Author Topic: Hydraulic Cam Chain Tensioner  (Read 1828 times)

Offline AshimotoK0

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Hydraulic Cam Chain Tensioner
« on: March 13, 2022, 10:44:35 AM »
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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« Last Edit: March 13, 2022, 11:04:58 AM by AshimotoK0 »
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline Laverda Dave

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Re: Hydraulic Cam Chain Tensioner
« Reply #1 on: March 13, 2022, 02:21:35 PM »
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.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

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Re: Hydraulic Cam Chain Tensioner
« Reply #2 on: March 15, 2022, 12:39:09 PM »
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.

Offline taysidedragon

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Re: Hydraulic Cam Chain Tensioner
« Reply #3 on: March 15, 2022, 12:45:18 PM »
Well that was a real yawn fest! 😳
Gareth

1977 CB400F
1965 T100SS

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Re: Hydraulic Cam Chain Tensioner
« Reply #4 on: March 15, 2022, 12:52:05 PM »
Well that was a real yawn fest! 😳

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

Offline taysidedragon

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Re: Hydraulic Cam Chain Tensioner
« Reply #5 on: March 15, 2022, 12:54:40 PM »
Well that was a real yawn fest! 😳

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

Nice. 😂
Gareth

1977 CB400F
1965 T100SS

Offline Laverda Dave

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Re: Hydraulic Cam Chain Tensioner
« Reply #6 on: March 15, 2022, 01:09:31 PM »
Well explained Nigel. But why do Honda have problems with tensioning the blade of the tensioner? As you state in your reply, the chain isn't tensioned as such but I guess the 'wear' is taken up by the tensioner blade changing the radius.  I get that bit but why do Honda keep changing the design, the tensioner on the 400/4 is a bit pathetic in design, the horseshoe pivot wears, the tensioner plunger sticks in the tunnel and the adjusting bolt is so thin it will snap at the first oppotunity (although to be fair, by a ham fisted owner). Cam chain tensioners do appear to be a problem area for Honda, that's why my everyday bike is a cam gear VFR ;D
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline AshimotoK0

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Re: Hydraulic Cam Chain Tensioner
« Reply #7 on: March 15, 2022, 01:32:57 PM »
Keep your detailed replies coming Nigel   ;D... I was hoping you would comment  ;).

Evidently , the story on the early CB250/350 K is that the cam-chain rattled like hell for the first mile or so and wore the chain prematurely but I still can't understand why, once the oil pump was pumping oil, that the stack would not be taken up. Perhaps it needed some kind of hydraulic accumulator to store and maintain pressure. There has to have been a Honda Service Bulletin on it but I can't find it.
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

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Re: Hydraulic Cam Chain Tensioner
« Reply #8 on: March 15, 2022, 07:51:22 PM »
Well explained Nigel. But why do Honda have problems with tensioning the blade of the tensioner? As you state in your reply, the chain isn't tensioned as such but I guess the 'wear' is taken up by the tensioner blade changing the radius.  I get that bit but why do Honda keep changing the design, the tensioner on the 400/4 is a bit pathetic in design, the horseshoe pivot wears, the tensioner plunger sticks in the tunnel and the adjusting bolt is so thin it will snap at the first oppotunity (although to be fair, by a ham fisted owner). Cam chain tensioners do appear to be a problem area for Honda, that's why my everyday bike is a cam gear VFR ;D

That old phrase "successful design has a foundation of many failures" springs to mind Dave. Obviously, it's ideal if they don't pass all the way through r&d then proof trials while still being vulnerable.
As your VFR,  Honda recognizes that gear driven cams are the ultimate solution, just expensive to engineer and produce for sale.
Designs, they are always trying to fold in details into compact design form to bring such compact engines. Comparison to others of the same era (Italian, British etc) shows how tightly the elements all fit together. 
The CX was an odd one (I believe the experience also influenced them more fundamentally in engine design though) as it had problems with tensioner, thought it was hydraulic and changed to mechanical?  (Trigger would know) but it's the cylinder angle that ultimately promoted the difficulty it appears. Narrow angle 70 degrees ish forced them to put the cam high in the block in comparison to a car V8 for example that has the two sprockets virtually touching each other and usually no means of controlling chain slack at all. Add those longer chain runs to the  firing pulses that give curios resonance, and you've got a challenging design.
But experience here may have led them to two significant engines later on. The F1 V10 that was in McLaren cars was something that most contemporary engine designers thought couldn't be resolved in  purist vibration terms that would give reliable results.  Then came the moto gp RC 211 V a 5 cylinder,  again in the design realm of cx500, those little mistakes seem to breed curiosity there within Honda.

Offline Bryanj

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Re: Hydraulic Cam Chain Tensioner
« Reply #9 on: March 15, 2022, 08:38:23 PM »
The CX 500 was semi automatic but not hydraulic, the big problem was that the engine went from not many valves open to most open in a short number of degrees rotation which hammered the hyvo chain and snapped the top tensioner mounting bolt. The mod kit included a large shaped steel plate to support the bolt along with new tensioner and bolt, if they had included a new chain as well it would have stopped the necesity for a further stripdown later.
I still have the deep 27mm socket for undoing the cam drive gear nut that cost me over £20 in the 70's and as usual because i have it never used again, still the best money i spent.
Honda aslo neglected to tell anybody to put the 1st ltr of oil after rebuild down the pushrod tunnel to fill the bath the cam and followers ran in, if you didnt the cam wore in the time it took to fill!

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Re: Hydraulic Cam Chain Tensioner
« Reply #10 on: March 16, 2022, 01:14:08 PM »
To the original question, I've not seen the hydraulic tensioner schematic Ash. Is it just that, pure hydraulic pressure, acting on a free floating chain wheel geometry ? Sounds like it from your rattling description, ie leaking out pressure during non running needs to be re established at startup.
If that's the case, then oil viscosity is going to be absolutely paramount to it's function, and could be the parameter that changed between field trials pre production and reality of normal service life.
What is the original oil specification for them, is it multigrade or straight listed/fixed viscosity.

The pressure "ram" would ordinarily have to have a bleed off port such that it can't air lock during initial pressure build at each start, which is sensitive to variation in oil temperature and specific viscosity for it's performance. 

There's something of a parallel in hydraulic lifters commonly used for years on American design V8 engines, but with each one inline with the pushrod for each valve individually.  They have a leak off port that will let the lifter recede if parked with that valve open,  this has to establish pressure again on start. Also, they can go over pressure (if that port can't leak fast enough) during high rpm running to give lifter pump that starts to hold the valve off it's seat and leak combustion. 
You can see the dynamic complexity in these systems as illustration for how they are designed.

The Honda one from description you've given of start up noise suggests to high a cold viscosity, such that the pump can't deliver the oil through the system fast enough to refill the chamber providing pressure. 
Their cold ambient temperature oil is only 20 viscosity as I understand it, that's below 59F from Honda specification.  Any higher and it would delay system filling, that's something that Jensen observed on the 450, going up in viscosity simply blows it out of oil pressure relief valve rather than put it through the system.  It has to do this to avoid oil pump failure, but I don't feel that proper consideration is given to how oil viscosity interacts in these engines.
Viscosity is not absolute protection as many views project, it's really just resistance same as electrical resistance. 

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Re: Hydraulic Cam Chain Tensioner
« Reply #11 on: March 17, 2022, 10:31:01 AM »
Looking at the schematic above (didn't realise the detail initially) the lower one showing the hydraulic item, you can see where the oil port to enter the casting is at the bottom between the two bolt holes.
Looks like that runs up the diagonal to feed the far end of plunger cavity, and (detail resolution poor) appears to have a bleed out hole on the domed cap that pushes the chain wheel carriage. This hole would prevent air lock situation and control outflow to mitigate full system pressure from being unconditionally acted onto the chain.

From Honda's own oil temperature charts it would seem logical to use something like a 5w30 or 0w30 oil to give assurance in initial cold start supply (neither of these available at time of design) which would likely give reliable response and avoid chain compromise.

We were getting to this type of balance in discussion with Jensen on the 450 thread a while ago. The fixation of higher viscosity as a protector is fundamentally wrong (he effectively proved that with very detailed monitoring ) and came to the wrong conclusion in my view.
Lower cold viscosity promotes immediate supply, without which the protection arguments are simply academic.

The stated oil product viscosity numbers are not what they seem and can cause the wrong analysis to be made about what will benefit the outcome.

Offline AshimotoK0

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Re: Hydraulic Cam Chain Tensioner
« Reply #12 on: March 17, 2022, 01:29:17 PM »
You have probably hit on something there Nigel ... many people back in the day used to use 20/50 multigrade,  as used in cars of the day or 'Filtrate' .. made in Leeds with colloidal graphite or Molybdenum di-sulphide in it. Perhaps Honda tested with the 10-40 recommended on the dipstick.  Filtrate was probably fine for bikes without a centrifugal oil filter but on a 250K4 I had,  the filter housing was almost blocked with what I assumed was the additive. The original  local Honda dealer Ken Blakeys used to swear by it though.
« Last Edit: March 17, 2022, 03:18:42 PM by AshimotoK0 »
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline Bryanj

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Re: Hydraulic Cam Chain Tensioner
« Reply #13 on: March 17, 2022, 03:51:08 PM »
That used to happen to the filters on any oil Ash, worse on the G5 as you had to remove the whole clutch case to clean it out

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Re: Hydraulic Cam Chain Tensioner
« Reply #14 on: March 21, 2022, 01:49:17 PM »
That used to happen to the filters on any oil Ash, worse on the G5 as you had to remove the whole clutch case to clean it out

There was certainly some suspect oils about then as working on engines (bikes and cars) late 70s found many with so much sludge in them. Contrary to how people thought about it, most of the engine material was still there  :) much of it seems to be from oil oxidation and breakdown of viscosity polymers that made up multigrade oils of the time. Speaking to a polymer chemist more recently who indicated that many of the products from this time had significant stability problems in use. I've seen some car engine head areas with sludge built up more than an inch thick.
Virtually all of currently available products have far better lifing performance than that era.

 

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