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Fast run-in is likely to produce accelerated wear on bearings and that will make looser bearings. So less friction and a freer engine but at the cost of a shorter life. But most "ride it like you stole" it riders aren't interested in how the bike will run in 100,000 miles or how it affects the next owner.
I've sold sports bikes with 100,000 miles on them all done by me and they still ran quite and smoke free. But each to their own.

As you know I'm no expert but my understanding is that white metal bearings (as opposed to roller or ball bearings) need careful bedding in. They aren't smooth and flat when new and nor is the running surface of the shaft. Excessive load and speed causes the high spots to heat up and expand and thereby increase friction and wear.
If you are unlucky (and I've seen this countless times) they will actually seize and melt. If your lucky they will just wear much faster and then be almost frictionless. But you've just chucked a good chunk of their running life away. White metal bearing run-in procedures often have a staggered run-in with very gentle at first and then building up to minimise the friction wear until the shaft and bearing surface are glass smooth. But this won't produce the least friction and free running bearing that racers want and need.

Re bores and rings. the risk with hard run in is that until the rings have bedded in (ie become glass smooth as will the bores) there is a greater risk of exhaust gasses passing the rings and this heats the rings and burns off the lubricating oil. The rings wear quicker and will bed in faster and will result in a looser fit again potentially giving more power and less friction but ring wear will have been accelerated by the process and extreme heat may have altered the temper of the sprung springs and reduced their pressure against the bores. Again great for racing but not so great for long life.
good points? are we running it in hard, only to spin bearings at 25,000 miles? or is this off base?
 

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i suspect i am getting on towards 800bhp on mine, i intend to pull the motor out well b4 25k, then if needs be just reshell it and away we go again, i think its optomistic to expect highly tuned engines to do 30k plus.but thats my own view:smokin:
 

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None of what that guy's saying makes any sense to me, he even states he's 'no expert' !

All the journal bearings are hydrostatic i.e. they do not run metal to metal & the actual bearing is a thin pressurised oil film, the only time there could be contact between the shaft & bearing is at start up or due to oil starvation. I think it's pretty much impossible to 'run in' an oil film!

How would bedding in faster result in a looser fit? If exhaust gasses can leak past the rings before they are bedded in & burn off the oil then surely you would want to bed in faster not slower?
 
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