engine mount - vibrations

[josefewald]

Hello,

can anybody help me with detailed information regarding the engine mounts?
Instead of the clutch type material I now have softer rubber between the small leaf-springs; the idea was to have a softer bedding of the engine. However, I still have vibrations that are being transferred onto the body by the engine at certain revs.
What is the correct type of material used between the leaf springs?
Any more insider information on the engine mounts?
Many thanks!

Josef

[GG]

Its very hard to judge what is the original level of vibration, but if its irritating, perhaps look at the details of the installation: look for any direct "metal to metal" contact from the engine side to the body side. Vibration on an Aurelia once took forever to figure out and solve. It was due to the motor mount, compromised and without effective rubber isolation between the engine and the car.

[ben]

As I understand it the flexibility of the engine mounts arises from the bending of the leaf springs together with the compliance and isolation provided by the rubber spacers above and below the brackets.These rubbers are or should be installed such that there is no metalic contact between the engine brackets and the springs and bolts.
The leaf springs should be clamped together with solid spacers between them,typically made from fibrous material such as clutch lining that you mention. They are there to separate the springs and allow them to flex freely.In practice they slide to and fro a small amount as the springs flex and hence they wear out!
If you have a transmitted vibration problem it might help to install the springs with grease in the interfaces.
I do not think soft spacers between the leaves is a good idea.
If your engine has been rebuilt with replacement pistons or rods etc perhaps you have a fundamental ballance problem?

[davidwheeler]

I agree, my engine does not vibrate after close attention from Vibration Free after I fitted steel con rods, shell big ends and oversize pistons.  They said that at first "it nearly jumped off the rig".   Aprilia engines should be inherently silky smooth but engine balance in narrow V4s is typically difficult - there is a long essay on the Lamda thread about it (highly complicated mathematics, I warn you).

[josefewald]

Many thanks to you all for your advice!

I will go back to finding the cause of the vibrations, sort this out (already talked to vibration free) and then check the engine mounting.

Best
Josef

[ben]

For general interest (!?!?!) I have taken some pictures of the Aprilia engine mount components.
In true Lancia tradition why make a single bonded rubber mount when an arrangement with about 20 individual elements will do!

Hopefully the pictures speak for themselves.
The tubular "bolt" clamps the leaf spring leaves and their spacers together under loading determined by the coil spring to generate friction damping as the leaf springs flex.
The inter leaf spacers are 5mm thick and those above and below the leaves are 3mm thick.
The engine weight (plus any vibration forces) are transmitted through the rubber bushings downwards directly into the leaf spring stack and upwards via the through bolt that goes down through the middle and holds it all together.
When assembling these mounts it is a bit arbitrary how tightly to do up firstly the nut on the hollow bolt clamping the leaves together and then the through bolt which squeezes the rubber bushes as it is tightened.
My recommendation is to compress the coil spring about half way with the tubular bolt.If you overdo it the spring becomes coil-bound and thus serves no purpose and the leaves cannot slide easily as intended.As shown in the last picture I have come across several instances of the hollow bolt having broken away from the upper "u-plate" which acts as the bolt head which is probably because it has been overtightened.
Then when the engine is installed I suggest tightening the through bolts about two turns beyond the point where the clearance is taken up.They then need to be locked with split pins of course!

[ben]

Ran out of space for this shot!

[ben]

whoops!

[GG]

And the technical thinking behind it - here is the patent, which was first filed in 1932, probably for use on the Artena first.

[simonandjuliet]

Fascinating document !

[josefewald]

Thanks to everybody for the advice. I think I made quite some progress, although involving some surprise.
I had the engine sent to Vibration free in England, had it balanced and sent back. They told me to look at the thrust washer since it had too much play. Mind you, the engine has run some 5.000 kms. When we had a closer look at this and the crankshaft as well as the bearings we discovered faulty bearings, some white metaling came off the bearings. I had these inspected by a bearing specialist and compared with the original bearings that I kept from the engine overhaul. Unfortunately, the new bearings were faulty since the white material did not stick to its base.
I will now have new bearings made by the white metaling specialist.
I think Aprilia owners should bear in mind that the bearings one can buy today from the main Lancia parts suppliers do not necessarily meet the required standards. This is my experience.
I will write up once we made further progress.
Best regards
Josef

[ben]

Hi Josef
          Sorry to hear of your continuing problems.
          Hopefully the balancing will still be of some benefit after you have remade the bearings---I assume it is the main bearings that are at fault rather than the big-ends---and you will have to have them line bored again after being re-metalled!!
          Are you able to say who supplied the sub-standard ones?
Ben

[brian]

As I have said elsewhere, I am a true fan of VibrationFree! They diagnosed a probable main bearing failure and not the propshaft that I suspected and Thornley Kellam are as we speak deciding what path to go down - white metal or shells.

[davidwheeler]

It is not difficult to modify the big ends to take shells and this would likely give a much longer life.  Mains seem to last a very long time anyway so white metalling would be fine.    Many years ago Harry Manning used to adapt Aprilia crankshafts to take shell bearings by building up the journals but I would think it easier to make carriers to fit in the big end journals to take the shells to substitute for the cariiers that take the white metal- that is unless you have original duraimin rods running directly on the big ends without any other bearing metal!

[brian]

The only (!) problem with shells is the requirement to put a modern oil filter on instead of the clutch-pedal-operated one.
Brian