Author Topic: 750 K2 Strip & Rebuild - help please  (Read 3462 times)

Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #90 on: April 05, 2022, 02:39:13 PM »
One for the alchemists….. Ash!

1/4 of the Airbox to Carb manifolds has mummified around 25% of the belmouth, ie the portion within the ‘box. The rest of it, and it’s siblings, are brand new pliable - which they should be as only a couple of years old. Heat makes it pliable, but on cooling we’re back to square 1.

Asking for Wintergreen draws stares here - unheard of. I can find some on eBay… but at a price.  So… does this mix of WG + alcohol (Isopropyl) REALLY work… or should I just spend the $$$ on a new set. (not cheap ☹️)

Notably these manifolds are not actually rubber (?) - and more of a shiny neoprene (?)

Ta again.

I used Reofos 50 but it's not readily available. I used to be able to get it from the old company I worked for 25 years ago but lost all of my contacts now... the chemist guy who put me onto it did suggest a more readily available alternative .. I will try to contact him.  https://polymer-additives.specialchem.com/product/a-lanxess-reofos-50

Rubber in this Youtube  video clip was rock hard to start with but after Reofos treatment remained supple even when cold and still is the same 7 years later  ;)


https://www.youtube.com/shorts/Y1kVSlLnR8k
« Last Edit: April 05, 2022, 02:41:37 PM by AshimotoK0 »
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Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #91 on: April 14, 2022, 12:44:20 PM »
It seems a fair bit of this thread has gone walkabout ….

A big thanks to you Oddjob, I took the bull by the horns and went for broke in sanding the badly pitted carb lifter. Initially I used my small (10mm wide) belt sander with 120 grit, followed with 200 Grit. Then Dremel bits (+ soaps) followed by the 6” polishing wheels / (grey / brown / white soaps) on full sized bench grinder machine. Good as new - amazed!

(The Dremel OEM bits are prohibitive - I got the set you see here off eBay for £8 delivered!)

Ash, the Wintergreen arrived and the manifold soaking as I write. It is softening (@ 24 hrs) but so far, has not showed signs of returning to original shape. 🙁

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #92 on: April 14, 2022, 12:47:54 PM »
Be careful now, once the polishing bug bites you start to look around and see the potential for other bits to be done.

Good result, might have some competition at last  :D :D
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Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #93 on: April 14, 2022, 03:56:29 PM »
A couple of post I put on here have gone missing, about the material used for these.

To reinstate,  the cast material just may be a magnesium alloy as it does feel very light, but also very rigid.  It has that magnesium-ee feel to it.

If that were the case, then the plating may be significant as protection against corrosion with these alloy being quite vulnerable.

https://www.arlingtonplating.com/substrates-specifications/plating-on-magnesium/ gives some insight. 

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #94 on: April 14, 2022, 10:28:35 PM »
…. you’ve worried me now Nige as I had to remove a fair bit of corrosion to get down to unspoiled metal. Happy though that I never (obviously) broke through to any base metal, nor had to remove any material from the critical dimension parts.

I’d say you’re spot on with the magnesium alloy thoughts, it certainly does feel lighter than aluminium, has a solid ping to it, and fits in with the descriptor of it being used in the automotive industry for paddle shifters etc.

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #95 on: April 14, 2022, 11:37:24 PM »
Try setting it on fire, if it goes up like a bonfire I’d say it’s most likely magnesium alloy.  ;D ;D
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Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #96 on: April 14, 2022, 11:45:34 PM »
… you’re a funny man Ken, however, I’ll pass on this one 😂

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #97 on: May 01, 2022, 01:11:13 PM »
Can somebody tell me what the ‘Sprocket Side’ plate’s job is, and the original finish pls (black matt / gloss, zinc, or chrome?)

At the mo non-existent on my K2.

Ta.

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #98 on: May 01, 2022, 04:28:44 PM »
Unsure if it's right, but always thought it's function is to stop a loose/failed chain falling between the swingarm and sprocket face, then jamming on the securing bolts to lock the wheel.

Early experience with some chain failures on the 750 may have caused this path to be explored.

As initially noted, I'm not sure and haven't any significant information to confirm this is correct.

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #99 on: May 01, 2022, 04:34:01 PM »
The 500 one was certainly zinc plated, sort of a dullish grey. I'd imagine it copied the 750 in finish. I don't think black ones came in until much later.

The were not only functional, as in what Nigel has described but also decorative as the sprocket was covered and lets be honest, a sprocket isn't that attractive to look at. Now you can get them in gold etc that's changed.
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Offline Nurse Julie

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Re: 750 K2 Strip & Rebuild - help please
« Reply #100 on: May 01, 2022, 09:56:40 PM »
Zinc is correct for a 750K2 .
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #101 on: May 14, 2022, 03:43:30 AM »
Can anyone advise how to separate the chrome cap from the rest of the gubbins please? Tried heat + gentle prying - to no avail.
Not esp happy to try a threaded bold through the lower cap holes to push against the chrome top ….

(Wanting to re- gold passivate the lower cap)

Ta.

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #102 on: May 14, 2022, 03:54:05 AM »
Hi Ash,

Wrt to my hardened airbox rubber and Wintergreen - sorry for the late reply….

Oddly, only 25% (circumferentially) of one rubber has mummified, and whist heat would soften it, within minutes it’d be back to its new norm.  I then put it in a jar of 25% Wintergreen oil + 75% isopropyl, and have left it there for weeks. It’s much better, but still retains a little hardness. Most surprisingly it’s shrunk in overall size - to the point of being unusable.

Can’t work it out, OEM and the other 3 fine. It’s defo the runt of the litter…

For the price of a single replacement I’ll skip trying to source Reofos 50 and call it a day 🙁 . Thanks nevertheless!

Cheers,
Simon.
« Last Edit: May 14, 2022, 03:57:19 AM by Lobo »

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #103 on: May 19, 2022, 05:01:28 AM »
A bit miffed last week as Autosol polish removed the Gold Passivate from the dipstick and Voltage regulator….

Managed to separate the dipstick components by drilling a 5mm hole in the circumference, and then tapping in a blunt 5mm grub screw to prise the chrome cap off. Worked a treat.

Dipstick innards + VR cap zinc planted and passivated - pleased with the results.

« Last Edit: May 19, 2022, 05:03:50 AM by Lobo »

 

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