Hello everyone,

I made a bo-bo: I broke all 13 of the cam cover bolts while trying to replace the leaky cam cover gasket.

And after trying, and subsequently failing, to remove the broken bolts, the only solution that I can think of is to replace the entire cylinder head.

Which leads me to the next problem/question: Is it possible to swap a cylinder head from a n/a X300 engine onto an XJR6 engine?

I tried looking up the parts on Jaguar's heritage website but was unable to determine if Jaguar used the same cylinder heads on the n/a and the supercharged engines. Maybe I am missing something?

Their technical staff was not able to find a definite answer either. And the various eBay-ers/online specialists I contacted have not been able to provide me with an answer...

I was able to conclude, from the information in the service manual, that the camshafts are in fact not interchangeable. But I should still be able to use my old camshafts if the cylinder head itself is the same across the entire X300 range.

Help?

Kind regards

 

Can't you find a way to extract them?

 

I think an XJR cylinder head is different, due to lower compression ratio because of it's forced induction

 

The pistons will probably be different for the lower compression. But it's going to be far cheaper to have a machine shop remove the bolts. A used head will not be be very expensive, even if you have to order in the US. Try Coventry West, one of the forum sponsors.

 

Not to pick.... am just curious so we know what "not to do", but how did you break ALL of the cam cover bolts?

I have to repair a leak in my #4 spark plug well sometime in the near future, so definitely want to avoid any issues with breaking bolts.

Sorry to hear this happened to you....

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Thank you for your replies!

@SD96XJ6L: I tried using those easy out drill bits but that didn't work.

@AL NZ: I think only the pistons have different dimensions and the camshafts have different shaped lobes to change the valve timing. But I am not sure.

@RJ237: I asked a machine shop but they told me to remove the cylinder head and bring it to them. And I thought it'd be just more economical to just replace the whole cylinder head but none of the scrap yards around me were willing to sell me just an XJR cylinder head--even if the engine itself was just a core.

I was able to acquire a cheap (US$60) cylinder head from an X300 n/a engine from a US based eBay-er but now I am not sure if it will fit.

I might try Coventry West too. Thanks.

@al_roethlisberger: I am glad you asked! I set the ratchet to operate anti-clockwise and started to reach for the cam-cover. But I did not have a comfortable reach from the driver's side of the car so I switched to the passenger side. But I also set the ratchet to clockwise direction--because you know I switched sides (yeah...I don't know what I was thinking either...)

I was surprised how easy it was to break the bolts though. I used a rather small ratchet, didn't use a breaker bar, and didn't have to apply much force. I suppose that's why the leak was there to begin with--the bolts probably were not tight enough/or had been over-tightned by a previous owner and had already broken off partly.

I noticed that some of the spark wells in mine were also leaking. Any ideas? I might as well tackle that issue while I have it on the operating table.

Thanks but these things happen...to me anyway

 

Big oops on the cam cover bolts, but having a shop help to remove them is the best way I'd say if drilling/easy-outs don't work.

The originals shouldn't be very tight, I can't imagine easy-outs not working.

Anyway, as for your plug wells, you should get a set of seals for those at the same time as replacing the valve cover gasket.

I got them from FCPEuro for pretty cheap, $1.99 each plus delivery. Others may have an opinion about other suppliers, these are working just fine for me, but I just now found them on xks.com for $0.52 each!

Part number is NBC2579AA, they press into a cast "boss" on the inside of the cam cover.

 

That's what I am in the process of doing but this being an XJR, it's turning out to be a nightmare to remove the darn head.

The easy-outs just can't seem to grip the broken bolts. I tried working on a few but I soon had to give up.

Ah. Excellent tip. Thank you for the part # and the link to the supplier!

 

Oh, btw.. a handy tip I used to get the oil out of the spark plug wells BEFORE removing the plugs (to stop all that oil running down into your cylinders):

Take some paper towels, roll them into a loose cylindrical shape, and slot them down into the well around the plugs. This will wick a good amount of it out after a while, then you can turn the towel upside down and reuse the other end. Repeat until it's pretty much clean in there. (A couple of mine were actually full to the top!)

 

Alright guys, I have an update.

I had someone remove the cam-cover bolts from the cylinder head. But in the process plenty of metal shards found their way to the head's crevices. I knew I had to clean them out but I noticed that the entire head could use some cleaning; Carbon deposits and gunk were everywhere.

The exhaust valves were pitted pretty bad. So I took a few out--more Carbon. Even relatively--relative to the intake valves--high up the valve stem too. (Please see attached photos).

I decided to take them all out and give them a cleaning. But it looks like a technical bulletin was issued to address the issue too (I have attached it as reference; got it from jagrepair.com Thank you!).

So I am seating there removing valves, that to my horror that I notice a crack in the cylinder head (as shown). I can feel the recess with my fingers. I saw the old head gasket and it showed no signs in the affected area (also shown).

What should I do?

And as for the interchangeability, I believe the cylinder head casting itself is the same (then why are their different part numbers? Hmmm...). I took apart the cylinder head (from a '96 XJ6) I bought from an auto-wrecker. Here are the results:

-I noticed that the both castings had the same number (shown in photos), but the N/A cylinder head had more squarish corners at the back end than the S/C one (kinda hard to see in the photos).
-On the backside, the panel held by six screws had a gasket between it and the cylinder head on the N/A head but a sealant on the S/C head.

Also how do I remove this panel on the S/C head? It's stuck there like superglue...

-There was a boss inserted into one of the cooling ducts in the N/A head--likely to ease installation--but none on the S/C one (circled in the photos), but there are bosses on the engine block.
-The camshafts (and consequently, I take it, their place holding brackets) are different for S/C and N/A--because of the different valve timing.
-The intake valves are different from the N/A and S/C engines but the exhaust valves are identical--unless you decide to update them so that they don't attract so much Carbon, as per the Technical Bulletin (confirmed with Jaguar's heritage page).
-The valve springs, seats, seals, collars and cotters are identical on the S/C and N/A cylinder heads.

I have attached the cylinder head overhaul procedure as reference as well--as required by the Technical Bulletin.

Anyone have any tips on how to go about this whole cylinder head overhaul business?

And lastly since I broke all the bolts, I requested technical drawings of the bolts from Jaguar. I thought I'd have some machined since I was having a hard time sourcing them. I ended up finding some off of eBay but I am attaching those in case anyone finds them useful.

Best of luck

 

-I noticed that the both castings had the same number (shown in photos), but the N/A cylinder head had more squarish corners at the back end than the S/C one (kinda hard to see in the photos).

My mistake, they are identical castings. I placed the two heads front to back and not side-to-side. (I don't know how to cut across text so I underlined it.)

 

If the cylinder head that you removed is cracked, sure you will want to replace it rather than "overhaul" it.


It would appear that Jaguar weren't very robust with their part numbering if they made part number changes, which keeping the number of the casting unchanged. This is bad practice for traceability.


The difference that you have identified might actually just be between different design changes, that were made over time, rather than specifically between NA and supercharged engines. I can't now remember why the bare machined cylinder heads were different, but my best guess is still that the valve seat inserts were of a higher specification for the supercharged engines. It seems unlikely to me that Jaguar would have wanted to carry the additional parts complexity of two different raw castings.


Which bolts were it that you broke "all of them"! If it was the head bolts how did you get then out of the block? If it was the cam caps, these are quite std so should be easy to source. The cam cover bolts might be a bit unusual, but not really specialist, so should still be possible to source them.

 

Thank you for the insights.

I will ask a local machine shop first and see if they can do anything about the crack before I go about acquiring a new head.

Though curiously one can purchase a 4.0L cylinder head from Jaguar (please see attached screenshot and the astronomical price point) without the camshafts and valves. If the NA and SC heads have the same castings, they should offer the SC head without the valves and camshafts for sale too.

And my understanding is that one can replace the valve seats (interestingly the valve seats aren't distinguished between NA and SC) so one should in practice purchase a 4.0L head and insert rest of the SC valve gear and camshafts. But somehow that doesn't settle well with me.



I broke the cam cover bolts. They are were difficult to source since no wrecker was willing to part with them unless the entire engine was bought.

I requested Jaguar's heritage division for the technical drawings. I thought I'd ask a machinist to machine me some. I was about to do that when a light bulb light up.

I did an eBay search for the cam cover and came across a listing for one. The eBay-er was willing to part with those bolts sans the cover. That problem happily solved.

I attached the drawing in the post just in case anyone else was interested.

 

Previously my replies on this subject have started from the position that other people have said that the naturally aspirated and supercharged engines had different cylinder heads. I have suggested why this might be the case. Now I have carefully studied the structure of the various assembly levels on the website. My interpretation of the information on www.jaguarclassicparts.com is that if the cylinder head assembly - less camshafts and valves is considered, then this assembly is common for all AJ16 engines and is NBC2510CA, and it supersedes the BA level part. The cylinder head assembly including the camshafts and valves has a different number for the supercharged engine, but that is to be expected as the camshafts are different. Personally I didn't think a price of £287.39+VAT for a cylinder head for a 6 cylinder engine was astronomical. You could therefore transfer all the valves and camshafts from the used head into NBC2510CA.

 

Agreed, that actually seems pretty "cheap" for a new head.

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Makes sense. The information from their webpage was not clear to me but I see the logic in your reasoning.

The pistons likely are to be different since the two engines have different compression rations.

And I did go to the machine shop, they said that it is just a scratch which will go away after resurfacing the area.

As for the price, at first it may not sound much but the Sterling appreciated quite a bit against the Canadian dollar in the past few months so importing the head (you also get dinged 25% on import taxes on top of the sales taxes and shipping too) isn't economical now. Maybe in a few months things might change. But meh, that's one headache I do not have anymore thanks to the machine shop guys

Thanks guys, I hope in the future my pain helps someone else out. Now on to tackling the front suspension... any tips to improve it would be greatly appreciated

 

If you want to improve the front suspension, then I would recommend that you fit my rose-jointed front anti-roll bar drop links. They eliminate the compliance in the standard metalastic bushes, without affecting ride quality. I would also recommend that you fit some uprated anti-roll bar to sub-frame bushes at the same time to get the maximum benefit from my drop links. I think it would be time start a new thread or read my old one on the subject.