4.2 water pump on 3.8 block

Dear all

I was told quite some time ago that somebody had successfully machined the recess in serviceable standard 3.8 front timing case cover to accept S1 4.2 pump.

I’d rather try that than purchase a new one as existing one is ok. But want the bigger pump one way or the other. Engine is being rebuilt now, early stages, pre machining work.

Searched archives but couldn’t find anyone reporting it successfully done. About a dozen years ago there was a post about possibility/sizes etc which was helpful. Has anyone actually performed this mod?



Would an early 4.2 cover fit a 3.8 as is? I have both and can check fitment tomorrow. I have spares as well.

Had to scratch the ol’ noggin forcefully…:stuck_out_tongue_closed_eyes:


Dear Jagman and Wiggles

Yes, it should fit as long as it hasn’t been skimmed during production or subsequently to a deck height lower than my block (which hasn’t been skimmed post production it appears) and thanks, I read that article years ago and thought it was very interesting.

My thoughts were to have a machine shop mill my existing timing case cover to accommodate 4.2 pump and skip a step as it were. I’m just not sure yet about material thicknesses remaining etc and that’s why I was curious to know if it had been done before.

If you’d care to message me about the item with a price that might be the easiest way jagman. A few places now produce them new and there are still odd MoD units around if you know where to look. I passed on one about 10 years ago but I really want it for this engine build.

Thanks again gents


I have a front cover off a S3 XJ6: yours for shipping, BUT… not sure when I will be able to pull it off my junk engine.

I think the impeller is only about 4mm bigger , can’t see there being much improvement in circulation, unless your fitting it for another reason :thinking:


Thanks for the kind offer but I’ll try to modify the one I have first. That article also mentioned a few little differences that I can avoid by sticking with what I have.

If by any chance you have a cylinder head from that xj for sale I’d be very interested.

Yes the difference/improvement isn’t massive, but it’s still worth the effort with engine stripped and requiring machining anyway. And if further investigation and measuring rules it out, I’ll know for sure.



The water pump cavity in the timing cover did not change when the 3.8 became the 4.2. It still has 2.75" impeller and square passage into block. Block still has 3 core plugs on each side.
The 3" impeller, larger passage into block, longer block with two coolant passages behind rear cylinder, and 5 core plugs in block with better control of internal coolant passages all came at the same time in mid 1969 model year.

Hi Greg

More than 20 years ago I heard about fitting a 42 timing case cover to the 38 block (with 42water pump) to improve cooling. This was from very experienced European engine builders specialising in jags, whom I trust 100%

Before now I haven’t had the need or opportunity to make this change.

If what you’re saying was true why bother with mods at all and not just bolt 42 pump on? That doesn’t seem correct

The 42 S1 impeller size is larger and deeper according to all reports. I have one but it’s way out east and I can’t get to it to measure it up myself.

Do I understand you correctly?

Not according to many reports I’ve read. Check the archives for details.

I think you’ll find that there are other issues to deal with when putting a 4.2 water pump on a 3.8 - pulley/pullley alignment and hose connections spring to mind.

Dear forum friends

With the very greatest of respect to everyone, this thread is suffering “mission creep” I thought this sort of thing only happened when people mentioned the dreaded Webers in place of SUs. Or wire wheel to steel conversions. That’s not worthwhile or original! - a little joke…

I am very well aware of (most?) the potential issues with all of the different ancillary items, etc. I’m going ahead with this work, not researching cost/benefits. I am not a professional engine builder but I have years of working on engines and 20+ on the XK unit. I did ask a fairly specific question in tne hope somebody could save me wasted effort or running into problems they’ve already encountered trying the same thing. Or even a success story!

If any kind person thinks they can offer constructive tech input I’d be delighted for the assistance. Please continue to reply if you think you can. Hope it will be relevant to the question though.

And hope this doesn’t appear rude. Keep suggestions coming. Thanks

Kind of, but I’m sure that wasn’t your intent, so let’s try to move on…

If you look at the Jaguar Parts Lists you will see that the Timing Cover used for the 4.2 Series 1 E-Types has the same part number (C.8614/1) as that used on the 3.8 Series 1 E-Types. So, this is not consistent with your suggestion that the 4.2 Series 1 E-Type water pump impellors are larger. If you then look at the Series 2 E-Type Parts lists you will see (just as @GregB asserted earlier) that the Timing Cover and Water Pump changed part way through the Series 2 Production. The Timing Cover Part Number changed from C.8614/1 (same as 4.2 S1’s) to C.28480. Simultaneously, the Water Pump changed from C.31144 (note that this has the same impellor part number as the S1 4.2 - C.22798), to C.30811 (often refered to by the Part Number of the Body Casting C.28414) with a new impellor Part Number C.28804. These changes took place at S2 Engine Number 7R.1914/5.

So, it is the later Series 2 E-Type Water Pump that has the larger impellor. Perhaps to get the best responses to your enquiry you should identify the Part Number of the 4.2 Water Pump that you are proposiing to fit to your 3.8 Timing Cover. I’m wondering if the confusion might be the reference to “Series 1 4.2” without clarifying which Jaguar Model. The Series 1 XJ6 (1968-73) perhaps used the later 4.2 Water Pump with the larger impellor? I know that I, for one, when looking at posts in the XK-Engine category, tend to forget that I’m not in the E-Type forum and thus miss the context of the question.

Assuming that I now understand your question - namely that you wish to install a water pump with deeper and larger 3" impellor in a 3.8 timing cover wherever that pump originated, I have also been unable to find any accounts of anyone machining an earlier timing cover to accommodate the larger impellor - whether successfully or not. When anyone has suggested doing this in the threads I’ve seen, the responses have been to recommend fitting the later timing cover that was designed for the larger pump impellor, though I know that this is not the answer you want to hear. As @Wiggles pointed out earlier, if you take this route you have to choose a timing cover that has a compatible outlet profile to the block, or coolant will end up in the oil sump…

The change in the water pump cavity in the timing cover and the impeller cavity in the water pump is what we refer to as the “water pumping” part of the system. This didn’t happen when they went from 3.8 E to 4.2 E. The pump changed at that point because of the pulley and water connections, but the items that affect water pumping didn’t. The only difference in “water pumping” is due to a change in the pully ratio difference running the pump faster in comparison to engine RPM on the 4.2.
The change in the “water pumping” part of the system happened with the improved block casting and coolant passages in mid 1969. Improved core support in the block casting process resulted in 5 core plugs on each side of the block. Other changes included larger water passages in block and timing cover, additional water holes in back of block and head, larger water pump impeller, etc.
The deeper impeller does not go deeper into the timing cover cavity. The increase is accommodated in the water pump itself. There is a lot more to cooling than just the impeller size as it is just one part of the system.
Here are labels from water pumps in our inventory for the two-fan vertical flow radiator cars 1968-7R1914/7R35388 and the improved system fter that change. You can see from the gasket diagram how the shape of the cavity changed along with the extra capacity for water to flow into the block.

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I fitted a early 4.2 cover on my 3.8 and the opening in the cover is larger for the water passage. The 3.8 block will accept it without problems. The original 3.8 timing cover had a slightly smaller opening.

Also a side not a late 4.2 timing cover is a totally different animal in regards to the water port. It will not work on an early engine period.

The impeller size and passage size on the later pumps is not a big deal. We were making 3.8 E-Types run cool in Los Angeles traffic and temperatures in the early 1970s. I wrote an article for one of the Jaguar magazines on that subject 40 years ago and will try to find it to publish here.
Water flow in the block, block to head, and out of the engine to the radiator is quite different from 3.8 E-Type to later engines. One of the designs I worked on resulted in the change in size of water passages side to side on the later head gaskets. The 3.8 E-Type Intake Manifold will only allow a certain amount of water flow out of the head so you need to have it remove as much heat as possible by making more of it go block to head on the exhaust side and making more of it go to all the way to the back of the engine. This is why they added the extra two passages on the later 4.2 engine. You can readily see this by looking at an early 4.2 head gasket vs. the later one.

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If you are determined to machine a timing cover before mid1969 to take a later 4.2 water pump, these pics from an article I was writing will help.
C2303 and C28656 Gasket on 1/4" graph paper for precise sizing.
C8614-1 Timing Cover (E 3.8 and 4.2 up to mid 1969)
C8614-1 Timing Cover with C28656 gasket on it for reference.
EAC2061 Timing Cover which uses the C28656 Gasket.
Early and late Timing Covers Water Pump Cavities are both 0.625" deep but early covers and repro covers are sand cast and not necessarily flat in impeller area as it isn’t important with the smaller impellers. Early 3.8 covers have a pronounced indent between the top pair and bottom pair of studs around the passage into the block. This will stop you from opening that are much to match the gasket but the passage is smaller at the back anyway going into the block so you gain little or nothing by opening it up.

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Here is the top of an original 67 Timing cover showing the recess between the top bolts and why you can’t try to open it up in between the bolts on the inside. Second Pic is 66 with a replacement timing cover showing another slight variation in that area.


Thanks GregB
Let me digest this when I have a moment to study it carefully
This is what I was really searching for

Not sure why Jaguar left it so long in to the XK engines life , to try and sort out the bad circulation problem .
Most people know there is a big problem at the back of the engine , with silt build up ,
I fitted a MK2 water pump on the front of my 1975 xj6 engine , bolted straight on , with no issues !
Thinking about the bad circulation at the back , I come up with a little help .
Removed the drain tap at the back , and fitted a straight conector , running a hose off that to a electric water pump , connected to a on and off switch , so every now and again I have it on , 10 to 15 min’s on a trip .
I do have a uprated rad core, expansion tank , electric fan , in the hot summer last year in the UK , only had to switch fan on a few times , and I do drive my car like I stole it :rofl:

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Thanks for that info

Yes block scraped clean (inside) of 50+ years of silt with a bent welding rod after core plugs pulled and sprayed pressure washer into holes after first block hot tanking. Then repeat. Filthy business.

I always fit a brass bung but thought your idea with electric pump was a good idea. I’ve heard of greater use of electric pumps and even fans for brake cooling after track cars are parked up and heat levels climb and climb with no coolant or air flow. And an electric fan moving water around seems ideal especially if coupled to an electric radiator fan. Think battery might need watching but nothing’s ever simple. Haven’t heard feedback on how effective it has been. Will share once I speak to people in question

Most illuminating fact was that larger impeller in S1 42 water pump doesn’t protrude further into timing case.Have enough to go forward with and will attempt to speak with one of original perpetrators this week in Europe if he answers his phone!



PS hot summer in UK an understatement!