SOHC.co.uk Forums > CB750

Oil pressure issue / motor rebuild

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royhall:
Been thinking about this for a few hours now and have come to the conclusion that if it was mine (although I did previously say to get them measured) I would just replace the cases. You can waste days playing with what you have and waste money at the engineering shop for no gain. Re line boring them is not really an option unless they are one off historic and valuable. The cost alone will stop that idea dead in its tracks.  I recently rebuilt a CB750K3 for MCTID (Alan) who had damaged cases, and when I put out the call for replacements there was loads available. Thats the way I would go. Cheers.

AshimotoK0:
I don't believe there are loads of K1 cases out there to be had...I know at least a couple of other people after them but I agree I would replace if at all possible. There would  always be a nagging doubt about it but it's  an engineering challenge for sure. My main fear would be thermal contact between the shell and the blasted surface of the crankcase. The only thing that would sway me is if the those surfaces are smooth enough  and , after measuring you find it's only the centre bearings nipping, then my idea of a shim foil to make those bearing clearing surfaces correct. Freddie has had some  cases for sale on eBay  for well over a year and they are unstamped. Trigger tells me they are not correct for a K0 but not sure which model they would fit. Sometime I am going to get my man in China to replicate some Honda stamps, so you could possibly and legitimatelly stamp with original numbers. You could make Freddie an offer if they are indeed suitable.

MrDavo:
See Trigger's comments above re the unstamped cases, they appear to be a non starter. A friend of a friend I met at Stafford has a ton of CB750 bits, a text has been sent to see if he has any K1 cases.

As all 10 journals were so FUBAR, I don't think it's just one pair. That said I have plenty of time until more cases turn up, and lots of Plastiguage.

Looking closely last night, the shell carriers are very smooth, I'm pretty sure there's a layer of silver paint, how thick could that be? It's got to be worth trying to strip it off and re measuring, it could be stove enameled/ powder coated, I really don't know, it's that kind of finish. If so, how to get it off?

AshimotoK0:
Methylene Chroride based paint stripper but be quick to remove once it softens and flush with solvent/soapy water. If powder coat , you will have to burn it off IMHO

MrDavo:
Unfortunately when I Google that, the word 'free' appears after it in every product, it seems the Eu have banned it for killing people. I'll have to see what strippers I can get down the DIY store.

Burning sounds scary in case I distort the cases, I guess a careful experimental wafting with the blowlamp if necessary.

I do wonder if I'm on to something, though, especially if the journals turned out to be dead round, I won't know until I measure, I'll see if my mate can get an internal mike from work. I'll have a close look at where the paint / whatever got chipped to try and get my head around how thick it is.

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