You do NOT remove the sprocket…you pull forward the serrated plate ONLY, when resetting cam timing…once the sprockets are fully seated on the cam’s flange, leave them be. The serrated plate has 131 serrations(or teeth) which engage with the sprocket…this “odd number” is the reason rotating it 180ish degrees will slightly change the bolt hole alignment.
Trying to remember the intermediate sprocket assembly(#11) and whether there are Woodruff keys that hold the sprockets to the shaft…I would think there are. If so, a failure of this key would allow the upper chain’s sprocket to just spin on it’s shaft, unable to “pull” on the upper chain.
Generally, using only one bolt in each cam during the setting procedure is fine as long as the bolt is tight enough to keep the serrations engaged with the sprocket. The cam bolts serve as locating dowels so it takes some fiddling to get the bolt properly situated and fully seated against the serrated plate. On later engines…the ones with 4 bolts…only two of the holes are designed to tightly fit the cam set screws, the other 2 being larger in diameter. Sounds like you have the 2-bolt style.
If both cam sprockets are not turning, there is some problem under the front cover.
Also, it sounds like a valve may have gotten bent. As a test, it would be worth doing that leak down test, after loosening up both cams so that the valves will be in the closed position.
I also have bent a valve while installing a newly rebuilt head; car started but did not run smooth.
When I pull the XK heads, I set the cams into the TDC position with the cam notches in the correct positions, pull head, and I don’t move the crank again until I am putting the head back on with the cams in the TDC position. If working on the chains or timing gears, make note of the positions of gears, pistons, ignition rotor, everything.
You WILL get this running.
All holes are the same on 4 bolt sprockets.
I have 4 sets of 4.2L serrated plates and all of them have 2 smaller holes and 2 larger ones, fwiw. There are also a couple of other differences between the 2-bolt and 4-bolt plates…as their function changed slightly.
I measured six and all holes are the same. Give us your two part numbers and workshop manual reference for the two different size bolts and mixed hole plates please Lee.
It does make it a lot easier to get the bolts to go in if not aligned properly if you drill the holes oversize. Not a fix but another bodge.
Right. I ran a tap down a hole once when it didn’t line up perfectly, rather than cross-thread a bolt. But they are all four the same size per sprocket and all the bolts should be equal as well, right?
The bolts have a smooth shoulder on them for precise fit and alignment. In setting performance engines, 1 degree one way or another at the crank will effect performance. The camshaft turns at half speed so 1 degree at the crank is 1/2 degree at the cam. This is a very fine difference and the adjustments is very precise so the bolt should fit exactly, not just close.
This “precise” fit is how I noticed the differences noted…I was assessing the cam timing components I had on had in order to choose the best parts for my rebuild operation when I discovered the differences in fit/tightness between all of the “meshing” parts, including the bolts/holes, and the slight design changes. For instance, the 4-bolt plates I have are slightly thicker and larger in diameter than the 2-holers, which makes sense since there was no longer any need to allow an oil flow-path into the groove on the underside of the sprockets and the added thickness might/should allow more clamping force between the plate and sprocket. Also, the mesh of the serrations is noticeably tighter on my original parts…I can lift just the plate by the threaded stem and the sprocket will come(lift) with it…no such luck with the 4.2 parts. I presume machining tolerances had degrading over time? And since you would only need two, opposing dowel holes to precisely align the plate with the cam, I was not surprised Jag didn’t care about making the other set of holes to such a tight tolerance…they simply had only one function: clamping force.
I don’t remember how the cam sprocket attaching procedure is described in the 4.2 manual but presumably one would not need to turn the engine at all to get the serrated plate properly aligned by using just 2, side-by-side bolts…installing the other 2 after rotating the crank one turn.
I just went and measured a few 4 bolt plates out of the buckets of them that we have. All very consistent. If yours are different sizes, then someone has modified them, not the factory. The flaw about 2 being there for just bolt on is that they are not marked so if you used the two holes that were larger, then you would have a heck of a time getting the proper two to align. Early 2 bolts were wire tied once installed. the 4 bolts used lock plates. Much more efficient in production assembly and less chance of the cam and gears getting loose.
Exactly right about the use of non-dowel bolts and holes to align things…that’s why I investigated this situation. My junkyard parts are CLEARLY factory, as evidenced by the differing hole sizes between the (inner) serrated plate, vs the (outer) clamping plate. The two pieces were made separately, drilled to differing specs, then sandwiched together. The serrated plate has four, equally sizes holes(.407"), while the outer plate has two at .407" and two at .387"…the size difference being observable by the naked eye, actually. You can see the “ridge” the smaller holes create due to their smaller diameter when sandwiched against the serrated plate. IF those holes had been reamed, all eight holes would be the same size. Factory original, Q.E.D.
Could be that you have an orphan set of cam plates from the factory?
We have a 3.8 engine in our club that has a factory fitted, confirmed by non other than Lofty England, hydraulic top chain tensioner.
Don’t know the pedigree of my parts, except they came from different cars, at different times, at different junk yards. Who knows how long these parts were produced? I DID have a chance to look at my manual…and…it looks to me that the OP’s problem is a sheared-off Woodruff key that locates the forward intermediate sprocket(28 tooth) to the hub of the rear intermediate sprocket(20 tooth). This might have allowed a temporary and short-lived “locking” of the two parts due to rough spots in the damaged area that the OP described but disassembly is required, I’m afraid.