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Bike engine design.

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stevo as b4
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PostPosted: 21:20 - 24 May 2018    Post subject: Bike engine design. Reply with quote

Just a quick question to all the technical people, but why do nearly all modern bike engines with a cam drive chain on the outside, use two little bolts on the outside at the head/block joint?

Can't they include the cam chain tunnel within the main head stud spacing layout like car engines? I mean there cannot be much clamping load on two small M8 bolts that only go 20-25mm into the block with no area of support around them?

Just looks a bit afterthought to me, but there must be a good reason why most engines are made this way?
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Octapode
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PostPosted: 21:50 - 24 May 2018    Post subject: Reply with quote

At a guess, they want the main bolts closer to the bore to keep the head from warping, but they also want a bit of clamping force on the gasket out on the far side of the cam tunnel. I'd assume car heads get around this by being beefier and thus being able to transfer clamping load further, and bike heads are just like that due to size.
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Pete.
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PostPosted: 22:29 - 24 May 2018    Post subject: Reply with quote

Loads of good reasons to put the cam chain at the end:

One less main bearing journal - lighter, shorter, stronger crank with lower inertia and therefore lighter narrower engine which can rev higher.

Camchain sprocket is by necessity small so if it's in the traditional position in the middle of the crank it limits the cross-section. You either have to suffer a skinny whip-prone crank or huge camshaft sprockets.

Even spacing on the cylinders and simplified/more efficient coolant passages.

Ease of assembly, not necessary to do a fully strip-down to change the cam chain.
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johnsmith222
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PostPosted: 22:53 - 24 May 2018    Post subject: Reply with quote

My ZZR had the camchain in the middle. I wasn't pleased about the idea of stripping the engine if I was replacing the chain properly, rather than the link grinding method.

So glad to have it on the side on my 9R.
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stevo as b4
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PostPosted: 00:20 - 25 May 2018    Post subject: Reply with quote

Sorry I wasn't very clear in my original post. I get and fully agree why it's far better to have a cam chain drive on one side of the engine instead of between cylinder bores. Kawasaki proved this in 1984.

But the two small bolts on the outside of the cam chain tunnel look too small to be there to do anything meaningful to clamp the head down. I guess that's not their reason to being like that, and it's more to do with preventing oil leaks or something? The bolts are outside of the cylinder bore spacing, but why not just have another couple of long studs through the block into the head instead of these small bolts?

Is it because it would add weight and width to the engine? Car engines tend to not have additional bolts in this location, but they sometimes have a separate bolt on timing chain chest outside of the block so I guess it's a whole different kind of design.

The Kawasaki ZX7R is a good example of what I mean with longer studs outside the cam chain tunnel, where as say an MT09 engine is an example of the silly little fasteners that don't look to be there for a structural reason?

Maybe it's because some engines have separate cylinder blocks to the crankcases, and better more modern monoblock engines don't need long bolts/studs due to their rigidity?
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Old Git Racing
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PostPosted: 00:23 - 25 May 2018    Post subject: Reply with quote

Simples - cost to manufacture.

OGR.
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stevo as b4
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PostPosted: 00:37 - 25 May 2018    Post subject: Reply with quote

Probably right there!

Thats also probably why they don't build engines with long through studs from the head to the bottom of the crankcase, that and difficulty to strip down.

I've always liked things that are designed from an engineering superiority perspective and not a maintenance friendly or cost friendly one.

A good example could be that manufacturers could use one piece camshaft carrier's/bearing caps, and line bore them in the factory so they only fit as a matching pair like crankcases do. Poxy little separate camshaft bearing caps on each cam isn't the most elegant design solution, but it's cheaper and easier I guess as well allowing easy removal of each cam separately.
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barrkel
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PostPosted: 13:36 - 25 May 2018    Post subject: Reply with quote

stevo as b4 wrote:
I've always liked things that are designed from an engineering superiority perspective and not a maintenance friendly or cost friendly one.

Engineering is an exercise in trade-offs. Superior engineering is finding elegant solutions on multiple dimensions, where elegance is strongly related to efficiency and economy - less is more.

I expect engineering an engine needs to trade off strength vs weight vs material cost vs assembly cost vs wear vs maintenance. It's the solving for multiple constraints that makes elegance elegant, otherwise it's just brute force, or flimsy, or overpriced, or over-engineered, etc.

Quote:
Poxy little separate camshaft bearing caps on each cam isn't the most elegant design solution, but it's cheaper and easier I guess as well allowing easy removal of each cam separately.

The engineering that most impresses me is little touches that make something fail in a safe way, or easier to work with when the covers are off, or harder to assemble incorrectly - things that the consumer doesn't normally notice, but someone paying close attention to the details can see the intelligence of.

For example, I really like the engineering of the IBM Proprinter, as explained in this video: https://www.youtube.com/watch?v=spDYSKl3kmo - this is superior engineering, in my book.
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