Camshaft longevity

[Athame57]

One of the things that quietly impresses me about the CB400f is the camshaft, it seems to go on forever and I can't put that all down to an aging right wrist. My string of CB250RS's in my dispatch days got through plenty of them. Which does it tell us more about and what sort of lifespan can I expect from my camshaft? Replacement doesn't look easy or cheap and I don't think they can be repaired!

[McCabe-Thiele (Ted)]

Most Camshafts can be repaired/reprofiled by specialists who will re-harden them as well as returning them to original specification by metal spraying.

I was offered a NOS 400 camshaft when I was rebuilding my 400, by the time I went back to the seller he had sold it & most of his slow moving spares as a job lot to a buyer in the USA.

[taysidedragon]

As long as oil and filter changes are done regularly and there's no problem with oil feed to the head the camshafts will go on and on with little wear. Problems arise when oil changes are missed, and/or lots of cold starts (where most wear occurs on any engine).

Kent Cams can reprofile cams if it becomes necessary.

[Athame57]

Kent Cams can reprofile cams if it becomes necessary.

Thanks for that! 

[K2-K6]

An interesting comparison between the two layout in them, and quite different in design.

Engines that "specialise"  in cam wear quickly become known by owners, trade etc and often resulting from higher load range in followers and lobes from that particular design.
That interface is, effectively, an open bearing with just oil film alone to maintain it's presence. That backed up, usually, by the inclusion of zddp component in the oil formulation needed (historically that's so, more recently though the reduced use of zddp has called for different metallurgy in this area) to be effective.

The process of wear starts with semi anonymous "pickup" with a small part of the cam lobe and follower being cold welded together as it passes one across the other. Oil, supposed to stop this, has limitation and zddp provides a backstop to that process by actively reducing friction under that specific load, and when oil film is broken through. That's a "normal" process in engine of this era, it's a highly demanding and punishing quality to maintain in oil mix.

The rocker leverage, having two valves to each follower, tight component size, small oil capacity, relatively high heat etc, all go to make the RS 250 design run very close to acceptable margins in reality.  Hyper sensitivity to oil life, oil specification, fuel dilution etc is just part of running such a design, successfully.  Trip up on that diligence and wear starts, which once going is almost self multiplying as the damaged surfaces pose really hard problems for oil film and zddp interactions to be effective.  A slippery slope (or not slippery enough in this case) in other words.

The SOHC Four engines are all very conservative in this design aspect. Generously proportioned critical working surfaces, mild lobe design with good approach and depart ramping, makes them fairly undemanding in respect of absolute at the limits oil performance. Still highly important, but as noted have a relatively comfortable life in engineering terms.

Given good oil condition, specification, and change interval, they generally live a happy extended life. If there's failure on these, there's usually a very obvious, and important, fault present.

Running with nil or compromised valve clearance can also be catastrophic. This because the oil film carried around the lobe circumference is facilitated by the gap that essentially takes the oil to the load site in replenishing that area between the follower and peak lobe siting/load characteristics.  Running with nil clearance stops oil film and very significantly heat up the component, which can also take the oil in that location over temperature and minimise its working capabilities.

[McCabe-Thiele (Ted)]

Interesting analysis by K2-K6.

[Athame57]

Thanks for the input K2-K6, that made good reading!

[honda-san]

My own experience....

My hack 400/4  was acquired in 1994 with just 11,500 miles showing, since when it has seen  22 years commuting 52 weeks a year followed by 10 years of use on nice days in the winter and has  this last week just had its 127,000 mile service .

EVERY major engine component is as fitted by the factory, including crank / shells, barrels / pistons and rings (barrels NEVER removed), cylinder head/cam/rockers/valves.
It has had a couple of head-gaskets, and one cam chain and primary chain (96,000 miles now since they were fitted). Also has been serviced to the letter of Honda's prescribed schedule - oil every 1500 miles, filter every 3000 miles, etc....

Does not smoke / burn oil / rattle, or give any indications of the need for mechanical work.

My conclusion would be that these things are basically just "right", and as long as they are serviced as Honda suggest are fairly un-breakable - as also suggested by the analysis by K2-K6 particularly in respect of oil condition/ quality and tappet clearances

[badger_eng]

I tip my hat in your direction Honda-San 🎩

👌

[Athame57]

Blimey Honda-San
You inspire bags of confidence! 

[K2-K6]

My own experience....

My hack 400/4  was acquired in 1994 with just 11,500 miles showing, since when it has seen  22 years commuting 52 weeks a year followed by 10 years of use on nice days in the winter and has  this last week just had its 127,000 mile service .

EVERY major engine component is as fitted by the factory, including crank / shells, barrels / pistons and rings (barrels NEVER removed), cylinder head/cam/rockers/valves.
It has had a couple of head-gaskets, and one cam chain and primary chain (96,000 miles now since they were fitted). Also has been serviced to the letter of Honda's prescribed schedule - oil every 1500 miles, filter every 3000 miles, etc....

Does not smoke / burn oil / rattle, or give any indications of the need for mechanical work.

My conclusion would be that these things are basically just "right", and as long as they are serviced as Honda suggest are fairly un-breakable - as also suggested by the analysis by K2-K6 particularly in respect of oil condition/ quality and tappet clearances

A very good account of real life experience in looking after one of these engine.

I've highlighted detail that's often missed, or confused in how people evaluate the oil filter change schedule. 

Its often given that "you might as well change the filter with the oil " in projection of that being an improvement in being more diligent.  In practice though, an oil filter (most filters actually) are more effective at the end of their life, notably in oil filters is the ability to catch smaller micron sized particles to improved filtering in the used filter.
Short changing the filter against Honda recommendations will fundamentally shift the efficiency to less effective throughput. That's in terms of what is desirable to remove/capture from the oil flow.

This flies against immediate and unconsidered primary logic.

[Laverda Dave]

Excellent analysis by both K2-k6 and Honda-san. I always change my oil and filter at the same time but maybe I should now reconsider?

Nigel, in view of your replies on this particular thread and others in the past I think you should fess up and admit your are in fact, an engine designer for Honda Moto GP . I can also recommend the book 'Classic Motorcycle Race Engines' by Kevin Cameron as a good read for anyone into engine technology.

[Athame57]

If anything I'm happy to hear it's not a good idea to change the filter with every oil change, I find it an awkward job myself. One thing though is I always choose oil for older bikes, my oil of choice for a long time has been Westway's 10W40 4T oil for classic motorcycles.

[K2-K6]

If anything I'm happy to hear it's not a good idea to change the filter with every oil change, I find it an awkward job myself. One thing though is I always choose oil for older bikes, my oil of choice for a long time has been Westway's 10W40 4T oil for classic motorcycles.

I uuse them too for some particular specification gearbox oils that are required in ZF automatic transmission.

Their oil spec is published to show Zddp concentration etc

Product Test Data:
Kinematic Viscosity @ 40˚C (cSt) : 92
Kinematic Viscosity @ 100˚C (cSt) : 13.8
Viscosity Index : 150
Flash Point (COC ˚C) : >190
Pour Point (˚C) : <-25
TBN (mg KOH/g): 7.00
Density @ 15.5˚C (g/ml): 0.87
Contains ZDDP Antiwear additives in the form of
1100ppm ZINC
1170ppm PHOSPHORUS

More or less at the upper end of what is ideal for that part. They seem to sell reliable and well specified products.

[McCabe-Thiele (Ted)]

Interesting idea about the coating of a new oil filter by fine sized particles being better at filtering through the interstitail spaces left as it it builds up during the filtering process.

Many years ago when working in a chemical plant in Germany you could extend the life cycle of candle filters used in the filtered flow process by coating them first with Sawdust to prolong the flow rate without too much change in the pressure needed to maintain a given flow rate, Fullers Earth was even better than Sawdust, it almost doubled the time between back flow cleaning  from every two hours, to every four hours whilst still maintaing the main flow rate.