Later Alloy Body Oil Pump in K0 Bomber

[K2-K6]

Why hide behind the sofa ?

I had not good results with 0W40 oil regarding cam issue's. The layer of oil seems not strong enough to resist the pressure of the tortion bar.

Jensen

The stated oil viscosity doesn't,  and never has done,  describe the oil film specification. They are two (it can't be said completely as they exist in the same fluid) separate properties that can, and are,  brought into the oil specification to accomplish different aims.

I'd not agree about the torsion bar spring either. The valve dynamics require a certain spring rate to operate at the given rpm,  that's delivered the same for coil or torsion arrangements to the same rating. The cam and follower "see" the same pressure. Torsion will have a different resonant frequency than coil and may make use of that to best use the cam profile and valve acceleration rate desired by the designer.

What they have done in original design is ask for a significant performance from the valve size and timing,  coupled with a relatively high rpm ceiling. That dictates a high spring pressure, which is compounded by using a rocker on which the cam profile operates between the pivot point and the valve tip. This feature alone amplifies any spring loading experienced by the camshaft lobe as it's working at a leveraged disadvantage.
Essentially,  they've produced a system that is very close to marginal. Any wrong steps in setup and looking after it are severely punished in breaching what an oil can achieve in keeping the parts frome breaking down their surface finish.

As the cam interface is open (at no pressure) the oil viscosity has virtually nill effect on protecting the components. At that point of interaction,  the oil is subjected to a swingeing massacre of any film properties it may contain. It really is down to the base components existing in the oil to prevent metal to metal frictional pickup. This has usually been the principle task of ZDDP content in oil.

[AshimotoK0]

Well I got a copy of the relevant CB450K0 Service Bulletin pertaining to  the oil filter screen problem, which  Jensen told us about  but it's a very poor photo of one,  so here is my 'translation'. The original was posted by Chris Saxby on HondaTwins recently (Chris has restored a lot of bombers, all early 4-speeds I believe) So many thanks Chris if you read this ... Why no join us on here ...your input would be invaluable ?

Not sure if the mod is to machine the pillars or fit an updated part but I can't see anything wrong with carefully milling the posts.

Anyway here goes:
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OIL PUMP INSPECTION/MODIFICATION

APPLICATION: Engine No. CB450E-000001 to CB450E-1021156

We have found that some top-end and oil pump failures in CB-450 units has been caused by
foreign matter entering the oil system through damaged oil pump filter screens.

The oil pump intake port is surrounded by four screen-supporting oil guide ribs. These
ribs must be separated as in Fig.1. If the ribs are jointed or partially joined, as in Fig.2, the oil flow to the oil intake port becomes highly localized. The localized flow will eventually
work-harden, embrittle and break the brass filter screen. Any break in the filter screen allows foreign matter, trapped in the oil, to enter the pump, possibly fouling the check valve and damaging the oil pump.

We recommend the following inspection and subsequent modification if, during routine
maintenance, any of the following conditions exist :

1. Cam chain dampers missing or broken.
2. Lubrication or camshaft failure.
3. The right hand crankshaft cover is removed to perform other maintenance.

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[MrDavo]

I took the 500T pump back out of my CL450 engine at the weekend and put the original back, I decided any perceived flow gain wasn't worth the risk of cocking something else up, as Ashely said, the engine had done fine without it since 1969.

Here's the 500T pump (now for sale if anyone needs one) as it came out, the circular marks on the washer weren't there when it went in, as far as I remember, so I wonder if there may have been a tiny alignment issue, which would have only got worse in serice. Remember it never ran like this, but was turned over on the starter for a while to get oil pressure up. I note the 500T ribs are as per that service bulletin. I didnt take a picture of the gauze on the other pump (I hadn't seen this bulletin then), but it was 100% intact, despite the odd knock pin and piece of cam having been in the original oil. I'm unsure of the arrangement around the intake port on this pump.



This is the cast iron bodied CL450 K1 original that went back in, the F mark matched one cast on the clutch inner by the way.



Back in place where Honda intended it:



All I can say is that the 500T pump did pump oil, but not worth the risk after considering all I've read.

The engine is now fastened up and in storage until the chassis is ready for it.

[K2-K6]

That modified oil entry point from the information posted by Ash would appear to be one of the most critical updates to the pump casting in terms of removing problems.

It looks like it would benefit from having the burr removed from the oil entry hole as the casting seems to be quite rough there.  Something like a half millimeter radius would help in reducing any tendency to cavitation for the oil entering the pump chamber.

The overall layout of the pump and arm are interesting. It looks as though the cranked arm is to facilitate a straight pull during pump fill phase as tension line will line up more closely to bore axis. The piston has the clevis pin located right at the "back" end to promote alignment during suction,  it's effectively much less lubricated during this phase as the oil is under vacuum around the piston so any clearing would not be penalised with bore or piston wear as the overall alignment seem arranged to mitigate this.
Conversely the pressure stroke is subjected to exactly that "pressure" as it pushes the oil into the engine and effectively makes its own load bearing film around the piston to prevent direct contact with the bore. It is in effect an oil bearing as having the clevis pin so far back it relies on this to prevent the leading edge of the piston being directly pushed against the bore when under sideways load from the crank arm being at more of an angle.

Why they changed to an alloy body is not clearly available.  It looks like that increasing the capacity may have caused (more torque required to drive it)  problems with the size of the clevis pin for durability anD bore in the aluminium piston.  In this case, a switch to steel piston would resolve that.  Which would bring a corresponding switch to the pump body the other way.  It doesn't really matter which is which material for the components in terms of longevity of bore surface as the wear characteristics work either way.
The materials in the component's do tell you about oil performance if they wear though. If all is well then they will show very low wear marks.  If the oil film breaks down,  the soft components will be worn by the harder material, generally. If the oil contains anything abrasive though,  the wear can switch because the hard particals become embedded in the softer material,  resulting in a wear pattern experienced in the harder material. Basically you can see what was going on with the oil after inspecting the wear patterns.
It's this area that would first be affected by increasing oil viscosity and/or pump capacity without changing the following engine architecture to accept those differences.  The load on the pump during pressure phase will rise but the oil film (unless you change its load properties) does not have a corresponding increase.  This may cause the piston to breach it's oil film protecting it's normal operation and give clear wear marks on the components.