I have been measuring my Mk3 big-end journals to see if a regrind is necessary. Measurement has been tricky with a digital micrometer, but there appears to be only moderate wear on standard grind, less the one thou ovality on one journal and no grooves or scoring.
in most When checking the existing shells (I have replacements) I was surprised to find that both rod shells seem to have very little white metal with a pronounced bronze appearance (see photos), whereas the cap shells a have an even, dark grey appearance. Over the years I have stripped Mk3, T120 and T140 engines (and a 3.8 Mk2 Jag XK engine) and never seen shells with this appearance. Given the lack of journal wear (or cylinder bore wear) the shells may be original. Perhaps the shells were scraped during fit, but I have never needed to do that with any shells.
Has anyone seen this sort of big-end shell appearance without any appreciable wear to the journals?
Andy
They are trimetallic…
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John, trhanks for info on…
John, trhanks for info on bearing shell construction. The photos were actually both the rod shells rather than rod and cap; the cap shells are plain. The shells have the Glacier Logo - not sure if they were OE? The backs of the shells are exposed steel, no coating at all. However, the new shells from A-N are coated on both sides as you described.
it is curious that even with the evident degree of shell costing ear, the rods have no perceptible vertical play and only the left rod has just a slight left/right rock. As the crank is still on STD grind and the shells are similarly marked, so no size mix up possible. I have not tried fitting the rods with the new shells yet; it will be interesting to see how tight they are.
Andy
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Any tight spot is not…
Any tight spot is not acceptable. And it can happen with new shells and a partworn crank.
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The plating is microns thick…
The plating is microns thick, so it not being there anymore will not change the size to the normal person with a vernier or by feel. Human touch does not detect movement until there is clearance of at least 3 thou, you are nowhere near that. A micron is 0.04 of a single thou not 0.04 of an inch.
Glacier were not OEM so fitted after it left the factory, but that does change it slightly.
They are still Trimetallic but with a sintered leaded bronze over steel and a leaded tin plated overlay or a few microns thickness, so about 5% less fatigue strength. Fatigue strength has the same properties as a water holding dam, does not matter if you have a 5m or 10 meter high dam if the max water level is 4 meters, neither dam is breeched. So for a road bike it makes no difference.
Glacier had a neat plating plant and the backs of the shells were shielded so unlike the Vandervell the steel back was not plated.
Fit new shells, there will be no detectable change in clearance.
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They are trimetallic bearings, steel back with leaded bronze cast onto the steel. Once finished they are overlay plated with lead indium giving a dull grey coating which also covers the steel back with a thickness of just a few microns. The overlay plating is to protect the lead from being attacked by acids in the oil. So those bearings are well worn, you are meant to change them the first sign of bronze being exposed. The combustion pressures mean most wear is on the con rod shell as the force bears down and breaks the oil film. You need a better oil that will stop the metal touching by forming a wedge of oil in the journal and rebuild the oil pump as it may be worn.
There are variations of trimetallic coatings, Vandervell used the soft lead indium, others used harder lead tin or even silver (a Ferrari requirement).
For a road bike a bimetallic bearing of steel with an aluminium tin overlay is a better option, no soft overlay to disappear. Trimetallic is for racing, stronger but faster wearing as your photo's confirm.
One other point, both your top and bottom shells have holes, only the top shell should have holes so either a bad replacement or the factory fitted the wrong shells. As it is I fit plain shells top and bottom, the hole loses you bearing surface area on the top shell where you need max surface area. The loss of the oil spurt is easily compensated with a shallow but wide groove on the sides of the alloy rod face bearing housing.