unidentified electronic ignition needs different rotor arm

[gmsclassics]

Just an FYI Graham, the Magnetronic unit will fit the 44D4 with the standard cap and rotor. I've been running the Pageant Sprint with that setup since April 11 (18000mls averaging 33mpg) without issue. So an electronic option is available, albeit not the cheapest.

Last year I replaced an ancient Lucas AB13 finned module with something weird in the distributor of the Mimosa Sprint with an Accuspark unit (that looks the same as yours) for the 45D4 distributor (kit 5). I used the standard 45D4 rotor and the 'Lucas' 45D4 side entry cap. It all fitted and works fine but clearly doesn't look original.

Hope this is of some help.

Geoff

[GrahamFountain]

Thanks Geoff,
But I'm giving up on the EI option for the nonce, and have bought a pair of points and condenser sets. So now I know where the 45D4 rotor arm I had in the draw came from.
I did shorten that to fit the Sprint cap. But as the Herald one works fine, that was a waste of time (not like that's in short supply at the moment).

So I've put the spare dissy back to points and fitted that. A couple of things about that have me perplexed (nought new there).
It was the spare because there's a bit more slack between the drive gear and the main shaft and slop in the mech advance. I though that might cause errors in setting the points static, and maybe some instability in tickover. But, I had no problems using the method of seeing the coil lead spark when the points are closed and not when there open (the back emf off that side of the coil only goes a couple of knuckles up, so not a worry). Also, it (with new points) gives a much smoother idle than the other (with nearly worn-out points). It idles nicely at under 500 rpm, though I'll not leave it there.
The other thing is that, with the new points in, set about 10-12 before TDC the retaining screws are right in the middle of the mounting slot, when with the old one they were at one end or t'other, depending on how the drive was engaged. I've looked at the drive, and it can't be aught like turing the drive gear on the shaft 180 makes a difference. So that means it's down to the points, and a much bigger effect than I expected.

I also have a question about how well the dissy drive shaft bearing is oiled through that small hole in the flat on the body that goes down the hole. The dissy I took out was a little stiff - about half as stiff to turn with the points closed as with them opened by the cam. I reckon it's done about 30k since it went in, maybe a little more. But I think the car it was in it sat in the PO's garage for 10 or 15 years, and I've had it 15. I put some light oil down the hole and spun it a bit, and it's freed off and doesn't seem to have any big play or float. But I am a bit concerned.
The other part of the question is, if you pour oil into the dissy (with the cap, rotor arm, and flash guard off) does any of that work down the shaft or does it all just pool on the block step?

Graham

[GrahamFountain]

I found why the two distributors (both 'A's) needed to be set quite different to get the same timing, and couldn't see why.
It looks like the vacuum unit on the one that needed to be set with the distributor close to the end of the adjustment has, in effect, a longer arm than the other, which sets in the middle of the slot. However, I think it's possible that its been bashed, maybe dropped at some time.

Is 15 btdc at 1000 rpm about right when set 10-11 at 500 and static?

Graham

[gmsclassics]

Sounds at the upper limit, but the rev counter may not be entirely accurate. If you can check that it would be good idea, my multimeter has an adaptor to check that using a plug lead 'clip' similar to a timing strobe uses.

With the vacuum advance disconnected, ideally the advance (in addition to static) should progress from 0-1 at 900 rpm, 0-4 at 1100rpm, 7-11 at 1600rpm up to 12-16 at 2000rpm and then no more. If it gets to max advance at lower revs, then the advance springs in the distributor should theoretically be changed. If the advance is more than 16 then the advance weights themselves may have worn where they touch the stops. ( However a race engine is likely to have the distributor advance modified so that it will run at a total advance of 32 degrees above 3000rpm! )

Geoff

[GrahamFountain]

With the vacuum advance disconnected, ideally the advance (in addition to static) should progress from 0-1 at 900 rpm, 0-4 at 1100rpm, 7-11 at 1600rpm up to 12-16 at 2000rpm and then no more.

Geoff

Which of the three (A, B, C) versions of the 44D4 is that the profile for? I have two of the A versions to hand for the Doly, and I think the one in the TR7 Sprint engine is a C, but I may be wrong.

Graham

[GrahamFountain]

After a surprisingly short search, I found the envelope I scribbled what data I could glean on the advance curves for the 3 versions of the 44d4 from MND Motorsport in the early 90s. If I remember correctly, these are measured values from distributors they had tested.

From earlier posts by MIG Welder:
Type A : 41402 : Stanpart 313177
Type B : 41589 : Stanpart RKC0695.
Type C : 41655 : Stanpart RKC3034
And:

[soe8m]

That makes not much sense. Were these new dizzies they tested? A sprint must not advance more than 32 crankshaft degrees because of high speed knock. The more efficient sprint engine has a lower max advance than an 8 valve 1850. The blue line sprint dizzy is far from correct. 19 degrees dizzy at 2000 rpm means over 40 degrees at the cranckshaft at 2000 rpm. Old worn dizzys were tested probably or the tests went wrong somewhere.

Jeroen

[GrahamFountain]

Does a Sprint engine still knock at more than 32 degrees with the throttles shut on the overrun?

I'd have thought, with that little fuel-air mix being inducted, there couldn't be that much of a bang, however premature. So, I'd have thought it should be safe, and should want, to use a lot of advance in that very limited condition.

I note that even MIG Welder's numbers say up to 41 degrees of advance for the A type, with 10 static, upto 19 mechanical, and upto 12 vacuum. Or do I misread those tables?

When I had noticeable pinking from too much static advance on a Sprint engine, it's was on big throttle openings (so small vacuum) and putting out big torque.

Graham

[gmsclassics]

I wasn't aware of and haven't seen any different advance specs for the Sprint that are specific to different model number of the 44D4. I can't see why they should be different either. Given none have been made for decades now, I suspect that any differences measured would be just due to wear - the weights controlling the advance with increasing revs do certainly wear against the stops, effectively increasing max advance by a few degrees

When I used 32 max advance in the racecar it was with twin 45 Dellortos and the vacuum advance was always disconnected.

Geoff

[GrahamFountain]

There are definitely at least two vacuum advance units listed for the various 44d4s - you can find numbers on this site. And they'll have different profiles against inches of Hg.

I'm pretty sure the A, B, and C versions of the 44D4 are supposed to have different mechanical advance values, i.e. using different strength and length springs and different bob arms - the limit at least is stamped on the bob arm. The A type I have to hand is stamped 12. I suspect a B would have 15 stamped on the bob, and a C, 9.

Perhaps MIG Welder can give a bit more on where the numbers he listed for the 44D4 A came from. It's the 9 degrees minimum I find most surprising. Could that be for a C? With the 19 for a worn B?

Graham

[GrahamFountain]

I found the data in the ROM and scanned it in:

So type A has a min mechanical advance of 12, as stamped on the bob, and B has a max of 19 as I speculated it might be.

Graham

[GrahamFountain]

From the table, my measurement of 15 at 1000 rpm, with 10 deg of advance at 500 rpm and static, suggests the springs are weak or stretched. Trouble is, I doubt I can even find the spec for the springs in the 44D, let alone find a pair.

Graham

[GrahamFountain]

Old worn dizzys were tested probably or the tests went wrong somewhere.

Looking at the data I got from Nick Dixon at MND, he must have read the numbers from the ROM, not got them from some old, worn dizzs or tests that went wrong.

It also seems MIG Welder collapsed the data for A, B, and C, and listed it all for type A.
Later Edit: My apologies for that. I meant the table MIG Welder posted collapses the data for A, B, and C, and lists it all for type A. And was not intending to attribute the error in any way.

Graham

[MIG Wielder]

Hi Graham, Sorry to be late with this. I see you have been busy. I originally did that Excel chart and the graphs to try and illustrate why fitting a Sprint distributor to an 1850 was not a good idea. The graphs are specifically for the A type dizzy.
I see the ROM has been updated since my manual was printed. The mis-print for C not A has been corrected.

The advance values for the Sprint are on page 05-1 of the Sprint workshop manual AKM3629. The tables there include the A,B,and C variants and if you look at the right hand columns they are specifically for Degrees Crankshaft Advance . The first chart on the page is for Centrifugal advance and the 2nd one is for vacuum advance.

The 1850 dizzy advance data comes from page 86.35.00 sheet 1 of the 1850 workshop manual dated 1977. Again the right hand columns are crankshaft degrees.

Thanks for pointing out those errors. Here are the revised charts and plots , mainly on the Sprint Type A centrifugal values.

And yes, I reckon you are quite right. Maximum advance can be 40 degrees with 16 deg of centrifugal at 2,000 rpm, 12 degrees of advance at 18 in Hg plus 12 deg of static timing. I couldn't find any info about advance being limited to 31 deg in the book. Is there a limiter ?

Tony.

[GrahamFountain]

I suspect if you go far over 30 degrees combined static and mechanical there'll be issues with pinking; especially with no 5 star fuel.

It was a long time ago when the timing slipped on my first TR7 Sprint conversion and it smashed the lands out from between the rings. But I think that had slipped to 26 BTDC static - something like 38 degrees of advance at revs. But memory is imperfect, and I could be wrong. It will also have been running on 4 star leaded at the time - I didn't switch to super unleaded till later.

That still only pinked at big loads with wide-open throttles. My only excuse for letting it smash the pistons is simple ignorance at the time (not that much smarter now really). Running on 2 star, it will pink at 10 or 12 degrees static.

But unless someone has evidence to the contrary, I'm sticking with the assumption that I can have nearly whatever vacuum advance I like (possibly none for preference) and it only affects emissions on the overrun.

The only related limiter I've heard of is that there was a centrifugal weight and spring on the back of the competition version of the rotor arm. Supposedly, that would come out and short the spark to the opposite terminal if the revs got too high. But I've never actually seen one of those. And I was only told that in answer to the question why the Sprint's rotor arm was such an odd shape.

Graham