Thunder conrods

Hi Tony,

In a mere 20 years of NOC membership, I have learned that of all the heavy twins, the 99 is the most likely to break a rod if taken to high revs. The original 99's did back in the 60's, and 50 years on, they won't be any stronger.

To me, for peace of mind alone I would go with the new Thunder rods rather than trying to refurb the unknown history originals. Might cost more now, but potentially a lot cheaper in the long run.

Regards,

George

The things I would be interested in would be  the size of the small ends ,and the weight . I have been considering buying rods myself, or converting the 99 to a 650 which would need a crank,rods and a little case welding.

Why not Andover Norton?

Fritz

No Norton rods for the 7,77,88,99  have been produced since the factory moved from Birmingham to Woolwich some time in the early 1960's , Dealers stock only, and that ran out pretty Quick.My contact who was based at Woolwich told me that no barrels and few rods came into his stores from Birmingham.Much of what Woolwich produced for Nortons at that time was poor and finished up in the scrap bins.Took a while to sort things out.

You can send Thunder-Race your con-rods and they will copy them, and they will be so much better and stronger than the originals, or OEM  items. I had a pair made as well as a crankshaft for a unit engine, and what came back was an amazing product. Dealers still had new 99 con-rods in the 1970's as I bought a new pair from Taylor Mattersons of Balham when they closed down, with a pair of new big ends shells. I still have them, and I have kept them just in case. The other option, is a pair of the American made Carrillo's rods in steel, but that would be an expensive option. I bought a pair of those for my 750cc engines in the 1990's and they are an amazing piece of engineering.  

I've had Thunder Engineering rods in my 99 for a few years now. I did check for clearance but no modification was required. I did get the crank balanced though.

I'm not sure how con-rods machined from billet alloy can be stronger than forged alloy versions.

On the exact material used and its subsequent stress relief and heat treatment. 

I agree that with exactly the same alloy, same dimensions and heat treatment the forging should be stronger when new, but aluminium (and most of its alloys) has a finite fatigue life, meaning that  it will fail eventually.

Thunder have been doing rods for a long time now so personally I think that they have sorted out what materials to use and what not to by now. 

George 

Hi George, as a retired civil/Structural Engineer I am familiar with metal fatigue, but that is proportional to use rather than age.  An old Classic that only saw relatively few miles won't have suffered from fatigue to a significant degree.  My 1959 '99' has only done about 34,000 miles so I'm happy to polish the rods and look at them closely for fatigue. (Using a Jeweller's 10x Loupe!)

Big end caps going oval are a definite sign of heavy use and anyone should walk away from those rods.  That shows that the rods have gone beyond their limit, whether through age or abuse.  Insufficient oil changes is the single most common cause of failure in any engine.  If you see a modern car (less than 10 years old) with a smoky exhaust, it will be due to inadequate oil changes, (or use of the wrong oil) unless they put diesel in a petrol engine!

If you intend to take your 60+ years-old bike to its limit, you MUST get the rods X-rayed or buy new ones if available - 'loadsamoney' though so perhaps beyond budget?

Hi, Saw on Ebay in the States a company making forged pattern rods a couple of years ago. They looked well proportioned. I believe I linked from Access Norton website to look them up. If old rods are dimensionally correct, have them shot peened to increase the fatigue life. I used to do that on Queens Flight helicopter driveshafts to re-life once. Replace the Bolts and deburr them properly. Take any "nicks" out carefully, blend smoothly, do it before peening. I used to "life" aircraft parts, amazing what one can do using careful dressing. Very brown stained rods are worth a very close eye if one wants to re-use them. best regards, Paul

What has happened to them to make them look 'worn'?

Steve