Ruston 4YHR big end query

Discussion in 'Help Wanted' started by amblejo1, Oct 25, 2022.

  1. amblejo1

    amblejo1 New Member

    Could anybody with experience of big end bearings take a look at the photos at the end of this link? big end.jpg?dl=0

    The photos are the big end of a Ruston 4YHR engine that I look after at Thelnetham Windmill in north Suffolk.
    On the left is the bearing in 2018 and on the right 2022. The engine has run for about 45 hours between the two examinations. I am concerned about the marks that are developing on the white metal surface. The bearing usually returns a temperature of about 30 C at the end of 1 to 2 hours running as measured by a non-contact thermometer . Early this year we noted 50 C after a run on a cold day and we discovered a slow drip rate on the mechanical oiler. After increasing the drip rate we have not seen any more elevated temperatures, though we haven't had any particularly long runs this season. We decided to take a look at the end of the season as a precaution.

    Today we used Plastigauge to look at the clearance across the width of the crank pin and found 5 thou with next to no variation across the marked and unmarked areas, so the marked areas don't appear to be high points. Blueing the pin and manually turning the engine did not result in significant transfer of blue to the marked areas on the bearing surface.

    After being recast in 2018, the bearing was scraped in by a complete beginner (me) and has behaved well even on runs as long as 5 hours until earlier this year.

    Does anybody have experience to suggest whether or not we should be concerned?

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