OW! My bottom! Block repair decision time

Continuing my journey… a summary so far.
1990 4.0 bought for cheap at auction.
89k original miles
Needed a head gasket
Found excessive corrosion of both head and block.

Now what do I do?
Option One
My local machine show is quite capable - they believe that both the head and the block can be welded and repaired. They have quoted me a pretax total of $1500 to do the work - not including parts, which I will need to source myself. They warned at least one cylinder sleeve will need to be replaced but possibly all 6. Replacing those - well I might need to replace rings at least then of course the possibility that bearings and even pistons could be replaced. Even at SNG barrett it seems like parts availability might be difficult at best, difficult and expensive at best. Pretty quickly I could add another $1000 in parts. Note, I’ll STILL have to reassemble the top and bottom myself. For maybe $2-$3K (and a lot of my time) I would have a rebuilt engine

Option Two
Source a used complete engine. There are a couple on ebay, another from a Jag scrap yard. So many variables there - unknown mileages, condition, fitment issues. I’d still probably pull the head for inspection and put a new gasket on, but I could get this option engine for approx $700-$1000 including shipping. Parts would be a wild card. Best case, bolt right up. Worst case, I get a second engine that also needs a top and bottom.
Again I’m doing all the work, and would be left with the original engine to dispose of/store until who knows when.
The intended result would be that I would get a working engine for less than a cost of the rebuild and less work for me to bring top and bottom together. Also have some choices for spares left over.

What do you think? What would you do?

Tough situation because neither of those seem to be great options.

What about cutting your losses on this car, looking for another one that runs, and then using your car as a donor car and/or parting it out?

Besides the fact that my wife would kill me? :sunglasses:

Other than the small issue of the engine, this thing is remarkably well preserved. Zero rust and everything functional. To part it out would be a shame, I think. I’d Lump it before doing that.

1990-1992 AJ6 engines are all the same so you have three MYs to pick from.


Seems like the going rate is $300 to $750 average.

I assume lots of gents on here have gotten over the fear of the wife killing them, although I agree it’s a completely rational consideration!

You’re right. It’s a beauty. I’m changing my vote to option two.

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From the photo’s the car looks far too good to break for parts. I think if I was in your position I’d look high and low for a replacement engine, one that you could see and hear running before you parted with any cash. Although you can never be certain you can usually judge quite a lot about the general condition of an engine that you can hear running. Obviously the coolant and condition of the entire cooling system would be a top priority in your assessment, but the xj40 engines have a great reputation for longevity if they have been well maintained in that department. Good luck with whatever you decide.

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Good options already mentioned. I would also (a) check with the usual reliable US parts suppliers/breakers, Coventry West in Georgia and Welsh Enterprises in Ohio, for known-good used engines and (b) try to find a (probably Northern or Northeastern) car with a horribly rusted body but good engine to use as a donor. My local pick and pull type yards (2 different ones) sell complete engines for ~$195. At least one of them also offers an (extra-cost) 12 month warranty.

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I would also source an engine for the car. Even if you get one that also turns out to be corroded and you have to buy yet another one, it will still be cheaper than the repair option.
I got a spare AJ16 engine for my x300 recently. It was marginally more expensive than buying the ignition coils I was after and now I have a complete engine should I ever need one.


As one of the few people who has done a full rebuild of one of these engines, I can attest that parts availability is awful. If you’re willing to live with something that isn’t perfect, a used engine is probably the way to go. The bottom end on these engines is typically very good, so its unlikely you’d have to worry about rebuilding the bottom end. Sounds like you’re already thinking about replacing the head gasket and a few other smaller items before you’d drop the used engine in, and I’d say that would be very wise.

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Fool me twice, shame on me!

But I think this thread has convinced me to source locally a suitable used replacement. In fact I think there is a 1994 with similar miles that is less than 100 miles away from me for good price. Thank you @motorcarman for the link reminder.

What differences would I find between my 1990 and a 1994 engine?

The 1993/94 engines will probably work but there are slight differences.
The cam covers are different as well as the injectors.
The GREEN band injectors have a twin nozzle but the engine management might work.
I think the Crankcase Venting is different. I used to know all the differences when I worked at the dealer years ago!!!

You can always swap intake manifolds and just use the engine long block if the replacement does not come with all the manifolds.

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Option 2: better to start with an engine with (possibly) less damage, and freshen it up.

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JT …

Well the block does look a LOT better after you cleaned it up :grinning: I feel your pain brother because I’m sure this was the last thing you expected to have to deal with.

There’s never a correct answer in something like this. Risk vs Reward … Economy vs Assurance.

It looks to me like the repairs to the block could be easily welded, but sadly at least one or two cylinders need to be resleeved. I would imagine that means the engine has to be removed. So Repair or replace the engine’s is probably coming out. With only 89K miles my guess would be that the bottom end of your engine is still in good shape, but that’s something that can be determined with the oil pan removed. Because of the constant lubrication I don’t believe corrosion will be a problem down there.

Why not pull the engine and have the bottom inspected. If that turns out OK (which would be my bet) then determine the cost of the welding, sleeving, and decking. If that price isn’t a whole lot more than a replacement engine I’d keep your known quantity original.

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Grooveman, your words are too kind. I appreciate you giving encouragement and advice.
I’m old enough to know that everything is Risk - of time, of money, of energy. But I jumped into the Jag with my table stakes covered. It’s a fun puzzle I get to figure out. You are right: it sort of feels like my puzzle has just doubled in size.
The good news is, I’m not afraid of it. It truly is a simple engine to work on and get access to in a home garage. I haven’t bought any special tools, in fact I had to dig all my SAE gear out of mothballs.

I’ve decided to go ahead and source a replacement engine, used obviously. I found one through the junkyard directly with low low miles and in a dry climate. @Grooveman , as you note, I’m sure the rest of my bottom end is pristine. (That came out weird) . The constant lubrication probably means the bearings and pump are good.
But I think rather than spend potentially 2k for a engine, I think I can get one for around 1k. And I’ll have two sets of long block parts to choose from. My wife took the news of a second non-run engine with surprising encouragement and patience. So… a second hand engine.

While thinking of a course of action - the clearest thing to be done remove the broke engine - it’s coming out no matter what. I found that after the stress and second guessing of getting the head off, everything else seems pretty easy to identify for removal and hoisting that AJ6 out of there.

I spent the last free days removing the radiator, the ac, the powersteering pump, the alternator, the intake, etc. etc.
The last thing to do is get the transmission disconnected. And pull 'er out.

Stay Tuned

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JT …

I certainly can’t fault your logic in going with a replacement engine. I think the poor condition of your’s (because of the corrosion) is the exception and not the norm. How many miles does your replacement have on it?

It’s great that your wife is a supportive wingman when it comes to your Jag project. Just remind her how much she’ll love driving around in the lap of luxury when you (and I have no doubt you will) get everything sorted. Please keep us updated on your progress

er …why is that? isn’t the car all metric (there are a few SAE remnants here and there but not much)

As god is my witness, this is the most confounding thing about this car… what IS it?
Because I am using both all the time. Metric AND SAE, its crazy. I spend most of my time trying to figure out what size nuts are!
What is a 1990 XJ40?

My gut feeling is you have made the right decision in replacing the engine. Looking at your pictures I can’t help thinking that previous owners have either neglected or haven’t known how to service and look after that engine. Although the bottom ends on these engines are renowned for being very durable and long lived, any engine would suffer from accelerated wear if the oil and filter changes have been neglected. You might spend a great deal of money having the head and block face rectified only to discover the remainder of the engine is badly worn and you are back to square one.

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This is the internal name for the sedan launched circa 1987 and first sold in the USA as an 1988 model. Known here and badged as an XJ6 but with other trim levels became the Vanden Plas, Sovereign etc

John I think the query pertains to what system WRT the threads used on the XJ40

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