One of the “usuals” should consider providing an upgraded spring with thicker end loops that won’t wear through as fast. I remember seeing the same thing with my spring end loops.
This is what chiefly bothered me about the original oil spray brackets. A single metal stud, or post serves as the mount for the entire blade. The other end just floats in a groove. The original in the background had messed up threads for the spring blade post, then someone attempted a thread repair which in turn also failed. I ended up milling and profiling the replacement out of steel in the foreground. This later had the mounting holes drilled and tapped after the picture was taken and now does duty on 670898. In hindsight, yeah, maybe I should have gone the hydraulic tensioner route per Roger’s original query here.
Thanks for all the input, chaps - I’ve decided to do the conversion. The Rolon-type tensioner is used in all sorts of other cars - I seem to remember my Stag having at least two of them - and I’ve not had issues with them in the past so I’ll take my chance with the Coventry Automotive kit. I plan to fit the 150’s small oil filter in the mounting too, just for added security.
Back to cleaning the engine parts. Boy, does the black varnish build up on those aluminium timing gear castings… thinners, brake cleaner, nothing seems to touch it.
Surely if the chain let go and the cams weren’t turning you’d have bent valves and/or holes in the pistons all over the place?
Back in the '70s the eccentric chain tensioner sprocket on my 120 slipped, as someone hadn’t tightened it up properly. The engine was only idling at the time when it suddenly stopped dead with an ominous clunk… Lifting the bonnet revealed fractured cam cover and front of head with a length of chain hanging out! Fortunately, on strip down, the pistons only had some tiny marks where valves had made contact. The head was junk, though. One cam had sheared as well - pity, as they were D-Type cams. If this happened at idle, I shudder to think what would have happened if this had ocurred when I was doing over 90mph a few minutes earlier… 
Wow. Is there any way to build in an anti-rotation device for the eccentric once it’s set? Shouldn’t the spring loaded toothed plunger do that?
Got the black varnish off. Decent quality paint stripper.
Hi Roger,
Gunk Carb Cleaner takes all that stuff off with very little effort, just soak the parts in a shallow pan for a few minutes and everything will be back to new condition in short order. Use a parts brush to work the heavy areas. The scent is very strong so do it in good ventilation.
Yes, it should. I seem to remember that the whole toothed wheel just dropped off after the nut fell off.
Yes it does, that’s it’s only job.
Well, there’s not enough thread on there to drill it for lockwire, but I guess a new toothed washer and a dab of red Loctite should be OK… after all, there are several thousand XK engines running around which haven’t had their pistons lunched by the valves due to this.
A few weeks ago someone posted the tear-down of a VW W8 Passat engine. It was interesting to watch the excessive engineering that went into it (3 cast intake manifolds and 3 cast oil pans).
What really caught my attention was the timing chain tensioner shown in the center of this picture. Anyone who’s rebuilt any variety of British engines will recognize it right away.
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Just an update - I eventually ordered a spring-type tensioner from Jaguar Land Rover Classic. It was around the same price as the major suppliers for their better quality offerings, but appears to be of a superior manufacturing standard. The cast body is completely different from the Rolon item, and it is supplied with two steel shims. The oil hole in the side is full size, not the Rolon pinhole. The tensioner head looks to be very well made with the rubber bonding covering the entire head of the part. The Jaguar box still states ‘Made in France’, but I’ll be perfectly happy to fit this.
Hi Roger,
Very interesting, yet another twist in the design of the tensioner. How does the size and location of the chain lubrication hole compare to the original part? Please post a picture of the face showing the hole.
Tom Brady
Hi Tom,
That is the hole in the picture! The base may be 180˚ rotated in the photo, sorry. The hole aligns with the holes in the shims and the block.
Roger
Hi Roger,
Sorry, I should have been clearer. I’m looking for the size and location of the hole in the face of the black rubber plunger that contacts the chain. That hole allows the oil to exit and lubricate the chain, and also bleeds off oil pressure thereby controlling how much additional force is applied to the chain due to hydraulic (oil) pressure.
In addition, what possible reason is there to supply two plates?
Tom Brady
That’s the same one I used. I’d bet is was made by Renold but not stamped such. The rubber shoe was well wrapped. Be sure to transplant the locating dowel from the old one to new. I was bit irked that it wasn’t just on the new one, because it was a pain to get out, but at least the hole was the right size.
The plunger lube hole is correct. Note there are two different versions of this floating around in LRover boxes. One has the tiny pinhole in the back. That obviously is not the one you want to find. The hole in this one is the same size as the original and the dower can swap from the old one to the new one. You use one or two plates to get it as centered as possible and moving without making any contact at all with the block. Having two thin ones is better than one thick one because you have an extra option.
Trying to figure out how that works. Apparently the plunger pushes a lever and the shoe is on top of the chain. I’ve never seen a tensioner design that pulls the chain inward toward itself. That’s some wacky German engineering.
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You should try to obtain the little locating/oil passage dowel for your new tensioner. The hole in THAT regulates oil pressure force the tensioner generates based on the difference in sizes between the dowel’s hole and the rubber foot’s hole.
I was planning to fit the small conical filter in the Coventry Automotive conversion block - I think it sits in the block, where the dowel would be. I don’t know if there’s room for both. The 150 had the filter as standard, I think, as it had this type of tensioner. Did the 150 have filter and dowel together?
I don’t see how this is a hydraulic tensioner. It seems to me to be more of a sprung tensioner with a spiral ratchet to move to the next tooth. Surely the oil is only for lubrication of the tensioner and the chain?
Oh no, if you measure the diameter of the tensioner bore, then do the math, you will see that the supply pressure from the oil gallery, minus the bleed(from the spray hole in the rubber foot), results in a net pressure increase on the chain above that of the spring alone. The springs I have only exert a pound or two of pressure so a larger supply hole vs bleed hole results in more pressure as the engine revs. This same principle is used on the Datsun Roadster 2L , only that engine omitted the ratcheting device, a foolish error. On the Datsun, the chain would rattle like crazy at low oil pressures, yet be properly controlled at higher revs. This was due to the increase in “hydraulic assist” provided by the oil gallery.