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connecting rods

Posted by Barry Carson at August 02. 2017

Hello has anyone fitted any of these con rods. it says they have to be balanced would that be the case or could i just fit some without the balancing.

https://www.rgmnorton.co.uk/buy/matched-pair-of-high-performance-conrods-small-journal_4196.htm?sid=1310720

 

Barry

Re: connecting rods

Posted by david_evans at August 02. 2017

I know someone who fitted a pair of Thunder rods to a Mk3 Commando. The clearance between the rod nuts and the crankcase was an issue as alluded to in the RGM advert. He had to chamfer the nuts and open up a channel in the cases. The rods may appear to clear the cases and in some cases they do, but when the pistons are fitted and the barrels, the rods are constrained to move in one path (locus if I remember my tech drawing lessons) and that might be the first time you encounter the problem. Judging by the finish I would be surprised if they needed balancing between the two, but to get your desired overall balance factor who knows.

Re: connecting rods

Posted by Barry Carson at August 02. 2017

thanks for that David. i noticed it said you may have to chamfer some off to make fit .it would take a lot of messing around to get that right i wouldn't consider it a direct replacement having to do that .i just wanted some new rods i notice they do the original looking 650cc type but i want some for 600cc i cant see any.

 

Barry

Re: connecting rods

Posted by robert_tuck at August 03. 2017

88 and 99 rods are the same part .  I don't think any new ones have been on sale since the mid 1960's . A few  very late  99 and all 650 cases have more clearance for rods , Some owners just swap in a 650 /Atlas motor  or Commando lump. New 88/99/650 Barrels may be availiable soon,  I know a guy who makes rods, a decent order for 88/99 rods might do the job ,though not sure if he can get ally forgings,might have to be steel. Another solution would be to cut and weld more room into the 99/88 cases , as in the 750  88 racer !.

Re: connecting rods

Posted by Gordon Johnston at August 03. 2017

Are Carillo rods still available for 88/99s? Being steel, there may be weight considerations. Les Emery was very doubtful about fitting them, reckoned it could lead to crankcase fracturing at racing speeds. In my view, steel rods would be an improvement on old alloy rods which can cut a crankcase in half when they let go. I have the evidence out in the shed.

Re: connecting rods

Posted by Barry Carson at August 03. 2017

thanks for the info Robert and Gordon. i am putting the engine together from a box of bits looking at the con rods after cleaning them up they have one or two dings in them i couldn't trust them the way they look. so just thought i would replace with new ones. i am not a speed merchant just like to think if i were to go with throttle up that everything would hang on as it should .

 

Barry

Re: connecting rods

Posted by steve_coleman at August 03. 2017

Previously Barry Carson wrote:

Hello has anyone fitted any of these con rods. it says they have to be balanced would that be the case or could i just fit some without the balancing.

https://www.rgmnorton.co.uk/buy/matched-pair-of-high-performance-conrods-small-journal_4196.htm?sid=1310720

Hi Barry, yes I fitted these rods to my 99. I got them direct from Thunder engineering around two years ago. They are fitted with BHB pistons and I checked the static balance at the time which was around 70 per cent. I part assembled one half of the crankcase with crankshaft ,pistons and barrel to look at clearances, it was ok but i gave it a little more clearance at the skirt cutouts to be sure.

I have now run the bike for 650 miles and it is running very well, I have ran it up to 60 a couple of times and there is no excessive vibration. I hope this helps, Steve.

 

Barry

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