Remember now. Well, the head has been machined, it didn’t fail from the factory… mistakes happen, even to the best!
I agree that once the temperature exceeds the thermostat opening temperature, it’s cooling as good as it can, just saying there might be a difference between 10000 cycles 20-72° vs. 10000 cycles 20-88°. Even though it’s just about 15°, there is also an extra cushion of 15° in earlier configurations. Maybe that has an impact, but - just maybe. Later configurations also have better cooling, theoretically, so there might not even be such a cushion, fact is that the youngest 4.2 engines seem to be much worse, especially those with cat and other emissions accessoires that make it run hotter and hotter.
Yes, that was always going to be uppermost in my mind, but having discussed it at length with the machinist I am satisfied that they did the best possible using best quality proprietary parts. It may be that the tappets are now only made in one particular size, I don’t know. But David was very happy with the fit on the new ones. I had changed the tappets, and wondered if there might have been a slight dimensional change in those, but they were within 0.0005" of the ones in the guides that failed so I’d say not.
I have a feeling that modern 98RON here in the UK (which is E5) runs hotter than the old 5-star petrol did. I don’t know - but at the moment, I’m putting the incident down to a new engine probably running slightly tight at first, my decision to change some components after the initial run (i.e. cams, as I’d set the clearances to 4 and 6 as per the book and had a completely silent top end, leading me to check the clearances, note new scuffing to the cam lobes, and ultimately change the cams and tappets).
A sequence of events, hopefully now sorted. But, nevertheless, I’d never build an XK engine without the hold-downs now. On both sides.
Also very sure that fuel quality (burns hotter? Lean burns hotter, timing is never that precise, a little bit of difference on a well tuned engine- think so?) and tappet size have nothing to do with what the guides do. If the tappet binds the valve will go before the tappet. Water under the bridge…
In the factory they had a consistent supply of new parts, everything was set up to make thousands and they had a lot of routine so I imagine it was a lot easier than today; I do hold today’s good machinists in very high regard, not trying to say it was bad work or anything.
Another question to go with the ones before - Who make the most accurate Camshaft Bearings? Most of the bearing sets are of half / split bearing shells. What about the type that is a complete circle? I was told that Holyoake make the best bearings. Is this a fact?
Would you believe this? I live in Michigan, near Detroit. This is supposed to be the motor capital of the world, but look as we may, We cannot find anyone in the Motor City who can align bore a Jag Camshaft bore in the Cylinder Head! If anyone knows of a service in Detroit or Michigan, please let me know. Thank you!!!
Are you sure you need it? Camshaft bearing wear is kind of unusual with XK engines.
They are always half shells, never complete circles like cams in the block.
The last set I had were made by Vandervell.
Karl, are you looking to redo the cam bearing bores because the head has warped ? As Rob point out the bores seldom need aligning. The heads can curl up when over heated and that will tighten the cam rotation.
Would go off topic to discuss straightening heads. Also to the above, the cam bearings are split. There is a shop in Detroit I think has a mandrel small enough to line hone XK cam bores but it would be really a unusual circumstance to need that process.
Can I please have the name of the shop in Detroit that can Align Bore the Jaguar XK Camshaft Journals? My head has a replacement set of Journal Caps that are not matched to the Head. Thanks!
cam bearings and caps…bearings…best-well Vandervell NOS if you can find them…but Country and others available now…half shells…press in by hand…with care…they can bend easily. As to non original bearing caps…as we know…original were all line bored…and matched…IF–just one or two to be replace…try a few…you may get lucky…once installed see if cam rotates freely as it should…but missing caps is a big issue…to replace all. As to guide hold down–as said…why not…put em in. Still–curious as I have found no period mention of problems, or race/rallye car issues with tappet guides and the factory did not issue a bulletin, nor a hold down, or change the install method…other than a oven temperature revision. --Have to look that up…maybe that DID have something to do with guide retention:??
Nick
If its impossible to get the cam bearings line bored, as a shade tree bodge you could try removing the locating dowels and nip up one cap at a time and see that the cam shaft rotates freely, rinse and repeat
Hello David,
I just wanted to know which brand of Camshaft Bearings was considered in your collective opinion to be the highest quality, Vandervell, Mahle or…? May as well go for the best, right?
Not precisely true: it’s certainly became more of a problem in the later engines, but I did do some tappet holddowns on older Jags.
I would use the method where you didn’t even take the cam cover off: you would drill a small hole into the tappet guide, through the valley area, then put in a small Allen head grub screw into it.
Vandervell was the brand used by Jaguar, at least in the 1950’s.
My original Vandervells were hardly scuffed, no wear detectable by plastigage and a micrometer and bore gauge anyway.
But that’s just the opinion of a dumb American degreed and professionally licensed mechanical design engineer.
Well I did find out something! Mahle now owns what used to be Vanderveen!!
And what’s wrong with trying to get the best? Like everything, not all bearings are created equal!!
The cams are never run over 3000rpm (half crankshaft speed) and you have answered your own question to a certain degree, as you say Mahle now own Vandervelle bearings, that halves your choices.
Tony Vandervell was the British engineer whose company produced Vandervell ‘thin wall’ bearings, running a British Racing Green Ferrari in formula one which was equipped with them (named the ‘Thin Wall Special’ in Indy fashion). He later funded the entire Vanwall formula one team, amongst whose drivers were Tony Brooks (my hero) and Stirling Moss.
Just thought you’d like to know…
edit - before Vandervell introduced his thin-wall bearings, steel backing shells with copper and lead-indium coatings, British engines mostly used white metal bearings, built up in situ and scraped back to size. Lovely if your craftsman knows what he’s doing, but an absolute and expensive pain if you need a set re-metalling in present times. Ask my Riley how I know…
Yep, Babbitt bearings (patented 1839 by Isaac Babbitt) are well known among fans of the Ford Model T.
Wikipedia has quite a good write-up about Babbitt alloys.
