Hi,
I have read this entire thread with great interest, and having read many of the other modifications to the CCT, HenryM's design is on the right track, IMHO. To his own admission, no real assessment of the additional loads on the system has been made and the spring rate for the secondary tension in the upper link was an ad hoc choice.

I want to carry out a study on this tensioner system, in order to understand the loads moving around the various pivots and links. To do this, I wonder if any of you guys have a CCT out of the bike to help me with dimensions of the setup? Of course, I could open the lid and remove the various parts, but maybe someone already has a tensioner and guide out of the bike to save me the hassle.

I have drawn a diagram of the system to avoid confusion with dimensions. I have made some measurements, and would welcome a check on these, and am missing other dimensions:

Dimensions I have:
Distance between camshaft centres (A = 136mm) – use this as our “horizontal”. We take the line normal to the camshaft centres as our “vertical”.
(Vertical distance measured from camshafts to crankshaft = 281.5mm).
Distance from each camshaft centreline to the crankshaft centreline (the engine appears to be symmetric, B1 = B2 = 289.6mm uisng Pythagoras).
Pitch diameter of the camshaft sprockets D1 = 92.98mm - camshaft sprockets have 46 teeth with a chain pitch of 6.35mm which gives a circumference of 291.1mm and pi does the rest.
Diameter of the crankshaft sprocket is half the camshaft value D2 = 46.49mm.
By inspection, the CCT is positioned mid-way between the 2 camshafts, so distance E is not needed.
Use one of the forward mounting bolts of the CCT as a reference (call this bolt 1). The horizontal position of the CCT rear mounting bolt hole centres from bolt hole 1 (C = 35.75mm).

Dimensions I do NOT have:
The vertical depth of the mounting face of the CCT below the line between camshafts centres (F).
The horizontal distance from bolt 1 to the link pins on the CCT body (H1, H2).
The horizontal distance from bolt 1 to the axis of the spring/plunger (H3).
The vertical distance from the CCT mounting face to the link pins on the CCT body (V1, V2).
The radius of the lower link arm to blade (R1).
The radius of the lower link arm to where is contacts the spring/plunger (R2). This is going to be difficult to determine with any degree of precision and will have to be estimated. The inner end of the lower link arm contacts the top of the spring/plunger at a different radial location depending on the angle at which the lower link arm is rotated. However, it does not look as if this will change by much.
The radius of the upper link arm to blade (R3).
The distance between centres of the blade link pins (S).

If anyone can provide an estimation of the spring rate this would be great. I'd also welcome any estimate of the damper rate although I understand this is going to be awkward to obtain.

Last of all, thank you very much for any help you can give.

 

I can't really help, but that is an excellent drawing. I'd love to hear the results of your analysis of the strain these units are under - especially on startup with no hydraulic pressure in the damper. I think you'll want to buy a used one for testing purposes. The spring rate and piston damper would probably be impossible to measure without sacrificing one anyway, and eventually you'd want one to use for a prototype

The thing that always nags me about these is the fact that Honda put a ton of time and money into developing this engine - after all this was after the VF-fiasco and it was a return to the inline four for the company that had revolutionized it some 20 years earlier. They dumped a ton of resources into development, and they had plenty of time to get it right. It's a solidly built engine, and they didn't skimp on the engine the same way they skimped on materials/finish elsewhere on the bike. Surely if they were trying so hard to build a reputation for reliability, they would have noticed the problem in testing. Maybe they didn't care. The thing is, it's actually a very reliable engine - or would be if people could get past the rattle

Anecdotally, I'd bet a Canadian twenty that more engines failed as a result of modification to the cct than ever did as a result of a sudden loss of timing due to failure of the tensioner itself. As Henry noted, the manual cct mod would tend to overstretch the chain, as zealous owners ratcheted down the tensioner until the sound went away, only to suffer premature failure in short order. I also recall a member who suffered from a sheared bolt in his modified manual cct, and it was enough to cost him an engine. This isn't including the number of engines lost to owners in pursuit of alternator chain rattle either. His mod is the best I've seen, but I'm not convinced that it's necessary

I can't find a single example of a chain rattle causing sudden failure of any components in the engine, even on the first gen 87-88's that were the only models to ever get a recall (where the dealership would fit the same part eventually used in later models, essentially a funnel that attached to the top of the cct and helped hasten the build of hydraulic pressure in the damper). Also it's worth noting that a lot of bikes of the period suffered from the same problem. This isn't just a Honda thing

To me I'm willing to follow the advice offered in the FSM about diagnosis of problematic rattling and function-testing the cct. I agree that sludge building in/around the damper could reduce functionality, and the solution would be to clean it out. If the bike's been sitting and you're going in anyway, it's not a bad idea to pop the valve cover and prime the cct. Mine has a slight rattle, and I don't think it's hurting anything. My engine certainly had very low-wear when I overhauled it, and I know for a fact that it had a pretty hard life

All that said, I'm interested what you'll find. I hope you update the post with any new info you find. As I say, it's a nag that virtually all of us have experienced

Good luck