Any engineers out there who can make a primary chain bracket?

[Oddjob]

Looking to fit a CB650 primary chain tensioner in my 500 engine whilst it's apart. However you need a special bracket making in order to do this. Aluminium is the normal choice for this bracket BTW.

I had a really good engineers drawing of the bracket showing dimensions etc but need someone with access to a lathe to progress with this little project. I have the tensioner BTW, I believe I also need the 650 sump and oil strainer but I want to see if that's true before I buy those.

Contact me via PM if you can help, of course suitable payment will be arranged. Maybe you could make a couple in case someone else wants one.

[K2-K6]

I've not the machinery to do it,  and the machinist I've used in the past appears about as frequently as Haleys Comet  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

[Oddjob]

Yeah spot on mate, Phil did promise to have one made for me but seems to have disappeared from the forum. I spotted a CB650 tensioner blade a few months ago on E-Bay and thought why not, now the bikes out of the garage after 30 years I can finally do it, makes sense as the engine will be totally dismantled anyway.

[Laverda Dave]

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

[Oddjob]

Cheers, I'll give him a ring.

Going to see if Phil can still help out first, I'll drop him a PM and see if he can still get me one made.

[K2-K6]

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.

[Oddjob]

The primary chain currently fitted to my engine has only done a few thou, I may change it when I dismantle the engine, I'll see how it looks. The main benefit to me is the noise, the primary chain on the 500/550 is great when it's new, it doesn't however take long for it to start to stretch, when it does start it tends to slap around on tickover, as soon as you blip the throttle the chain comes under tension again and the engine sounds great again. As the chain stretches further the noise gets worse until the chain starts to hit the oil gallery located directly under it, then you can really hear it on tickover. I've seen loads of 500/550 engines with this sort of damage, most just have a thin groove ground into the gallery, on some it's really deep, left uncured and it's not long before it bursts through the wall of the gallery and that's all she wrote as they say.

So the 650 tensioner mod stops a lot of this, by keeping the chain under permanent tension there is far less noise and hopefully no oil gallery damage.

When I rebuild the engine I'm going to mod back in the early 80s I fitted all new bearings, chains and dampers, I could get the engine ticking over at 600rpm and it was still totally silent, that's the effect I'm looking for by fitting the tensioner but hopefully that silence will last a longer time this time.

That's the theory, we'll see what happens in practice when I do the mod, I've not heard any negative comments about the mod from anyone who's done it and Honda clearly must have known about the oil gallery problem in order for them to have fitted the tensioner to the 650 engine as that's essentially the same engine as the 500.

[deltarider]

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?

[Oddjob]

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?

Because the ability to tickover at such low revs shows the engine is in fine fettle, increasing the tickover justs masks the problem IMO.

[Bryanj]

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.

[Oddjob]

I've stripped around 30 or so of the 500 and 550 variant engines. Most of these were foreigners as it became known this was my favourite engine to work on and people just referred them over to me, I've yet to see one engine without the oil gallery damage, most were just slight markings on top of the gallery, some were almost all the way through. It was one of the reasons I replaced mine so often, the mileages I did on my 2 engines were excessive and they both went through numerous primary chains, the K reg engine had at least 6 fitted but it did have over 200K on it. Last time I took that bike out for a run I could hear the chain slapping around, it bugged the hell out of me TBH but my brother in law was running it at the time and I couldn't fix the problem as he needed the bike for commuting. Now it's off the road again I may get round to fixing it if I can ever get him to give it back, it was part of the agreement that he bought parts for it and I lent it to him until he got sick of it, seems he not getting sick of it yet 

I think I've got around 3 sets of crankcases in the shed, I think they've all got the same damage, next time I'm in there I'll take some pics if I can drag them out of where they are.

Never spotted a difference in the 500 and 550 crankcases Bryan, except the holes where the bores go and of course the oil feed to the gearbox bearing among the little differences, never noticed any difference in the oil gallery location myself but then again I wasn't really looking.

[Bryanj]

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

[K2-K6]

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.

[Oddjob]

Heard back from Phil who's asked his mate if he'll make me one. Luckily he still had the CAD drawings so hopefully this is in hand now. I was considering asking him to make 3 or so in case someone else wanted to do this mod but it would depend on the engineer I suppose, he may find it easier to make 3 than 1 or it may just be too much trouble.

[Oddjob]

I have had 2 of these brackets made by Phils mate and damn fine work they are.

If anyone wants the spare one they can have it for what I paid for it, £50.