineer would seriously be concerned about this.
I would think Moto GP engineers know what they are talking about. Obviously race engines and street engines are in a different state of tune.
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Look at Yamaha going with the cross-plane crank. When you are at 18k+ RPMs, every bit counts. Simply the rotating mass of the center pistons tied together and the outers together - its not hard to imagine a crankshaft flexing.
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Mine breaks apart just right of centre about every 1367 kilometers. It's a pain, but I've come up with a system of latches and a thick gasket to put it back together quickly and easily. Together with the bottle of pre-loved 20W-50 tractor oil I carry around with me, I'm usually back under way within 15 minutes or so.
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(02-03-2015, 05:29 PM)Cormanus_imp Wrote: Mine breaks apart just right of centre about every 1367 kilometers. It's a pain, but I've come up with a system of latches and a thick gasket to put it back together quickly and easily. Together with the bottle of pre-loved 20W-50 tractor oil I carry around with me, I'm usually back under way within 15 minutes or so.
