Change the XK con rods for the XJ con rods

Hello again, I was planning to change the pistons of my engine to higher compression, having a 3.8Litre engine with 8 : 1.
I had several pistons and con rods for sale, but no one wants them here in Holland, so I heard the XJ con rods are the best there is, so to combine them with 9 : 1 pistons,
However the con rods of the XK’s do have a oil line and the XJ’s not.
Is it then a good idea to change, what happens in the engine without the oil line?
Can anybody answer me?
Frank, e type '63.


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Dag Frank

The XK and XJ rods are the same until the later rods with no oilway. The later ‘wide-blade’ rods (e.g. Series 3 XJ are the best. These rods have just a chamfered hole at the top of the small end and in each piston boss. This is enough for a fully floating pin.

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He Pete, goeiedag, so XJ series 3 are the best, I have the series 2 con rods, looked fine to me. My engine is a 8 : 1 compression and i want a upgrade to 9, so thinking of the XJ con rods, there strong to put in.
Chamfered hole, will look for it, don’t think so and in the piston boss, too. Very good.
How are you nowedays. Still searching for an ID, there was a firm Hilltopjags, who has something, but it was to vague.
Greetings Frank.

None of the rods are bad Frank - they used standard parts at Le Mans after all (after careful prepping). The S3 ones will stand race abuse but there’s more to it than just one design vs another.

I just sold an engine and IRS to Dan at Hilltop. Nice guy. I may soon ask my nephew in Kentucky to get a replacement title for my 68 2+2 shell maar ik zou daar liever over spreken tussen ons getwee.

Hi Pete, “standard parts” been used at Le Mans, sure, but the XJ’s con rods don’t have a oil line in it, isn’t that a lack of oil then for the cylinder wall’s.
Is it true that the early pistons had an " off set " pin, so the piston didn’t hit the wall to much and don’t they have them in the new Hepolite pistons? Later?

The oil drilling is old fashioned. Small ends do not need pressure feed as the bush and pin only move slightly, especially on long rod engines like the XK.

Cylinder wall likewise gets plenty of lube from the oil mist in the crankcase. I’ve never seen an XK rod with a drilling in the rod shoulder (or bearing shell) at 11 or 1 o’clock. That too is rarely used in road engines today AFAIK.

All the standard Jag pistons I have see use offset pins except a racing set I have.

Thanks Pete, that’s clear then, I want to use the XJ con rods and the higher compression pistons in my 3.8L Jaguar. I read somewhere that the 3.8L engine had low oil pressure, maybe the oil line in the rods take some pressure and lower the bearings.

Hi Frank, my Series 1 rebuild included: Mahle 9:1 pistons, Series 3 XJ6 rods (crack tested) and a Series 3 XJ6 oil pump and filter head to take a spin-on filter. It was an e type 9:1 engine to begin with. FWIW, Paul.

The 4.2s had the exact same rod Frank, so they would have had the same supposed low pressure effect on 4.2 as 3.4 and 3.8.The effect would be minimal because the bush is a snug fit around the pin, even allowing for grooved bushes.

I think the plain wide-blade rod came in at S3 stage, or maybe late S2 when the US got EFI and Opus ignition. I assume it was used on the later type 3.4 engine too, which replaced the 2.8 at the same model change (not in the USA).

Pete, I have small hole lower then the bush where the pin is seated, is that normal?


The rods have the same dimensions regarding length and bearings but they are not the same.

There were at least five different con rod designs during the 3 1/2 Litre pushrod engine

I needed a set for my 1947 engine but in the end I modified and balanced what I had.

My problem is that none of the 4.2L XJ6 S1, S2, S3 con rods, of which I also have a couple of sets, fit inside the old pushrod engine.

But all Jaguar 3.4L and 3.8L original con rods do.

I have now inside my engine four original steel rods C.2448 and two late 3.8L con rods C.7917 that have been lightened a bit.

I also have two incomplete sets of 3.4L C.5835 and C.7917 con rods.


The little pinhole jet that is on the side of the rod? That is for lubricating the cylinder walls and should be directed at the thrust side. I had it wrong and had to go back and turn them around, not that I believe it matters much.

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I was just refering to XK rods in XK engines, where I believe all long block rodscan be physically interchanged from 1949-1992, albeit with many detail differences over the years. I could still be wrong,but I certainly wasn’t including pre XK engines in my remarks :slight_smile:


Sure. And I was only pleasantly surprised that the big end, small end and length are the same. The 3 1/2 Litre stroke is 110mm when XK is 106mm.

The only problem with the XJ6 con rods is that they are too sturdy for the pushrod crank and crank case and would hit and scuff the block and the crank counterweights. No problem in an XK engine.

Just that if someone has 3.4L or 3.8L con rods they can’t or don’t want to use, I could have them for a possible next rebuild of a pushrod six. :slight_smile:


Good thing you did: it matters a LOT!

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David, thank you for telling me that the little hole is to lubricated the thrust side or in this case the inlet side. Is it affected enough to lower the friction piston/cylinder wall?
If I change the con rods, this could be a problem, without those lubrication .
Plus the counterweights of the crankcase is different.
Not easy at all.

It’s more about the wear of the pistons I think, they rub on that side especially and I am by no means an expert but would think that the later shorter skirted pistons may not need it, and there seems to be plenty of oil splashing around to lubricate everything even without the drillings and the small hole.

If you refer to Pekka and his different crankcase, that is not for our XKs, the rods will fit the 3.8 without trouble if Peter says so.

Starting this week to change the con rods and pistons in the Jaguar 3.8Litre engine.
Bought old original pistons in Germany when I was going to the Balkan.
XJ con rods and high compression pistons, so the car can be raced.

What kind of racing will you do wit it?

Well Paul, this idea was not mine to begin with, but having problems with the ID.
For racing it itn’t necessary, so can finish it all.
For the time being it is my biggest hobby, working on the project every day, now.
Searching for the best options there is for a Jaguar e type, combine the best in the car.