Scraping white metal bearings

[Colin Reed]

HI All,
One contributor on this forum regarding reconditioning in NZ is talking B/S

Colin 
NZ

[Ian Williams]

Oh goodness Colin I am shocked by that, even if its true you are not allowed to say so.

[Zetomagneto]

Oh how friendly we are! There are more than a few elements of truth in there if you look for them.

[Stuart Palmer]

Ivor has alluded to it, but no one has said it.
In a non pressure fed engine like a seven, a bigger working clearance in a big end is not only acceptable, its a benefit! One of the functions of the oil is to cool the bearing, as well as lubricating it, this is a function of flow, which is increased with a greater clearance. I would suggest that the "falls under its own weight" test is the very tightest a splash fed A7 big end should ever be, a little looser will not hurt. Remember, the oil is arriving at the big end through centrifugal force, the oil needs to escape to allow new cooler oil in. Tight big ends will over heat and run, due to excess friction, and lack of cooling. signs of squidgeing white metal show that it was very close to doing so!

Pressure fed engines are different, very little of the above applies to these.

[Colin Wilks]

Well that's certainly my logic Stuart, absolutely no stiffness when assembled dry and making sure the oilways in the crank are as clean and clear as possible. I've aimed for .015" clearance between the big end and the web of the crank. Although my rods were tight on the pins, there were also tight spots between big end and web.
Thank you to Robert Leigh for his very useful tip about nipping the rods up without blue. The burnishing of the tight spots in the white metal is very obvious and gives a more accurate picture than the inevitable smear of blue, no matter how thin and even I managed to get this.