Re: Roll pins and oil pressure

[Jaap Bouma <j.h.bouma@domain.elided>]

At 09:53 AM 4/9/99 -0400, Andrew Watry wrote:
>Aside from their job of helping hold O-rings in place, do roll pins in the
>cam gallery oil passages really increase oil pressure throughout the engine,
>or merely create a restriction and resulting higher pressure in the vertical
>oil gallery, giving a higher oil pressure READING at the sending unit (and
>so at the gauge), which on most 105/115/116 cars, is tapped into the right
>rear oil gallery below the roll pin?  I would think you just get a higher
>reading in that passage, and the apparent higher pressure, shown on the
>gauge, would be phantom, and not really helping the engine out at all.

You can compare the lubricating system with a tree, with the pump at the
base of the trunk and the various bits to be lubricated (bearings and such)
at the tips of the branches. The pressure in the system is determined by
the flow rate from the pump and the sum of all the restrictions through
which the oil leaves the system. The higher the flow rate, the higher the
pressure you get. Similarly, the narrower the restrictions, the higher the
pressure will be.
By restricting the flow to one branch, less oil flows through the bearings
at the end of that branch, reducing the pressure there. In contrast, more
oil is forced through each of the other branches, which leads to a higher
pressure in those branches. So restricting the flow to the valve train
would improve the lubrication of the other parts of the engine, such as the
bottom end and turbo compressor.

All this assuming that the pressure is less than the limit imposed by the
pressure relief valve.




Best, Jaap Bouma (Netherlands)
'87 GTV6 2.5 Grand Prix

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