Will my engine crack in half?

N

Novice_imp

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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?
 
Novice_imp said:
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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I would toss in some zip ties along with the JB Weld to help hold it until it sets.
 
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.
 
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.
 
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.
 
Flynrider_imp said:
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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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.
 
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.
 
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.
 
Cormanus_imp said:
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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:rofl:
 
On the first episode of Naked Speed, a custom builder who specializes in Honda restorations acquired a complete basket case of an SOHC Honda 750 engine in a cut up and rusted frame. When he removed the drive sprocket he discovered a cracked case and claims that it was not unheard of that early Honda's throwing a chain could crack cases. Urban myth? Dramatic effect? Total BS?
 
Actually CB4ME I saw that several times on CB 750 that were drag raced or street raced. 1969 Chain technology was not too good and a slightly built 750 could easily out power the stock 530 chain which would snap and as the sprocket is turning counter clockwise as the bike rolls forward the chain follows the sprocket and ends up wadding up under the front counter sprocket hitting the case and punching a hole on it. Quite often ( but not always) they the pieces could be rewelded. If not new cases were in order, and since they were split horizontally instead of vertically like a Brit bike, it required a set of cases.
 
Yep, read all the time on the SOHC4 forums about somebody picking up a barn find 750 only to find the case is damaged around the chain sprocket. :dodgy:
 
I ain't skeered. Instead of working, I scanned the various forums and entries and it appears the issue is operator error mostly in America. Go figure. Who would have guessed? The fix included going to a different chain. I suspect abusing a four cylinder engine with gobs of torque can be risky, being the intellectual giant that I am, I figured that out by myself and so I ain't skeered of breaking this amazing engine.
 
Having worked on both British and Japanese motorcycles, I found the Japanese horizontally spilt cases much easier to disassemble and re-assemble. Everything sits nicely in the Japanese lower case.

Having things fall free while opening British crank cases can make things hard to re-assemble properly. Wrestling the halves of the British cases together while hoping everything stays in place is also a chore. I was fortunate enough to have both a genuine BSA shop manual and parts list that I imported from England along with all the shop tools. I liked my two BSA Lightnings, but they were more difficult to work on.

We may complain about the service interval between valve adjustments on Japanese motorcycles. But my experience with British motorcycles is that they needed a complete motor overhaul every 10,000 miles.
 
2010 and up chains are not 1969 to 1976 chains. Manufacturers ahve increased the pin, plate and tensile strength tremendously. Doubt anyone has to worry about the chain on their CB 1100 breaking and going thru the cases these days.
 
The ferret_imp said:
2010 and up chains are not 1969 to 1976 chains. Manufacturers ahve increased the pin, plate and tensile strength tremendously. Doubt anyone has to worry about the chain on their CB 1100 breaking and going thru the cases these days.
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As long as you install and maintain it properly. Every chain break incident I've ever seen (including one that cracked the crankcase) was caused by someone botching the master link installation.
 
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