OT - Vibration and crankshaft damper on Mark IX

[christopher storey]

Apologies for this being slightly off the beam . As some of you know I have recently bought a Mark IX. It drives well, but I have noticed a vibration which concerns me. It is not transmission related ( except possibly if the torque converter is duff ) because it is present both when the wheels are turning and when the car is stationary. If the engine is slowly speeded up in neutral, at about 1000 rpm a moderate frequency vibration can be felt through accelerator pedal and steering wheel, the amplitude of which increases progressively to about 1500 rpm when it abruptly disappears. It can be felt both on accelerating the engine and decelerating and is more noticeable if the throttle is abruptly opened. For this reason I do not entirely exclude the exhaust system touching the chassis somewhere, although i have not been able to find a point of contact

However, the crankshaft damper concerns me . It is not like an E type 4.2 one but is similar to all earlier ones for 3.4 and 3.8 engines( including the 3.8E) with a thin large diameter outer ring bonded to the central disc to which the drive pulley bolts. With a screwdriver used as a lever by resting it against the dynamo bracket and twisting it right and left, I can make the outer ring move perceptibly back and forth perhaps 1 or 2 mm using only light finger pressure to twist the screwdriver

2 questions for collective wisdom please

1.Is the pattern of vibration consistent with incipient damper failure ?

2. Is the fact I can move the outer ring fairly easily normal, or a sign of failure ?

I should have added that with the engine rotating the disc of the damper appears to run completely true

[Hugo]

First thing I would do is take the fanbelt off & see if that makes a difference. It would be a shame to change the damper only to find out that the imbalance is in the fan ;)

[christopher storey]

Thank you Hugo : a very good idea which I shall try ; the fan is a multi-bladed one so I suppose there is plenty of scope for imbalance

[pmansson]

On my Mk9, I had a hard to trace metallic noise which kicked in at 1500, whether driving or parked in N. It was very hard to determine the source, even with my stethoscope. When the car was with CMC they found it to be at the bottom end of the downpipes, I think, and difficult to locate. This was a few yrs ago, so I canˋt be more specific.
Look forward to your findings as regards the vibrations...

[christopher storey]

I finally bit the bullet, and took out the radiator which was about the only way to get the fan belt off! I closely examined the harmonic damper in conjunction with a very experienced friend, and we both thought that although there is some very slight movement on the rubber if it is pulled in a fore and aft plane, it looked generally in good shape , and there was no discernable radial movement. The ancillaries had nothing to do with it, since the vibration is still there . The cold tappet clearances are very suspect, with five of the inlets being diminished by 50% ( ie from 4 thou to 2 thou ) and one having no measurable clearance at all. Compressions are just about ok when cold, but down to about 70lbs/sq.in when hot... Ouch . So, I have come to the conclusion that there is nothing for it but to remove the head and do a proper valve job on it

[mgcjag]

Hi Christopher...great stuff....you know you really wanted to dive in ...just make sure you enjoy it.. Steve

[Hugo]

There's a quicker way to get the fan-belt off - with a Stanley knife ;)
Rather than poking and prodding the damper, I would watch it very closely with the engine idling; - if it's running out of true you will soon see it.
Sounds like you've got bigger fish to fry anyway. Why would your valve gaps close up like that?

[phil.dobson@mac.com]

Before you dive in Chris ..could you not remove the damper and see, with a quick test f the problem is worse? if it isn't then there is little else to check other than the 'other end' of the engine/drive train? so you might be faced with an engine out anyway?

[Hugo]

That's a good point - I have a similar if very slight vibration on my Chevy Impala in Florida. I replaced everything up front (damper, water pump, fan) & I ran the engine while it was all off. The vibration was, and is, still there. It's not bad, and most people would never notice it, but I am quite good at picking up things like this, and I reckon a V8 should be smooth!
Another important thing to try is to see of the vibration is still there with the car in gear and the clutch depressed. That takes the clutch centre plate and gearbox out of the equation. That is exactly what I did with my Impala, and the vibration is still there, so I'm looking at the clutch cover next.
Mine might even be something stupid like a bolt missing from the cover. If not, I'll probably remove one bolt at a time & see if it gets better or worse.
Incidentally I just bought a Lagonda 2 litre with a similar annoying vibration. Very easy to spot
the cause though; the intermediate shaft between engine & gearbox is running out of true -
it has fabric discs each end, one of which has seen better days. Consequently, when you
depress the clutch & put it in gear (or hit the clutch stop) the vibration stops.

[pmansson]

How did the story finish Christopher?
I have a wobbling damper on a 120, and yesterday looked at Rob Beere´ s alternative to the stock item.
Can the damper be replaced from the front/oitside, or does it involve a lot more work?

[ralphr1780]

Christopher, sagged engine mounts can result in similar symptoms, did you examine those closely?

[christopher storey]

Peder and Ralph

I changed the damper for a new one, and it made no difference, and nor did running it with no fan belt, so it was not the ancillaries. I had a look at the engine mounts but they were changed very recently so I feel they are unlikely to be the source . However, as over this summer I have done some mileage - not a lot but perhaps 250 in all, the vibration seems to have lessened even if it has not disappeared altogether. I still do not rule out the exhaust touching somewhere as there is very little clearance where it goes through the chassis . So, I am going to live with it for a bit longer to see what happens