MKV Moss Gearbox Vibration

Since money appears to be no object, to those with MkIVs or MkVs…:wink:…is there a modern, easily-obtainable alloy rod one could use, instead of steel?

I don’t understand “integral to the damper” if the damper is the same part number C.533 as for Mark V. Roger’s thought suggests that the half pulley has the tapped or threaded holes, and therefore it must have the keyway and be sized to fit the end of the crank. If that is so, then it makes sense to me. What material is this Mark IV half pulley made from? Mine on the Mark V is aluminum.

Here are the 3-1/2 L cranks:
45729 or C.940 - engines M1 to M1600 and S46 to S59
50159 or C.543 - engines S26 to S45 and S___ (left blank)
C.543/1 - engines S___ (left blank) and subs.
C.543/2 - Mark V (all T and Z engines)

I don’t see any clue as to the difference between C.543 an C.543/1 unless it is something to do with fitting the damper.
I see that the C.533 damper was fitted on S.1201 and subs. with a C.1930 Center for Damper, item B10 on Plate B, which is the half pulley, so I guess that is the answer.

Yes Rob incorrect of me to state integral to the damper, the exploded dia indicates integral
to item 10, C1930 recipient of the 8 screws. Thanks for the engine numbers. The inset dia
showing just the pulley (item 8) indicates that a crank with the same nose length is/ was used
for both pulley only and damper…
That Jaguar rearranged the front of the engine just to accomodate the dyno for LHD I find
hard to believe !! A more secure fixing for the damper is my thought, I will expand on this later
after I have machined one of the earlier pulleys to accept a collet used with the damper.
Re the dyno, if repositioning was not possible surely Jaguar would have requested
Burman gears to “waist” the outer steering columm, easily done before assembly of a box, ,
gaining far more room than moving the dyno one inch. The MK 5 inner columm @ I" rather than the larger dia of the earlier 2 1/2 3 1/2 boxes would enable this “waisting”.
Peter B.

Here is a photo of both a Mk1V & V crank balancer. The Mk1V crank part of the belt pulley I had to barstardise to make sure I didn’t damage the nose of the crank removing it.

Peter

Peter thanks for the photos. The non damper pulley changed from a alu casting to a steel casting,
looking at the break on the MK4 crank adapter cum 1/2 pulley I assume it`s also a casting?
Is the internal dimension of the crank adapter from the collet seat to the chain sprocket abutment
face the same on both, or shorter on the MK4 please?
Peter B.

Here is the front of my LHD Mark V steering column.


The steering arm is pretty close to the top of the chassis frame.

Thanks for the pictures Peter Biskit, that explains it all.

Peter

The Mk1V half pulley is I assume a machined steel casting.

The distance from the collet seat to the sprocket face of the crank adapter is plus or minus 16 mm for the Mk1V & 17.5 mm for the MkV. I guess that means that they are meant to be the the same distance when taking into account they are two different machined castings.

Cheers Peter

Eureka!

The source of the engine vibration was the rear engine and gearbox mounting rubber. The original mounting had more or less delaminated and so was replaced with a new rubber mounting from Worcester Classic Spares. Having fitted it, the vibration was worse than I had recalled. That was due primarily to the rubber being of a fairly rigid construction which didn’t provide the vibration absorbing properties that the originals had, perhaps being of a softer rubber construction. After disconnecting the mounting and lifting the rear of the box with an extendable stand while the car was on the hoist, the vibration disappeared. I am going to fit one of the redesigned rear mounts (previously shown with the two rubber bushings and a cradle like structure) which, interestingly, has a similar geometric layout to the front engine mounts. I guess alignment is critical as is the need to absorb the twisting motion of the motor! Worth mentioning is the fact that I happened to chat to a fellow today who has had extensive experience with MKV’s and he said right away, “Rear engine / gearbox mountings are notoriously troublesome and cause vibration!” I wish I’d spoken to him weeks ago.

Just to note, for the sake of the record, the harmonic balancer was tight and in beautiful, balanced order. The flywheel, looking through the inspection hole in the bell housing, was true with no sign of being loose. Crankshaft end-float was also perfect. All in all, a great relief to have resolved the issue without needing to remove the engine!

Now I can enjoy the lovely, smooth and powerful car on weekend drives with my wife.
36D17A5D-1C24-4623-BF05-AE3E8E452B4E_1_105_c
Thanks to all for your ongoing support, suggestions and encouragement.

Cheers,
Tim

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Well Tim now you have hopefully solved your problem, the MK5 drives as well as it looks, two tone is always my preference, as per photo !
Perhaps Jaguar were presented with this problem in the day resulting in the change from slab mount to inclined cotton reel mounts on the XK120, and , what must have seemed strange at the time, the introduction of the pin / spring and bush mounting of the unitary saloons, now termed as MK 1s.
Threads often go of at a tangent , but,
info and insight is hopefully garnered,
the purpose of any technical forum one hopes ! There’s always the PUB for general chit chat and pleasant discourse of course !!!:rage::mask::grinning:
Peter B.ss100%20020 ss100%20008

Good news!
Was it Peter Scott said his new C478 rear mount was too stiff?

I somehow thought you already had the twin C4304 spool mounts. They were on the last Mark Vs and XK120s.
image
Someone on this forum sent me these pictures.
The splash shield is shown upside down in this picture, it should hang down and cover the rubber mounts.


With the mention of crank dampers, SS s didn’t have and I have never noticed them needing one . My sallon doesn’t have one and is beautifully smooth
Rolls Royce bought a 3 1/2 SS saloon from SS to test the oppositions product , as is still done. Having damaging the engine with sustained hi speed laps at Brooklands they put in a Warranty claim , which Bill gave short shrift to.
Possibly being miffed they claimed a harmonic vibration which may have inspired Jaguar to fit a damper.
The vibration as descibed seems exactle what happens with too heavy , later jag rods being fitted.

There are no off the shelf alloy rods. It was explained to me that alloy rods on dragsters are replaced after every event.
One can have rods made but that isn’t cheap and I think the money would be better invested in a new modern crankshaft.

No, it’s not, and yes, it would.

My understanding of crankshaft dampers is that they are fitted to minimise the risk of shaft breakage due to torsional vibration.

If the natural frequency of the shaft in torsional vibration is low enough to be matched by the rate of firing impulses then the twisting and untwisting relative to the flywheel will often cause breakage near to where the shaft attaches to the flywheel.

Rolls Royce went through a period of shaft breakage and overcame it by damping the torsional oscillations. See: https://www.mechanic.com.au/news/torsional-vibration-dampers-here-s-how-they-stop-crankshafts-from-breaking

Also: http://www.kda132.com/wp-content/uploads/2018/04/HistoryGrylls.pdf

Peter

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Hi Rob,

It’s odd that the ‘spool’ type mount wasn’t fitted to my car as it is one of the last MKV’s?
Chassis 625723.

Thank you for the photo’s. Do you think the splash guard is necessary?

Cheers,
Tim

Very interesting and authoritative documents, thanks Peter for the links.
I saved them both.
The source of the first is Australian, so Ed you should be proud and change your flag back.
I would imagine Wm Heynes was at the presentation of that Rolls Royce paper and could have been muttering to himself, “We did that too.” while he listened. Didn’t he write a paper about the XK engine development?
A good quote from the Rolls guy is about the development engineers always having to diagnose the cause of a failure from the tangled remains, and considering themselves lucky seeing the beginning of a failure accidentally.
So our pushrod engines were really designed only in the beginning stages of that vibration knowledge, and we don’t know how much was transmitted to Standard, nor how much they transmitted to Jaguar.
That torsional vibration harmonic couples and mathematical fun stuff was in our engineering textbooks by the 1970s.

Tim, perhaps your rear mount was changed for any number of reasons with the change in engine. The splash guard may have been more relevant in the days of unpaved roads, so perhaps not as important now, but not that much work to make yourself if you want to, just sheet steel with 4 holes and a bend. I think I once gave dimensions for it on the XK forum.

Hi,

Yes he did. I have a copy of it somewhere.

Cheers!

Hi Rob,

Yes, you can get the article here

Then of course there is my own learned article here. :innocent:

Peter :wink:

I like sharing good news about Pre-XK cars!

Having removed the old, damaged and poorly welded sump with a lovely, undamaged replacement sump, I discovered that the engine had been completely overhauled (and very well done) not so long ago. What a joy to have such good fortune for a change. I’m really beginning to fall in love with this car.

Cheers,
Tim

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Surprises like that are priceless!

Hi Tim, just a tip, if you separate the downloads it makes the photos just that little bit easier to discern, just make sure you pick up the exclamation mark at the start of the line: