Author Topic: Mk Engine bushings  (Read 3004 times)

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Offline Clive

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Mk Engine bushings
« on: 15 Jan 2010 at 04:47 »
Crankshaft front bearing, camshaft bearings
What grade of Phosphor Bronze  material is most suitable for the manufacture of these bearings ,i ask this question because the bearings in my Mk3 are only showing about 1thou of wear outside the manufactures specs . The shafts on the other hand are all worn 4 to 5 thou , suggesting that the bearing material is too hard or incorrect for the job .
Any comments Please

Offline eddie

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Re: Mk Engine bushings
« Reply #1 on: 15 Jan 2010 at 06:18 »
         If your shafts are worn more than the bushes, I would suggest that this is probably due to some impurities in the oil (overdue oil changes, etc.) rather than the wrong grade of bronze for the bushes. Whatever grade of bronze is used, it will be softer than the shafts, so any impurities will get embedded in the soft bronze which then becomes a lap and gradually wears away the shaft.
        Another possibility is that in the past your engine has been rebuilt with new bushes but using the worn cams and crank - in the hope of not having to get them reground.
       When rebuilding your engine, bear in mind that Mr Douglas recommended 3 thou clearance in the bore of the front main bearing bush - any less and you risk the bearing nipping up, which usually results in the locating peg distorting the flange on the bush - necessitating another strip down. Also bear in mind the camshaft bushes are only splash fed, so there has to be enough clearance to allow the oil in to do it's job.