Alternator / dynamo swap

Will the alternator and bracket from a 150 swap with a 140 dynamo ? Will the pulley be correct size and width to use as is ?
Thanks Jim


The XK150 also came with a generator. See for details, including belt and pulley sizes.


Fan belt and pulley data on different page:


Thank you Clive
Still not cleare to me .
SNG Barratt list a belt that fits both , but other supply list two 10mm and 13mm.
Coventry Auto Components list a alternator conversion kit with different size pulleys for a 140 and 150


There are in fact two elements within your question: you talk about an “alternator” and about swapping between XK 150 and XK 140. If you mean with “alternator” an AC generator then this has been a later addition to the XK 150 and would require similar modifications on the XK 140 if you want to use it. If you mean the DC generator from an XK 150 to be used on an XK 140 then you must first have a look which generator has been used on the 150. Early 150s continued the XK 140 generator Lucas 22462/E (and are a simple swap) but later (post May 1959) XK 150s used a different generator Lucas 22496 which requires a different fan belt and Regulator box as the output is now 25 Amps. See for the correct fan belt the second page as quoted by Clive.

Hope this helps,

Bob K (a.k.a. “Bobine”)

My plan would be to use a later 150 alternator AC generator on a 140 and change to negative earth and do away with the controld box.


As no xk came with an alternator, it is not possible to know what pulleys you have. For example, my xk150 has been fitted with W pulleys and fan belt from later Jaguars.

You will need to have matching width pulleys for alternator, water pump, and crankshaft. I think any pully for water pump and crankshaft will fit any engine, but the generator/alternator pulleys are matched to shaft diameter. That is they are not all interchangeable.

The website I referenced is more accurate than the suppliers!


'Fake" generators are sold which look like the old Lucas but have an alternator inside. This would mean a straight swap. Mine has the old Lucas pulley on it.
And if you ask them , they’ll turn the outside of the barrel t look like the special eqiupment finish… and you could stick the oval tag on.

Jim I put a lightweight alternator on both my 150 & 120. It takes the worry out of having and electric fan and being stuck in traffic. Totally reliable and the installation is simple. Happy to provide details if you want.
Best regards

I service a couple of cars with Dynator/Dynalites. They work well, and fit the original pulleys and brackets for the Lucas units. If you also buy one of their RB control box substiutes then it’s almost invisible.

They are even available with the rear flange ready to fit the Hobourn-Eaton PAS pump as used on some of the saloons.

Whilst I agree the dynator/dyalites are an alternative that fit easily, I worry about the breakdown event.

With best regards
Philip Dobson

It is a concern, but are they any slower to source a replacement for than a Lucas generator?

20 years ago it was relatively quick to have a genny rebuilt here, including rewinding. Those shops are almost all gone now.

Sorry my point was a modern/ lightweight is easier and cheaper to either find a spare part or replacement if you are away from home.

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Only one left in Denver… had the Rover gennie freshed up there. Place hasnt changed in 50 years!

What in reality is the risk of a failure, as opposed to any other part. In many decades with old Jaguars the only item I recall stranding me was a modern Eklin condensor.
The generator/alternators available here to my understanding just have a smaller proprietary alternator inside

If it did cease to operate, how far can you drive a car on the charge left in the battery.? Quite a way. A Few members of the SS register too their 4 WDs across the Simpson Desert a few years ago. One RR had the alternator pack up about the 2nd day. But kept going minus air con , lights etc for the rest of trip by recharging from a solar panel they had.
What irked him was that after suffering without air, at the end they washed down the cars inc under the bonnet and the alternator came to life. Apparently some salt had splashed into it and the cleaning washed it away.

Here’s my other sports car’s Dynator, bought from AES:

Does the job really nicely, no problems with it. This one’s the C40T Lucas with the tacho take-off, gives 55A max.


I bought a new old stock alternator listed as for a 150 conversion (I have a 140) . .
It came with an engine mount bracket and a loom . I can’t figure out how it is intended to be wired .
The new loom has three spade terminals , 2 heavy brown and a small brown/yellow
to connect the alternator and I imagine it would travel along the left wing to the bulkhead and behind the dash . The small brown yellow wire exits the loom for the warning lamp ? The loom continues and the two heavy brown are connected together with 10mm eye ends . Where do they go , the solenoid ?
I am converting to neg earth .
Thanks Jim


Brown/Yellow is used on E Type for part of the alternator warning light circuit (goes from the alternator to the relay for what is known as the idiot light). I can’t find it anywhere in the Lucas colour codes though. Maybe the ones I looked at were pre-alternator. I guess you put the ring connector on the battery side of solenoid. Where else could it sensibly go? The control box just becomes a terminal block if you leave it in place, I suppose?


That’s my guess , so what do I do with the old heavy brown and white that went to ‘B’ on the control box to the ammeter ?

Yes, if you want to see the charging current, I think you will have to connect the alternator brown lead to the D terminal on the control box and then link the D and B together. That way, the output of the alternator goes to one side of the ignition switch and then via a terminal on the lighting switch to the ammeter. The other side of the ammeter is then connected to the battery side of the solenoid.
You will maybe need to shunt to ammeter as your alternator should be able to produce more than 30 amps. And thinking about it, you may need to reverse the connections on the ammeter as well.