Distributor advance

[A TR7 16V]

Does anybody know how many degrees of mechanical advance there is in the distributor on a late MkIV Spitfire?

Graham

[Dannyb]

Factory settings are I believe 10deg BTDC.   However, modern fuel burns at a slower rate than the old leaded 4* and ignition timing must be adjusted to compensate for this. There is a lot of information on the web and this forum about setting ignition timing.

 

[RobPearce]

Danny, I don't think that's the question Graham was asking.

Unfortunately I don't have the figures for a MkIV and even the earlier WSM is hiding in the garage. It's 24-28 deg (crank) on a GT6.

[Clive]

There are 2 distributors for the mkIV, early and late. Early I think has the mk3 spitfire cam profile, the later one is the 18-58 IIRC

https://rimmerbros.com/Item--i-GRID005800

 

As to spec, google isn't helping much at the moment....

[Clive]

There are 2 distributors for the mkIV, early and late. Early I think has the mk3 spitfire cam profile, the later one is the 18-58 IIRC

https://rimmerbros.com/Item--i-GRID005800

 

As to spec, google isn't helping much at the moment....

[A TR7 16V]

Quoted from RobPearce-

Danny, I don't think that's the question Graham was asking.

Unfortunately I don't have the figures for a MkIV and even the earlier WSM is hiding in the garage. It's 24-28 deg (crank) on a GT6.

You're right, it's the additional advance as the centrifugal weights throw out at higher rpm I'm looking for. On a Lucas 25D4 distributor there's a number stamped on the limit arm under the plate that carries the points that gives the value at the distributor. But I have no idea about Delco ones.

I'm asking because I have what seems to be a late Spitfire MkIV engine, with twin HS2s, in a Herald (though I'm not sure of the cam), and want to fit a Lucas distributor with the right advance for the engine. And have more time than money, and a growing collection of Herald spares, including advance springs.

The 13/60 Lucas 25D4 distributor (41127) has 7 degrees of advance at the distributor, or 14 at the crank.

I have a 12/50 one that gives 20 degrees at the crank, but want to avoid pinking. And I think that may be a bit much considering the MkIV engine has better breathing than the 13/60, which is reckoned to want less advance, not more. 

Graham

[Matt306]

I too am interested in this as I am going Megajolt shortly on the Spit IV.

 

I also have a Spit head on my 13/60 herald engine. I dont know about the dizzy as its a lucas and i'm using factory timing on the crank. 

 

Keep me posted on what you find. 

[A TR7 16V]

As I understand it the twin carb, bigger valve (higher compression?) arrangement on the late IV engine will want less mechanical advance than the 14 degrees (crank) of the 13/60. Though that already seems small in comparison to the 20 degrees on the 12/50.

I put a distributor from a spare 13/60 engine on the car and had some problems with pinking, but one of the springs seemed to have been stretched - the other 41127 25D I have had both springs tight at 0 rpm.

I've now fixed that other distributor: a prev. owner had put a rubber O ring under the screw that holds the cam down and locked the mechanical advance, which then seized; I assume the O ring was to get rid of the end float in that mounting (must have been trying to build the mythical rattle free Triumph, LOL).

With that distributor in, I've no problem with pinking, but I don't know how close it is if the springs in that stretch. They are also thinner wire in comparison to the ones in the 12/50 distributor, which, I guess, means the 13/60's advance comes on sooner (and has no bend in the curve, as the springs are the same length).

Graham

Don't

 

Graham