Pinking - Wrong dizzy?

[Freebird]

Hello everyone

My Vit pinks badly in the mid range once it's warmed through. It has a 2.5 saloon engine with 1 3/4" SUs, PI head, pistons and cam.

I suspect the ignition timing is advancing too much, but there are so many different things that can cause this that I don't know where to start.

It has a 22D6 distributor - original on the 2.0 Vitesses I believe. I see from the tecky sites that the 2.5 engines has 25D, 43D or 45D depending on spec/year etc. Could this be fundamental? I have no idea what the differences are.

Glen.

[Nick Jones]

Hi Glen,

Is this full throttle or part throttle pinking?  Is the vacuum advance connected - if so, does disconnecting it change things?

There are lots of changes that can be made to any of the distributors - doen't really matter which one you start with so long as it is decent condition.

Generally speaking they work like this:

Static advance of 10º BTDC.  Full centrifugal advance of 32º @ approx 4000 rpm, which means the distributor needs to supply 22º advance.  Note that this equates to 11º distributor degrees because it rotates at half engine speed.  The actual distributor advance of your unit will be stamped on the mechanism, visible once you remove the points plate.

You will see that the centrifugal advance mechanism comprises two weights, each with a control spring.  The rate that this advance is tipped in depends on the strength of the springs and the weight/shape of the weights.  One spring will usually be quite light and this controls advance lower down the rev range and the other stronger one starts to act as the revs increase. Moss used to do packs of springs of various strengths so you could play around.

Under partial throttle, the charge in the cylinder is less dense and burns slower, so needs more advance to get the best from it. The vacuum advance exists to give additional advance under light throttle to improve torque and fuel economy.  It has no effect at full throttle.  There are a range of different vac capsules available for the lucas distributors and their characteristics are marked on them.  Usually two double digit numbers and a single eg 10.15.8, where the first number is the vacuum (inches Mercury) needed to start it moving, the second is the vacuum needed for full motion (inches mercury) and the third is the total advance given in distributor degrees (so double it for crankshaft degrees).  These capsules vary alot and if you have part-throttle pinking which is cured by disconnecting the vacuum pipe, this is your culprit.
If your distributor is from a Vitesse Mk1 2L, there is a good chance this is the problem as the vac capsule gives alot of advance.

There is then plenty of scope for tuning your distributor, but it is very fiddly and time consuming - I love my electronically mappable system!

Good starting point is to set the maximum advance.  This should be around 32º BTDC at 4000 rpm with the vacuum advance disconnected.

This quite a bit of info about this on the web - google is your friend...... here are a couple of links to get you going....

http://www.teglerizer.com/mgstuff/advance_curves.htm

http://www.triumphclub.co.nz/technical.html

http://www.triumphowners.com/resources.cgi?articleID=111457&parentID=111456

Good luck!

Nick

[mk2vitesses]

I thought we just did this one on the "rolling road" thread??

[Freebird]

Hi Simon

We did and thanks for all your help. I just wanted to do another post with a title aimed more closely to the problem as it has emerged.

My mechanical advance is stamped 11, so I've already got the right one to give 32 in total - so that's good.

I will try disconeecting the vac advance today, after that I'm taking the prop shaft off to fit new UJ's and get it balanced.

Glen.

[mk2vitesses]

I thought I was having a touch of deja vu!

[Freebird]

Simon

Apart from the above post. you post at strange times of the day (night here) - where are you?

Took the vac pipe off and the pinking did go away. Performance went a bit flat, but not too bad. Now need to source an alternative unit - the distributor doctor is supposed to be good.

http://www.distributordoctor.com/

Glen.

[Freebird]

I can't see any markings on the vac diaphram casing apart from LUCAS, made in England and all that.

The dizzy body is stamped 41273A and 1268, the latter meaning Dec 1968. This all seems to point at it being the original mk2 Vitesse distributor.

[mk2vitesses]

Freebird wrote:

I can't see any markings on the vac diaphram casing apart from LUCAS, made in England and all that.

The dizzy body is stamped 41273A and 1268, the latter meaning Dec 1968. This all seems to point at it being the original mk2 Vitesse distributor.

The numbers are around the vac feed pipe conection, you will need to wire brush the area, they are not easy to see!!

[mk2vitesses]

Freebird wrote:

Simon

Apart from the above post. you post at strange times of the day (night here) - where are you?

Took the vac pipe off and the pinking did go away. Performance went a bit flat, but not too bad. Now need to source an alternative unit - the distributor doctor is supposed to be good.

http://www.distributordoctor.com/

Glen.

Location Essex, England.

[Clive]

The vac advance may be only part of the problem. You may well need stronger (or just new) springs in the dizzy to reduce the advance.
http://www.jcna.com/library/tech/tech0015.html
explains it all. Probably the second spring needs beefing up, they are often all soft and useless. See what rpm you get max advance too, that my be an indicator of soft springs if below 3000rpm.