SOHC.co.uk Forums > CB750
750 K2 Strip & Rebuild - help please
AshimotoK0:
--- Quote from: Lobo on April 04, 2022, 11:40:20 AM ---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 ☹ï¸)
Notably these manifolds are not actually rubber (?) - and more of a shiny neoprene (?)
Ta again.
--- End quote ---
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
Lobo:
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. 🙁
Oddjob:
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
K2-K6:
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.
Lobo:
…. 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.
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