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by Mal Marsden - 06/16/22 7:00 pm
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kevin, Mark Parker, NickL, pidjones
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Original Post (Thread Starter)
by Stein Roger
Stein Roger
Most if not all modern plain bearing engines are designed to strict tolerances and offer a range of shells with minute differences in dimensions to be able to compensate for the tiniest deviances. Not so with our triples, one size is supposed to fit all, which must mean that there will be differences in bearing clearances between individual engines. When I changed the crank in mine, I measured the journals to be at the upper limit of the as new specs, but I didn't measure the bearing housing or the shells. Nor did I use plastigage, so unlike a proper engine builder facepalm I don't know where my clearances are at. I did check the housings for roundness, but that was all.
Now a bigger clearance means more oil flow, which is overall a good thing, and the pressure will be lower, not necessarily a bad thing. My bearings came in a plain white box with no clue to who made them.

To the question: Is there a chance that one could possibly get bearing shells that are on the large side, and/or have housings also on the large side, and could that possibly lead to a sub-standard oil pressure? If so, does it matter as long as you get say 10psi/1000rpm with the oil at 85C/185F?

Liked Replies
by kommando
I would leave it be and not ruin a good oil tight build. What you can do to keep your mind at rest is to send your used oil off for analysis. The first test sets a benchmark and subsequent tests will highlight any increases in metals and chemicals in the oil. As you used Glacier bearings made from Aluminium and Tin (about 15% Tin) then increases in Aluminium allied with an increase in Tin tells you the bearings are losing oil film thickness and being touched by the journals. There is so much other Aluminium in the engine an increase in Aluminium alone is not bearing related but likely to be pistons or crank touching the crankcase.

For the meantime you want an oil which will provide a good oil film thickness under high pressure (not oil pressure) so fully synthetic POA 4.

As TM says the oil pressure is a proxy reading, it just tells you there is a flow of oil to the bearings and decent resistance, the real critical but unmeasured metric is the oil film thickness inside the shell bearing which allows the crank to float on oil and not touch the shell.
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by Tridentman
Stein Roger---- you mention the comparisons with the rule of thumb of 10 psi per 1000 rpm and imminent disaster if your oil pressure is less than that.
However i strongly suspect that these "norms" have been established with triples in standard form.
In particular I mean without an oil thermostat in which case oil temperatures will be lower that the stat setting of about 85C (185F) and so oil pressures will be higher than at higher oil temperatures.
It might be useful if you ran the bike for a trial with the oil thermostat out of circuit---that is--full flow to the cooler at all times---and measured oil pressures in that condition.
Just a thought.
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