crank set screws

[cbrown@xxxxxxxxxxxxxxxxxxxxxxxx]

Having just fitted set screws to a crank in the last two weeks, here's how I did
it

73,  Alfetta 1.8, relevant history
Had had 2 aluminium plugs fall out with the typical ca 10psi drop per plug,
about two years ago. Replaced in the car with std Al plugs, straightforward,
although getting the sump off, in the car is a bit contortionist, without
removing anything else, even with a pit (thanks LLyod). 

Motor now has 300,000 miles

The crank
An engineer in the club actually is involved in nitriding cranks etc. Although
their applications are industrial, he suggests depth on something like an Alfa
would probably be ca 0.003". Nitriding is a gas process, so does get up inside
the galleries.

The crank galleries are best drilled by hand held electric drill, trying to line
up in a drill press is hopeless. Going up in 0.2 to 0.3mm increments, allows the
drill to self pilot, and minimises risk of snatching. Secure the crank on the
bench with a couple of lumps of wood, so that the plane of the crank is
vertical, and secure,  this aids alignment, trust me. When drilling insert a
rod, a 5mm pin punch is ideal (it won't fall out), through the journal cross
drilling, this prevents swarf from being pushed down the gallery, across the
journal and into the gallery segment between the main bearing and the journal 
cross drilling, from where things may be impossible to get out. The pin punch
will move sideways slightly as the drill point contacts it, indicating enough
depth. This also effects drilling a stepped gallery. I think the gallery was 5
or 5.5mm, wrote it down but not to hand. Drill out to 6.9mm, for tapping an
8x1.25mm thread. A set of 0.1mm drills are required (thanks Carlo). Drill using
a real cutting oil, eg CRC Cutting Oil.

Socket head set screws in this size 8x1.25mm, are readily available and cheap.
Why make brass? The length can be 8, 10 or 12mm, it doesn't matter. For those
concerned about imbalance, look at the screw, they are mostly hollow, what has
been removed is about what is being replaced. I've weighed them , the number
temporarily escapes me. Forget exotic sizes such as 7mm, as suggested by one
widely read source, they don't exist in most places. 

Tap slowly, and use a real grade of tapping lubricant, eg. Trefoflex. With pin
punch in place, taper then intermediate. If you don't know how to tap a hole,
this is not the time to learn. The correct tapping drill size is 6.8mm, drilling
to 6.9  allows a looser tapping. Liberal backing off and the extra-correct
(6.9mm) size ID makes it a clean tap, minimal friction, straightforward as any
other hole. Unless a tap breaks. If it does, spark erosion is the only option I
know, that works. Costly, probably easier to junk the crank.

( Maybe building up with tig, if you can get at the tap, tigging on a bolt,
screwing the combination out, may work. I mention this as it is the easiest way
to get roll pins out of the cam journal feed galleries, in the block deck,
although a slide hammer approach is taken with the tigged on bolt) 

Loctite in place. The thread absolutely must be primed, totally oil free if the
loctite is to bond correctly, acetone (thinners) is the frequent substitute for
the Loctite product.    Most appropriate grade is hydraulic sealant  , probably
more resistive to erosion due oil under pressure weeping past the thread, don't
recall the source or inspiration for the logic (auto-cortical probably), dont
have the number to hand.  262 super stud lock (red) works as well. Loctite data
sheets are quite good. Staking high tensile steel, or the gallery wall, down the
well, seems optimistic. By drilling and tapping as described, pin punch in
place,  the set screw will bottom out securely (as the gallery has effectively
been step bored) meaning it can be tightened, without risk of projection into
the journal cross drilling.

300,000 miles, lost plugs, a hard life, frequent new oil was not part of its
diet,  the std. journals only required a linish. Nitriding is effective.

one last side bit, someone recently mentioned how to get the flywheel bushing
out (socket, pack with grease, hydraulic it out by wacking with a hammer). Well
this is also used to get the two dowels out of the block deck, fill with grease
or plasticene, pin punch, ...



chris brown

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