The service manual for the MK V contains the following sentence:
Always use new connecting rod bolts and nuts at overhauls.
Is this a must, or just a recommendation? If so, where can I get the new ones. I haven’t found them at Worcester or SNG Barratt.
Thank you very much for your help.
British Tools and Fasteners (britishfasteners.com) might be a good place to start.
If bolts have been used only in “elastic” range, my experience is reusing has worked fine. New bolts removes all concerns about past usage at low cost fraction of whatever work led to this assembly point. If memory serves, I’m now using XKE connecting rods and ARP conrod bolts.
I am about to undertake a similar task later this year for my 3.5 and I would like to install new big end bolts. I have put an enquiry to Alan Gibbons at firstname.lastname@example.org about availability.
The risk, as I understand it, is that these bolts endure millions of cycles of a ‘stretching’ load imposed by the suction cycle and at some point they could fatigue and let go. In saying that, I had a car for nearly 30 years and 500,000 km and did two engine rebuilds without changing these bolts. Now, having a more valuable and desirable classic, I prefer to eliminate expensive risks. If I find I have alloy rods, I would seriously consider eliminating that risk too.
I found the screws at Limora the piece at € 37.64 blus the nut € 10.98.
Many thanks for the help.
Check at least one place for fit when you receive the new conrod bolts. The bolt head may have slight overlap onto the tiny radiused portion of the conrod where the bolt head snugs down. If the bolt head lays flat onto the conrod surface, then fine. If the bolt head slightly hits the radiused conrod surface, then some relief of the bolt head is needed to obtain a flat joining of the head onto the conrod.
Important what Roger wrote. I have used in all my rebuilds the ARP style XJ6 Series 2 bolts and nuts. The stroke is 110 mm on the 3 1/2 Litre engine. I would never use the original castellated nuts and cotter pins. If you do you are asking for trouble.
One could interpret the sentence as a strong recommendation, from back in the day when these parts were readily available at any Jaguar dealer at a fairly low price. The assumption at the time may have been that if the car needed overhaul, the rod bearings were probably somewhat worn, with the rod bolts taking more knocking than was intended in the initial design. The manual was written so that anybody working on the car, whether a Jaguar trained dealer’s technician or an untrained mechanic in a small town shop, would be able to take care of the car.
Certainly if you are going to use the original or duplicate parts, at the very least, always use new split cotter pins of the correct size, and correct installation procedure. I have found broken cotter pins in a Mark VII engine, and every single one of them showed twists and pliers marks, clear evidence that they had been used several times. On the other hand, I have had several pushrod and XK engines in which the cotter pins were all in excellent condition, clearly factory original or correct duplicate work.
The subject of rod bolts is controversial, and there have been several threads on the XK and other forums which have degenerated into near-arguments. For this reason I am being careful not to give an opinion.
There is a philosophy in mechanical engineering which says that a bolt operated within the elastic deformation range is not subject to fatigue failure; in other words like a spring, if it lasts 10 miles it will last 200,000 miles, if nothing else changes.
There is an alternate philosophy which says always use the newest most modern parts if you can get them, because it gives you peace of mind.
Jaguar engines are not known for breaking a lot of con rod bolts.
The pushrod engines have a reputation for breaking aluminum con rods. Unfortunately this reputation dates from long ago in the Mark V era, and it is impossible to thoroughly investigate this phenomenon 70 years later.
My own personal theory is that it was oil starvation at the wrist (gudgeon) pin due to incorrect or mismatched big end bearings, the oil hole in the wrong place relative to the oil feed passage in the rod.
But like I say, unless it would happen to somebody in this era, and we could examine the broken parts, it is impossible to be certain.
I fully agree on everything you wrote, but would like to point out that as I had also found the remains of (incorrectly applied) cotter pins in the oil sump of both my ex 4.2L E-type and the MKIV engine I have in my MKV, and in the former case some of them had also travelled through the oil pump.
So for me getting new, inexpensive Jaguar parts for a Ser. 2 XJ6 that are surely up to the job and that do not need any cotter pins was an easy solution. I am not sure they would fit all engines and con rods, but in my 3 1/2 Litre engine they fit perfectly. YMMV.