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Conrod dimensions

Submitted by colin_eggleton on Thu, 22/12/2011
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Heavy Twins

Anyone have the big end dimensions of the con rod for a 1956 Model 88, without shells? Having trouble getting some .010 shells to fit as they seem too big round the circumference and the rod is locking up.

Thanks, Colin.

Submitted by Xanna_jeannett… on Mon, 26/12/2011

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Previously wrote:

Anyone have the big end dimensions of the con rod for a 1956 Model 88, without shells? Having trouble getting some .010 shells to fit as they seem too big round the circumference and the rod is locking up.

Thanks, Colin.

Hello Colin since no one as answer your question, I will take it up with you, have you tryed Rodger At RMG Motors ,Have A word with him , he may say to you send your con-rods to us and we will sort them out, Hope this may help ! yours anna j

Submitted by eugene_brolund on Tue, 27/12/2011

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Hi Colin,

My '50 model 7 (500cc) con rod big ends measure 1.605 - 1.608 with the shells removed. Be sure and check your journal diameter on the crankshaft. I assume you have the right crank (journal diameters are not the same on all Norton twins). It may bepossiblethat someone sold you .010 shells for a 650cc or 750cc twin?

250 / 350 / 500 / 600 cc twinswith standard journals measure 1.500 -1.5005 , .010under sizewould measure 1.490 - 1.49005 etc.

650 / 750 /850 / 920 cc twinswith std. journals measure 1.750 - 1.7505, .010under sizewould measure 1.740 -1.7405 etc.

If you still have the box your shells came in with a part number on the box:

The correct part number for .010 shells for a 500cc twin would be:02-0251 (or 020251)

the part number for the 650-920cc twins .010 would be :06-4286 (or 064286) these would be wrong for your engine.

Hope something here helps!

Skip

Submitted by colin_eggleton on Tue, 27/12/2011

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Many thanks for your reply,the con rods measure 1.600-1.601"and are concentric so are good.The std shells that came out were ok.Mick hemmings did the regrind and are measure up to within 0.001" so are good.Its wierd.Mick has been excellent and has sent me another set of shells but still nip up when i tighten the caps,not even reaching torque tight.He told me to get a set from RGM so i am waiting for them.The shels he supplies come from david holder and hes not had any trouble before.The part nois 17828,but what that refers to i dont know.I may have to revert to the old scrape and blue method but what a pain.Anyway thanks again for the replies and thanks to mick and ange for there help so far.

Submitted by phil_hannam on Tue, 03/01/2012

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Colin

Have you checked out the journal of your crankshaft?

Isay this because, many years ago, I made the mistake of having my crankshaft reground by a local engineering firm with no real previous experience of Norton engines. The result was a crankshaft that was reground nicely, as requested,to minus 30" but the journal corners all had a radius that was much too shallow. (Usually they are ground much too tight and can weaken the crankshaft)

Anyway, on rebuilding the crankshaft, the edges of the big end shells tightened up on the journals as soon as the caps were torqued up.

It took me a little while to twig what the problem really was, because on measuring the journal diameter and the internal diameter of the rods with shells in, there was always a running clearance.

The solution was quite easy but not the cause ofthe problem.

Submitted by colin_eggleton on Sun, 08/01/2012

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Previously wrote:

Hi,i have checked the conrod dimensions and it would appear that they are slightly undersize.Mick hemmings had the crank ground by his usual firm so i would hope that they would have got it right.I have measured the crank and all seems ok but not the radius on the journals.Mick has given me the correct conrod size less shells which is 1.645" to 1.605"as given by glacier who originaly supplied the shells.My conrods are 1.600 so i am going to polish /ream them to this dimension.Let the battle commence! How did you overcome the problem? Many thanks,colin.

 


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