Another day into the mystery vibration and after an analysis on the oscilloscope we can eliminate the crankshaft, pistons and con-rods. A few people have suggested that the Harmonic Balancer might be loose. The rubber in the balancer is supple and the unit is undamaged. It might be that the balancer has not been installed correctly (centred) so it might be worth removing it and reinstalling it. What do people think? What sort of torque setting would be adequate on the main retaining nut? If that doesn’t solve the issue then looking at the flywheel and pressure plate will be next. I don’t know what Pressure Plate assembly has been fitted or what condition it could be in? If it is serviceable and correct for the car then it certainly won’t hurt to have the complete unit properly balanced. I was wondering if the balance could be affected by worn locating Flywheel dowels? Perhaps also there might be no locking tabs washes under the nuts on the flywheel allowing it to become slightly loose? I was also wondering what would happen if the Starter Motor teeth on the Flywheel were worn, damaged or even missing in places how that would affect the balance? All will be revealed if the Harmonic Balancer isn’t the culprit.
It will be very satisfying to resolve this issue and begin to enjoy this lovely car.
Cheers,
Tim
That’s a great picture, Peter. It never occurred to me that you could run the engine with the gearbox out.
The Mark V does not have the left side stabilizer found on Mark IV and our SS’s.
I found a picture of the back of my damper before I restored it.
I don’t think you can really install it wrong.
There doesn’t seem to be any torque spec for the crank nut, so give it a good normal tightening.
Talking of balancing clutch pressure plates, here is what I found on the one from my '38 SS.
A strip of steel welded on one side, and two holes I suppose for lightening because the strip was too heavy?
There are no alignment dowels on this flywheel.
My balance shop always recommended balancing the cover and the flywheel as a unit: if/when that car needed a new one, he’d balance the replacement cover to match the old one.
Yes, XK engine clutches are all balanced on the flywheel at the factory, and there are B balance marks. I was surprised not to find them on this car.
There were balance marks on my Mark V clutch, same letter B as with XK engines.
What about running the engine for a brief test without the harmonic balancer? The 2 1/2 litre engines did not have harmonic balancers. A brief test without balancer would also mean no fan belt and water pump operation, but for a minute or two that seems fine.
Another thought, is the fan blade assembly balanced and centered on the water pump?
What does this stabiliser look like? The motor in my car is an S-Series from a MKIV but has all the MKV bits. This was done by Jaguar when they had the ‘swap and go’ practice for engines and gearboxes at the dealerships.
To follow up on the posts. The motor has been run with the fan belt removed to rule out water pump or generator or even the fan belt, I guess, however the vibration still persists. The two front engine mounts are fine and tight but I must check the rear mount again. Is it possible to misalign the rear mount? The harmonic balancer will be checked for tightness next Monday.
Cheers,
Tim
I will ask the workshop to check for signs of one on Monday. Do you think that it would make a difference as the motor is a MKIV S-Series engine? So the engine has two front mounts and a rear mount, as well as the stabiliser? This might be the issue if the S-Series motor is designed to have one?
I don’t think you could really mis-align the rear mount, but it could become spongy and gooey.
Early S engines did not have the crank damper but later S engines did.
If the S engine was converted to a T or Z spec Mark V, by putting on the Mark V damper and centering flange, in theory it should not need the side stabilizer mount.
Is it put on the same way as mine? Or the opposite way as Mark IV had it?
It seems like the next suspect to question is the damper. You can take it off and run the engine for a minute or so as Roger suggested. But with no damper at all it might vibrate in a wider range.
I see what you mean about them being reversed on the MKV compared to the MKIV. I assume that this was done to align it with the water pump on the MKV which has the spacer bringing the pulley forward allowing for greater coolant flow? I’ll have to look at it next Monday. I will also have it removed and run the motor briefly to see if that makes a difference. Perhaps it’s out of balance? Do you know if would have been balanced before fitting and how? I note also that the means of holding the damper in place is different on both models and due no doubt to the alignment with the water pump pulley.
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I’ve just been chatting with an engineer who said that the Jag Harmonic Balancer is a Zero Balance which means (as far I could take on board) that it could be fitted any of six possible ways by virtue of it being bolted on. Would that would mean that the unit itself would need to be balanced in it’s own right?
Cheers,
Tim
Additionally, can a MKV Harmonic Balancer be fitted to a MKIV S-Series crankshaft? Part number 7 in the MKV diagram is not fitted to a MKIV. Is it just a distance piece to align the pulley with the water pump?
So presumably that means it was simply turned around on both engines to change the position of the fan belt pulley to accomodate the variations in water pumps?
What is the purpose of Part 7 in the diagram? Is it just a distance piece?
The part 7, the offset water pump cover, and the altered air intake pipe for the carbs allowed the left-hand drive steering column of the Mark V to clear the generator by moving the generator forward relative to the earlier cars.
And my memory is that the harmonic balancer should be balanced by itself prior to mounting to make it zero balance at static. Since the balancer is only helping with rotational issues in frequencies, it should be zero balanced and not matter which orientation for mounting. My memory is the harmonic balancer has voids machined on the flat side to bring it into balance after construction.
I think that I’ll investigate the harmonic balancer a little more by having it removed, checked over and balanced before refitting. A website for a company that specialises in harmonic balancers says that if the nut securing the balancer is loose then that will cause vibrations.
It’s like most things, the answer will be obvious when the right question is asked!
The balancer is the way you have it on your car and all MKV’s. Roger’s point that all balancers on MKIV and MKV motors are the same part number was very interesting.
Not being too bright, I hadn’t realised that the the rubber gearbox mount is also the rear engine mount which has been renewed just over a week ago. In Australia there is a company which manufactures a mounting bracket which incorporates two rubber bushes. It is said to reduce engine vibration so I may as well fit one. You just never know!
Just to be clear, my suggestion regarding this torque reaction strut is that you remove it just to see if it alters the vibration that you have. If it removes the vibration then it would be worth experimenting with different softness of the rubber chassis mounting (or possibly just placing a softish rubber washer on each side before screwing it down.)
As to the crankshaft damper, I suspect this is a very minor player in any vibrations that you are experiencing. I think it was fitted to minimise the risk of crankshaft breakage due to torsional vibration and it was only added to the 3.5 litre because they increased the weight of the flywheel on that engine which puts greater stress on the region of the shaft where it attaches to the flywheel…
