SOHC.co.uk Forums > CB750

Oil at Tappet Covers

<< < (2/4) > >>

adespin:
No, i havn't timed it, it just seems like a couple of minutes, thinking about it, 2 mins is a log time, so tomorrow i will time it accurately from cold.

K2-K6:
 You have to get a normal confirmed timing of oil arrival visible at the tappet covers to compare this one too.

On the contrary, the "oil jets" should be doing exactly this.  They prioritise the crankshaft as it's turning with as close to instant pressure build up.  You really don't want the crank running while waiting to build oil supply to the cam area which has, in effect, a holding bath for the critical cam lobes to dip into while it's waiting for oil to arrive from the gallery.

I know it's probably pedantic  :),  but jets ordinarily speed up output from the flow coming in to the flow going out as in jet engines, carb jets etc. These are "pressure limiting restrictors" and do exactly that,  to protect the oil pressure supply to the crank and big ends as their first objective. 

I'd clarify if it's normal before considering taking it apart.

adespin:
So am i to understand that there is no pressurised oil feed to the top end except for the jets, therefore basic splash lubrication Briggs & Stratton style, if so quite primitive.

Nurse Julie:
There is some pressurised oil getting to the top end but because they are restrictor jets giving priority to the bottom end, the pressure is diminished alot by the time the oil gets to the top end. It really is a gentle spray by the time the oil get to the top end. Basic but works fine as long as the jets are 100% clean and clear and you have good oil pressure in the engine. The minutest blockage will reduce the spray effect as the holes in the jets are very, very small.

K2-K6:
Yes, correct. You've in effect got two oil systems,  high and low pressure, supplied by the same pump and divided by those restrictors to hold the main shells at maximum pressure.

They just push it through the cam journals so that they have constant supply,  which leaks out and variously fills what I'd guess you'd call a series of wiers to retain oil at levels around the components and always give them a supply.

In all fairness,  many engines do the same as this as they have no need to do anything more complex. The cam lobes on any engine are effectively open/ non pressurised bearings really so you can't do much more than chuck oil at them or dip them into the oil as here.  They mostly are very rudimentary but work well. And only rotating at half crank speed demands aren't that high realistically. 
They are more likely to be compromised by too tight a tappet clearance as it prevents the oil film establishing round the cam lobe if it's continously wiped even round the base circle diameter of the cam.

Navigation

[0] Message Index

[#] Next page

[*] Previous page