4.2L engine rebuild question
 

Hello all,

After trying unsuccessfully to get the stuck engine in my '86 XJ6 un-stuck, I ended up pulling it and the transmission. I still haven't successfully gotten it unstuck - even with the head off, the oil pan removed, I can't see any reason it won't turn. Perhaps I'll find a seized bearing when I start to remove pistons/crank, but the oil was clean and I just don't see any evidence of it.

But regardless of this I may as well fully overhaul it. Is there a good guide for overhauling this engine that anyone can recommend? Or best source of rebuild kits (in the US)? Not sure yet if new pistons will be necessary. This is my first time working on an XK.

Thank you!

loosen the con rods and crank bearing caps, use a spray lube or fine machine oil (baby oil) around the edges of the pistons to get lube down the bore & rings, then try turn it

can't you get a replacement engine where you are ?

Thanks, will give it a try.

There is a used junkyard engine available nearby. But it seems likely I’d need to rebuild that one too. I figure I’ve got the old engine out and there doesn’t seem to be any catastrophic damage, so I may as well do at least a cheap rebuild.

hate to say it but a rebuild is never cheap. Machine work and parts will cost thousands.

if you can free it up easy, just check crank shaft mains & big ends, then you'll know if it's worth while or not

Now you've got the head off, is it a slotted block you're looking at ? If it is, then just a light skim of the block deck will be OK, not forgetting to bolt the timing cover on before you skim. The timing cover is part of the deck face. If you don't the head gasket may not seal properly at the front of the engine. Also check the timing cover for corrosion around the coolant passage which allows coolant to flow into the block from the pump. It is not unknown for corrosion to get so bad that coolant escapes into the timng chest and into the engine oil.

Also religiously clean out the coolant jacket in the block and renew all the core plugs. Plus take out all the crankshaft plugs and clear out the crud. Replace and stake them.

Much appreciate the advice! Just a few questions...

When you say "a slotted block", I assume you are referring to the slots between cylinders? If so then yes. Here's a pic - the block is actually in very good shape, with very little corrosion and the cooling system was very clean (oily grime notwithstanding):
https://cimg2.ibsrv.net/gimg/www.jag...4b142b70a3.jpg
Is skimming the deck really necessary if it cleans up nicely?

Also here's what bearing surfaces looked like:
https://cimg5.ibsrv.net/gimg/www.jag...d2486a2345.jpg
https://cimg7.ibsrv.net/gimg/www.jag...a0d324a456.jpg
One of the rod bearings wiped clean

I forgot to take a pic of the crank bearing surfaces - they're quite good, although not perfect.
Here's what cylinder bores look like:
https://cimg8.ibsrv.net/gimg/www.jag...4a490bc58c.jpg

Given all this I'm thinking of not worrying too much about deck skimming, opening up all the plugs, etc. First a careful but not too thorough cleaning, then I would have the crank polished (TBD if necessary), replace all bearings and seals, lightly hone cylinders, new piston rings, new timing chains, and a valve job (head looks pretty good, so TBD if necessary). Am I grossly underestimating the size of this job? Tell me if I'm nuts. I have to be honest here - I have done a lot of repairs but this would be my first engine rebuild. Trying to create a reliable driver but not spend a fortune.

I still have one stuck piston to get out too - trying to be very careful to not score any surfaces or damage the block.

going well, check if the ridge in the bores needs a skim, stuck piston, thin machine oil or dilute engine oil down around the piston edge, leave for a while then try move up a little then down then up and so on till it feels free to move out......do you have a 3 arm deglazer or brush type for the bores?...can you post a pic of the studs into the lower block?

Good news today - after letting the stuck piston sit with a bit of PB Blaster for a couple of days it came out with a couple of bonks with a 2x4. The bore actually looks pretty good - I think it should be pretty clean with a light honing.

I don't have anything for the bores yet - will need to buy something. Pics:
https://cimg8.ibsrv.net/gimg/www.jag...98f3d3f6d5.jpg
(middle cylinder in this pic was the stuck one)
https://cimg6.ibsrv.net/gimg/www.jag...3d4452670f.jpg
View of block from timing cover area

looking good, a 3 leg deglazer or bore brush will do, either of those should clean up those ridges, looks like you'll be able to do the bare minimum to get it running again.....i'm sure you'll get lots of expensive advise on how many thousands you should be spending but i'm a cheap-o, don't cut corners - just do it on the cheap...

That's exactly what I'm shooting for! Cheap but decent. Not looking for perfection or big upgrades, but a solid runner.

i have a 75 xj6 s2, same motor, what i'm working on next is an electric oil pump to pre-prime the motor before start, mine sits for quite a while between drives, so elimate that initial start up rattle and a back up if the oil pump fails

I may have been overly optimistic when I looked over this engine block initially. Taking a closer look one of the cylinders has me worried. Thoughts?
https://cimg5.ibsrv.net/gimg/www.jag...f4c98b922.jpeg
https://cimg6.ibsrv.net/gimg/www.jag...b8247cec7.jpeg

Is that a crack going allll the way down the cylinder? Is this block now scrap?

At first I was thinking it was just surface residue but I tried to scrape it away (probably shouldn’t have) and the more I look at it the more it looks like a crack. Might have to take it to a machine shop for evaluation.

A crack to me seem to be unlikely given the construction of the block (no wet liners) but I doubt that you will get away with a light honing as the ridges in all cylinders seem to be quite deep. But difficult to judge from the pictures only.
If the deck of the block cleans fine I think you may get away with it without skimming. but I advise to have the head checked and if necessary skimmed as they do have a tendency to distort.

Being a 4,2 Liter it shall have dry liners if I'm rigth.

Crack ?
 

Get a dye penetrant kit !

Mistake. sorry

The slotted block engines don't have liners. Liners were used on the 7L and 8L blocks to cover machined coolant passages in the block. To be frank, the 4.2 was probably the worst of all the XK engines, although the earlier 4.2s, with their short head studs were mostly OK.
If you look at the videos on ths YouTube site, you'll see these coolant passages exposed. The block was being restored to use after suffering cracking between bores, by the use of lipped liners
https://www.youtube.com/@JAMSIONLINE/search

Accusump
 

Have you heard of an Accusump? It T's off the pressure port and saves it in a remote "can" under pressure. So before you start the motor you open the valve ( manual or electric) and prelube your motor. If a pump failure, it'll give you a chance to stop the car.