^^^^^ Sounds like an explanation my mechanical engineer son would give me.
Cracked cam cover, has anyone ever seen this?
Road Warrior
Joined: Jan 2006
Posts: 1,793
Likes: 1,186
I'm going with the "cold temps" theory or, as was said, the "cold temps plus overtightening theory." Anything inside the chest that would let go with that kind of force, you'd have worse noise and a non-running bike.
Anyway, you'll know soon enough. Please report what you find.
Also, you're a brave guy for riding to work in those temperatures. I've done it when it was in the 20's, but never the teens.
Anyway, you'll know soon enough. Please report what you find.
Also, you're a brave guy for riding to work in those temperatures. I've done it when it was in the 20's, but never the teens.
Seasoned HDF Member
Joined: Aug 2009
Posts: 9,239
Likes: 3,261
From: west Michigan
Maybe check the torque on the cam cover bolts before loosening them to remove the cam cover?
I can tighten engine case cover bolts alright by feel but it's best to torque them to spec, in the proper sequence.
I can tighten engine case cover bolts alright by feel but it's best to torque them to spec, in the proper sequence.
Road Master
Joined: Sep 2006
Posts: 1,232
Likes: 986
From:
First crack I've seen in a case cover bolted down tight around the perimeter like that, much less a cam chest cover, and I've been doing this a lot of years. Think about it, for the crack to occur due to thermal expansion stretching and cracking the cover, think of the deformation in the crankcase that would have to occur between the 2 screws on either side of that crack! However, stranger things have happened; I just ain't buying it until I see more.
Aluminum (is that cover Al or Zn die cast?) has a high thermal conductivity relative to most structural materials - that's why we use it for convection cooling of mechanisms. But, Al casting alloys generally don't have much ductility before cracking. If designed correctly, heat will conduct and propagate through the parts stack so fast that expansion is uniform and stresses are minimized if you stack up similar metals. Start bolting together parts with varying expansion rates and you can wreak havoc. The only thermal expansion stress cracks I've heard about on modern motorcycles were due to water dousing, like running a red hot dirt bike motor into a creek, or pulling up and spray washing hot motors immediately after shutdown. But never out on a case cover. A gut suspect of mine is that cover had a flaw in the casting in combination with a lack of proper stress relief during manufacture. Again, not saying the outside temps weren't a factor, but the study of Fracture Mechanics tells us cracks generally start with stress risers, and that one may have had one built in. I.e. maybe that was an event primed and just waiting to for the right impetus.
Aluminum (is that cover Al or Zn die cast?) has a high thermal conductivity relative to most structural materials - that's why we use it for convection cooling of mechanisms. But, Al casting alloys generally don't have much ductility before cracking. If designed correctly, heat will conduct and propagate through the parts stack so fast that expansion is uniform and stresses are minimized if you stack up similar metals. Start bolting together parts with varying expansion rates and you can wreak havoc. The only thermal expansion stress cracks I've heard about on modern motorcycles were due to water dousing, like running a red hot dirt bike motor into a creek, or pulling up and spray washing hot motors immediately after shutdown. But never out on a case cover. A gut suspect of mine is that cover had a flaw in the casting in combination with a lack of proper stress relief during manufacture. Again, not saying the outside temps weren't a factor, but the study of Fracture Mechanics tells us cracks generally start with stress risers, and that one may have had one built in. I.e. maybe that was an event primed and just waiting to for the right impetus.
senior experienced all-knowing leader of the unwise
Joined: Apr 2008
Posts: 1,957
Likes: 351
From: USA
Looks like that rear head pipe is awfully close to the cam cover where it cracked. Maybe the ice cold cam cover got hot in that one spot from the head pipe, and combined with overtorqued bolts caused the crack. On the other hand my Dyna has a pipe just like that and i've cranked it in awful cold temps over the years. It's never cracked. I've never seen or heard of anything like that.
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