Can someone tell me the valve clearance on a 150 S? Also, how can I verify that it has the original cams?
(The engine is reputedly original, but you never know…)
Valve clearance is 4 thou inlet and 6 for exhaust as shown at the bottom of your ID plate pinned on the firewall.
Verify the cams by removing the rocker covers and read off the part number stamped on the shaft. Inlet and exhaust will have different numbers Inlet co-13081 exhaust co-14985 Cam lift is 3/8th lift.
I always set mine to 0.006”, in., and 0.008”, ex. Not much more noise, and an extended period before needing a readjust.
A two-bolt system was used to mount the sprockets to the early cam’s mounting flange. If you have this system, the tighter clearances are called for.
4 and 6 are what is on the plate, but as I don’t know the history of the car (nor am I all that familiar with pre-'60s Jags) I’m just trying to ensure that the bits are right.
Still trying to get to the bottom of what may not be right with this engine.
What casting marks should I find on a 3.4 head for a 150 S?
What I am faced with is gaps that are way out of spec (one single tappet would be within the standard range).
The valve guides are very sloppy.
The head has the right number stamped, but the water passages show none of the typical corrosion, and there is no indication that they’ve ever been welded.
My spider senses are tingling.
Andrew,
If you are getting concerned, a few photos of subject head will help.
If its a 3.4S head, then Engine Number stamping will be VS1001 to VS2211, and a clear photo of that stamping will quickly reveal if stamping is original or altered.
If still in doubt, at the rear of the spark plug valley you will find another AB123 format stamping - this is the Head Sequence Number (my terminology), and there are those of us that record these and can correlate whether the HSN is consistent or not with the stamped in Engine Number.
If still in doubt, the actual casting (before machining) is unique, with cast in lettering/numbers on the underside of the head - again there are those of us that can quickly ascertain whether the actual casting is consistent with being a 3.4S head or not, regardless of the Engine Number and HSN stamped in.
But you should be aware that early 3.4S heads were Part No. C.12600 and these were unique to early XK150S 3.4 litre engines, with later 3.4S heads being Part No. C.14957 and these were shared with 3.8S heads and 3.8 E-type heads. So underneath photos of cast letters/numbers helps.
But by checking Engine Number and HSN stampings, and underneath casting numbers; you can positively identify head.
Now I also take to task your comment about ‘typical corrosion’.
No such thing.
Corrosion or not, and if there is any, to what extent is totally variable depending on a number of factors, not least of which being the quality of the water used to top-up the radiator, and indeed whether any additives added to water and again quality/type of additive.
My Sept 1955 XK140 clearly had good quality water and indeed apparently an anti-freeze/boil/corrosion additive from new, and when I pulled down motor forty years later for a head job, there was wear in the valves and the valve guides that was sufficient to warrant their replacement, but as far as could be assessed there was ZERO corrosion in either the head or the inlet manifold, apart from some minor pitting on the radiator hose outlet pipe at its very end, that did not warrant doing anything.
Growing up in the 1960s/70s in Melbourne, known for amongst the best water quality anywhere, playing with Jaguars, head and inlet manifold corrosion was unheard of, and we just used tap water with no additives, Except if a used Jaguar had been purchased from Interstate (depending which State). Indeed one car purchased from Sydney with (in Australia) notoriously poor water quality (ph level and inclusions) in the 1960s/70s, with then little use of additives, had a head that was so badly corroded throughout all the water galleries it was not considered worth salvaging. These days, additives are used widely as a matter of course, but for an 1950s XK150S head, depends where it has spent all its early/previous life whether it will have corrosion or not. But nothing wrong, having no corrosion and badly worn valve guides - they are mutually exclusive concerns. Valve guides are easily replaced by a competent engine shop, corrosion repair a very specialized job, that does not always save a head.
Valve Clearances are of course dependent on having original/correct cam shafts, but an original VS head would have left factory with .004 and .006 valve clearances, and indeed one only .085 to .110 SHIM fitted per valve. Valve seat wear can to some degree be compensated by SHIMS now offered after market to sizes outside factory range, but it gets to a point where valve seats may need replacing, and that is not a job done lightly or my a machine shop not specifically experienced in XK heads, and the interference shrink fit of valve seats and the essentiality of uniform heating of the complete head casting. Wider than .004 and .006 clearances don’t cause any problems, albeit generate ‘tappet noise’ to various degrees, but a properly set up head at .004 and .006 will last for years without attention, with a circumspect check every few years. You only get a problem when clearances close right up to zero or less, with .004 and .006 having a good margin before trouble.
Roger
We in Colorado were, apparently, also similarly blessed.
I could tell if a Jag was a ‘native,’ when pulling its head, and looking at the corrosion.
I’ve just had my 3.4 C-Type head totally rebuilt with valve seats, new valves, valve guides, intake valve seals, and steel spark plug thread inserts (not Heli Coils). The shop I used specializes in rebuilding aluminum cylinder heads and has done many XK heads.
If you can no longer adjust the valve clearances using the smallest Jaguar SHIMs of .085", then you should be considering new valve seats. Many of these 60 year old heads have had so many valve grindings, that it is now impossible to obtain correct valve clearances using the range of Jaguar SHIMs. In the case of my C-Type head, the seats were receded so far that previous clearance adjustments were obtained by trimming the tips of the valve stems.
If your head is at the point that the seats need replacement, purchase 12 new SHIMs midway between the .085-.110 original Jaguar SHIM range. For example .097 or .098. A competent shop will have the capability of cutting the new seats to obtain the .004 and .006 clearances using the 12 new .097 or .098 SHIMs. Setting the head up with 12 new SHIMs (and new valves) in this manner will allow future valve clearances to be accomplished for many years into the future. I would avoid using any shop that recommends trimming the valve stem tips to set-up the valve clearances.