Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: WestMids-CB on July 26, 2026, 11:43:31 PM
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The new to me cb750 four needed the tacho drive seal changing so I ordered a new one and whilst I was waiting on arrival I thought I'd take my time getting the old one out, and bloody hell, what a pain, it wouid not budge! In the end a dental pick managed to get the seal out but here's the issue, the tiny o ring that sits inside the seal is missing!!! I carefully felt around the tacho drive shaft to see if it had come away and positioned itself around that but I couldn't feel anything, I looked for it on the garage floor but could not see anything, my worry is that it may have fallen inside the rocker cover itself :o if that's the case it means having to take the motor out of the frame as the rocker cover won't clear the top rails whilst in situe, what should have been an easy jobmsy prove to have been a nightmare.....
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Dont remember an O ring in there, and from memory the drive shaft is a bearing fit in the cover so nothing can get inside.
Have you checked a parts list?
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I’m like Bryan, can’t remember an oring. There is usually a small spring inside the seal to keep the lip of the seal tight around the tachometer drive shaft. If you have the spring then you haven’t got a problem in my opinion. Even if there was an oring it’s ting, fragile and will get chewed up by the valves etc long before it can become a problem.
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There's no o,ring just the main seal. Couldn't get into the rocker box anyway unless it's 1 thou thick. Just fit the new seal and your good to go.
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cheers for the replies , Photo of the seal that came out and the replacement next to it. I could feel the elasticity of the o ring with the dental pick when trying to get the old seal out.
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Looks like you've torn out the centre part from the old seal and perhaps mistaken it for an 'O' ring.
Anyway job well done, the new seal can be pushed in nicely with a 1/4" drive 9mm deep socket.
Good luck
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I agree definately no O ring on a 750
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I agree definately no O ring on a 750
I know it's not an O ring per se, but there is a rubber/silicon centre on the seal, I can feel it on the new one and that's what has been pushed through the old seal and causing me the worry.
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Its all part of the moulded seal, it can not get into the engine
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Cheers for the reply Bryan,.