Help Anybody know how to manipulate the chain and chain tensioner on a V12 HE

Hi Marek,

Glad you got back to me. I have no problem putting all communications on the forum. However, right now I need to get to a position where I know where I am and where everything else is at. Besides having difficulty with the engine, I’m having problems with being able to use my computer. My computer is 6 months old/new and I have all the latest and greatest programs, Browser, etc. So everything is 20yrs new and unfamiliar to me along with the same being true of using the forum. With that and never doing an A Bank head removal and re-install, I’m in a tornado spinning around with me and everything up in the air spinning with all being out of sight and in a grey dark opaque, soupy mix.

I’m trying to get a handle on several unknowns, not just the engine and get to a baseline so that I can communicate intelligently while getting bit in the dark by unknowns while trying to figure out what’s what. Right now everything seems camouflaged encrypted and booby trapped.

To get to a baseline, there are several questions I have and because there are many, I would like to intersperse them within your message below. I don’t know if this will work or not with everything being new but here goes.

I’ve got two styles of interspersed replays below. You can tell me if you prefer one over the other. Probably just using the different color is the best way to go as in the 2nd interspersed reply. I think this is much more efficient than having an email for each question.

One thing, I don’t make assumptions on understanding things but always verify before going forward. I hope I don’t become a royal pain in the arse. So here goes.

Paul

Hi Marek,

Well, that didn’t work. More than half of my response is missing so I’ll ask the questions again with this response to my own response.

MarekH
July 19
Dear Paul,

I got your messages. It may be best to put your questions up on the forum so others might benefit from the answers at a later date.

The tensioner is just a spring loaded bit of plastic, pushing the chain towards the centreline of the engine by default.

When the chain is worn down too much or the cam sprockets not fitted onto the camshafts, the tensioner is very much an inverted “U” shape and the chain contacts metal on the engine.

I have 110k on my engine and looking at the tensioner for the first time ever, I can’t relate to whether it is worn or even broken or not. I only have the A side taken apart.

When the chain is still good, i.e. unworn (and within its operating length) and the B cam sprocket is on its camshaft and the A sprocket is very [Not true but I’ll get into that next if this reply gets delivered properly] close to being mounted onto the camshaft or on the camshaft, then the tensioner is “U” shape is flatter than before and the chain is not contacting any engine parts.

Paul

“I have 110k on my engine and looking at the tensioner for the first time ever, I can’t relate to whether it is worn or even broken or not. I only have the A side taken apart.”

If you look at the before and after pictures, then a worn chain is one which has all of the roller links worn down and this makes it sit lower on the sprockets. To the naked eye, the chain links are not even imperceptibly lengthened but compared against a new chain, the tensioner would be more U shaped and the old chain can (almost) scrape against against some of the metal surfaces and bolts as it whips about. A new chain, by contrast, is shorter and the tensioner and chain are both under tension and kept away from engine metalwork.

From my old photos, look at where the arrow is and see the clear gap (or lack thereof) between the chain and the centreline of the block to judge wear as compared to the new chain. Perhaps someone has better pictures.

If the tensioner is broken, you ought to hear a horrible rattle when you drop from high rpm to low rpm as the chain slaps around and metal cuts metal. Sadly, to fit a new one, you need to take the timing cover off. After you have finished crying that is. That’s because it’s about three days work to strip everything off, replace and build it all back up.

Given the A side is loose, you should be able to work out whether the plastic U shaped arc is in one piece or not. If it isn’t, it’ll be in several pieces like the one pictured.

Next question?..

kind regards
Marek

Hi Marek,

I will inspect the chain and the tensioner tomorrow when my son and all get back from vacation. Right now I can say that there are or were no broken tensioner sounds when running.

Also in taking the A Bank off I removed the retaining clip that holds the sprocket and the center piece of the sprocket together. After the inspection I will have to put them back together. Looks like the two pieces are still at the same spot. The two pieces did not come off altogether. Only a portion of the splines came out of the sprocket on one side. This lopsided holding of the sprocket on the sprocket holder away from the Cam maybe what is causing the chain to be bound up. I will know if that is true or not once I get the sprocket and center piece with the splines appropriately back together.

Got to get to work now. I will let you know what I find Saturday Eve. By the way, what time zone are you?

Oh and another thing. When I go to the link you provided, I can see the three pix of the tensioners on the page but when I click on the individual pix to look at each individually and bigger, all I get is a Qtr inch icon of something, no pix at all on all of the three pix. Same whether using Brave on both or Firefox to verify browser operation. I refuse to use Explorer. Oh, at home I have a PC with OS7 and a Mac with OS14.5 both operating at the same time at all times. I’m on one or the other depending on what function I am performing with both always on simultaneously. Necessary as a minimum when one trades.

Thanks, Paul

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Nonono! That clip isn’t removed to disassemble the engine. It’s only removed during reassembly when you decide to adjust the cam timing. With the sprockets in place, the chain tensioned, and the crank and cam timed correctly, you remove the clip, take out that center piece, and turn it some multiple of 90 degrees until the bolt holes line up properly.

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Dear Paul,
The old photo albums were never fully transferred over when the new website replaced the old, so although the text and thumbnails of the pictures exist, most of the links to the old photos were not translated. It’s nothing to do with your browser.

I am in the UK - timezone wise.

kind regards
Marek

I’ve dug out the original pictures, plus one other.

There is a picture of the old chain but with a new tensioner fitted. The chain is stretched beyond its useful working life and metal has been rubbed away where the white arrows show. Also note where the latching mechanism of a brand new tensioner sits against an old worn chain.
Next, there is a picture of a brand new chain with the brand new tensioner. Look at where the latching mechanism sits.
Finally, there is a picture of the timing cover of a v12 so you can see where the black access plug sits.
Cross index these and what should be apparent is the position of the latching mechanism gives you a steer as to how worn the chain is because the only difference between the first two pictures is that a new chain has been rolled in and another picture taken five minutes later.

kind regards
Marek

3 Likes

Simply awesome post, Marek.

It only took five minutes to roll in the new chain? This is presumably using the idea of breaking the old chain, attaching the new one to the end of the old, and turning the engine over a few turns to roll the new chain in and the old one out? And the new chain is reconnected using a master link?

Yup, spot on.
Master links rock!

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Thank you for these pics, this will help me a bunch when it comes time to put my V12 back together!

How many miles did that old chain have on it, Marek?

I just asked the PO. He said ~50k miles so there is no clear guidance there as to why it failed. A relevant disclosure as to cause of death:- the car had been thrashed around a racetrack by an ex racing driver and it was then driven 300 miles with a rattle coming from the front end whenever the revs dropped. (“Yeah, that’d do it” - I hear you say.) I diagnosed a broken tensioner as soon he revved it on the driveway.
Basically, every time the revs dropped it sounded like shaking a bag of nails somewhere towards the front of the engine.

The car was short of ~1.5litres of coolant and only 13pints of oil came out when I stripped it down. The tyres were borderline illegal. The “missing” oil appeared to be all over the front suspension, so much so that I told him it’d be an MOT fail as I couldn’t actually see the front brakes.

I’ve also looked at my records.

It actually took five days work before it was back on the road.
The new chain (180 links) was a doubled up length of 59.5cms, i.e. 90 links.
The old chain hanging doubled up (90 links) was just over 60cms long, i.e. worn internally by over 1cm over 180 links

That doesn’t quite scan versus the pictures I posted as four up and down lengths would make the latching mechanism sit only 3-4mm lower down if it were 1.2-1.6mm longer, so it must have also been sitting lower on the sprockets, i.e. the external roller bits must have been substantially worn although I never measured that. The photos show the latch about 1cm lower, implying 4cms more length overall.

Using this logic to judge wear is only sound if the dimensional drawing for the new tensioner is the same as that of the old one, i.e. the length from the end to the latch is different because they’ve changed the design then you can’t universally judge wear from how far down the latch sits.

One thing you can do to judge wear, if your have a mobile phone, is photograph yours now and then track how much lower your latch sits as time goes by.

kind regards
Marek

EDIT:- someone else please decide if that 4:1 logic is sound - it’s late over here.

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I don’t understand it. Fundamentally, the lengths of the rest of the chain path is fixed. Only the one span, from A bank cam sprocket to crank sprocket, changes length with wear, so your entire 1 cm of additional length in the worn chain appears there. The question is, what would 1 cm of additional length look like bent over the arch of the tensioner? I suspect it’d look pretty much like it looked, moving it quite a ways.

Logic:- If you skim the heads by 20thou, the chain is 80thou “too long” because it goes up and down twice, so I applied that backwards. What you are saying is that the tensioner just takes up 1.2cms of slack, because the circuit it goes around hasn’t changed and the chain is 1.2cms longer. OK. I told you it was late…

Perhaps just blow the pictures up to full scale and measure it with a piece of string - the old chain is too long - it rubs. The new one misses the metal where the white arrows point by a country mile.

kind regards
Marek

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Hi Marek,

Couldn’t get to the engine on Saturday but I did on Sunday and here’s where I’m at.

Sprocket with inner spline adjustable portion back together.
Engine hand spun to TDC on #1 and disty rotor pointing at #1 distributor lead.

Using the picture of the disty and rotor, the rotor could be adjusted slightly to be dead nuts over the market on the base of the dirty. The rotor is a little retarded from TDC. This can be done by adjusting the disty with the two Allen screws at the bottom of the disty plate. Should I do this?

Using the picture of the sprocket with the inner adjustment set up, the placement of the four holes as compared to the four holes on the cam, the left upper is Higher that the right upper most.

Therefore All timing is correct and I should slam the head on and tighten it up. Correct? Haven’t forgotten anything? All aOK? When I get the head on there may be a need for a little adjustment of the inner wheel with the sprockets but I can see that it will not be known until the sprocket and the cam get connected.

By the way, the tensioner is not broken as far as I can see and it is tensioning. Lotta tension but I could pull the sprocket up and out of the block by hand, release it and do it again.

Thanks, Paul

Correct cam timing is determined using the special tool that fits into the notch in the camshaft. When the crank is at TDC, the cam tool should fit in place properly. Of course, that’s only if you want the stock timing; if you opt to retard the cam timing a bit, things get trickier.

Whatever, officially you put the crank at TDC and the cam exactly where you want it. If the bolts go in, put 'em in. If they don’t go in, remove the clip and futz with that splined center piece until they will.

As far as your dizzy timing is concerned, just make sure the timing plate by the crank damper is correctly located. Then you can fiddle with the dizzy to your heart’s content after the engine is together.

String tied to that little clip. Very wise, grasshopper!

Hi,

I’ve been looking through this series of posts and others and see mention of locking or fixing the position of the jack shaft to maintain the existing ignition timing when disconnecting the cam sprocket from the cam - how do you do that- lock the jackshaft in place?

Also, I plan to remove and then replace one cam sprocket at a time (so I can fix leaking tappet block joints) - is this OK? Does it matter whether I do A bank or B bank first?

Thanks for all the great information on this forum.

Jeff Todd
1989 XJS Convertible

The sole purpose of knowing where the jackshaft is at is to make sure the distributor rotor points to the same direction as it did before when you reassemble. You can either bolt something across the jackshaft sprocket or you can pull the distributor cap off an just make a note of where the rotor points to. Jaguar made a special tool for the former, but the latter is just as easy a method.

Similarly, it makes no difference what order you tackle the heads in. The objective is to put the camshafts back on exactly the same way as they came off. If you fail badly, the pistons will smack into the valves, so just pay attention to where the cam notch is and will be fine so long as you don’t remove the circlip from the cam sprockets and inadvertantly separate the the two halves of the cam sprocket from each other. It’s quite hard to be 90’, 180’ or 270’ out.

kind regards
Marek

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The cam sprockets can be removed and replaced without touching the chain tensioner if you utilise the support brackets and a holding tool for the sprocket is used.
There is a good chance you will have tensioner issues if you disturb it on anything other than a recent install.