I will try Erica’s 8 steps and report back. I have to say, however, that the Jag design for the adjuster, can sprockets and chains is the clumbiest mechanical design I have seen since engineering college over 60 years ago.
Let me defend Jaguar. This design was made right after WW2 and was introduced, I think, on the XK120 in 1948. This is a 72 year old design and it worked well. Yes the engine is a boat anchor compared to today. Yes, today’s engines, with same displacement have multiples more horsepower.
But it was reliable and it worked for high mileages.
And I understand from those who build Jag race engines, that the best crankshafts are those from factory unmodified. Their balance apparently cannot be achieved by today’s machines
Looking at the timing chain diagrams above makes me really appreciate the simplicity of the Vega cam belt design. Yeah kinda strange to have to drain coolant to replace a cam belt but cuts down on engine parts by having the water pump do triple duty. Four bolts to remove fan. Six bolts to remove belt covers, four bolts to loosen pump and 1 bolt for alternator belt and cam belt is off. Less than an hour to do the job. First time in the early '80’s I did it in front of some guys house when the belt broke right before I was about to get on the Dallas North Toll road. My fault since I knew belt was well overdue. You do not have to worry about bending valves on a Vega engine either.
Erica,
Thank you for your six step process for getting my upper chain to rotate when the bottom one does. I followed your suggestion closely and found very little slack in the chain when I finished.
Then I rotated the crank and saw the cam sprocket start rotating. But then it stopped and does not move when the lower chain moves. So I may have two problems with two questions:
Is it possible that the chain has build too much slack over many years and doesn’t engage the intermediate gear right enough.
Separately i find that it very hard to rotate the camshaft. I grip it with long handled priors and can rotate it only a very few degrees one-way or the other. Is this Normal? Or did the machine shop install it too tight when I just had the head rebuilt.
I addressed this to Erica but hope anyone will respond.
On the first question I can only say that it’s never happen to me. Did you happen to notice if it has a master link? Some of the replacement ones have that, but I don’t think any original ones did.
When you say it stopped turning, did the whole thing lock up or you’re saying the crank would still move but the upper chain started slipping? I wonder if you might have broken teeth or extreme wear on that intermediary gear? Do you have a USB wand camera? They’re just 20 bucks on Amazon. It would be great if you could actually see what it looks like down there.
I reiterate that you must not move the crank more than a few degrees by itself or it will crash the open valves. You must also not rotate the cams independently of each other or they’ll collide with each other. You can nudge them a few degrees just to get the tool to line up with the notch but you can’t rotate them very far. I’m hoping that isn’t what you attempted to do? When mine need to be manually rotated I grab it with a pair of vice grips. They can be difficult to move because of the valve spring pressure.
Normal chains shouldn’t get so long I think. It ran that way, did you surface both block and head by a lot? If the crank moved further significantly without the cams following check for slackness again.
You have a problem, who knows where. Rest per Erica.
I need to correct/supplement my last post. The cam is now ok and turns. (Not much as you warn). It had just not been as fully detached from the chain sprocket.
Re the intermediate gear, I can see it ok and gear teeth are in good condition as I rotate it full turn.
Re the chain, I find I can easily rotate it both ways by hand without the intermediate gear moving when the chain is fairly slack But when I pull both sprockets up tightly, it is impossible to rotate as it is engaged with the intermediate gear.
My conclusions from this info is that either the chain has too much slack from wear Or I don’t know how to connect the sprocket and chain properly and tight.
I doubt the latter possibility as I have tried about 5 times including the last with Erica’s advice.
So that leaves only a worn out chain but before starting to replace it, I would like to know if others have had a similar problem.
Do you have any idea how many miles are on the car? If it could be said that this chain is too slack to tighten sufficiently, then you’d have to be worried about the lower chain as well. As it stretches the tensioner shoe piston protrudes farther and farther until it gets swept out and your engine could get bricked.
I assume the engine is in the car? It’s not a ton of fun but a timing replacement could be done. Pan off, head off, cover off. I also have to wonder whether something has gummed up your adjuster. Assuming you mounted the cam gears with the outer chain segments as tight as possible and you then tightened the adjuster all the way, I can’t imagine it slipping.
Had it ever been rebuilt? I wonder if someone could have rebuilt it with a too long chain.
Erica, I really value your comments and questions so let me give you some background on the car. I bought is cheap off a salvage lot so know nothing about it’s history. The body and interior are in very good condition so I assumed it had a bad engine.
It was missing carbs and exhaust so first I checked cylinder compression and.found two cylinders with low numbers; others ok. I then took off the head and had it rebuilt by good machine shop shop. I reinstalled the head and then found “loose timing chain” problem.
I am tempted to conclude the chain is loose but that contradicts the high probability that the chain was ok before I took off the head: not only did I find compression with valves obviously working and, if the cam was not turning when I cracked the engine then the valves would have been bent and they weren’t.
So they leads me back to the view that I am not connecting the cam sprocket correctly. Does that make sense? I don’t want to go through the work to remove the chain. But I don’t know what to do next Any more ideas? Thanks
I’m out of ideas on this one. It does sound like it was probably timed okay when you pulled the head if no valves were bent. I assume it’s the original 9:1 engine? It’s typically bad news for the crank to interfere with full open cams. I imagine 8:1 might have much lower risk due to to the shallower piston domes. Just a guess. In theory, given where it’s suspected to be slipping, only the crank would go out of time since both cams would grab at once or not at all. So maybe the valves wouldn’t get bent? If you’re looking for a reason for a parked no run car, a slipping chain would be a reason.
Why did you rebuild the head if it had decent compression? Did you turn it over at all manually before disassembly and see rotating cams? I’d hate to see you go to the trouble of replacing the top chain if you just end up back to where you are. Trying to do it by itself would be a frustrating job since it probably doesn’t have a master link. You’d have to try your luck with a chain breaker and then marry a new split chain to it and drag it through. And how do you do that if you can’t get it to turn reliably?
I think you should repost this to the XK Engine forum because you’ll get a lot more experienced opinions. They’re mostly all the same engine for decades, so I always ask there for engine assembly questions.
Last suggestion, if you pull the cam gears and hold both outer segments of the upper chain in your hands and pull tight do they fully engage with teeth so it can’t be tugged to one side or the other?
Erica
Some answers to your questions/comments:
Mine is 9/1 ratio so biggest chance of bending
The head was rebuilt due to two bad valves
I will not try to separate chain
I will repost on engine forum
The chain will not turn if I pull on both outer segments
If interested, follow on engine forum. Many, many thanks for all your help. Phillip
