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SOHC.co.uk Forums => CB750 => Topic started by: archmill on April 28, 2024, 08:57:14 PM

Title: CB750 F2 Primary chains
Post by: archmill on April 28, 2024, 08:57:14 PM: Hello, Have at last started re-building the CB750 F2 as a cafe racer and started building the engine this weekend. The last time it ran was 1982 and the guy who passed it on to me said it dumped all the oil on his boots so he stuck it in a shed. Have stripped the engine completely so I am starting from scratch.
Measured the primary chains and got a size from the oil pan face to the tensioner of 69mm so I recon they are done. Bike had only 25,000 miles on it.
Where is the best place to get new primary chains and tensioner.
Any advice greatly appreciated.
Title: Re: CB750 F2 Primary chains
Post by: Athame57 on April 28, 2024, 09:05:43 PM: I'd check out David Silver Spares for something like that. https://www.davidsilverspares.co.uk/
Title: Re: CB750 F2 Primary chains
Post by: Martin6 on April 28, 2024, 10:47:31 PM: Wear limit spec is 70mm. Does anyone know what this measurement is with a brand new chain?
Title: Re: CB750 F2 Primary chains
Post by: Athame57 on April 28, 2024, 11:17:04 PM: Quote from: Martin6 on April 28, 2024, 10:47:31 PM
Wear limit spec is 70mm. Does anyone know what this measurement is with a brand new chain?

If you place a primary chain upright and the top row sags to contact with the bottom row the chain is finished. As to how close you'll let it come to that I guess is up to you.
Title: Re: CB750 F2 Primary chains
Post by: Nurse Julie on April 28, 2024, 11:28:56 PM: Quote from: Athame57 on April 28, 2024, 11:17:04 PM
Quote from: Martin6 on April 28, 2024, 10:47:31 PM
Wear limit spec is 70mm. Does anyone know what this measurement is with a brand new chain?

If you place a primary chain upright and the top row sags to contact with the bottom row the chain is finished. As to how close you'll let it come to that I guess is up to you.
George, that only works on Hyvo primaries, like the 400/500/550's. 750 chains are different, they are not Hyvo, they are a lot thinner and there are 2 of them, side by side.
Title: Re: CB750 F2 Primary chains
Post by: archmill on April 28, 2024, 11:55:58 PM: Seemingly new chains have a measurement of 65mm, at 70mm they are done.
Title: Re: CB750 F2 Primary chains
Post by: archmill on April 28, 2024, 11:57:36 PM: Nurse Julie, how are you doing. You did the camshaft on this engine a few years back.
Title: Re: CB750 F2 Primary chains
Post by: Athame57 on April 29, 2024, 12:12:27 AM: Quote from: Nurse Julie on April 28, 2024, 11:28:56 PM

George, that only works on Hyvo primaries, like the 400/500/550's. 750 chains are different, they are not Hyvo, they are a lot thinner and there are 2 of them, side by side.
Ding dong....getting ahead of myself Julie!
Title: Re: CB750 F2 Primary chains
Post by: AshimotoK0 on April 29, 2024, 07:00:12 AM: When you replace. "To stagger or not to stagger ...that is the question"

I chose to stagger mine.

[attachimg=1]
Title: Re: CB750 F2 Primary chains
Post by: Nurse Julie on April 29, 2024, 08:26:56 AM: Always stagger Ash, I like a good stagger 😂😂😂
Title: Re: CB750 F2 Primary chains
Post by: Skoti on April 29, 2024, 07:35:02 PM: Also there's reinforced heavy duty primary chains available that sag less than the standard original RK ones.

I think they are made by IWIS in Germany.

https://www.classiccyclecity.com/gallery/thumbnails.php?album=48 (https://www.classiccyclecity.com/gallery/thumbnails.php?album=48)
Title: Re: CB750 F2 Primary chains
Post by: Nurse Julie on April 29, 2024, 07:39:47 PM: Quote from: archmill on April 28, 2024, 11:57:36 PM
Nurse Julie, how are you doing. You did the camshaft on this engine a few years back.
Hi Archie. How are you, still fettling I see. Good on you.
Title: Re: CB750 F2 Primary chains
Post by: archmill on May 11, 2024, 07:07:43 PM: " Wear limit spec is 70mm. Does anyone know what this measurement is with a brand new chain? "
And the answer is 63mm. Brand new chains and tensioner from CMSNL.