Aircraft engines also need to be broken in pretty similarly to the article
referenced, and for the same reason. As far as boring accuracy, If the
bores aren't true, break-in technique probably won't help much in any event,
and babying will only make it worse.
The pressure in the cylinders gets behind the compression rings and expands
them into the cylinder, wearing them in to a good fit. If that doesn't
happen, oil will burn into the voids and prevent proper seating from ever
occurring. Many rings are actually beveled on the top inside corner (or
tapered a bit inside) to ensure that gas pressurecan get into the area
between the ring and the piston groove for just that purpose.
My Stearman was babied by the guy who restored it, and he failed to bed the
rings in a fresh set of Cermichrome cylinders after 50 hours. The engine
guy then sent him a fresh set of plain steel cylinders, but he glazed those
up too, again by babying it. He figured it had to be something else, and
had the mags rebuilt ($1500), but it still fouled.
I bought it (not knowing about the problem) with 50 hours on the replacement
cylinders and had constant fouling on the bottom 2 cylinders from the first
hour, and above-normal oil consumption. After a year, I pulled those two
cylinders, honed them, installed new rings, and broke it in like the book
says (flew it at the top of the cruise RPM range, long flights with little
idling) and voila - no fouling, not even once, in 35 hours.
As far as saving the bottom end during break-in, once there's oil pressure,
there should NOT be any metal-to-metal contact in plain bearings. That's
what the oil is for. Hydrodynamic pressure keeps an oil film between the
surfaces, as long as the pump keeps a supply to them. Especially with
today's oils. Plain bearings wear out on start-up, or under horrendous
loads without enough oil film, not in normal running.
A friend once talked about taking a power plant generator apart after many
years of non-stop running, and the (plain) bearings still had the scraper
marks from their original fitting, because they'd never touched
metal-to-metal since initial start-up.
Karl Vacek
> And you change the main and big end bearings every racing season. I'm
> suspicious of the article because I can't imagine the bottom end of a
> motorcycle
> has much in common with the bottom end of car, or have motorcycle engines
> changed in recent years.
>
> Pistons and rings have a lot more in common across motorcycles and cars
> except motorcycles to more high rpm.
>
> As far as the MORE power goes - how long do you get MORE power for - until
> you sell it 12,000 miles later or not as long as that.
>
> Regards
>
> Daniel1312
>
> In a message dated 02/01/2008 03:15:02 GMT Standard Time,
> soavero@yahoo.com
> writes:
>
> Agreed. You can get away with it (like in a race
> engine) if a torque plate is used when boring.
>
> Ron
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