Honda-SOHC

SOHC.co.uk Forums => CB500/550 => Topic started by: K2-K6 on August 11, 2019, 07:26:17 PM

Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: K2-K6 on August 11, 2019, 07:26:17 PM
I've not the machinery to do it,  and the machinist I've used in the past appears about as frequently as Haleys Comet  ;D so no bloody use at all.

Is it this from old post you're looking to get?  http://www.sohc.co.uk/index.php?topic=11741.0
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: Laverda Dave on August 12, 2019, 11:53:43 AM
I would like to help you out Oddjob but after studying the drawing on the link Nigel supplied I honestly think its a bit beyond me and my little Myford  :(

Someone I can highly reccomend though is Pete Lovell of Pete Lovell developments.  Pete is a precision engineer and a toolmaker.  He makes a lot of parts for Norvil and his work is exceptional and is a really helpful guy, he'll chat for ages on the phone!  He used to race a Trident. He helped me when I needed the rocker shaft pins of the CB250RS spark eroded out, he was the only person willing to do the work of all the people I called. His charge was very reasonable.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwip_LP7kv3jAhW0gVwKHTlqDIIQFjAAegQIAhAC&url=http%3A%2F%2Fpetelovelldevelopments.com%2F&usg=AOvVaw0RF3X5HzbCFiOBBVR7ZPIu

Good luck
Dave
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: K2-K6 on August 13, 2019, 10:43:39 AM
Out of interest,  what's the final aim of fitting a "tensioner" to the primary chain? As it wouldn't change the lifing of the chain,  just stop a worn one flapping into the nearby components.

If they get too worn it risks the chain pitch overriding the sprocket teeth which will cause failure of the chain anyway.
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: deltarider on August 13, 2019, 12:42:31 PM
Out of interest,  what's the final aim of fitting a "tensioner" to the primary chain? As it wouldn't change the lifing of the chain,  just stop a worn one flapping into the nearby components.

If they get too worn it risks the chain pitch overriding the sprocket teeth which will cause failure of the chain anyway.
Good point. I myself have more or less volunteered to be a guinea pig. I don't know if I hold a record, but mine is in there over 135.000 kms, shows slack ofcourse, but so far I do not hear alarming sounds (ignition is equally set and carbs are in sync), so... I'll see where it all ends. Nevertheless I'm much interested in any such improvement be it that I would not like to have my engine run under 1000 rpm. For those that want to get rid of noise, why not have it idle at say 1200 rpm?
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: Bryanj on August 13, 2019, 03:44:48 PM
The 400/500/550/650 primary is a "morse" type chain which, in theory, tensions itself by the inverted "teeth" climbing the slope of the "gears" it runs on efectively making the slack dissapear.
This relies on an even speed of rotation something you just dont get on a 4 cylinder engine, even in perfect tune you will still get some variation.
When they were a current production bike i only stripped very few, usualy for accident work, and the wear to the oil gallery was not really noticable. Now with age and more use it is.
I believe the 550 cranckse was cast slightly different and the oil galleries are slightly farther away from chain run as i have had a few of these apart now and only seen light marking.
Honda obviously did not forsee this problem but modified later models to overcome it so why not do the same if possible similar to the later cam covers with locked rocker spindles to stop rotation and wear, again not a common sight but known off.
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: Bryanj on August 13, 2019, 05:46:15 PM
550 was totaly redesigned at clutch cover and perhaps my veiw was subjective but there looked more gap between mains and oil gallery.
I too am working on old memory tho' so guaranteeing nowt
Title: Re: Any engineers out there who can make a primary chain bracket?
Post by: K2-K6 on August 14, 2019, 09:53:53 PM
The 400/500/550/650 primary is a "morse" type chain which, in theory, tensions itself by the inverted "teeth" climbing the slope of the "gears" it runs on efectively making the slack dissapear.
This relies on an even speed of rotation something you just dont get on a 4 cylinder engine, even in perfect tune you will still get some variation.

As above,  they only fire one every 180 degree so although we think a four is smooth they are quite lumpy for crank pulses. As well as this they have reasonably low mass crankshaft to spin up easily but also something of fairly high (in percent terms of crank mass)  mass in the clutch and gear assembly,  particularly contents of first shaft.  Plus initial primary shaft,  all connected directly through that chain.  The clutch cush drive will try to mitigate this,  but it can't absorb vibration at all frequency it would receive at varying rpm.  This is why pulling the clutch lever in quietens them down as it just reduces the total mass the crank pulses are trying to speed and slow. 

You've got a very good comparison with this layout (as Benelli pinched the design) if you've heard a 750-6 as they can even use some common components. They do just sound so smooth. 

This mod is not that invasive so be interesting to see how you get on,  although that same arrangement doesn't seem to make any difference to noise levels on a 750 Honda.
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