Rod Nuts

[RichardL]

Gents,

I'm afraid I don't understand the rod nuts that were sent to me by my favorite "machinist." If you look at the photos (click to enlarge) you will see that they seem to be slightly dome-shaped on the cylindrical end and flat on the hex end. I think it should be the opposite, as the socket doesn't want to get all the way down on the hex, due to the relief in the end cap. Does anyone know what gives here?

Richard

[bsa-bill]

If they were hex all the way down they would probably catch the case, so they machine a bit of the hex off to be safe.
I bought a set that came hex all the way and the supplier asked me to send them back so he could machine some of the hex off for the above reason

Al the best - Bill

[RichardL]

Bill,

My confusion is with the doming that is on the turned end, that is, the end I would assume to go against the journal cap. If that dome goes in that direction, I am fairly certain it is going to distort the cap.

Richard

[groily]

Don't know Richard, but other way round, methinks, as a dome like that can't go against the cap, for the reason you give. Hate to ask, but given the provenance of the nuts, do we know they are high tensile and suitable for a con rod? Would you be better with something of known heritage from someone of repute rather than with a 'reputation'. Should they be, or is there an option to have, self-lockers? I ask that in all innocence because, again, I don't know). Groily

[bsa-bill]

Think wer'e not on the same wavelength here, if by the "turned end " you mean the end that is circular and Not Hexagonal, then it is the turned end that is farthest from the rod not next to it.
Putting it another way looking at your pictures it is the left side of the nut that contacts the rod.
As I said before if the nut was hex all the way down the nut would possibly scrape the crankcase, so they machine (turn ?) some of hexagonal off the bottom of the nut

All the best - Bill

[RichardL]

Bill,

We are now on the same wavelength, in that I understand your point about machining away ("turning") part of the hex to avoid the crankcase. The problem is, with the hex end against the cap, the socket barely goes halfway down the hex before contacting the relief in the cap into which the nut sits. This seems a bad way to use a tool and abuse the nut.  Also, my previous rod nuts, acquired from a trustworthy source, were domed on the opposite end (as you can see in the photos) and did not hit the crankcase. I am beginning to think that there may be rods from other models or manufacturers which allow and prefer the hex against the cap, while, it seems, the A10 rods do not. If so, my supplier may have just grabbed the wrong ones (he has already demonstrated some lack of attention).  Bill, I trust you don't take this as arguement, but I still see problems. 

Groily, point well taken about the provenance. If I believe the invoice, the nuts are locking and intended for connecting rods.

If it were not Sunday (Happy Easter, by the way), I might be able to speak with the supplier, but I thought we might resolve this in the forum, so I could get my rods mounted and crankcase closed this weekend. Right now, that seems unlikely- read, "impossible."

Richard

[RichardL]

So, I am told by the supplier that the nuts shown in the first photos are actually BSA nuts and there was a special socket/wrench for them. I don't really know what to believe, but he's sending me some that are like the second set of photos. He says they are Triumph. Regardless, that's the type I want and he told me to just keep the first set. In other words, "Nuts to me!"

Richard

[a101960]

Richard,

Forgive me if you already know this. It is crucial that you use the correct type of nuts and bolts on your rods. I had my engine rebuilt a while back and at that time the only way I could get the right nuts and bolts was by using Triumph items, and that required 1/8" to be machined off of the caps. It is imperative that you use drop forged bolts with rolled threads. CNC and or machine cut bolts and threads will not do. The reason for this is two fold. There has to be some pre-stretch built into the bolts, and a machine cut thread is a potential source of stress failure. The bolt may not "let go" until a few thousand miles have been covered, but let go they will.

SRM list suitable bolts 67.1536 Conrod bolt forged (£5.96 each) and nuts 67.1537 (£2.31 each). I am not sure if these nuts and bolts are Triumph items or BSA. I bought my bolts from SRM and they were Triumph, and it was not until I placed my order did they tell me that they were Triumph items, and that the caps would need machining. The Triumph bolts are the correct specification and will be perfectly allright to use. If you want to fit genuine BSA specification email me off list I can put you in touch with another supplier who has had BSA big end bolts made to the correct specification, that is to say drop forged with rolled threads.

[RichardL]

John,

Agree completely about using the correct type bolts and nuts. Your comment about Triumph bolts requiring machining the cap was also told me by SRM, as they only have the Triumph bolts right now and advised regarding the machining. My bolts are at least 30 years old (maybe 50+) and, I am rather certain, original BSA parts. I know that, in another topic, you advise replacing the bolts every time the rods come apart. I have also heard others say this. On the other hand, I have heard it the other way around as well, from my favorite technical source (not the "machinist," but I heard it from him also - I am trying to keep in mind that, despite the screw-up by his helper on the skimming job, he is still a respected guy). Basically, I think I'm keeping the originals (I don't race, I don't even want to go very fast), however, I think I should do due dilligence and check out your other source, so I'll drop you an email.

Richard 

[bsa-bill]

Richard I wont take any offence or take your reply as an argument
I don't strip engines down that often so I'm of the school of thought that as the bolts have been stretched once they should be replaced with new.
The bolts I used were purchased from a BSA guru who had a batch made with a racing spec - high tensile steel - rolled threads - special lubricant supplied with detailed fitting instruction giving torque and stretch dimensions.
They did have a deeper nut than yours
I know where your coming from regarding the socket, you need one with a thin wall, you could of course sacrifice a good one and grind down the socket wall as you are not going to put lots of torque on it.

Anyway I will watch your mails with interest

All the best Bill

[RichardL]

Gents,

I received the new Triumph nuts and am quite happy. They have the obvious locking dimples, they are not plated and the hex is on the top. Finally, I can attach the rods to the crank and move on.

Richard

[a10 gf]

A great story this one, showing the need to always keep alert and having attention for details, and to never automatically trust the suitability or quality of parts one may receive in the post. Good luck with your work.

e.