ConRod bolt over torque or under torque

I am in the process of checking and installing a new set of rod bearing in my 3.8. I am using the stock bolts and castle nuts, in some cases the holes do not line up to install new cotter pins, do I over torque to align or back off the nuts. Or does one use shim washers under nut so it comes out correct for 37 ft lbs.

thank you,

I’d just pitch those nuts, and use Chevy rod nuts.


EVERY time I read of someone wanting to reuse the old slotted nuts and split-pin rod bolt, I ask that same rhetorical question. Personally, I would not reuse the old rod bolts. The later XJ6 bolts are better. I would rather stick that split-pin cotter device in my eye. I’ve found pieces of them embedded in bearing shells and oil pump rotors.

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I’m with Mike, if you can’t afford new bolts and nuts, you can’t afford a Jaguar.


I can afford new bolts, but reading on this forum on installing the new bolts that XK’s carries requires some fitting which may cause me some grief. I am checking what I perceived as rod noise at certain RPM. So far plastigauge says everything in spec. The motor is in car so working from underneath. So doing fitting that that is easily done with motor out with rods on bench isn’t in cards.

If you use Jaguar bolts, there will be no issue: it’s the ARP bolts that require fitting.

Con rod bolts are slightly stretched when first tightened and used so it would be advisable to order twelve new bolts with locking nuts via Jaguar. This would be safer. Whilst you are there. Don’t forget to check the oil pick up pipe and seal where it bolts to the block as this can come loose over time.

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Been looking for replacement bolts, but all I can seem to find are the ARP bolts, any hints who would have stockers like the ones from an XJ6 as suggested?
My local Jaguar dealer is a total JERK, they don’t work on or parts support Jags over 10 years old.

Call SNG Barratt: they’ll have them.

Check your piston pin fit in the rod small end very carefully. I had a tap when hot. With the engine apart my machinist found a bit of axial play. I missed it. New bushings, no knock.

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We seem to go round and round on this subject. Certainly NEW cotter pins is a must, the right diameter and length and properly installed. I’ve never seen a new one break, but have found some with twists and pliers marks proving that somebody used them at least twice.
Torque is a secondary way to measure what you are really after, which is bolt stretch. The exact torque is not that critical, that going over or under by a 12th of a turn doesn’t make much difference.
Ultimately any system where the nut doesn’t work itself loose is a good system.

Here’s the thing, properly installed, bolts are stretched every time they are torqued, but only only within the elastic region. They perform like an extension spring. Any bolt that has permanently stretched, yielded, does not return to its original length, is trash. If the rod bolts you have, have only been installed once, they are not likely stretched and could safely be reused. That leaves the nuts. You can safely buy aftermarket nuts. It won’t make the bolt any stronger, but you can eliminate the slotted nut. Very good alloy steel 12 point nuts are a couple of bucks apiece. You need to make sure that the flange on the nut is no larger in diameter than 5/8". Here’s one that would work:

Great respect for @Rob_Reilly, but am dead serious when I say I would stick that cotter pin in my eye before I put it in a connecting rod. I have found pieces of them in main bearings and once found one in an oil pump, where it had split the stator (outer gear).


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Agreeing with Mike here, if you have been running with a worn out to the point of audible knocking rod bearing, your bolts and nuts have been taking an overload and are suspect.

A member of our club which has built a number of Jag motors agrees about using to original bolt and nut. I did purchase 100 of the 7/64x1 cotter pins as original, they are inserted and bent once, if I have to pull they are discarded. The noise I am chasing isn’t a knock, but more of a slight rattle I hear at a certain RPM. Since I had to pull the front suspension out to swap another rebuild unit and I had a pan with a marginal drain bolt threads I decided this was the time to check out the bottom end. So far the journals have miked to 2.086 on the money, gauging the bearings show they are running at .002, all good. I have three more to check. I did find a couple of rods with no cotter pins in them and they perfectly lined up to accept a pin, so the oil pump will be pulled too.
Looks like whoever rebuilt this motor used the cotter pins over again and some undersized ones in some spots.

One thing to keep in mind about any critical threaded fastener is that the stretch does not occur uniformly along the unthreaded shank, but in the exposed thread roots where the cross section is the smallest. So while the amount of stretch is quite small, it is occurring in a very specific location.

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Well guys, here is the update. finished running all the rods and everyone was in specs. I found one with a variance, the crank was 2.085 and it plastic to .003 clearance, still within specs. I did put new rod bearings in as I reassembled the bottom end. I just torqued everything to 30 till I finish looking around, Had to order more Loctite.
I did order those new nuts from McMaster, (thanks, Mike S for the link), so now I am still wondering what is the cause of my perceived rod noise.
I did mention some cotter pins were missing, and the ones still left wobbled in position so they were incorrect for the application. Guess next is the oil pump, any recommendations for a nice high capacity one.

I second that. Here is a pin bushing that fell out when I removed the piston and pin. You can still read the Vandervell marking. This was likely the cause of some little ticking noise.

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Removed oil pump and checked unit, I did not find any damage that indicated it ate any cotter pins. It was OK on a couple of the specs, but was out by +.002 on the inside rotor measurement at .008. It looks like an original Hobourn-Eaton unit, probably put in there in 1966.
As far as checking the small end of the con-rod, I am doing this with motor installed in vehicle, so I won’t be pulling head and removing pistons to check that measurement. One thing that is also out of spec is that the motor was assembled with the rods with 1 at the front rather than factory numbering.

Terry’s has genuine jaguar replacements as well as ARP.
Terry’s is owned by Engle imports which is an authorized Jaguar dealer.

I got nuthin’ I can say on that. Were the caps on the correct rods?

Make sure you do a thorough cleaning of the oil filter mount internals. It would make me very nervous not knowing where all of the missing split pin pieces went.

The 4.2L pump is higher capacity. Compared to 3.4 and 3.8, 4.2 pumps have a larger suction tube, so it requires either reducing bushing, adapter or a 4.2 pickup tube.