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Big end to crankshaft clearance

Submitted by dean_miller on Fri, 29/08/2014
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Commando

Hi all

Can anyone tell me what is the ideal clearance for the conrod bearings should be. The manual says rod end clearance less than 0.001".

The guy that I have found locally ( here in Abu Dhabi ) that will grind the crank for me wants the new shell -0.010" and will grind the crank to suit. He said he thought it should be 0.003". They manly do Small Diesel engines From what I have found online for common plain bearings I think it should be about 0.0005" taking into account journal size rpm oil pressure etc.which lines up with rod end clearance statement in the manual.

help please.

cheers Dean

Submitted by phil_hannam on Fri, 29/08/2014

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Unless this guy knows about regrinding Norton crankshafts you are going to waste your money. The shoulders of each reground pin must have the correct radius/radii or the crank will soon fail. See attachment.

I believe that the running clearance on the big end is 0.0005" or half thou.

Attachments crankshaft-regrind-data-bmp

Submitted by Xanna_jeannett… on Fri, 29/08/2014

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Previously phil_hannam wrote:

Unless this guy knows about regrinding Norton crankshafts you are going to waste your money. The shoulders of each reground pin must have the correct radius/radii or the crank will soon fail. See attachment.

I believe that the running clearance on the big end is 0.0005" or half thou.

Hello As a engineer I will back Phil-Hannam up on this subject

! yours Anna J Dixon

Submitted by dean_miller on Fri, 29/08/2014

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I have given the machinist this same figure from the overhaul manual and he assures me that he can grind the crank to the correct dimension especially the all important 0.09" radius. He is also quite happy for me to be there while he does the grind so I am happy to "give it a go"

the cost of sending the crank to the uk to have it done would be huge so I just will have to work with what I have.

I am also a licenced aircraft engineer so have a fair bit of knowledge when it comes to machining so feel confident to know what's what although this is my first time with plain brgs.

thanks for the input,

D

 


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