hello

A clicking noise has been evident from the upper part of the 4.2 XK unit in my Daimler. I finally got the courage to remove the rocker cover. There were metal fragments sitting in the top of the cylinder head, both in the recessed area next to the cam lobes and I removed several more from inside next to the tappet itself. When i reassembled the fragments, it became obvious that a small amount of metal is 'missing' from what was originally a ring shaped peice of metal with a ridge running around its circumference..

I want to replace the inlet ring thing but am unwilling to take off the head needlessly and investigate if there is any damage, the vehicle drove well enough, it just made this awful noise which obviously was the edge of the tappet slapping against the head itself. Both areas are undamaged and the cam lobe is smooth.

Are there any pitfalls that i have to watch out for when removing the cam shaft? Haynes is once again next to useless.

regards
nick

 

Greetings,

Presumably this is a 4.2L six cylinder you are working on, and the problem you have is a common one on that engine.

The cylinder head is amuminum, and steel tappet bores are installed in the cylinder head during manufacture by heating the head and pressing the bores in place. Each tappet moves ininside the bore, but the bore must be retained or it is broken if it moves up and is contacted by the camshaft lobe.

There is a factory fix for this fault, and aftermarket sources for the same components. The repair kit consists of three retaining plate and six screws, enough tolock down the tappet bores on one side of the engine (normally the intake side of the head does not have a problem).

If damage to your broken tappet bore is not severe, and there is enough of the top flange remaining for the retaining plate to register against, that's all you need to install. You can replace a damaged tappet bore without removing the head, but it takes a bit of time. Installation of the retaining plates does not require camshaft removal. If the bore is badly broken:

Align the exhaust cam timing slot and remove the cam and tappet. You will likely have to drill down through the wall of the tappet bore in order to split it before you can pull it upward from the cylinder head.

New tappet bores are suppliedoversize, and are intended to be machined before installation... so you need a good used bore. Message me if you need one. I put the replacement in a freezer overnight, smear a little locktite on the outside and drive it into the head with an appropriately sized bearing driver. Double check that the tappet can move freely in its new bore, install the reataining plate kit, and reassemble the engine.

Maybe a six hour job, and change the oil when you've had it running up to temperature afterward. Only other comments to add is that you want to make sure you follow the numbering stamped on the camshaft caps, and adjust the upper timing chain after you refit the cam.

 

Thanks for the info.

The tappet ring is completely shattered into 12 or so pieces; I 'reassembled' it only to see how much had vanished into the engine, certainly it is unusable. There are no remaining pieces to be removed (except maybe small, loose pieces possibly lurking in the springs etc) so I don't have to drill down (if this is what you are referring to) I will need a replacement unit.

It appears from my mediocre engine diagram that only the inlet valves have tappet rings, obviously this diagram is wrong; I've never had the exhaust rocker off. There are no holes for the retaining product you speak of. I'm guessing that I have to drill these into the head myself. Should I get the product for both sides as a preventative measure? Does it come with decent instructions; I'm loathe to get a drill out and start milling around in the head. Do you have a part number for this? Is it the same for both the inlet and exhaust sides?

Another question; will a compression test reveal if there is significant bore damage in the cylinder concerned?

regards
nick

 

Yikes! That must have been making noise for a little bit of time.

I guess that's fortunate that the tappet bore has broken up completely, as you said the removal process is now somewhat less complicated. With the tappet rocking around once the bore is gone, it's possible that the valve stem is bent. I would perform a cylinder leak down test on that cylinder to make sure the valve is sealing, and then proceed with the fix.

The pieces don't go too far, if you fish around with a magnet through the oil return holes in the head you will retrieve the majority. Nothing can get into the combustion chamber, no worries there.

Installation of the tappet bore kits does require drilling holes in the cylinder head for the retaining plate screws. And since you lost an intake bore, I would definitely install a set on the exhaust sidebores as well. These are usually the ones more likely to come adrift, and it became a common problem once the U.S. specXJ6 started using catalytic converters.

I'll send you a PM later today to answer your other questions.

 

Great information, thanks, I'm getting more courage for the job!

A cylinder leak down test...would this be as simple as pouring petrol past the offending tappet?

cheers

 

hello again

my tappet bucket is around 34.49mm/1.358inches diametre. i cant get the measuring calipers into the head but am assuming that there is a known standard recorded size for the bores in the cylinder head that house the tappet bucket guides. i cant find any reference to head machining in my almost full service history either so i assume they not all rebored.
would you know the size to machine the tappet guide i have; it currently measures
34.4mm inside of tappet sleeve = 1.354 inch, 41.75mm outside of tappet sleeve = 1.644 inches; obviously the inside diametre to machine to is the diametre of my bucket above.
regards
nick

 

do these seem correct to you guys?

34.4mm inside of unmachines tappet sleeve = 1.354

41.75mm outside of unmachined tappet sleeve

41.2mm bore of cylinder block (final machined outside tappet sleeve dimension)

34.49mm bucket diametre/tappet sleeve bore = 1.358inches (final machined inside tappet sleeve dimension)

41.75 - 41.2 = 0.55mm = .022 inches to be taken off of outside of sleeve
34.49-34.4 = .09mm to be taken off of inside of sleeve
regards
nick