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Jag-lovers XK Engine Tappet Retainer Stakedown FAQ

Jag-lovers XK Engine Tappet Retainer Stakedown FAQ

Lawrence Buja

Part of this file is also available at

A. Overview:

Jaguars with the classic XK straight-6 dual-overhead valve engines are prone to having the steel tappet guides in the aluminum head come loose and crash around inside the engine with disastrous results (see section C).

A common fix is the "tappet guide stakedown kit" which mechanically holds the tappet guides in place.

B. Questions:

    • This problem does NOT affect the V12 engined Jaguars. (all years) This problem does NOT affect the XJ40 and X300 sedans. (post-1987)
    • This problem may occur in any of the Jaguars with the classic XK straight-6 2.4L, 3.4L, 3.8L and 4.2L displacement engines.
    • Since these failures appear to be related to the degree of heat cycling which the engine experience, the most susceptible engines seem to be the exhaust sides of later, emissions equipped, 4.2L in XJ-6 sedans in the years 1974-1987.
    • The most common fix is to install a "tappet guide stakedown kit" which mechanically holds the tappet guides in place.
    • The stakedown kit are three small metal plates bolted to the head underneath the camshaft on the exhaust side of the engine (see question 8). These metal plates hold the press-fitted tappet guides in place.
    • If you own a 4.2L XJ6, you stand a non-zero chance of destroying your engine. Replacement XK engines cost around $US4000. See the first posting in section C.
    • The retainer kit is relatively inexpensive, around $30. Expect to be charged around $300 for a mechanic to install it.
    • This is probably not a do-it-yourself job unless you are very experienced with engine work (see the postings below).
    • Old graybeard XK mechanics have been known to use machine-screws screwed into the aluminum head to mechanically hold down the tappet guides. Do this at your own risk.
    • The cheapest and easiest way is, with the engine off and cool, to take off the oil cap and feel under camshaft, between the first two tappet locations, for the metal retainers mentioned in question 8.
    • Viewed from the top, your engine looks like:
    •       ___       Intake side
           |   -------------------------.
           |                            |  Figure 1  (top view)
           |   -------------------------'
           |--| *   *    *   *    *    *
           |   -------------------------.
           |                            | 
                      Exhaust side
    • Take off the valve cover on the exhaust side of the engine.
    • Disregard the round camshaft which sits on top. Underneath the round camshaft, you will see the tops of the 6 exhaust side tappet guides staring up at you as shown in Figure 1.
            ___       Intake
           |   -------------------------.
           |                            |                      
           |   -------------------------'
           |## -------------------------.
           |##+ O   O    O   O    O   O |  Figure 1  (top view)
    • Again, disregarding the round camshaft, the retainer kit in my XJ6 looks like:
    •      |--|
           |## -------------------------.
           |##+ O===O    O===O    O===O |  Figure 2a  (top view)
    • where each === is a metal retainer.
    • From the side, it looks like:
    •      |##+                         
           |##   ===      ===      ===  |  Figure 2b  (side view)
           |##  O   O    O   O    O   O |
    • The retainers themselves are metal plates which look like:
              ___________________          Figure 3a: Top view.
             /                   \   
            /    *          *     \                * indicates a bolt
           |                       |
                 *          *              Figure 3b: Side view
                 *          *
                 *          *
    • Note: The retainers are not centered on the 9 or 3 o'clock positions, as shown in Figure 2. Rather they are shifted outboard from center and grip the tappet guides at the 7 or 4 o'clock position.
    • Also, I'm assuming the existence of the lips shown in Fig 3b. For some reason, I think they're there, but I've never had the retainers off, so I haven't looked underneath them.

C. Postings from Jag-lovers on the subject:

Randy Wilson

My 1985 XJ6 4.2 (88,000 mi.) developed a tapping noise recently. My mechanic removed the valve cover and discovered a broken metal sleeve (valve lifter). Unfortunately, metal pieces are circulating throughout my engine. I'm looking at an engine rebuild or a new engine. My mechanic says he can install a new engine for around $7,500. A mechanic who read my message posted in the CompuServe Auto Forum says that new engines are not available and that a rebuild should cost between $3,500 and $4,500.

I'm most disappointed. I was under the impression that the XK engine was one of the best. Has anyone else experienced this problem? And, can anyone shed light on this new vs rebuild dilemna. I'd appreciate advise.

Mark B.

Common enough. You missed the critical beginings of the tapping, when the tappet guide first started working it's way up (it broke the tappet guide, BTW, not the lifter). This is exactly what the stakedown kit is for.

Rebuilt engines (including installation) typically run in the $4K range.

However, what evidence do you have that the entire engine is shot? Yes, the tappet guide needs to be replaced. If the damage is not too severe, it is possible to replace it and install the stakedown kit with the head still on the car. However, I do not recommend such things. Pull the head, do a proper installation of the guide, and a valve job while you're in there.

If the engine has had some milage since the guide got broken, I would not be too concerned about the metal pieces. The big chunks will migrate to the bottom of the sump, and possibly out during the next oil change. the littlest ones, the filings that can make it through the pickup strainer, will get trapped by the oil filter. The biggest danger is the pieces getting caught up in the timing chains/sprockets on their migration downward.

John McDonagh

I have heard of the problem with loose tappet guides but it is very uncommon in New Zealand and no one here "stakes down" their guides as a matter of course. This would tie in with the posting about emission controls and higher engine temperatures. We have no emissions requirements on vehicles and overheating problems in Jaguars are also uncommon so I would assume all these things are interrelated.

Silas Elash

I have heard all kinds of opinions on the list. I talked with a mechanic about it, and he told me that the problem really started to appear on the XJ6 when emissions testing required a higher combustion chamber temperature to get the emissions down. So the later model cars have a more restrictive water inlet into the head. This higher temp causes the problem due to the continual cycling from hot(now hotter) to cold, etc, etc...- over time the cycling loosens the tappet sleeves. He told me that the problem was unusual on an older car like my 62 MK2, unless it had been over heated. The older motors run cooler and thus have less stress on the tappet guides due to the lower temp range they cycle thru.

All any of this tells you is that odds are lower on an older car. If the car has been run hot- maybe you get the problem. Later model "hotter" engine, more likely to get the problem. I would think that a very old engine could also eventually have the problem, just because it has gone thru more cycles???

Anyway, thats the scoop as far as I can tell. Predicting if your car will have the problem, is like rolling dice. I guess most of us don't feel lucky- or don't want to risk it, so we stake them down. I don't know if I would do it just for the sake of doing it - if I had no other reason to open things up. In fact I have not done it on my 84 XJ6 (59,000mi.), but it has relatively low miles and I am going to wait.

Good luck,

Jeffrey Gram

Hi, As some may remember I fumbled my way to mount a stakedown kit with the head on.

It is not as easy as it sounds the hardest part being drilling exactly where you want to drill. The drill bit is very prone to "wandering" while getting the first grip in the light alloy, and the tolerance on the holes in the stake down plate do not allow much error. I had to drill up the holes on several, and I damn near splintered a tapped guide, when "easing" one into position with a sledgehammer. One tappet bucket didn't fit after the stake down kit was mounted, until i realised the guide was under deformation..... Own fault of course. Off again and drill the hole in the stake down plate bigger to correct for the drill position error. One fatal error and the whole work is lost and professional help is needed to get head off , new guides in.... $$$$$$$$$$$$

Dont forget you need to get camshafts off, where there are other traps laying waiting for the innocent DIY'er : you could lose a valve sprocket bolt or lock plate down the chain housing - this will set the repair back by another two weeks, getting either the engine front off (bonnet, radiator etc.....or turn thecar upside down and shake it vigorously....

Or you could get the valve timing wrong an re-assembly - Just ask Ryan Border :-)

Still want to do this ?

OK :

Tapping in aluminium requires the tap to be wetted with alcohol, however for this particular operation a more sticky material is better to get the cut bits up. Compressed air is great (when all other oil holes are covered up with cloth.

There is a way to tap which is called two step forward, one step back, two step forward, etc. This MUST be obeyed or the risk is a broken tap in the head and then you are really stuck.

Holding the tap perpendicular to the head is also not that easy especially if you have never done it before., buy extra taps and train yourself on a scrap piece og aluminium.

Frankly speaking, I would not attempt this if I hadn't been drilling and tapping for 25 years now on a DIY hobby basis, (Ok less experience will also do). But realise there is a fair chance to get it wrong.

I will send you my description from february this year.

Tony Gardner

I have just completed fitting a tappet hold down kit for an XJ6 SIII, with the head on the engine, and thought the list might benefit from my experiences. First of all a caution about undertaking this job (previous JL posts have given similar warnings). If you have never broken a tap into a piece of metal, your cylinder head is not the place to get the experience, so I suggest you do not attempt this without a lot of practice. Also, the job involves removing the cam shafts which can, in itself, be intimidating on the first try.

My main concern was to keep swarf (metal chips) out of the oil galleys. Overall, the job proved a lot easier than expected but the swarf problem was much worse than envisioned. The alloy of the head tends to fragment during both drilling and tapping and gets everywhere (bits even found there way onto my windshield). Therefore, the rule is, use lots of masking tape and seal every aperture through which swarf could conceivably enter. A shop vac is handy to suck up the excess.

For drilling it is essential to use brand new, good quality, drills. Two are needed, a tap drill (the instructions for the hold down kit should tell you the size of the tap drill) and a drill the size of the holes in the hold down plates. This latter is used to spot drill the position on the head for the smaller tap drill using the hold down plate as a jig. Hold the plate in position using a tiny, three quarter inch jaw, G-clamp (obtained from Sears in the US). The clamp can be inserted through the obvious elongated holes which reside between each set of valves. Note, that without spot drilling using the larger drill, and the plate as a jig, it is very difficult to prevent the tap drill from wandering off position.

The next challenge, is to avoid drilling through the head into the oil galleys beneath (this is not a problem with the head off the car as the swarf entering with the drill is easily cleaned out). I used a piece of thick walled rubber tube with an inside diameter slightly less than the tapping drill diam and cut to allow the drill to protrude just beyond the length of a hold down plate retaining screw. This is slipped over the drill and acts as a depth stop against the plate. When the holes have been drilled, keep the plate in position as a guide to start the tap. Cut the threads using a quarter turn down and a half turn back (to break the chip). As a lubricant I used WD 40. Because this is a blind hole being tapped, a finishing tap must be used after starting the threads with a tapered tap. I used a taper tap to start all of the holes and then ground off the taper to bottom the tap. This is the point at which it is very easy to break the tap in the head - be careful, extracting a broken tap can be a nightmare.

After drilling and tapping the holes with meticulous care I was chagrined to discover that on three of the tapped holes, the bottom thread had broken through into the oil galley. I would not have noticed but I attempted to fill each hole with solvent to remove the WD40 prior to using Loctite on the hold down screws and found the solvent disappearing into the head. I managed to retrieve all (I hope) of the swarf after swabbing inside the galleys for an irritable two or three hours.

The process is so much trouble I recommend you do both sides of the head, as the inlet guides have been known to come loose and the drilling and tapping is a minor part of the whole job. If you do not have the skill necessary to undertake this, and again, I stress this is no place to get experience with metal tapping, I suggest you tell the shop you select that you want to examine the head after they drill and tap the holes. Then you will have a chance to look for any evidence of breakthrough of the threads (pour a little solvent into each hole). If it has occurred, no matter how slight, chips will have fallen through to the oil galley but with care and patience they can be removed. However this will probably have to be your care and your patience, at least to be done properly. In any case, there was probably never a better time for an oil change.

Rich Mentions a New Possibility

I bought the kit at Terry's Jaguar through the mail. You can look up the phone number. Like I said it was about $34.00 but don't forget a valve cover gasket (another $5.00). Now for the important stuff. I have a lot of more tips but I'll give the basics and you can repost with any more questions.

The kit has self tapping screws. No silly tapping required. Very smart. All you have to do is remove the valve cover. Fill the oil return holes (under the cam) with towels to prevent any shaving from falling down in. You do not need to remove the cam!!! Very smart. Have someone hold the high quality plate in place and drill through the holes into the head. Clean up the area and screw the plates down. Replace the valve covers. You are done.

Now the most important stuff. Use plenty of lubrication during all the steps. I used a cobalt self starting and self centering bit; I believe this to be very important. It will help eliminate creeping (a very big problem without this bit). The bad thing about this bit is that it will leave a pointed hole (I hope you understand that). This should be straitened up with a regular type bit. Definitely use a stop on the bit. Depth control is vital. On this soft aluminum the bit will tend to grab and go in too far. Very bad. Unfortunately the room for this stop is limited due to the cam. I used a metal brake line and slipped it over the drill bit to prevent the drill from going to deep. Sorry if I am being too rudimentary but I don't know all of your experience levels. The directions tell you the right size drill bit to use and try to be straight. Two more tips and I will go. The shavings are a pain. I tried to clean, pick and wipe them out ... no good. You must recheck that all the oil holes are still filled with towels and cover the timing chain. Use compressed air to blow out the shavings. The aluminum is so light it flies away. I am very meticulous and I after a good minute or so of air I couldn't find the smallest piece of shaving. Wear safety glasses. Lastly, go very slow with screws, use a lot of lubrication, and make sure you drilled deep enough (but not too deep) or you will bottom out the screw and pull out the threads.

I hope I helped. I have done almost everything on my car so if you need help on anything don't be afraid to ask.

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