Doubt it: you’d see that evenly distributed.
I’ve never seen such additives leave those kind of deposits.
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Also, we had a similar substance and it wasn’t any fuel additive. Unless it’s ethanol but one would think it would reach all 6 ports.
The first thing I would do, (if the head is not yet off), is to measure and record the valve stem clearances, as that will give a clue if the seats are recessed.
If you are to far in to do that, not to worry, as it can be done with the head off (following the right procedure)
As I said, once the head is off, posting pics to the experts here will probably allow them to tell if the valves are too far recessed in the seats
I took an otherwise good-looking head to a Jag Pro who does all his own machining, as I was a suspect of the amount of recession. He took one look and said they were too deep
You can check your valves & guides at home
Check the head for flatness
It may not be needed for a head rebuild
I do not wish to be the bearer of bad tidings, but have learned from this list, and club members that one thing for certain, is the crankshaft plugs are an absolute must for an old engine that has been sitting, as gritty sludge will be there, waiting to destroy brand new bearings, likewise the conical filter for the timing gear if present on your engine, even the camshafts (if they have a plug)
The crank plugs are very hard to remove, and normally most resort to a machine shop for this task
afaic, that dust is normal, and wouldnt worry me, however most of the Jag engines I have taken apart have some critical problem that means they need a full rebuild
I just heard back from the friend I bought the car from about fuel additives. He always used lead additives on all his old cars. So, there is a possibility for the residue. The motor could be low on the #1-cylinder end and that could explain why the powder was just on that end. Good advice checking the valve clearances now. I’m going to do that first thing this morning. Are the OEM valve seats hardened? Years ago, it was recommended to have the head on my Series 3 Land Rover rebuilt with satellite valve seats for unleaded gas. I’ll have to research the tip on the crank shaft plugs more to be sure I understand what you are saying. Later today I’m going to drain the oil to see what it looks like. You folks have been great on helping. This may turn in to a miniseries.
Yes, but over the years, they can still recess.
I also highly doubt the powder you’re seeing has anything to do with gasoline additives.
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I’d suspect the head gasket. Long slow leak over time.
The vertical distance between the tip of the valve and the machined area on the head for the cam cover should be 0.850".
You do not require hardened valve seats for unleaded. The original ones are fine.
An even more accurate one, is the measurement in the Jaguar shop manual that specs 0.320" between the base circle of the cam and the top of the valve stem.
I didn’t get a chance to work on the car today. I did put in another order to Moss. I didn’t have the cam positioning plates or a head gasket.
You can even do it by eye. Just position the center of the cutout for the timing guage at 90° to the machined cam cover surface, it’ll be close enough to run well.
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A few mm can make a noticeable difference though.
Should be able to get it closer than a few mm, but it can always be finely adjusted later when you have a guage, using the vernier serrations on the sprocket center insert.
I’m not in a big rush to pull the head. I’ll wait until the gauges come in. I just got an order in from Moss yesterday so, I’ve got other items I can be working on. I worked on some custom radiator mounts for a friend’s pickup most of today. Thanks for all the help.
I just centered the notch on (Ithink) the “1” that’s cast into the cam cap, and that works fine. I only ever used the tool once or twice to calibrate my eyecrometer… 
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Andrew, I am interested in the measurement of 0.850 from the valve tip to the Cam cover machined surface on the head. Is this a measurement buried in the Jaguar “how to do” somewhere. Seems like a much easier measurement to make than the 0.320 from the valve tip to the base circle of the cam?
Russell
It is easier. It’s what our machinist quoted to me once. I don’t think it’s “from the book”
I suspect that it’s what you see when the 0.320" measurement is correct. Certainly it means that if you start with a 95 thou when setting up the shims you end up close.
I haven’t kept this tread up to well but, I’m pulling the motor for a complete rebuild. I took the bolt out of the crankshaft that holds the harmonic balancer on by hand. The taper cone piece was in four pieces and the keyway in the crank was in a “V” shape. So, along with finding a long piece of plastic in the oil pan (part of a timing chain guide?) it is time for a complete rebuild. any suggestions of design flaws or preventive items I need to take care of in either the motor or transmission?. I was wondering if the rear mail oil seal conversion that Moss sells is worth the cost. I will finish installing the tappet guide retaining plates. Thanks.
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I would measure the pistons bores first, as it adds a lot to the cost if you need a rebore, which is fairly common