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Messages - K2-K6

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16
Project Board / Re: My 750F2 project.
« on: February 14, 2024, 08:13:15 PM »
For us on here ordinarily accustomed to std Honda pistons and their metallurgy https://www.jepistons.com/je-auto-blog/2618-vs-4032-piston-material-differences/ gives good appreciation of that supplier and the alloy specified as used here.

You can see,  just within their own range of alloy, that 2618 expands at + 15% over the alternative, let alone the stuff we are referencing and of cast higher silicone content Honda OEM parts....these effectively expanding more or less a match with the cylinder construction.

They'll get to the same clearance once warmed up though.

17
Project Board / Re: My 750F2 project.
« on: February 14, 2024, 10:49:11 AM »
With no idea what their machinery is like, it's speculative to assess from me.

Usually associated with feed rate in general machining, the tool has to be buried into the material it's cutting, with a wedge shape of the base material being sheared out of its structure as the tool is forced through it in removal.
If the entrance feed was cautious to preserve face of bore, speeded up through mid part, then slowed for exit, this could produce a barrel effect. Basically with higher feed it has more aggressive cut width on each revolution, with the tool being "pulled" further into the wall as it travels with that difference in feed. Its a bit like stripping wallpaper, when you get too much angle on the blade and it's goes "oink~twang" taking a neat little triangle of your plaster with it  :)

You'll get it on a lathe too, with a longer tool extension being a little flexible if reaching a long way in. On that you try to offset that little wedge of removed material by grinding a back rake on top of tool face to minimise that wedge in size, the angle of attack effectively.

Drill bits in lathe headstock do it too, you have to go at it really slowly to stop the drill nose "walking" around in a circle if biting too hard, especially as it's likely there's imbalance across the drill cut blades from one side to another.

It shouldn't happen obviously from a good machine shop, often you'll see experienced machinists going about something in a certain way that may look odd, but experience in that process gives them ways to mitigate shortcomings in process.

18
CB350/400 / Re: Seizing horseshoes
« on: February 12, 2024, 10:53:41 AM »
Yes Ted, I've experienced it literally inches deep in chocolate fudge cake like consistency within early 70s car engine, particularly aluminium cylinder head that look to have a higher heat transfer to the oil near and around the combustion chamber "skull cap" areas.

19
CB350/400 / Re: Seizing horseshoes
« on: February 12, 2024, 09:54:10 AM »
To remove the carbon deposits in the pivot I soaked mine in oven cleaning gell for a couple of days, refreshing the gell after the first 24 hours when it had turned black.

It is exactly this that "seizes" them, oil going over critical temperature and baking into a harder sticky residue to stop movement.

Many engine from that period had been affected by such, with reformulation more obvious in products of early 1980s that show less susceptibility.  One of the most useful aspect of synthetics too, their vulnerability to high heat break down being moved substantially out of component latent heat operating range.

The chains are affected too, needing just pure oil flow through the pin/pivot sites to prevent captured oil there from passing critical temperature, the hi-vo primary an absolute copybook example of this working characteristic.

20
Other Bikes / Re: Makes Mr Milliard look like he's playing at it
« on: February 05, 2024, 11:23:42 PM »
He's right about being heavy, virtually no one could hold that up at anything off upright I understand.

The engineer he referred to taught me during apprenticeship  :)

21
Misc / Open / Re: Engineering interest
« on: February 03, 2024, 09:53:04 PM »
Do you have metric screw cutting facility on your Myfords?

22
CB500/550 / Re: I'm curious as to what this would really do
« on: February 02, 2024, 12:24:51 PM »
CBX camshaft had "Oldham" coupling.

A way of connecting two shaft like that directly to each other, even if those two shaft bores were to be slightly displaced. The joint then just "shuffles" the error without any real affect, as opposed to trying to wear adjacent bearing surfaces to correct itself if was solid shaft.

Would cope with potential machining tolerance if they were there.

23
CB500/550 / Re: I'm curious as to what this would really do
« on: February 02, 2024, 12:19:12 PM »
The 24 tooth on drive side will raise the output gearing, less revs per rear wheel revolution.

So gearbox will be going faster for each rpm of crankshaft. Probably accommodated by the increased torque potential of the 550cc

24
Project Board / Re: My 750F2 project.
« on: February 02, 2024, 10:54:16 AM »
I thought nice machining work on the collars too.

I've not tried BOGE dampers on a bike but they have very good reputation and capability in car products.

25
Project Board / Re: 30 years of storage later, the project begins.
« on: February 02, 2024, 09:35:11 AM »
I'll get off Ken's thread with it  :)

But don't think there's appreciation for structures and the impact it can make, or is seen conventionally. The swingarm bracing as it goes down along the arm is supposed to be a "soft" finish and why most bracing like this is shaped similarly. Welding that opening together in fixing it to the main tube changes that characteristic, first to remove flex and putting a circumferential weld halfway round the tube, making a failure pathway in that material section. Its now got a raised stresss point halfway along the arm, and with compromised structure potential as it was never designed to be welded there.

We could all see the problem of replacing a fuse with a stout woodscrew for example, feeling that's obviously going to risk a potential problem, but it would work all the time the circuit wasn't under too much stress. Modification like the brace compromise do exactly this though.

It doesn't matter to me what people do individually to their own frame, but I don't think it should be viewed as a reasonable path in modifications.

If anyone wants to feel swingarm flex, then hitting a dip in the road at speed while in a corner (amplified with a passenger) and the bike wallows, the line is altered and you can feel the steering move, that's swingarm flex, present in many of these old bikes with one arm moving up and the other down as the wheel cocks sideways from the load coming in to it.  That squirrely feeling  ;D

26
Project Board / Re: 30 years of storage later, the project begins.
« on: February 01, 2024, 10:25:55 PM »
Generally the joints are designed into it from concept, r&d then durability testing to ensure they perform adequately.

Specialist frames likewise, but you'd not ordinarily change one to the other without good cause or background information.

A lot of special hand-built frames historically have been brazed joints that doesn't melt the steel during that process. These don't then have the same pathway through the principal structure t give failure of base material if that bronze material should crack.

27
Project Board / Re: 30 years of storage later, the project begins.
« on: February 01, 2024, 06:14:07 PM »
"Onto the powder/ceramic coaters, dropped the frame off so they can grit blast it, then they'll return it to me and I'll drop it off at the welders on my way back, again filling in all the brackets and lugs etc that Honda again didn't seam weld, stuff like the lower front engine mounts, water gets under and rots the frame underneath the lug and you can't see it. When the welders finished I'll bring it home and inspect it to see how the metal has held up, dress all the welds and get rid of all Honda weld splatter, I want the frame to feel like glass so the powder coating comes out as well as it can"

The gaps are left as stress mitigation in part of the design and testing, normal to not connect bracing completely to avoid failure.

The swing arm ones (in exaggerated illustration) if you push one arm up the other down, then those gaps will move like a fish mouth as the bracing takes the stress. The top and bottom welds running along the arms themselves are in shear stress, with the brace itself in compressive and tensile loading diagonally across the flat surface.

Welding the "open" ends on the arm constrains it such that it can crack rather than "breath", the crack can then travel into the main arm tube via the weld, just where you dont need it.

Welding is often delineated in structure to avoid stress cracking to follow along the weld route in causing ultimate failure of the main component.

28
They can be really well stuck from that corrosion around the seal.

The rears on many VAG cars are usually aluminium  caliper and very similar bore to our Honda type, with a seal boot to cover piston. If that seal is compromised though the corrosion builds such that you can't turn them at all, even with proprietary tool engaged.
The mechanical handbrake is concentric with the hydraulic piston too, and can sometime not be operational even pulling the lever hard. The only way to get them out is to pump them with footbrake, then they creek and groan like an old wooden boat in protest as they move. It's literally just the corrosion around the seal holding them, once cleaned and refitted they are fine again.

29
Misc / Open / Re: Engineering interest
« on: February 01, 2024, 12:32:18 PM »
Quite a cool in depth look at the process as it was then Dave.

I started at the other end from you,  making metal into recognised components in aero R&D.

A friend's mum was draftswoman at Brooklands and on the Concorde project, but I didn't learn that in time to speak to her about that. Would have liked that inside view.

Current RB F1 team design is led by advocate of first drawn on a board as it used to be. They employ people (CAD jockey, as described in that video) to take the work downstream from there as I understand it. Not doing too badly either it seems  :)

30
CB350/400 / Re: Elusive springs!
« on: February 01, 2024, 10:29:04 AM »
As noted already, if compression is in spec there'd be no reason to change rings. New rings...and you'd conventionally need to hone the bores at least to get them to run in properly.

The springs...are highly resistant to change and should be OK to keep if the length checks out in specification.  Spring steel is heated toward 1000 C then quenched to first harden it and give spring characteristic...then tempered at around 350 ish to stress relieve the grain structure and bring long lasting resilience to the component. Theres really not that much can change a well made spring when used in this situation.

Valve springs have a much harsher life and survive fine over the same period.

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