Re: alfa-digest V7 #1213 - Alfa Main Bearings

[bearbvd@domain.elided (Greg Hermann)]

>
>    So what else can you do?  Heat treat?  Cryogenic treatment?  How many
>dollars you gots?  Check out Jack Beck's available services at
>http://www.orionmotorsports.com/  Or check around a large airport for a shop
>that does air plane engines.
>    What part of the world do you call home?  I might be able to refer you to
>some experts closer to home.
>Ciao,
>Russ Neely
>Oklahoma City

Nice post, Russ!! You got all of the details except one--

With an aluminium block, like the Alfa, I like to set the main bearing
clearances up to be where I want them _AT_OPERATING_TEMPERATURE!!
Remember--the aluminium bearing saddles in the block expand faster than the
steel crank does as the engine warms up.

If grinding an Alfa crank .010" undersize, this can be dealt with by
getting your bearings before you let anybody TOUCH the crank. You will
likely end up grinding the mains more like .0085" or .009" undersize once
everything is measured up, should you choose to follow the advice below!

What I learned (both through experience and through calculations) is that
setting  the main bearing clearances at 0.001" to 0.0012" _AT
_ROOM_TEMPERATURE_ will give an operating clearance in a warm engine in the
0.0023" to 0.0025" _AT _ OPERATING_TEMPERATURE_. Which is where it SHOULD
be at operating temperature for the diameter of the journals involved.

NEVER had ANY bearing trouble with an Alfa engine set up this way, and
also--NEVER_ saw less than about 35 to 45 psi of oil pressure at an idle of
700--800 rpm with the engine STINKING HOT!

The only cautions which are applicable to using this approach are--

1. GET and USE a block heater if you live in a climate with sub-freezing
weather and plan to use the car in cold weather. The contraction of the
aluminium will actually seize the mains at about 0 F. if they are set up
this tight!

2. Warm up the engine very gently--the price of having the main bearing
clearances where they ought to be (and having excellent oil pressure) when
the engine is warm is having the mains on the tight side when the engine is
cold!

Regards, Greg

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