Bill:
When drilling the oil feed to the starved rod journals, do you cross
drill the mains from side to side first? Have you run into grooved main
journals on the B?
I had a crank done a number of years ago. If I remember the mains
were drilled from side to side, the journals were grooved, then the oil
feeds cut to the #2 and #3 rod journals from the #2 and #4 mains. The crank
was also nitrided.
This was all done by the British car guys who were sponsoring me.
The crank was destroyed later when a cam went flat.
I'm very interested, as I want to put a spare race motor together
using some of the components from the old engine. It's crank time, and I'm
trying to figure out the most economical way to go.
Kelvin.
> -----Original Message-----
> From: WSpohn4@aol.com [mailto:WSpohn4@aol.com]
> Sent: Thursday, August 03, 2000 11:58 AM
> To: matttrebelhorn@netscape.net; mgs@autox.team.net
> Subject: Re: Race Prep
>
>
> In a message dated 03/08/00 9:58:03 AM Pacific Daylight Time,
> matttrebelhorn@netscape.net writes:
>
> > I'm a bit slow following up on this, but I've got some questions.
> >
> > First, what is "cross-drilling" the crank? How does that
> help? I assume
> > that
> > this is a "find a good race prep shop" type thing, and not
> an off-the-shelf
> > item, yes? What are the methods and reasons for
> strenghtening a crank?
>
>
> Well, I just did an article for an upcoming MGB mag on this,
> but I'll give
> you the thumbnail version. Over about 6500 rpm, the stock
> crank will not flow
> sufficient oil to some of the rods to keep the wolf at bay,
> so you drill
> additional oil passages from the intermediate mains to the
> adjacent rod
> journals to increase oil availability.
>
> Strengthening? You can make sure that your grinder uses a
> properly radiused
> stone (no sharp corners and resulting stress risers) and shot
> peen the
> surfaces (not the journals) for the same reason. You can also
> nitride or
> tuftride the journal surface. This doesn't really make it
> stronger, just
> toughens the surface layer so that when you do ruin a
> bearing, you are less
> likely to wear the crank and have to cut yet another slice
> off it. BTW, .020"
> under is no real problem. It isn't so much a strength issue
> with small
> undersizes, as it is a cooling question. The thicker the
> bearing shell, the
> poorer the heat transfer. This won't bother you much on the
> street, but can
> make a big difference on the track.
>
>
> >
> > So, I'd say that my motor has spent maybe 15 seconds of
> its life at 6500+
> > RPM,
> > with maybe 5 of those at over 7000. Is the crank just
> going to snap one of
> > these days, from the repeated abuse?
>
>
> I'd say not - you may have taken a few thousand miles off the
> life of the
> bearings, but a fairly momentary blip to higher rpm shouldn't
> cause the crank
> to crack, though it may have moved it a couple of steps
> closer to the day
> when it will.
> I doubt in fact that you actually got anywhere near 7000 rpm,
> as your valve
> bounce rpm would be around the 6400-6500 range with uprated
> springs, 6200 or
> so without. What did happen, was that the tach needle swept
> way high, but the
> engine itself would likely be sitting at the valve bounce rpm, not
> progressing much if any past that point.
>
>
> Hope that helps.
>
> Bill
>
|