Early XK120 crankshaft


I need to source a new crankshaft for my engine rebuild. Current shaft is original 6 bolt part number C2239. Big ends are already at 0.040" and need cleaning up.

What crank can I use, keep in mind that I would like to use original flywheel and front pulley, etc. I will be using an upgraded rear seal.

What are my options, I have seen some suppliers have 0.060" bearings, but they aren’t in stock and are very expensive.

Thanks in advance,


Any decent machine shop should be able to sub-arc the journals back to standard.

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Wow this really is a thing. I was nervous about having to have mine cut again, nervous no more


Yea: ooold tech! Many was the irreplaceable crank I saved, by using sub-arcing.

Looked at that but not cost effective for 13 journals. That would only be last resort.

are they the same as early MKVII cranks ?

I was talking to a bloke had an entire engine for sale for a few hundred $

Thats what i am hoping, couldn’t be that lucky

sorry for raise yr hopes…dug out my MKVII Parts book…shows only one crank part num c.4808

Was there much of a difference in the crankshafts between XK models that anyone knows of?

I forgot I have the electronic pdf of XK Parts

for the early vs late crank in XK120, some very important other part nums are different,
such as flywheel, conrod, and conrod bearing

You will need a definitive ruling from an XK120 guru on interchange

For everyone who can add I will provide the following info:
Engine No. W2524-7
Chassis: 660365
Photos of the crank and flywheel. Note the flywheel seems to have been lightened.

These are all the photos I have and the machine shop is 40 mins away.


Your flywheel doesn’t match your crank. 6 bolts vs 10 bolts.
You might be better to get the Mark VII engine and use that crank and flywheel.

BTW the earliest crank C2239 had Welch plugs, where your C2239/1 has screw-in plugs.

Wait: that’s a 6-bolt crank, and a 10-bolt flywheel??

What engine would have had that flywheel then? When did they go from six bolt to 10 or 12 bolt. There was no part number stamped on it anywhere I could see.
Which crankshafts can I use?
I am imagining from what you are saying that the mark vii flywheel and crank are a straight swap into the engine I have. Is the mark vii flywheel the same amount of teeth?
Thanks for replying.

All Mark VIIs and Mark VIIIs used the same C4808 crank and C4809 flywheel, though not of course automatics. Near as I recall it was 132 teeth when we discussed flywheels on this forum. There was a weight reduction with flywheel C5808.

Hmm, 6 bolts at 60 degrees with 2 dowel pins at 30 degrees, vs 10 bolts and 2 dowel pins all at 30 degrees, so I guess it works. Odd though.

Since we are on crankshafts, notice another bit of fun.
So 3816 XK120s and 6199 Mark VIIs or 10,015 engines had the starter jaw bolt on the front of the crank, but only 96 XK120s had the starting crank handle.

If you go for a rear seal conversion you can use ANY 3,4/3,8 crank. The early cranks are lighter
and the counterweights are set in a different possition, but both do the job, Your flywheel
will fit any 3,4 /3,8 crank Having mounted both types of crank ion a mill, to machine off
some of the forging irregularities, the early crank is tiougher to cut,. I was informed some yrs
ago by a ex Jaguar engine man that the early crank is EN24 and the later EN16. How true
these specs, I know not…A factory lightened flywheel looks as photo.
Peter B


Thanks for that info. Now I can move forward. In a way having a flywheel with 10 bolt is a blessing and means I can use any crank.
I can confirm my crank has the starter jaw bolt and I just assumed someone had changed out the radiator core as there was no crank handle hole.


That is exactly what I needed to hear. Thanks for your help. The flywheel I have has been lightened but is not factory. All this was done way back in the early history if this car. Your photo will help in identification.

I will work out what I am going to do and will post back here so anyone in the same position can have a reference.

Once again thanks for sharing your knowledge.


Only the first 99 cars had the hole in the radiator.

I suspect the person responsible for ordering parts from outside sources ordered 100 of each part, radiators, steady brackets and handles, but somehow got 10,000 starter jaws. Perhaps the supplier quoted a price for one batch (of 100) and the buyer ordered 100 (not knowing it was batches).

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