Do I need a new distributor

[Clive]

23 minutes ago, Wagger said:

Pete is correct. There are many long articles available on this topic. We would need to fit an up to date engine management system to make timing correct across the whole rev range, Then, we would not be able to tinker!

Might just as well have a newer car. No fun in that is there?

More addvance at light cruise does create more torque, and the car drives better. I guess the economy is a function of that.

But megajolt or similar gives plenty of opportunity to fiddle. It is done via tapping keys though. My boss has spent many hours sitting in the passenger seat with a laptop, adjusting cam timing, fuelling and timing. And before I had barometric correction, had to fudge the fuelling as we went up into the Alps but "altering" injector size. 

Up at the top, there is about 25% less oxygen. Carb cars self-correct pretty well. PI cars don't. 

[cliff.b]

Checked my timing at various engine speeds with the strobe again and seeing 14deg at 600RPM, 20 Deg at 1400, 22 Deg at 2000 and no more, whatever the revs are.

Took the Dizzy apart again and everything is still moving freely but there is a lot of play in the mechanism. 

I have ordered a new Lucas boxed replacement from Moss as they are on offer for £40 incl VAT and I needed some other bits anyway.

Plan is to fit that then investigate the old one in more detail off the car.

[Clive]

1 hour ago, cliff.b said:

Checked my timing at various engine speeds with the strobe again and seeing 14deg at 600RPM, 20 Deg at 1400, 22 Deg at 2000 and no more, whatever the revs are.

Took the Dizzy apart again and everything is still moving freely but there is a lot of play in the mechanism. 

I have ordered a new Lucas boxed replacement from Moss as they are on offer for £40 incl VAT and I needed some other bits anyway.

Plan is to fit that then investigate the old one in more detail off the car.

Well worth checking that the new one is correct when it arrives. Remember Lucas now only make boxes...... contents are all outsourced.

[cliff.b]

3 hours ago, clive said:

Well worth checking that the new one is correct when it arrives. Remember Lucas now only make boxes...... contents are all outsourced.

I intend to 👍

[cliff.b]

Ok, to continue this thread, I fitted my new, cheap distributor to the car and have been investigating the old one further.

Found that if I forced the weights out manually I could get full advance to the stop but the weights stayed there. Dismantling, cleaning and oiling the entire mechanism has cured this and I don't actually think it is too worn. However, it looks like the springs are either incorrect or stretched so will need to find some suitable replacements.

Interestingly, the car runs much better with the new distributor but as was suggested, that isn't right either, with no mechanical advance at all until about 2500 revs but then full advance coming in by just under 4000.

I am trying to understand what could be causing this. Incorrect primary spring? Something sticking which frees up with higher revs?

I would appreciate any thoughts regarding this. I will prob put the old dizzy back on when sorted but still interested to understand what could be causing the issue with the new one.

[Clive]

34 minutes ago, cliff.b said:

Ok, to continue this thread, I fitted my new, cheap distributor to the car and have been investigating the old one further.

Found that if I forced the weights out manually I could get full advance to the stop but the weights stayed there. Dismantling, cleaning and oiling the entire mechanism has cured this and I don't actually think it is too worn. However, it looks like the springs are either incorrect or stretched so will need to find some suitable replacements.

Interestingly, the car runs much better with the new distributor but as was suggested, that isn't right either, with no mechanical advance at all until about 2500 revs but then full advance coming in by just under 4000.

I am trying to understand what could be causing this. Incorrect primary spring? Something sticking which frees up with higher revs?

I would appreciate any thoughts regarding this. I will prob put the old dizzy back on when sorted but still interested to understand what could be causing the issue with the new one.

No advance until 2500? That is when the advance should be almost all done, weird! Sounds like the primary spring is too strong. Maybe swapping that with one from your old distributer would improve it? I have played with springs, just a bit time consuming. 

[Pete Lewis]

this wont solve the erratic curve of the new one but advance curve tests are generally done decelerating ( the opposite of how most strobe the things)

most triumph data in the wsm is decel  not accelerating  so rev past and drop the revs to check what you have 

max on most normal engines of our era   the dizzy will max at 29/30 deg at 3000   + static 

Pete

 

[cliff.b]

14 minutes ago, Pete Lewis said:

this wont solve the erratic curve of the new one but advance curve tests are generally done decelerating ( the opposite of how most strobe the things)

most triumph data in the wsm is decel  not accelerating  so rev past and drop the revs to check what you have 

max on most normal engines of our era   the dizzy will max at 29/30 deg at 3000   + static 

Pete

 

Thanks Pete, I didn't appreciate the deceleration thing 

Also, do you mean 29/30 deg on top of the 10 Deg static or including it?

[cliff.b]

17 minutes ago, clive said:

No advance until 2500? That is when the advance should be almost all done, weird! Sounds like the primary spring is too strong. Maybe swapping that with one from your old distributer would improve it? I have played with springs, just a bit time consuming. 

Yes, makes sense 👍

[Pete Lewis]

think i said  + static 

Pete

[cliff.b]

1 hour ago, Pete Lewis said:

think i said  + static 

Pete

That's what I read but just checking as that would suggest a total advance of 39/40 Deg.

The original dizzy has an 8 stamped on the cam stop which I assume means 16deg max at the crank and adding the 10 Deg static gives only 26 Deg max (without vac connected, of course).

[Pete Lewis]

whats the number on the side of the   orig  dizzy ???

most of the specs are in the wsm i can have a look up 

Pete

[cliff.b]

1 hour ago, Pete Lewis said:

whats the number on the side of the   orig  dizzy ???

most of the specs are in the wsm i can have a look up 

Pete

It's a 45D 41449, which I believe is the correct dizzy for the UK 1500 Spit. 

Happy to be advised if opinion differs on this 🙂 The original Lucas has it stamped on the casting & the new one has it printed on the box, but nothing on the casting.

[Colin Lindsay]

The data I have on that one says:

Zero degrees advance below 600 rpm 
2 to 6 degrees at 1100 rpm 
6 to 10 degrees at 1400rpm 
8 to 12 degrees at 2000rpm 
12 to 16 degrees at 3200rpm 

I've found more detailed data on a USA Triumph website:

"The specification for the vacuum unit fitted to the Lucas 41449 distributor (Lucas code 54424752) is given by the number of degrees of ignition advance (measured at the crankshaft) applied by the vacuum unit for various amounts of depression. As you might expect, the vacuum depression is specified in inches of Mercury.... 

Zero advance below 2" of mercury 
0 to 1 degree at 3" of mercury 
1 to 6 degrees at 6.5" of mercury 
5 to 9 degrees at 8.5" of mercury 
9 to 13 degrees at 11" of mercury 
10 to 14 degrees at 18" of mercury 

The vacuum advance unit will be stamped 3-18-7 , which means:- 

Vacuum advance begins at 3" of mercury 
Full vacuum advance at 18" mercury 
Maximum vacuum advance is 7 degrees, measured at the distributor - equivalent to 14 degrees at the crankshaft "

 

The MG Guru site has the data for most distributors, just scroll down to the 41449:

https://mgaguru.com/mgtech/ignition/pdf/lucas_distributor_specs.pdf

[cliff.b]

4 minutes ago, Colin Lindsay said:

The data I have on that one says:

Zero degrees advance below 600 rpm 
2 to 6 degrees at 1100 rpm 
6 to 10 degrees at 1400rpm 
8 to 12 degrees at 2000rpm 
12 to 16 degrees at 3200rpm 

I've found more detailed data on a USA Triumph website:

"The specification for the vacuum unit fitted to the Lucas 41449 distributor (Lucas code 54424752) is given by the number of degrees of ignition advance (measured at the crankshaft) applied by the vacuum unit for various amounts of depression. As you might expect, the vacuum depression is specified in inches of Mercury.... 

Zero advance below 2" of mercury 
0 to 1 degree at 3" of mercury 
1 to 6 degrees at 6.5" of mercury 
5 to 9 degrees at 8.5" of mercury 
9 to 13 degrees at 11" of mercury 
10 to 14 degrees at 18" of mercury 

The vacuum advance unit will be stamped 3-18-7 , which means:- 

Vacuum advance begins at 3" of mercury 
Full vacuum advance at 18" mercury 
Maximum vacuum advance is 7 degrees, measured at the distributor - equivalent to 14 degrees at the crankshaft "

 

The MG Guru site has the data for most distributors, just scroll down to the 41449:

https://mgaguru.com/mgtech/ignition/pdf/lucas_distributor_specs.pdf

Thanks Colin. That tally's with the figures that I was working with and broadly inline with my original distributor up to the point where it stopped advancing any further 👍

[cliff.b]

Ok, an update and hopefully conclusion to this issue.

I contacted the supplier of the new distributor and told them their part did not perform as expected. They offered to send me their advance spring tuning set free of charge, which arrived yesterday.

This is a "carefully chosen" set of 3 X primary springs & 2 X secondary from which they claim a "wide variety of curves are possible".

I fitted the lightest primary spring to my dizzy and the curve now appears to be pretty much exactly what Colin's chart suggests. The car is transformed with far better performance and the exhaust sounds great 🙂

In case anyone is interested, the new primary spring fitted is 15.6mm long and only 4.95mm dia. It is noticeably a very light spring. The one that was originally fitted was 16.5mm long & 7.2mm dia which is almost identical to the heaviest primary in the kit supplied 

[Pete Lewis]

so what spec was the new unit supposed to replicate ????

sounds a bit one size fits all just modify it to get it right !!!

a very wrong curve can quickly end an engines life 

Pete

[cliff.b]

25 minutes ago, Pete Lewis said:

so what spec was the new unit supposed to replicate ????

sounds a bit one size fits all just modify it to get it right !!!

a very wrong curve can quickly end an engines life 

Pete

It was being sold as a 41449 spec Lucas 45D to fit a Spitfire 1500 and that's what it said on the sealed box.

The car ran more smoothly than with the old dizzy but felt sluggish at lower revs which is why I investigated further and found little, if any advance occurring below about 2500 RPM.

Either this was a one off or it is likely other people could have the same issue. Could just be the wrong part in the box I suppose as I couldn't find any identifying markings on the part itself. 

Or maybe, whatever car you buy for, they are all the same inside.

[daverclasper]

4 hours ago, cliff.b said:

This is a "carefully chosen" set of 3 X primary springs & 2 X secondary from which they claim a "wide variety of curves are possible".

The bob weight springs are the same size I understand?, are these the primary and the vacuum spring the secondary?.

Thanks Dave  

[cliff.b]

8 minutes ago, daverclasper said:

The bob weight springs are the same size I understand?, are these the primary and the vacuum spring the secondary?.

Thanks Dave  

No, the springs are different, both for mechanical advance but with different purposes.

The springs aren't directly attached to the weights. The weights try to turn the cam assembly as they move outwards and the springs connect to the cam assembly, resisting that movement.

The primary spring is weaker, is always under some tension and stretches quickly as the revs rise and the weights move the cam.

The secondary spring is stronger and at low revs it is loose and has no effect.

When the revs increase enough so that the cam movement takes up that slack (about 1400RPM in the Spit), the heavier secondary spring starts holding back the cam as well as the primary one.

This is why there is a "kink" in the advance curve with the first portion being steeper than the remainder. The rate of increase in advance slows down once the secondary spring is engaged.

The length of the secondary spring and therefore the amount of slack determines at what RPM this happens and therefore where the kink in the curve will be. The strength of each spring determines how fast the advance will increase before and after the kink.

 

 

[cliff.b]

A picture might be clearer.

This is my distributor before I removed the existing primary spring (the bottom one). If you look closely you can see the top secondary spring has some slack.

The black bit that both springs attach to is the cam assembly. The other ends of the springs locate onto the top of the bob weight pivots, but are not connected to the weights

[cliff.b]

Here is a dismantled picture of the mechanism showing how the inside ends of the weights will move the plate that the cam assembly locates onto.

As the weights move outwards, the hook bit on the inside will try to turn that plate anti clockwise. 

The holes in the cam assy locate over the studs on this plate and then the springs are attached to them, resisting this anti clockwise movement.

This pic also shows the primary spring (on the right) being far lighter than the secondary.

[Pete Lewis]

 Cliff    thats a  good job now   well done 

Pete

[cliff.b]

40 minutes ago, Pete Lewis said:

 Cliff    thats a  good job now   well done 

Pete

Thanks. Just need to put the old one back together now as a spare

[cliff.b]

Just to follow up on this thread, and as it's particularly relevant at the moment, I definitely seem to be getting significantly better fuel consumption since replacing the distributor. The last 2 tanks used worked out at 34 & 36mpg whereas previously I was getting around 30. 

Also, apart from running better & feeling more lively, I can now get a stable tickover 👍

Overall, £40 well spent and probably soon paid for in saved fuel costs if they stay at these sort of prices.