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Big End Wear

Submitted by martin_seymour on Thu, 07/09/2023
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Commando

Is it usual for the T/S big end to wear out before the D/S?

I ask because I've just taken the conrods from the crank and the D/S is on a standard shell and looks pretty good but the T/S is down to the copper and is on a +.020" shell !!

Submitted by jan_nelder on Thu, 07/09/2023

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It is  more likely for drive side to wear more, from rider reports I have seen. So yours must have been reground because one side needed it and other not, reason unknown.

Submitted by jonathan_newton on Thu, 07/09/2023

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… an original build rework due to defective finish?  With the reduced surface area due to diameter  decrease, wear would show up slightly earlier? Just a thought….

J

Submitted by martin_seymour on Thu, 07/09/2023

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Well it appears to of had two regrinds - that wouldn't of been just because of the finish. My concern is that if I had it reground will it just for the 3rd time happen again?

Submitted by barry_carson1 on Fri, 08/09/2023

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hello,

maybe conrod fault. possibly oval big end. mixed up end caps.

see if you could check the crank internally for dirt .

measure what you have so theres no mystery surrounding the outcome.

 

i am not an expert, just trying to help

 

barry

Submitted by peter_shand on Fri, 08/09/2023

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It being a 3 piece crank it could be a mix of two, possibly three different cranks. I.e. assembled with whatever the previous owner could get his hands on.  

 

Submitted by robert_tuck on Fri, 08/09/2023

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Sounds like someone at some time  fitted the cap the wrong way round and damaged a journal..  Check crank is clean inside Could be an oval rod eye, Rod should be really free to turn with new shells.

Submitted by martin_seymour on Sun, 10/09/2023

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I tried to measure any ovality in the conrod but my internal mic was too big.  But wahat I did find amongst the marks in the Alloy part of the big end eye was an imprint that coincided with one on the back of the shell. Looks like builder didn't clean the parts before assembling the conrods!!

I'll see if the Machinist who'll grind the crank can measure the rod end for ovality.

The engine is out of a Grass Track outfit - rigidly mounted, the fly wheel doesn't appear to look as if it's been rebalanced but the conrod's steel caps do look like they've had some meat taken off

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Submitted by robert_tuck on Sun, 10/09/2023

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If they ground the mating marks off in an attempt to balance rods then its easy to assemble incorrectly. Those srfaces for the nuts to bear against look horrid,ask your engineer to clean up .

 


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