Big End bolts - servicability check?

How can I check used big end bolts (ones taken out with the rods) for serviceability?

Magna flux and x-ray and sonic testing might pick up microscopic corrosion faults developing between metal element grains but its way more cost effective and security to just replace with Anover's real quality cap bolts to avoid chance of counterfeit bolt let goes. Otherwise only run to failure will tell ya what ya didn't want to know. If the engine has a history of seizure failure definitely get new ones.

Hi Hobit
Thanks for the reply. I know its "best working practice" to replace everything but 18 pounds each plus tax and shipping is an amasing price. I am sure they are the worlds best, superbly engineered, manufactured to the highest tolerances etc but it seems I can junk almost the entire bike just to be on the “safe side”. All getting a bit ridiculous.

Nigeldtr said:

Hi Hobit
Thanks for the reply. I know its "best working practice" to replace everything but 18 pounds each plus tax and shipping is an amasing price. I am sure they are the worlds best, superbly engineered, manufactured to the highest tolerances etc but it seems I can junk almost the entire bike just to be on the “safe side”. All getting a bit ridiculous.

Click to expand...

That sounds like a potential 'my kingdom for a horseshoe' statement! If you're that far into the bike, then new big end bolts cannot be such a concern... given the consequence of their potential failure!
Or, if you buy Carrillo rods, I think their bolts can be re-used ad-infinitum!

If this is the first time the engine has been opened up and it has not been raced then I would reuse the rod bolts.

If it has been opened up before and you don't know who torqued the bolts or how much torque they used or if the engine has been raced or there's more than a gazillion miles on it I would think about replacing the bolts.

If it was opened up and some ham fisted hillrod of a mechanic had his or her way with the rod bolts and over torqued them, then I would definitely replace the bolts.

Norton rods and bolts are plenty adequate for most service when properly installed.

My two pence worth.

I have seen low grade shat being supplied in the aftermarket, for that reason, I have chosen (in a few instances) to re-use the bolts, I knew the engine's (gently used) history. With critical components, I always assume poor quality, and try to prove to myself otherwise. Sad, but that's where we are.

As a point of interest, the con rod bolts are probably the highest specification parts on a Commando motor. Shape, material, tolerances, finish, everything. Its probably safe to assume that all that care in production is there for a reason.
cheers
wakeup

FWIW, I reused stock rod bolts for years on my race Commandos with no problems. I had them magnetically inspected (Magnaflux machine) every time the engine was apart. This was back in the '70s and '80s, and I knew they were all original bolts or genuine replacements from Norton. I ran those engines in well over 200 races. I'm still running a set of them in stock rods in the 920 engine I'm running at Bonneville, although I've mostly switched to Carrillo steel rods for serious builds.

Dances with Shrapnel's advice sounds pretty good to me.

Ken

Norton rods and Norton rod cap fasteners are toughest items on Commando, then maybe the Z plates. With the reassuring feedback that' if no prior blow up forces - likely even ham fisted assembler like me couldn't really hurt them and if they were run like that, then proven good to go again. Measure their length to the n'th degree then put in caps and torque to 20' ft lb and see if they stretch about .005", if so they are the good guys and only needs 5-7 more ft lb to get the ideal elastic stretch length ~.0063" which is within the manual listed T-value range, obtainable w/o lab grade instruments. If was me I'd have em cryo tempered which mailing or driving to would cost more than the process, so might toss in some other hi load stuff like cam and lifters and rings and shoot even the pistons and valves and springs, if not the bearings too...

Personaly I am fitting new genuine bolts just for piece of mind an also I have new genuine fasteners for crank head an barrels but the last man to build my engine used a hammer an chisel to tighten cam nut an rounded few head bolts plus wrecking the 4 long socket head type bolts that hold barrels. So it was nobrainer just throw them all away fit new but at same time its having big valve head PW3 cam an lots of other stuff so its just drop in the ocean.
If you are planning on getting your tested how much would that cost you an do you know where to get it done??
But as you are asking the question I (rightly or wrongly) assume that for whatever reason you don't wish to spend money on bolt be it replacing or testing them (which they could possibly fail) so then apart from their outward appearance an condition the quest you should be asking yours is how often am I going to ride the bike an how much strain is my personal riding style going to put on these bolts?? An then knowing that answer will you feel happy as the engine revs raise??

If you re use, which I would if engine not injured prior, don't sweat being careful because I've proven if there is a fault in the bolts then just about coasting throttle on the level barely 50 mph is enough to fail them. Racing just might happen sooner and closer to retrieve. Always get new nuts for sure and check the cap/rod seats are flat and clear of burs.
Next time its ash trays get full just buy a new everything.

Hi Guys,
Thanks for all the reply’s. I have one engine treated really badly (monkeys with hammers and chisels) and almost everything has to be replaced (a real bag of Sh**). The other, is almost perfect, original grind, bores on plus 20 with nearly new pistons, superblends fitted, just needs a clean and back together. The problem for me is simply where does it stop? If I replace the bolts then perhaps I should replace the rods they are 40 years old you know. If I replace the rods why not go for lighter pistons, have the crank rebalanced and treated etc. However, from what I have read and seen, the crank could break on me so perhaps a new crank is also a good idea. I don’t give these bikes a hard time, we are both too old but I might just miss the odd gear when quick off the lights!

That's the problem I had an that lead to big valve head as I needed new valves an guides anyway then why stop there. The bores needed first over size so new pistons an the crank needed first grind so as there were signs of some bodged work in the past it was throw everything away (will almost everything away) an start from new.
According to Mick Hemmings (who is doing head an machining an balancing for me to assemble) the rods if not damaged will not break an are even good enough to race with and the crank an flywheel are fine at normal road engine speeds.