XJ6 & XJ12 Series I, II & III 1968-1992

Engine rebuild advice

 
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Old 05-31-2016, 09:11 PM
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Default Engine rebuild advice

I realise this may be a how long is a piece of string question but, I am interested in opinions on how far to go with an engine rebuild.

Some background.
The engine is the 4.2 in a 1971 XJ6. At this stage I have not tried to start it. When purchased the PO said it ran when the car was parked up 14 years ago. The head will be coming off at some stage as there is a helicoil on one of the plugs that I would like to remove and have repaired. The head will be refurbished at the time. The engine will be removed from the car and welsh plugs removed to allow for cleaning of water passages in the block.

So to some questions.
1) should I try to get it running before taking the head off to try to determine any other problems first?
2) would you expect that replacement of bearings, rings etc will be required, or should I just do this while the engine is partially dismantled?

Any other thoughts would be appreciated.
 
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Old 06-01-2016, 01:26 AM
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Here is thread my thread on a simple head gasket leak, came in just under 7K. Good luck.
Just a bit of light reading.

https://www.jaguarforums.com/forum/x...157830/page10/
 
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Old 06-01-2016, 01:56 AM
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Thanks Clarke,

I have read your thread. I don't recall though, what was the reason for not continuing the repair on your original engine?
 
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Old 06-01-2016, 02:04 AM
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Originally Posted by MalnFaye View Post
Thanks Clarke,

I have read your thread. I don't recall though, what was the reason for not continuing the repair on your original engine?
Once we broke the stud off, it was a choice of repair the broken stud and risk the chance of breaking more. At that point we had a 40 year old can of worms and a quick calculation came to many $$$$$ for a strip down and rebuild.(not knowing the history or internal condition)
A short engine was on the shelf available at a local Jag engine specialist for not a great deal more than the parts and machining I was up for anyway, so decided to take that path.
 
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Old 06-02-2016, 03:59 AM
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Pull the engine apart and see what you find, personally i would refit a later model series 3 head with the bigger standard valves ., if all looks okay inside the engine i would re ring and new bearings and seals but thats just me,
When i bought my series 3[3 years ago] it was last on the road in 2007 and had sat but it did run with a miss that turned out to be a bent valve, on the pull down i discovered that the cam followers had all been staked down and the block was resleeved with top hat liners, crankshaft was 10thou under, i still replaced all rings and bearings and timing chains just so i know what i have, importing the parts from all over the world at the right price
 
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Old 06-03-2016, 08:46 AM
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Malcolm:


Three comments:


1. The Helicoil is the repair. As good as it gets. I suppose the hole
could be TIG welded, drilled and tapped, but, why? Steel threaded devices into alloy holes with threads has always been a bit problematical. Helicoils fixed a few issues in an old Corvair for me.


2. Engine fixes range from merely swapping in new rings and bearings and "grinding" the valves. Old tech, but often fine. Labor likely to exceed the parts costs. Or, "all the way". Rebore the cylinders, new pistons and rings. Grind the crank and install new
bearings. Rebuild the head with new cam bearings, springs, and valves. New cam chains and oil pump. Toss ion a balance of the recip parts. A lot of $'s, but done well means a great engine, as good as or even better than new


3. Given your engine, I would seek to fire it up. Access it then. Smokey, noisy, oil pressure, etc. Once fired and run a bit, shut it down and do a wet and dry compression test. Oh, check for blow by and oil in the coolant. Now, you will have a solid basis for decision making. Old axiom in my camp. "Gather as many facts as you can to evaluate and decide". Very useful in my former profession. Still works!!


Carl
 
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Old 06-03-2016, 09:45 PM
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Thanks Carl for your thoughts.

I seems to make sense to see what's working before I start pulling things apart.
 
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Old 06-06-2016, 05:42 PM
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Is it a long stud engine ? Engine number will start '7Lnnnn'.


Once you have the head off, if it is long stud, look for cracks between the bores. If they are present, it is not worth rebuilding the engine unless you totally strip it back to a bare block and get top-hat liners put in. This or find an uncracked block ! Hooter was lucky as his engine had the top-hat liners.
 
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Old 06-06-2016, 10:41 PM
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Default Long Stud Engine

Originally Posted by Fraser Mitchell View Post
Is it a long stud engine ? Engine number will start '7Lnnnn'.


Once you have the head off, if it is long stud, look for cracks between the bores. If they are present, it is not worth rebuilding the engine unless you totally strip it back to a bare block and get top-hat liners put in. This or find an uncracked block ! Hooter was lucky as his engine had the top-hat liners.
All series 1's are 7L engine numbers, early series 2 have the 7L. Later series 2's and all series 3's have 8L engine numbers .
So all series 1/2/3 are long stud engines.
7L 1968-1975
8L 1975-........

At best the 4.2 litre Jaguar/Daimler engine block could be described as suspect and its quality further declined throughout its production. It was designed in the early 1960s to give more torque and better low to mid range performance than the 3.8 litre engine, which it genuinely did. Early examples (fitted to the last Mark Xs, the E-types and the 420s until about 1968) are easily distinguishable from the XJ6 blocks by two fewer waterways at the rear (watch your cylinder heads), three large core plugs per side and studs screwed directly into the block face. The later engines are usually prefixed 7L (all 4.2 litre engined Jaguars from 1968 to 1975) or 8L (1975 onwards) and these are the ones covered in this article.

The pre-XJ6 block was said to be improved upon by the 7L block, which had a more efficient internal cooling flow. The problem was that the cylinder head studs screwed directly into the base of the block, through the waterways and, if the correct coolant is not used, then they will rot out very quickly. These studs are also twice as long as the pre-1968 blocks, allowing more stretch and therefore more variation in clamping pressure against what has been set with the torque wrench and this makes it more prone to head gasket problems. This improved block cracks, usually hairline cracks appearing in the block, eventually becoming stepped (when one side becomes slightly higher than the other) and the liners drop. The 8L block, a strengthened 7L block, cracks even more than the 7L, and this may be due to an increase in thermostat temperature or to unweathered blocks being used or, possibly, a reduction in standards under British Leyland.
 
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Old 06-07-2016, 08:34 AM
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I recognise that text, it comes from the AJ6 Engineering website.


Cracking of the blocks was endemic and only cured by Jaguar in the early 80s, with the slotted blocks. These didn't crack, but even so, headgaskets were pushed to get past about 85k miles. My own 1980 had said syndrome and was only cured by rebuilding my engine around an uncracked block. Uncracked blocks are rare, so I was lucky. I had no more trouble with the engine after that; plenty of trouble elsewhere, mind you !


The XK engine of 1948 was way, way, past its sell-by date in the late 70s, early 80s, and the aluminium AJ6 engine that replaced it was far better, as it had to be. The AJ16 was even better. Then came the disaster with the V8 !!
 
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Old 06-08-2016, 06:03 AM
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Originally Posted by Fraser Mitchell View Post
I recognise that text, it comes from the AJ6 Engineering website.


Cracking of the blocks was endemic and only cured by Jaguar in the early 80s, with the slotted blocks. These didn't crack, but even so, headgaskets were pushed to get past about 85k miles.
Once we had my head off we discovered my engine was a 1983 (S3) slotted block. Same as we replaced it with.

Engine rebuild advice-dsc_5443.jpgEngine rebuild advice-dsc_5568.jpg
 
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Old 06-10-2016, 04:15 PM
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Originally Posted by o1xjr View Post
Once we had my head off we discovered my engine was a 1983 (S3) slotted block. Same as we replaced it with.

Attachment 131442Attachment 131443
Whilst the slotted-block engines are not perfect, at least one has the certainty that a head gasket repair will last a long time. On my engine before I was informed on the cracking problem, I put a head gasket on that lasted about 6000 miles before it blew again.
 
 
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