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Con rod clearance #773724 05/14/19 8:13 pm
Joined: Oct 2012
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seismech Offline OP
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A friend of mine has a new pressed up polished and numbered crank supplied by a well known Gold Star specialist. It looks really good. Does anyone know the correct con rod side to side clearance? This crankshaft has fifteen thou, side to side at the crankpin. Too much? or is that ok for a pressed up crank?

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Re: Con rod clearance [Re: seismech] #773789 05/15/19 1:20 pm
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Mal Marsden Offline
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Seismech
Assuming the good crank assembly came from Phil Pearson, why not just give him a phone call and check what he recommends. He is more than helpful whenever I have called him.

I have just had a look at my crank, number 814, but it is in a set of cases so best I can do is slide a feeler gauge down side of rod and 0.015” is a nice fit. It’s never been run yet so still brand new.

Mal


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Re: Con rod clearance [Re: seismech] #773889 05/16/19 6:26 am
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seismech Offline OP
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Mal,

Thanks for taking the time and checking your crank, we really appreciate your help

Last edited by seismech; 05/31/19 3:01 pm.
Re: Con rod clearance [Re: seismech] #774999 05/28/19 10:25 pm
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Dave - NV Offline
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Semismech … I have fitted 4 Pearson cranks in my Goldies and must admit I have not checked their rod side clearance nor their balance. 'Fit and forget'. hmm.
But here's a side clearance experience 'story' for you regards a OEM GS crank... You didn't ask, but... and I believe this is a repeated story... On a road ride on the CA twisties with my NoCA rider friends I was being gentle with my recently built up GS, never exceeding 4k revs and the crank pin broke at 70 per on a open road. aargh. After trucking home and opening the engine I discovered the cause. Luckily there was no case damage after some serious clattering! The timing side wheel was seriously gouged up and unusable and the pin had broken at the weakened area at the oil feed hole.

So I ordered up my first Pearson crank. But having a 'need to ride' I pulled another used GS crank I had on the shelf to fit a new crank pin I had on hand. These fly wheels had fret marks in the tapered bores as we've all seen in used OEM wheels, evidence of the tapered pin shifting in the bore. hmm. Pearson describes the issue as the wheels "breathing". So I decided to lap in the new crank pin to clear the fret marks in the used wheels for a better fit. My machinist friend tried to spin the pin to help the lapping process, but this didn't work out. So I laboriously did it by hand for hours using valve lapping compound. Using 'engineering bluing', the bores in both wheels had finally a good tapered fit. However upon reassembly I had nil side clearance of the rod. I then took the rod to a local auto machine shop and using a magnetic fixture in their grinding machine ground the big end faces of the rod to give me 15 thou side clearance. And rode happily until the New Pearson Crank arrived! yeah … Life is Good, let the Goldie Fly!

BTW, needing to reduce my stuff this 'fitted' crank assembly is for sale at a modest price. Offers?

On and on we go, sheeze,


Dave - NV
Re: Con rod clearance [Re: seismech] #775153 05/30/19 3:04 pm
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998John Offline
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The Bruce Main Smith book recommends .014" rod side clearance. I had to skim the thrust washers to get this clearance.


Moderated by  Rich B 

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