The 'E' Type Forum

I have a two part question regarding the crankshaft damper;

Should a C. damper bought off the shelf be balanced to any engine? and if not how could this be balanced with the engine still in the car?

At 3500 rpm the damper seems to be out of balance, given a standard diff ratio and a standard moss 4 speed box, what speed would it be doing?

At 3500 rpm the damper would be rotating at....ahem....3500 rpm Assuming a 3.07:1 diff the workshop manual says 90 mph at 3521 rpm....so a considerable tad beyond what is allowed by the highway code

Dampers are usually factory balanced as evidenced by drill marks on them.
You could remove it and get a machinist to have a look at it.
The 3.8 dampers do delaminate so if you are suspicious of it it would be prudent to get it looked at.

cactusman wrote:At 3500 rpm the damper would be rotating at....ahem....3500 rpm Assuming a 3.07:1 diff the workshop manual says 90 mph at 3521 rpm....so a considerable tad beyond what is allowed by the highway code

The swing of the needle is another item in need of attention, (right angle drive changed, speedo head next on the agenda) anywhere between plus/minus 20 mph officer!

Isn't it a legal requirement to have an accurate speedo on a road going vehicle? Sorry lad, that's no defence

mark10337 wrote:Isn't it a legal requirement to have an accurate speedo on a road going vehicle? Sorry lad, that's no defence

I assumed officer it was the third world condition of the roads that caused the needle to swing

abowie wrote:Dampers are usually factory balanced as evidenced by drill marks on them.
You could remove it and get a machinist to have a look at it.
The 3.8 dampers do delaminate so if you are suspicious of it it would be prudent to get it looked at.

The only things changed to cause the 3500 vibration are the fitting of a new damper and the distributor having been overhauled by the Doctor. In my mind I find it hard (not impossible) that I have a faulty new damper, being a relatively simple device to balance when manufactured.

The remaining issue could be the timing, and having set this firstly in static method 10o before tdc and then by strobe light could it be affected by the incorrect position of the metal pointer?

Hi Richard....yes pointer would make a difference to the timing......is your vibration when you are driving or stationary...if when driving could be quite a few things that have just gone wrong....lost wheel weights etc

mgcjag wrote:Hi Richard....yes pointer would make a difference to the timing......is your vibration when you are driving or stationary...if when driving could be quite a few things that have just gone wrong....lost wheel weights etc

The vibration is when driving and engine related for when dipping the clutch all is immediately well.

I'm going to re check the pointer and timing!

Hi Richard....if you dip the clutch the engine is still running at the same speed so why does the vibration stop

Dumb thought...when you dip the clutch and unload does the engine/transmission relax and stop something banging ever so slightly.....

I recall discovering the marker was at one stage (last Autumn) bent against the former damper and as a result had become worn to create a thin needle point, I believe I may have set the static timing on the wrong side of the pointer i.e. as in the engine running anticlockwise. This would I believe have retarded the engine by 10o would it not? and if so could that be the cause of the vibration?

First thing to do then is to set piston at tdc and re position your pointer......then set static timing

I can't be sure as I have never tried but if the ignition timing was 20 degrees off I doubt the engine would run well enough at 3500rpm for you to be able to notice a vibration caused by a minor imbalance in the harmonic balancer. In fact it might not run at all.
What led you to replace the old one? Sadly new replacement parts provided by our various suppliers are all to frequently not suitable or broken...
As others have said you need to check your timing.
Personally I'd set the engine to TDC with the pencil in the spark plug hole method. Then you can accurately mark TDC on your new damper. If it lines up with the existing marks well and good. If not, then you can calculate the exact positions for the 5 and 10 degree timing marks and put them on the damper too.