Hi all!
Recently ran into a plethora of problems on my 86' Xj6 that all point to either a cracked block or blown head gasket (fingers crossed for the latter) and decided to get the job done myself instead of running the risk of somebody else making a mess of things.
I plan to use this thread to ask any questions that may come up during the process to avoid making a ton of unnecessary threads.

So far the process hasn't been too bad ive gotten everything disconnected from both the intake and exhaust sides of the engine aswell as the radiator, and am just about to begin pulling off the cam covers and removing the camshafts.

Before I did though I wanted to ask around on here on what the best method in doing this is as on the "jag-lovers.org" guide to removing it it makes a note of valve destruction if these are put back in incorrectly, im aware of a cam alignment tool available but have also seen a number of people saying it is unnecessary and can just be eyeballed.

Besides this I also found a considerable amount of oil on the throttle body butterfly valve I wasn't too concerned with it since im already in the process of removing the head and anything else is somewhat of a secondary issue at this point but figured I would bring it up and ask.

appreciate any and all comments or advice!

 

Update.
the heads off and sadly no good news just yet.
The gasket seems to be fine but the pistons are absolutely covered in soot and the valves are caked on with some sort of nasty reddish stuff.
(piston 1 is also badly scarred on its head this is due to a previous mechanics error and I dont think is the cause of the coolant loss)
the other pistons (besides being a little dirty) seem to be alright as well as the piston walls, so im a bit at a loss for what could be causing these symptoms.
there was for sure some sort of coolant entering the engine somehow as the hydrocarbon liquid test did indicate but at this point im a little lost and any help or guesses would be great.

(there's only one part of the head gasket that leaves me with some hope that it still may be that it would be the small peices that stick down into the coolant passages between each piston seemed to be worn down)

 

my current guesses in no particular order are
1) a hidden crack in the block (least favorable outcome)
2) a small crack in the head ( I noticed one on the picture I uploaded of the closeup of the valves above)
3)The head gasket is broken/was leaking somewhere I didn't notice.
any other places I should check before cleaning it all up and putting a new head gasket on and seeing if it leaks (will have the small cracks in the head machined if possible before reinstallation regardless)?

 

another very odd thing ive just realized is that piston 2 ( or 5 depending on how you count em) is completely spotless aswell as its valves, is this telling of any possible issues? maybe this is the piston that coolant is entering? although id expect the pistons burning coolant to be dirtier so maybe its the only one NOT getting fouled by coolant?

 

Piston 2 could be being "steam cleaned" by coolant. Commonly coolant getting into the combustion chambers does have this cleaning ability that we don't actually want ! Loss of coolant can be at strange places on these cars. For instance the heater valve on the bulkhead at the back of the engine compartment is vacuum operated. If the diaphragm fails, coolant can get sucked in to the vacuum circuit and obviously ends up in the inlet manifold where the vacuum is generated.

Other thing is that the inlet valve guides have seals on them which will be getting worn out so need replacing to stop oil getting into the combustion chamber.

 

Appreciate the info!
especially the "steam cleaning" bit as it gives some hope that it is simply the gasket.
regarding the intake manifold, there didn't seem to be coolant in there but there was indeed a good amount of oil as well as oil on the butterfly valve.
still, definitely worth looking into.
most likely outcome here is just replacing everything it could be (besides the block) put it back together and pray it doesn't leak
unless I happen to come across something that signifies it was for sure the problem.

 

I agree with what Fraser says: I think you have coolant getting into cylinder #2 and that has steam cleaned it. Looking at your photos of the block and gasket, I think the gasket has failed between the slot and the bore between cylinders 1 and 2.

I had a lot of trouble curing coolant loss from my slotted block engine and eventually discovered that pattern part head gaskets are poorly made with the firing rings not accurately placed. So after you have cleaned up and checked the block and head for trueness (skim if required) and absence of cracks, do ensure you buy a quality head gasket such as Payen to reassemble.

 

thanks for the reply!
the area you pointed out is the area I also had some concern in.
in doing some more research ive learned HGFs arnt always super noticeable (apologies for my lack of knowledge this is the first time ive ever taken the head off an engine), so this is hopefully the problem area where I am losing coolant.

I plan on taking out the studs and feeze cores/plugs and replacing them as well as trying to clean the inside of the block the best I can without removing it.

as for a few other things, do you think the scarring on the face of piston one is an issue? (It has been like this for a few years now and ive only recently had these issues)
and any advice on cleaning the valves/is it necessary?
also, during compression testing all cylinders read 120psi besides cylinder one (scarred piston) it read 90, after dropping some oil into the spark plug hole the reading jumped up to 115ish, is this indicative of bad piston rings? or could it just be due to the possible HGF being next to this cylinder?
finally, ive seen a few people mention two types of these later series 3 XK engines with the visable coolant passage between the pistons, one referred to as a "long stud" block (apparently less crack resistant) and the other a "Short stud" any idea which this engine is?

(its also worth nothing this engine only has 29k miles on it! with the head gasket supposedly replaced only a few years ago , although this was also done by the same untrustworthy mechanic who scarred piston one so who knows)

As always appreciate the help and info, you guys area. godsend!

 

You (and I) have the 8L version of the engine with the slots between the bores. This is a long stud version, as was the preceding 7L type, so the head studs go right through the block immersed in coolant and anchor in the base of the block. When you take out your core plugs, check carefully the condition of the studs near the base as they can rust away if insufficient antifreeze has been used (or perhaps anyway after 40 years or so). If in any doubt about the condition, you should change them or you might get what happened to me first time - one shears off when torquing down the head. Consider changing them anyway (and the acorn nuts) due to thread stretch each time they are torqued down. There is a lot of advice in existing threads on the forum about making sure the nuts don't bottom out on the studs before tightening the head down - the studs come in various lengths depending on the location fitted so you need to make sure they are fully tightened into the base of the block (with clean dry threads) and do not have too much length above the top face of the block.

I wouldn't worry too much about the marks on the top of piston number one, nor about the minor difference in compression test readings for that cylinder. Getting a higher reading after adding some oil does imply a bit of blow-by the rings but I wouldn't think that amound justiifes a full rebuild unless you are seeing noticable wear on the bores (unlikley with the low mileage you mention). When I had the coolant loss problem on my engine, the compression readings were all good despite the gasket failure. I think perhaps the gasket failure worked a bit like a one-way valve, allowing coolant into the cylinder, but not allowing cylinder gases out into the coolant passage. Just a thoery, mind!

You should definitiely remove all the valves and clean them up as well as the combustion chambers then decide if the head needs any work before refitting. I had to have coolant passage holes worked on as well as a skim because there was corrosion in the passages which had enlarged them. After that, when refitting the head, you will have the fun of re-gapping the valves with shims, but if yours were done recently as you say, they old shims should still be good to use.

If you are interested in reading about my saga, look here: https://www.jaguarforums.com/forum/x...nifold-253516/

 

Brought the head to a shop today for cleaning, trueness checking and pressure testing, Hopefully all comes back well but well see.

I went ahead and removed the valves prior to sending it off (Put them back on for pressure testing however) just to see what they looked like and what the guides looked like.
it seems some of the intake guides have either sunken into/twords the camshaft or are cracked (the valve guides not tappet guides)
the exhaust valve guides all seem to be sunken in aswell so those will likely need replacing.

Also after further inspection ive learned my valves were never shimmed properly but were instead shaved down so that will be fun to deal with assuming the head itself isn't shot.
any recommendations for measuring clearance between the buckets and bottom of the cam lobes and determining what shims I need?

is a feeler gauge, some math and a lot of patience the only way to go here?

ive seen several people say shimming is the way to go instead of shaving and they only shave when the smallest shim is still too much, my question is what is the downside of shaving the ends of the valve stem to fit instead of shimming?

finally where do you guys recommend getting shims from? ive seen a few different places with varying prices and seemingly different looking shims, just want to be sure im getting the correct things!

 

Basically, what you do is assemble the head with cams using the shims you've got, noting what thickness you've inserted into each of the 12 buckets. Turn each cam and measure the gaps. Then knowing what the gap should be, you calculate the shim you need, reassemble with all the "correct" shims, and recheck the gaps. Of course usually you find one or two are not correct despite all your care and diligence, so you then have to recalculate for the incorrect ones, and reassemble.
The shims have a letter etched onto them, but this will have disappeared when you remove them; you'll only find the letter on new shims. I used a Moore and Wright micrometer of the old type bought specifically for the job in the mid-eighties, , and it is still sitting in my tool drawer ! A caliper gauge can also be used, but a micrometer is more accurate.

 

I would use one of the Cometic MLS gaskets that Terry's Jaguar sells. They are more leak resistant than the standard factory kind. They also come in various thicknesses to adjust the compression ratio if the head has been milled excessively. However, this is more of an issue with engines with 9:1 compression than the 7.8 in the XJ6.

Here is an example, but I forget what the standard thickness is - you'll have to measure your old gasket. https://www.terrysjag.com/product//TJP500.html

 

You can grind the valve stem tips, but not a lot. The reason is the shim has to sit above the spring keeper surface and if the shim is too thin then the underside of the bucket can contact the spring keeper and cause the valve stem keepers to lose their position and the valve can drop out.

 

Thought it was about time to update this thread


Just painted and added new head studs and timing gear.




Head was rebuilt and valve lash set.

It's finally coming together!

 

So that looks like a bit more than just fitting new valves. What's the story? Its looking great!

 

Not sure how I got directed to this thread?! Thought I was posting an update on the engine I'm rebuilding for my 66 S Type I started on the old spoon forums