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Hydraulic Cam Chain Tensioner

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AshimotoK0:
A friend of mine, who I swap parts with, was lucky enough to get enough NOS parts to build a genuine CYB350 race bike ... introduced in the late 1960's and quickly discontinued when Honda temporarily  pulled out of racing to concentrate on car production. A large amount of the the remaining stock of CYB parts were all held at Honda UK's  Nottingham's Service Centre and it's head man Alf Briggs was allowed to keep all of the parts as a personal gift from Mr. Honda himself.

Along with parts from that source and others, my friend has finally built up a genuine CYB350 but he was short of the original hydraulic cam chain tensioner, first used in 1968. Luckily, I had 2 of them so I just donated one to him. But I often ask why Honda introduced it onto the first CB250/350Ks ? From what I know Honda hastily did a recall and swapped to a mechanical tensioner very similar to what they subsequently used on the CB750 in 1969.

Two of my CB250K0's were owned by an old chap who used to buy Honda's with very low mileages including the two  1968 built but registered in 1969 CB250's, which   I got from his estate. One (showing 5.9k miles) he dismantled to a large extent and kept in a garage  but the other got left in his garden to decay for many years (see picture !) The one in the picture was showing 4.5k miles and both bikes had escaped Honda's recall and had their original hydraulic cam chain tensioners fitted.

It seems odd though that a bike that was such a  radically new design for Honda  in 1968 and went on to sell a million units is all of it's model guises, could have been developed and tested by Honda R&D and reached full production and then it's cam chain tensioner mechanism recalled as being problematic.

Did any later models have some kind of hydraulic tensioner ? ... I know that some Ford cars had it ..maybe still do for all I know. A question for Nigel 'K2-K6' I guess.

By the way, the bike in the picture had one of the centre stands I had to drill out the pivot pin last year,  as no amount of hacksaw cutting would free it  ... but looking at the state of the bike, is that really surprising?


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Laverda Dave:
What is it about Honda and poor cam chain tensioner design? Considering Honda were really the leaders in four stroke motorcycle engines in the 60’s why are the tensioners their achilles heel. The 400/4, CX500, CBX550 all suffered, Honda never seemed to get it consistently right. The likes of Suzuki, Yamaha and Kawasaki who were all 'late' to the four stroke party didn't suffer the same problems although I think the Yam TX of the early 70’s had some issues in the tensioner department.

K2-K6:
Interesting that they had used hydraulic tensioner originally.  Presumably (it must have been) failure in service life caused the revision.

Projection of original design (guess  :) ) is to make them completely automatic in use, so avoiding the need to set them at service intervals.
Commonly referred to as chain "tensioner" but to be pedantic chains are just not tensioned.  To describe as optimum geometry in coping with chain bearing wear is more accurate in talking about what they do, but ridiculously clunky as name.

The chain has to have no geometry change on the pull side to the camshaft, else it would change timing throughout service life. All chains are highly efficient in transmitting load, and completely brutal in resonating the pulses put into them. Most chain are going to be strong enough for load but ultimately fail if resonance/harmonics are not controlled.
The design method to control the resonance is to split the chain run up into shorter sections such that ultimate destructive effects lay outside normal operating range of the engine.
The pull side on these engine has that guide in a curve (that's often used in many engines) to try and seperate the crank pulses from going straight into the camshaft and causing problems there. Not much, but some help.
Coming back down to crank, usually split up into shorter sections with the opposing wheel arrangement used on that side.
Setting it is actually very simple, with slack that side, light spring pressure (to avoid the mechanic putting excess load on the chain) the geometry is locked off until next inspection interval arrives. It's really that simple.
What this is doing is to prevent any slack from travelling to any other part of the chain run. Unlikely you'd get a failure here.
The most likely point of failure is coming into mesh with the crankshaft on the pull side as it needs relatively little shift in slack at this point to meet the sprocket teeth straight onto a bearing location,  then it's a very quick failure.
The correct geometry on adjuster makes no slack (or very little) available to be excited by harmonic interaction on that long front chain run.

What could have caused the failures?  I'll go to next post.

taysidedragon:
Well that was a real yawn fest! 😳

K2-K6:

--- Quote from: taysidedragon on March 15, 2022, 12:45:18 PM ---Well that was a real yawn fest! 😳

--- End quote ---

Glad you appreciated it  ;D if you're here to draw attention to your own ignorance, then who am I to argue with that.

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