Early 4.2 block types

Is there such a thing as a 4.2 block with dynamo mounts in the same spot as a 3.4/3.8? I assume not as the 4.2s were all alternator equipped?

i believe the early variant had all the same boltig geometry and hece the confusion same as 2.4,3.4,3.8 before bores respaced? there is good info in books i seem to remember? are you contemplating more toque for “D”?

Not sure if the very early 4.2 with the round core plug at rear had them , but I doubt it.
By ‘64 thereabouts the dynamo mount was combined with the engine mount on MK2s, but of course the original dynamo mount bosses remained.

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Just thinking way too far ahead. I don’t recall ever seeing a 4.2 block of any sort with the dynamo bracket bosses bottom left front, drilled or not. Tilted to the left it is very tight but a home made combined dynamo/engine mount makes it all work nicely and look original with a dynamo block… .

I am very slightly concerned about my refurbished old rods (balanced/honed, magnafluxed, but not polished/peened…I’m comfortable enough not to put a 1,300 dollar set of Rob Beere ‘Sportsman’ H beams in yet, but if I ever missed a gear/lost a rod or block I’d go up to 4.2 if I knew to keep an eye out for some rare block spec in the meantime. Don’t think one exists. Others here have built far more XKs than me so I thought I’d ask…

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I can’t say I ever remember seeing one with theses holes in.

i would mirror polish rods and do real test , wet fluorescent mag particle or gamma ray. let a boiler aircraft testing agency do it for training (cheap) john

I have an early 4.2 block (around # 200 made) , but don’t think there were any low bosses other than the motor mount. I do seem to remember motor mounts that were also used for mounting something else, like AC or power steering. I’ll look in my box of motor mounts for something that had dual use. I parted out a 420G or two years ago. If I find one it’ll probably be for a 3.4 or a 3.8.


Yes the torsion bar E used front mounts and vertical downpipes. For use in subframe 4.2 cars all the 4.2 blocks also got mid mounts and downpipes swept back, with empty front lower bosses used for ancillaries.

What about 4.2 MK10 and 420 Peter re front engine mounts !

i still think the early ones still had same geometry bosses and and mounting possiblity from mid fiftys to mid 60s. 2.4,3.4,3.8. 4.2 mayy have had additional that i never used. simply use prop- er stock mounting with theier scabby welding if not cracked esp mk2 and s . mk 10 differs slghtly because wider and 420g because of bigger pump and alternator. ?? peter C may even be able to use 420g as start point for his project?

They’ve all got usable engine mounts to the last 1991 DS420. My query was re dynamo bosses on 4.2 blocks, of which there are none, as expected.

I have just installed a MK 10 4.2 in my 150, I had to make a Left hand mount with a generator mount included as the block did not have any lugs

Hope these pictures help.

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looks good Morris . did the bits work out ok? if i remember correctly the 420 g it came from had the alternator and power steering off the front mounts and it was completlely different from mk10 that had the typical dyno and integral pump. how did it perform?

Thanks Morris but we’re talking at crossed purposes. I already have a special engine mount with generator/dynamo mount included and it uses the generator mounts as a major attachment for the engine which is tilted left (therefore needing a mount higher up that side).

The absence of dynamo mounts on all 4.2 blocks means that to use one would be impossible without re-engineering the re-engineering already done, which I’m not interested in doing as it is fine for all 3.4/3.8 blocks.

If it were a fabricated steel box I’d just weld a couple of large lugs to it, but as it’s a 250lb weight-bearing lump of cast iron I’d rather just pass.

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