Crank pulley

[Dusty56]

I have a Marina engine which I am preparing to put into our Minor.
The engine has been fitted with a Minor crank pulley.
Would it be better for me to fit a damper pulley and if so is a "performance" pulley worth the extra cost over a standard item?

[kevin s]

Yes a damped pulley is a good idea (even on a 1098), the pulley is usually matched to the flywheel, unless you are planning a significantly lightened flywheel / clutch I would stick to a std one.

[philthehill]

The pulley is not matched to the flywheel. The flywheel is factory balanced separately as is the crankshaft damper pulley on a master (for want of a better word) crankshaft and therefore the flywheel and crankshaft damper can be fitted to any engine without any concerns.
The damper crankshaft pulley is a must for use on a 1098cc engine as the 1098cc is more prone to vibration than say the 948cc engine.
All of the damped crankshaft pulleys are suitable for fitment to the Minor engine but you may have to remove the engine management timing disk (drill out the three rivets). The timing 'V' in the rim of the damped pulley may not be in the right place but it is easy to re-align the marks.
You can retain the Minor starter dog when fitting the damper pulley.
There is absolutely no need to fit a performance pulley as the standard BMC/BL damped pulley is more than adequate for the job.
There are various ex factory damped pulleys available but they all do the same job at the end of the day.
Below is a BL damper pulley which has had the engine management disc removed, the rivet holes tapped which can be used to remove the pulley with a harmonic pulley remover tool.

Damper puller.JPG (873.97 KiB) Viewed 816 times

There are several damped pulleys on 'e' bay - here is one that looks useable.
https://www.ebay.co.uk/itm/295435791477 ... R761kr6uYQ
If buying S/H make sure that the rubber between the inner and outer parts of the pulley are not cracked or starting to peel away from each other.

[Dusty56]

Very helpful, thanks

[kevin s]

Not the balancing but the rotational inertia of the pulley secondary mass and rubber stiffness on a damped pulley are based on the rotational and bending dynamics of the crank, the flywheel/Clutch inertia is one of the most significant factors.
A good example of this is most modern diesels which have different crank pulley tuning when moving from single to dual mass flywheels.

[Bill_qaz]

If buying S/H make sure that the rubber between the inner and outer parts of the pulley are not cracked or starting to peel away from each other.
[/quote
BMC truck engines used to have an alignment reference on inner and outer hubs to show movement when rubber was deteriorated not sure if A series has the same but if so useful check if buying second hand.

[philthehill]

kevin s
The damper pulley can be machined to vary its mass to match the balance and dynamics of the crankshaft/flywheel.
The Cooper S damped pulley is different to all the other BMC/BL damped pulleys as the engine characteristics are different. The Cooper S damped pulley is a two piece item and is much lighter than the other BMC/BL damped pulleys.
Below is a photo of the Cooper S damper pulley as fitted to my race tuned 1380cc engine. The pulley is much lighter than the normal damped pulley because the useable engine revs are much higher than used on a normal road car. Therefore the Cooper S damped pulley should not be used on a normal road engine without having the whole rotating mass i.e. crankshaft, flywheel, conrods etc balanced both statically and dynamically.

WDF engine 6.JPG (1005.87 KiB) Viewed 771 times

[Bill_qaz]

Sorry Phil, somehow got my comment in response to your post blended as if your quote

[philthehill]

Bill, no problem.
Having the alignment marks is a good idea.
Because of the way the BMC/BL damper pulley is manufactured it is near impossible to fully ensure that the three parts of the pulley are not coming apart. You just have to look very carefully at what rubber is visible and if there are any cracks or rubber loss do not use.
Below is a BMC/BL damped pulley with a chunk out of the rubber shroud. With the shroud in place you cannot see the state of the rubber damping material.

Damper pulley 3.JPG (1.05 MiB) Viewed 695 times

Below is the same pulley with the shroud removed. Removal of the shroud allows for examination of the rubber damping material.

Damper pulley 1.JPG (914.82 KiB) Viewed 692 times

BMC/BL latterly made the damper pulley without the shroud.
Phil

[Bill_qaz]

Very similar to the ones use on smaller bmc truck engines, the larger ones used viscous dampers.