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Oil pressure issue / motor rebuild

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MrDavo:
The good news is Candy runs well, looks wonderful, getting compliments from everyone who sees her, and has won best Japanese Classic at 2 of the 3 bike shows she has been entered in. However, it looks like she's about to be pulled apart. She has been restored at some point while in South Africa, but I've no idea what engine work, if any, was done until I get inside.

Fault 1:

While Candy runs ever so sweetly, with very little mechanical clatter, when she gets proper hot, such as after a run 2 up with the camping gear on board, I am sorry to say there is a definite low 'knock' which I can feel as well as hear. Pulling the clutch in makes no difference, so I don't think its the clutch basket rattle that some have suggested. Also, the oil light comes on at low revs, to be expected I know, the manual says it is normal, however the hotter it gets the higher the revs needed to make it go out again.

Fault 2:

This has only happened twice to me, but she is 45 years old, so who knows how many times it has ever happened.

200 yards from my house, (the same piece of road both times) the oil light comes on solid, not flickering, whatever the revs, and a clatter - as fast as I can pull over it goes as quickly as it happened and doesn't reoccur.

I suspect that fault 1 (the knock) was caused by fault 2 (oil starvation), and was already there when I bought her - coming back from the MOT (my first ride) I had issues with the oil light coming on at idle and being reluctant to go out again as I revved.

I have replaced the oil pump 'O' rings, oil pressure light sender, and tried heavier (20/50) oil. An experienced race mechanic I spoke to at Classic Le Mans last weekend suggested I could try over filling, with thinner oil, he suspects the thick cold oil just isn't flowing fast enough to keep up until it gets warm, leaving the oil pump trying to pump fresh air,  he agrees it may have done for the main bearing shells over time. He also told me about classic Bugatti race mechanics having to warm rear axles with blowlamps, the lubricant they use solidifies to something like candle wax at normal temperatures!

I'm going to try pulling the oil supply line at the motor, to see what the flow is like when the engine is cold - maybe it's partly the viscosity, but perhaps there's a partial blockage or collapsed rubber inner in the oil feed line (every other bit of rubber on the bike was shot due to a combination of age and long term storage in a hot climate).

Even if I can stop it happening again, the bottom end won't fix itself, and I am reading up about using plastiguage to measure running clearances. I wanted to take the motor out anyway to polish the cam cover. D'oh!  ::)


 

Trigger:
Have you tested the oil pressure ? And is oil spitting out the tappet caps, when removed ?

MrDavo:
No I haven't tested the pressure yet, but the local garage that does the wife's car has said I can use his gauge, he has a range of fittings so I'm hoping he has the one to fit on the end of the gallery.

There is oil at the tappets (and a slight top end leak).

K2-K6:
Something really strange there.

You're already effectively running 20 viscosity oil anyway when the oil temp is down as the base oil is that rating and only behaves like a 50 when heated via the performance of its viscosity additives when reaching 100 deg c as I understand it.

Honda's manual for that engine states that SAE 20 oil is ok from zero deg c so you should not runs into problems from it at current temps.

I also ran these 750's on 20/50 oil including winter use of below zero and even got a K6 stuck in the snow with never any problem with oil pressure.

The pump is a dry sump so should never be able to suck air, as long as the levels are ok.

You may be onto something in verifying the oil hoses are intact internally as that could cause starvation. Have you checked the pressure relief valve on the pump?

Bryanj:
There was a batch of oil feed lines fitted from the factory that had an internal "Kink" and restricted flow, as far as I know they should all have been changed under warrantee along with the crank and shells.

If you "clonk" is a bad bearing you will need a different crank and shells as these cranks can not be re ground

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