Been having an issue lately with a strange "rattling" noise coming from the engine compartment area upon acceleration, but not present at idle, and disappears whenever the engine gets above a certain RPM. At first I thought it might be anything from "bad gas" to some kind of engine "knocking" or "pinging", or even a spun bearing. I even checked the area (and exhaust) for any loose metal parts that might account for it. AT some point, it dawned on me that the sound itself was actually kind of familiar. I then remembered that Superblue always made that noise during the first few seconds of engine start up, apparently caused by a delay in the timing chain tensioners getting up to full/sufficient (oil) "pressure" at the time (Jag did make an "upgrade" via T.S.B. to solve this issue for owners that were bothered by it enough, as noted below).

Last night, my tech friend and I, using a very long socket wrench handle as a makeshift stethoscope, were able to determine that the sound is definitely coming from behind the timing chain cover. Again, as I told him, I can’t believe there were issues with that part of the AJ6 engines, but maybe mine was just an isolated one.

After doing a lot of research last night, digging into the factory workshop literature as well as the Heritage parts website drawings, it looks like one of the remaining issues is determining whether the problem is with the upper tensioner or the lower one. The lower one is of the “hearty” design, as I put it, composed of very heavy metal parts, and from what the literature says I get the impression they very rarely fail, and hence usually need just some disassembly, inspection and “clean up” before reinstalling (vs. outright replacement). The upper tensioner is not of quite such a robust design, and it seems to be the case that usually it just has to be replaced. The third possibility is that something could be amiss with one or more of those “guide rails” used to keep the chain from whipping around into adjacent parts of the assembly. Question is how to determine which of the three it is before you start the job. ?

Also, apparently from the literature r/r of the two tensioners is relatively simple. The PITA is removing the timing chain cover. The procedure outlined in the literature involves something like 50+ steps in the process , inc. the removal of the hood, the cylinder head, the intake manifold, the distributor, the air cleaner/intake assembly and even disconnection of the exhaust system. wth ??? We’re talking a 4.0 here, not a V-12. I notice that Kirby (Palm) mentions in the Book there is a shortcut method of handling the task at getting the cover off, but no mention as to whether this is possible w. the 4.0. Anyone know? One thing I did notice, if in fact it is the upper timing chain tensioner at fault, is a mention at the top of page 12.1-80 in the factory manual of an “upper chain tensioner valve clamp” assembly that can be removed w/o the cover having to be removed. Remove this assembly and the tensioner assembly may be “withdrawn” (apparently through a hole in the timing chain cover?). Although it seems that this can be done w/o removal of the cylinder head, I notice when it comes time for reversing that procedure (bottom of page 12.1-82) on reassembly that section mentions having to then reinstall the cylinder head. Confusing! Does anyone know what this is all about? (I’m hoping it might mean a way of putting in a new upper timing chain tensioner w/o removing the timing cover, of course ).

If there is no shortcut to the procedure, then it looks like I’ll have to try the engine flush and/or additive route that I mentioned earlier, thinking that maybe the reason the tensioner is not working properly (if it in fact is not) is due to some accumulated crud in its oil passage(s) over the years, and hope for the best. I wonder what the risk is that the engine would actually jump time on me? Otherwise, it seems it would be easier and cheaper to just install another good used engine. ? If I were an unscrupulous Jag owner, I could try selling it as is w/o mentioning the issue and unload it on an unsuspecting buyer, but I just wouldn’t feel right about doing something like that.

One thing I do note is that MotorupMan’s earlier mention on these forums of a T.S.B. about an “upgrade” for XJS owners concerned by the typical timing chain sound made at start up: could not having this upgrade done eventually cause the issue I am now experiencing @ around 130K miles? If so, then sounds like all owners should do that upgrade a.s.a.p. if they have the noise at start up (assuming those upgrade parts are still available).

 

AttyDallas,

You only remove the timing cover (& therefore cylinder head) if you're removing the timing chain.

Just changing the tensioner takes only a few minutes. See this thread from the X300 forum with a link to the Jaguar TSB to fit the revised tensioner.

https://www.jaguarforums.com/forum/x...sioner-111051/


Hope that helps

Paul

 

Great! Hopefully this upgrade will take care of the issue described I have been having with Superblue. Thanks!

 

Thanks to AttyDallas for the original post and Paul's response.

On cold start, my 3.6, AJ6 (139,500 miles) makes more of a "faint screech / chirrup" rather than a rattle from that area so it sounds like I should be adding the modified tensioner to my to-do list.

Be interested to hear how the repair goes and if it quietens things down.

Cheers,
LeeP

 

Lee,

It's worth sticking your head in the engine bay whilst someone starts it, as that sounds more like an alternator belt or similar. Mine us currently doing a squeal on first start and throttle blip and it's the belt.

Cheers

Paul

 

Good point Paul - I'll check that first.
Cheers,
LeeP

 

While going over the parts needed for the job, I see now there is a gasket and a (rubber) o-ring seal that appear to need to be replaced whenever the tensioner is. Has anyone here actually done that when they put in their upgraded tensioner, or just went with it "as is" ?

 

AttyDallas, Here's the best tutorial I've found on the details of the upper tensioner.
Starting at about the 14 minute mark. (Everything CampChaos does is first rate)
You'll see 1 external O-ring, flat paper gasket, and 2 more tiny O-rings internally for the one way check valve. All the o-rings are almost guaranteed to be hardened unless the head's been off in the recent past. AFAIK, they only come with the head gasket kit. Or you get boxes of every size oring and painstakingly mix and match.
Focus your attention on the check valve. It moves oil one way from external pressure source, around the internal steel ball bearing check ball (rattle rattle rattle, no?) , out two small holes into the interior of the tensioner. Carb cleaner both ways around the check ball, it must be perfectly clean to seat and stop reverse flow, otherwise the tensioner depressurizes, causing chain slap.
Mine had the opposite problem, flow obstruction in the two small discharge holes, requiring poking with fine steel wire to dislodge the crud and more carb cleaner to blow it out. Then the satisfying rattle rattle rattle of the check ball was restored. Put it in your mouth and blow from out to in and hear air passing the ball and exiting the 2 holes. Turn it around and blow, ball seats, no air movement. Success.
The painstaking level of detail in these Jag motors is exacerbating. Don't even get me started on those effing two piece cam sprockets, brilliant, but infuriating.

 

Excellent job in the video, although I did point out in the comments section that the tensioner shown is apparently the OEM style, and not the "upgraded" tensioner that Jag put out to eliminate chain rattle at start up. I'm also confused about the removal of the disbtributor, which the YouTuber says is necessary, as well as a long-time poster on here who was a Jag tech back in the '90s. However, the member who posted earlier about his experience in r/ring the tensioner does not mention that is necessary, and the actual Jag T.S.B. for replacement with the upgraded version does not mention that requirement either. So which is it?