Okay, I already made a little post about this in the X300 section, but time really is of the essence because I'm really tired of having a broken car.

Long story short I broke two of the valve cover bolts on my 1997 XJ6L. Assuming I don't have any trouble removing the broken bits, can I use these other bolts in their place? They are the same length and thread size and all that such.

imgur: the simple image sharer

The black is the original. If I can't use these new bolts, where can I find the OEM style bolts?

 

OK, I'm gonna step out on a limb here because the best rule by far is to use the right part of the job.
Secondly I know NOTHING of your car, motor or its design as I am new to the Jag world.

That out of the way, I see no reason why you could not substitute the bolt until a proper one was found. This is an educated guess with a few conclusions from the image and info you provided.

First, its a "valve cover". These typically share no load or stress in their design. Bolts normally used are for clamping pressure only. I say this because normally when I see a wide un-threaded shank, it is usually installed where "shearing" forces require the extra thickness. I just cant see that as an issue with a valve cover.
So another possibility is for the un-threaded shank to seat, and provide a solid vertical post to keep the cover in an exact location. If you have several others still in tack, your cover should not shift about on its seat and you could get away with using a standard bolt.
Its my guess that the shank design would most likely be to prevent over-tightening the cover, as it would seat against its mating surface on the head.
A forth possibility is the solid shank is used for oil retention? Maybe through a close tolerance fit, or even a rubber seal in the gasket.

All that has me believe you could use the threaded bolt provided you are able to seal against oil seepage, and not over tighten it (remember the shanked bolt will seat and not tighten beyond that point where your temp replacement can be over tightened.)
If you are insistent in trying, I would clean the threads, use RTV on the top quarter of the bolt, and maybe a little lock-tight on the base. Hand tighten via screw driver handle only to avoid damaging the cover.

Again, I'm against using make shift hardware in general, but believe you can find a way to get by until the correct part is ordered.

Can't stress the caution on over-tightening enough, because you expose yourself to a far more expensive repair if you crack or damage your valve cover.

I now fall back to the position of "I take no responsibility for damages caused by my recommendations". The correct bolt for the job should always be your first and best choice.


BOL
Vince

 

When I looked at your pic, it became plain how special the Jaguar bolt is, being specially machined to have a very wide shank far larger than the securing thread at the bottom, which seems only about 1/2" long. What is also puzzling is how the original Jaguar bolt on your engine could have got damaged, as it would not have been done-up all that tight, and should have been easy to remove. I suppose over time, the steel of the bolt "glues" itself into the aluminium of the head from corrosion.

I am not totally familiar with the AJ16 engine, but if this is one bolt of many similar ones, then you can probably get away with using your replacement, but do check very thoroughly whether the Jaguar design serves another function apart from holding the valve cover down. Engine designers don't use special bolts if they can get away with normal ones because that special bolt will cost probaby 10 times more than a standard bolt. BTW your proposed replacement is called a 'set screw', because it is threaded over its whole length. Other thing I noticed is the Jaguar bolt head is of greater diameter to the one you propose. I would expect there to be a sealing washer underneath the head, and suspect your new bolt will not secure it properly and oil will leak out.

If it was me, I'd use it as a temporary fix, and get the correct parts as soon as possible, assuming they are available, of course. Looking at a couple of pics of the top of the engine, (on the internet), these special bolts seem to hold down the cover and do nothing else, but the wide shank looks as if its there for a location purpose, (like a dowel). Are all the bolts the same ?

 

Hi, another post !

I had a look around the internet, and found this: -

Jaguar ISOLATOR, BUSHING, FOR CAM COVER BOLT. - NBC2575CA

It is the sealing bush for the cam cover, and immediately makes it obvious why Jaguar use the special bolt. The wide shank passes through the bush which has internal protrusions to make a seal, whilst the head of the bolt clamps down the bush and seals the outside of it, (apart from the bush itself). The bush is clearly made of a rubber-like compound, likely to be neoprene or suchlike, so the long shank of the bolt is of a certain length to stop overtightening the bolt and wrecking the cam cover.

So you proposed bolt will not act correctly on the sealing bush unless you can get a spacer the same length as the original bolt made up, and also put a wide washer below the bolt head to give extra clamping area, as the head of the new bolt is too small.

 

Yeah. I'm going to attempt a trip to a salvage yard, but at the moment, the only Jag they have in stock is a 86 Xj6 and I'm quite worried they'll have different bolts. It's also a rainy day and I may not be able to get much of anything done.

The old bolts broke off because a short 5 minute youtube video on how to use a torque wrench is not enough instruction to teach me how to use a torque wrench. I over tightened the bolts and they broke.

I have the seal and washer that are used with the original bolt, and to the best of my knowledge and by the looks of things the bolts are used to keep the valve cover set and to stop oil leaking from the top where the head of the bolt rests (hopefully by using the seal and washer with the new bolt oil won't leak).

At the moment I guess my current plan of attack is to remove the bits of broken bolt and install the valve cover with the two new bolts (in addition to the old ones too of course) and see how that works (still searching for OEM style bolts).

 

An '86 in the junk yard is likely an XJ6 Series 3 with the XK engine of 1948. This is completely different from your AJ16, except it still has 6 cylinders. I am not sure about the AJ6, though; this might have similar bolts. The AJ6 was the engine that superseded the XK engine in 1986 (in the UK) in the XJ saloon. The new saloon was the XJ40 model. The AJ16 was a development of the AJ6 on sale in the US from 1987

Apologies if I have told you something you know already !

I haven't found any of your bolts on the internet, so you will maybe have to use the one you propose, with a length of tube cut to the correct length to mimic the Jaguar wide shank, and a wide washer at the top to mimic the wider head of the bolt.