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Re: Race Prep

To: matttrebelhorn@netscape.net, mgs@autox.team.net
Subject: Re: Race Prep
From: WSpohn4@aol.com
Date: Thu, 3 Aug 2000 14:58:09 EDT
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

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