Life of Hi........................Vo

[K2-K6]

Topic as title,  often comes into focus in different threads with detail embedded but a little difficult to find.

The primary drive chain of smaller Honda 4 cylinder engines appears to be one of the most frequently worn  components, even if the other parts show very good lifing for the mileage they've completed. It may not show a good condition with even the most diligent of servicing, and so to consider some of the influences that could bring this about.

It's a Morse type chain design, developed into "Hi-Vo" as a defined product by Borg Warner transmission company.  A combination that's split between very clever design and mechanical performance but opposed by very simple materials (could be considered crude) and construction that gives some fairly unique properties.

Essentially could be considered as a linear gear drive with soft engagement to rotating gear pairs,  it can mask mechanical condition exceptionally well from new to old tolerances.  High torque capacity but with the trade off being it's relatively heavy for given size that has an effect of centrifuge at high rotation speeds. This aspect of the design seems to be one of the contolling parameters in Honda using two small diameter gears,  then changing ratio onwards to gearbox by using differential clutch drive gears to complete the primary route.

Still,  it's capability has to be rotating at 10,000rpm crank speed and keep together with that attendant centrifugal force acting on it.  This does in reality  provide the "tensioning" with this type of drive, and why they are usually used without such devices.

[K2-K6]

To divert a little,  tensioning,  of a chain, is really the wrong description.  Tensioned in it's true sense would simply add excessive load to the whole drive train,  and then wear the chain bearings until it creates enough gap to run without that tension.

Our use of the word can more easily be explained as controlling the slack side of chain run.  Usung camchain as example,  the drive / pull side of the chain is run over it's guide in a gentle arc to prevent a straight pull and leave that chain run vulnerable to being exited (like a double base string) from differing frequencies coming from both crankshaft and camshaft pulsed rotation.  The "tensioner" side run, then has to be arranged that the unloaded section doesn't flap and cause unwanted effects while returning to the crankshaft to go round again. It can't use a cush drive as such which would cause timing to oscillate, so effectively has to involve a more consistent guide (that curved run) to prevent frequencies getting into a problem phase that could potentially destroy the chain. 

The primary has a much greater torque loading than the  camchain,  with it's tension/pull side unlikely to live with the duty cycle it has when pulled across a guide as the camchain does. But then it uses the first cush drive to dissipate torque frequency pulses input by the crankshaft.  This results in the highest peaks of the crankshaft pulses being absorbed by the cush drive rather than shocking the  chain components,  additional to that is preventing those severe peaks passing further down the drive train into the gearbox.  If the cush drive fails to respond in the correct frequency band as designed (deterioration to hard) then the surrounding components still have to absorb that unwanted oscillation.  Ultimately that's going to shorten the lifespan of these components. 

Putting anything on the non pull side has difficulties as when the throttle is shut the over run torque coming back through the gearbox is also potentially high,   with the same durability problems as above. A jockey wheel here may keep it quieter if idle is uneven, but can't ultimately change the loading the chain receives.

[taysidedragon]

In short, Honda got it right. 😉

[K2-K6]

Which makes me wonder why Honda didn't fit a tensioner like they did with the 650 which was essentially the same lower engine as the 500/550.

I'm adapting my restoration 1972 500 with a 650 tensioner, we'll see how long it lasts when that's fitted although reports say it seems to last extremely well from those who have done the mod.

It "looks" like they've responded to customer observation,  and perhaps service workshop feedback about noise at tickover and the risk of wearing the oil gallery.  Quite plausible and possibly effective but appears more to deal with symptoms than why the chain wears faster than most of the other components in the same environment.
It'll be interesting to see a first hand experience when you get yours running.

[K2-K6]

In short, Honda got it right. 😉

It looks close to right as so many aspects of it look to be a very good answer to provide a solution for their drive design needs.

As any engine is though, a collection of bits that given correct research and development, will live well together. Some of those components may be much closer to their wear margins than the others. This one sticks out and selects itself for scrutinizing as virtually all that come apart seem to show fairly advanced wear of this chain over and above the other parts.

What I'm curious about is that this type of chain has extremely long lifing in other transmission systems, it's easily capable of getting to 200,000 miles in many 4WD transmission with sizeable loads in comparison to it's dimensions.  But here it wouldn't appear to get anywhere near that service life.

[Bryanj]

Higher revs and more snatching would be my thoughts

[K2-K6]

In comparison to use in different systems there's some interesting details that come up, which I feel impact how it runs in these engines.

Primarily it appears that the oil fails to sufficiently protect the chain's load bearing surfaces, but notice how it doesn't impact the drive teeth on crankshaft and layshaft.
They appear to make grey oil "slurry" that's consistent with the metal product left on an oil stone when you grind/finish working tools during sharpening. 
You get this ferrous oil "peanut butter" stuck to the sump  plug/magnet on engines as collected evidence some times. As most of the other engine parts are usually still in place (on well lubricated examples) although it's small assumption,  reasonable to think it's primarily coming from the chain.
If the oil film fails,   it's most likely causes are;- not meeting a standard suitable to prevent wear or condition of oil that stops it holding it's designed qualities, inability to replenish at acceptable rate to prevent localized breach of film, and associated with that,  going over heat to cause breakdown of film when exceeding operating temperature range.

[Laverda Dave]

Back in the day (70's/80's) bike testers would always mention 'backlash' on Jap bikes. Is this backlash a result of using HY-VO chains for primary transmission and would backlash be an issue if the primary drive was by gears and not chain? Would backlash also increase as the primary chain wears? Or is backlash a result of designed in freeplay on the gear shafts to enable gears to engage properly?

[K2-K6]

There's a specific part of the design that may have influenced that scenario.

The Japanese gearboxes being generally oriented such that the drive comes out of the clutch through gearbox main shaft,  then crossed to the secondary gear shaft to go out of the box from that shaft. This involves two sets of gear dog backlash, one on each shaft for all ratios.

Whereas some of the British boxes favour the output on the same, principal, shaft as the clutch.  This gives intermediate ratios going to the secondary "lay" shaft and then back to the main shaft to get out.  But the top gear would be direct from clutch to output sprocket on the same shaft. Most car gearbox are like this too. In effect no backlash at all for top gear, additionally it has no paired gear losses for top gear either, and so has a frictional advantage. 

Steady cruising with throttle on/off would show more shunting on the first type.

[K2-K6]

To add, most (well all really) road vehicles have built in "lash" between engine and gearbox as they are quenching the peaks of crankshaft speed oscillations to prevent them hammering the onward drive components. Hugely helps to take out noise and vibrations rather than amplifying them.

Generally it'll be at the clutch, with things like current diesel engines using dual mass flywheel in which one of the functions is to allow the crankshaft something like 120 degrees rotation freedom ( contained by springs) to filter out the chunky bits of torque at low rpm and make them sound more sophisticated than crankshaft pulses would allow. 

[Seabeowner]

Same chain of course on the Kwaka 550s and they were using it without a tensioner into the 90s. But GPX600R has an upper and a spring loaded lower "guide", uses the same chain and handles considerably more power with no (or less) flapping around.

[K2-K6]

Same chain of course on the Kwaka 550s and they were using it without a tensioner into the 90s. But GPX600R has an upper and a spring loaded lower "guide", uses the same chain and handles considerably more power with no (or less) flapping around.

Yes, it appears to draw the very same observation in that use, rarely if ever breaking, not liking the "clanking" when idling after reasonable mileage and reluctance by owner to accepted it as normal to split the engine to change it. Also looks like the Kawasaki engineering dept had a good look at the Honda when planning theirs.

The "tensioners" appear to be aimed at addressing noise/quietness once worn here to.  With the tensioner effectively ejected once under high torque loading, it wouldn't seem to be able to significantly change wear rate.

[K2-K6]

While looking at them for a different application it became clear that they are sensitive to oil viscosity.  Original development and oil range has requirements of 5 viscosity ATF with maximum of 20, making them effectively used out of range for this application. 

It specifically relates to how the oil travels through the plates to reach the loaded pivot surfaces.  Too high viscosity and throughput of oil is insufficient to keep the oil from having it's protection breached. In other words, it stays at load site too long to be reasonably replenished at a rate that allows the oil to carry away the heat generated,  oil breaks down at extreme localized temperatures and fails to prevent metal to metal contact. It looks like this that results in the grey slurry.
In extreme cases,  the pins and chain links get so hot that the components can fail (not in the bike engines) with that laying at the outer limits and the condition we see between this and zero wear.
They are though hugely strong with failure in bikes unheard of realistically but contrast this area with how the drive faces and crank etc don't wear, and you can see how the pins lay the other side of a tolerable boundry for the same oil.

[K2-K6]

Thinking about original development of the engine, you can see just why it was attractive to Honda. They are really quiet (often referred to as "silent" chain) with really compact dimensions for the torque they can carry, with the possibility of an assessment made to understand if they could use it within their engineering demands with that viscosity essentially out of range. Also cheap compared to a gear drive (one of Honda's favourite methods) in engineering terms.

We know the answer if that took place (it must have done during original conception) with the R&D phase looking to answer that fully.

I know it's conjecture,  but it could be things like continuous endurance running keeping oil temperature fairly at target (thinner viscosity at normal running temps) that gave lifing assessment better than we'd see with shorter runs and cooler ambient temperatures.  Whether any significant cold climate testing would have taken place we don't know,  likely though that hot weather testing would be fairly extensive given their market scope. Higher ambient may disguise this particular wear site with oil able to flush through the link plates more efficiently. 

It seems their philosophy would preclude these bikes lasting so long,  which of course affect decisions made as to suitability for sale.  Always heading for the "new" with interest on future development, it probably surprises them that so many are still being used.