Alternative cylinder head for XK 120

I am currently having cylinder head isues on my XK120 and would like to investigate an interim fix whilst my current cylinder head is fixed.

Can anyone tell me if a ‘B’ type cylinder head from a Jaguar 3.4 Mk1 or Mk11would be a suitable direct replacement without needing modifications?



Tony others will doubtless give more specific info but the head almost becomes the secondry issue in so much that whilst the b type head will physically fit it’s the ancillary connections/interfaces that need thinking thru. Eg what inlet manifold and carbs will you use cams and tach drive connection, (I assume you will just swap them over but then you need to swap the studs etc.) and obviously the throttle linkage etc.

It will fit perfectly, and your original inlet manifold will fit.
The tach connection can be done using the original camshaft.

Thanks for the swift responses Phil and Peter,

Your replies sound positive and yes in the short term I would just transfer over the peripheral items, cams, manifolds, carbs etc.

Now I just need to find a serviceable cylinder head.

If you use a B head you will gain a significant amount of power. HP goes up and torque comes in much lower when it is most useful. Do you need an early “studless” head, w or w/o siamesed plug wells?

I think the B-Type head as fitted to XK150, Mk I, Mk VIII will be a direct swop as regards the camshaft take-off from the exhaust side? you’d need to swop the inlet manifold over. If the tach take-off happens to be on the RH side, then perhaps a 90 deg angle drive could be used? I don’t think it wouldn’t make sense to use the earlier A-Type cams in a B-Type head - you’d lose much of the power advantage, surely? Just throwing these things out there…

Don’t the cams have an oil slinger bolted into the rear? I presume you could remove that and put the tacho drive in there. Agree about about the low lift cams, though, pretty pointless retaining them with a B Type. As with Tucurious, the performance improvement will be significant, you may end up keeping the B Type in there and keep the A for posterity to be sold with the car.

Something to consider, 2.4 Mk 2 s use the B Type head, but have different cams, so if you buy a complete head, check the engine number on head; 2.4 prefix starts at BG. All others should present no issues.

This is interesting. Do you know where I can find the specs on those 2.4 cams?

Make sure whatever head you use is not from a 240 or 340. They both use straight port heads. Your XK120 intake manifold won’t work with them.

So 2.4 engines use the same head and only the cam is different?
Please excuse simplistic questions but I am on a steep learning curve and new to XK lore!

The cam shaft part numbers are stamped in very tiny numbers on the rough shafts between two lobes.
The 2.4 L Mark 1 saloon used cylinder head C.6733 with C.4488 Inlet and C.2237 Exhaust cams.

I think they used the same 3\8" lift cams as the big engines.

Edit: manual says all 2.4s used 5\16" cams.

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2.4 Mk1 used the A type head with smaller valves and different valve seat angle. Camshaft lift was deliberately small initially to prevent valves clash during handling by inexperienced mechanics; later it was determined this was not much of an issue, so later cams increased from 5\16" to 3\8". Mk1 2.4 produced 112bhp, MK2 with B Type, but still Solex carbs 120bhp and 240 with straight port and 1 3\4 SUs 133bhp (claimed)