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Date:         Mon, 19 Feb 2001 16:27:56 -0500
Reply-To:     Robert Donalds <bostneng@FCL-US.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Robert Donalds <bostneng@FCL-US.NET>
Subject:      flexing cranks and Yielding Bolts one last time
Comments: To: pensioner <al_knoll@pacbell.net>, Wolfvan88@aol.com
Content-Type: text/plain; charset=us-ascii

fellow listees and learkers I found a great article about the stretch to yield hardware in this months automotive rebuilder magazine it is also on line at http://www.automotiverebuilder.com under feature articles. I hope this will clear up the confusion about the hardware on the 2.1 rods the bug crankshafts as everybody knows flexes. when I was building formula vee engines that would spin up to 6k on the track flexing could be a problem. After all the 40 hp crank was much better at flexing than was the 1500 or 1600 cross drilled cranks To get around this problem I always had the center main ground .0015 ths. below the low limit and that gave the crank the needed room to flex, live and see yet another race The first symptom of a flexing crank is that the case takes a pounding at the center main web. The common belief is that the crank flexes when it is at top dead center There is a second symptom of the bug crank flexing that I have never heard discussed and that is the crank center main bearing journal ware. I have inspected and measured lots of cranks in my time and the one place the bug crank shows it ware first is at the center main oiling holes. It is not uncommon to see 0015ths. out of round at this spot This is not from lack of lubrication but a result of the crank flex then the pistons are half way in there travel. I have never seen any signs of this in any 1.9 or 2.1 crankshaft that I have measured ever. It is not uncommon to put a 2.1 case back into service after 150k because the case measures fine you could not say that with any bug case with even 1/2 that number of miles sure its been done but the person that did it never measured the case and sure it didnt bind until it got hot but how would whey know the cranks binding the only symptom of this is it ran really hot and didnt make allot of power Bob Donalds http://www.bostonengine.com as always all rights reserved

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