Removing head on a frozen motor

Greetings all and Happy New Year!

This weekend, I will attempt to remove the head from the engine on my 1951 XK120 OTS. The car has been in storage for many years and the engine is well and truly frozen. I have used a borescope to examine the cylinders and nothing looks amiss. All piston tops appear to be in good shape and the bores appear to have light surface rust only. Despite that, any attempts to turn the engine are futile. The bores have been soaked with a 50/50 mix of acetone and ATF for a couple of weeks. The engine is destined for a complete rebuild and must come out. Once out, I’ll find a way to unstick things. Of course, the head must also come off which brings me to my quandary. In the current position, I cannot get to the the camshaft sprocket bolts to remove them. What is the process for head removal in this case? I found one thread that suggested cutting the timing chain - which is not a problem, it will be replaced anyway. But if there is a less destructive way, I’m interested.



You could try removing the cam shaft bearing caps , loosen off the cam chain tensioner , may give you enough to remove the cam shafts by wiggling them about

You’ll find everything much easier to access once the engine is out.

But before you do anything you might want to plumb the archives for insights into head removal and what you can do to facilitate the process. Given that the engine is frozen there’s a very good probability that the head will be very difficult to separate from the block.

Thanks Nick and Ian. I am fully prepared for the possibility of difficulty in removing the head and have thoroughly researched all the options for dealing with it. I am optimistic on that score though. I have removed the head nuts and three studs came out in that process. The studs were surprisingly clean. If the remaining studs are that clean, the head should be relatively easy to remove.


The sprockets are held in place with a clip , removing the clip may help things ! s-l16002 (3)

As Ian said, the chain sprocket can be moved off of the bolted plate. It only needed to move about 1/8". The sprocket will still trap the plate but you will be able to turn it to access the bolts.

USE CARE if you’re going to turn the cams with the head in place. The pistons may be at the top of their stroke. If you manage to free the sprockets, don’t turn the cams until you raise their bearing shells a bit.

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Thanks Ian. If I am understanding the anatomy correctly, the adjuster plate is held in place by the circlip and the bolts (though my understanding may be incorrect). If that’s the case, removing the circlip won’t help things.


Push 9 in and rotate 8 , that will slacken the tension off , remove 3 , and the sprockets will be lose on there mounts 2
The bolts hold the sprocket mount to the cam shaft !

Thanks Ian and Mitchell. I see it now. That makes perfect sense.


The sprocket mount in the diagram is a later one-piece, scalloped style. It’s actually the problematic version that sometimes slips, allowing the camshaft to go out of timing. Ask @ajdell about it. The earlier mounts were actually four pieces, the toothed adjusting plate, the centre guide pin, a star washer and circlip - the four arrowed items in this rather cluttered diagram:

removing the circlip and star washer will not free up the adjusting plate, only the guide pin.

Thanks Nick. Now I’m thoroughly confused. It seems you are telling me that removing the circlip and relieving chain tension will not allow me to remove the sprocket. Is that correct?


I just grabbed a random sprocket, bolts and camshaft to see how it goes together (or comes apart). The toothed sprocket is sandwiched between the serrated drive plate and the flange on the cam. Removing the spring clip with the bolts in place does not free the sprockets from the cams. I think the bolts have to come out to remove the head. The serrated plate allows you to change the individual cam timing, but not without also removing the bolts. The spring clip only holds the sprocket and drive plate together until you can fit the bolts.

Thanks Mike. I suspected as much. There is no way to get to the bolts. It looks like breaking the chain is the only option.


I’ve stripped frozen engines before. My recollection is that the cam bolts were fiddly, but not impossible. I recall the lock/safety tie wire being a pain to get at and remove. I know I have never cut a timing chain.

This is worth extra emphasis. I would not turn the engine with fixed cams or turn a cam any significant amount with the fixed rotating assembly.

The head was replaced some time in the past, and indications are that whoever reassembled it did a poor job. There is no safety wire on the bolts. I was able to loosed two (one on each side) and they were gorilla-tight. The other two are the problem. I spent an hour or so trying to find a way to get a wrench on them, but couldn’t. I’ll try again, bit I’m not optimistic.


Agreed. That’s not in the cards.


Can you try modifying a ring spanner with a gas axe to gain a better attack angle to get to the other bolts?

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That is correct. What Mike said. You need to get those bolts out before you can remove the sprocket.

Edit: If you can get those two remaining bolts loose they don’t have to be removed completely to free up the sprockets.

Safety wired by someone who knew NOT how to safety wire…!