The Triumph Dolomite Club - Discussion Forum

Hi All, I'm also rebuilding my spare Sprint distributor, and I have come across an anomaly.
When I move the bob-weights outwards, as they would do with increasing engine speed, the rotor arm moves anti-clockwise when viewed from above.
Since the rotor arm rotates anti-clockwise this would appear to retard the ignition, not advance it as I would expect.
The vacuum advance appears to work correctly, i.e. increasing vacuum advances the ignition.

Photo enclosed, of the set-up, with the bob-weights shown fully extended with blu-tack to illustrate it.

Where have I gone wrong please ?
Thanks,
Tony.

The cam does indeed rotate anti-clockwise as the bob-weights come out. And that is in the same direction that the rotor arm turns. But that means the lobes on the cam meet the cam follower on the points a bit sooner in the engine's cycle, i.e. the timing advances.

I also note that your 41589 44D4 (unless you've swapped a 41589 main shaft into a 41655 body) has the same hooked stop on the beak like mine does, where the 41402 and 41655 have flat stops. Which, I think, is kind of interesting. Have you checked it's limited to the 9 degrees of distributor advance (18 at crank) as is stamped on the beak?

I also note the springs you have fitted are not like the 41589 set that the Distributor Doctor sells as spec. They look like a set from one of the 45Ds to my eye. I have to go count turns and such to be sure, though.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

The first attachment is a pair of unused 41589 springs from the Distributor Doctor. The second is a set of used 41655 springs that might or might not be the right lengths. But the wire thickness, coil diameters, and coil counts are right compared to the new set that replaced them, which are currently in the car.

I've not yet found anyone that says they have the correct replacements other than the Distributor Doctor.

It's possible I can give some data on the curve you'll get from the asymmetric set fitted. The curve calculator is coming along surprisingly well.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

Hi Graham, Thanks for your replies. Yes you are quite right , this is a 41589 B44D4 2875 but was fitted to a 1979 Sprint.
The larger spring is 6 coils of 0.92 dia wire and the smaller one 6 coils of 0.75mm wire. And yes the rotor spindle is stamped "9" but the spindle has difficulty reaching max; advance smoothly right now. I think there must be a burr on the weights somewhere. I'll have a look later.
If you need a couple of circlips for the top assembly I do have some spares you can have.

Cheers for now,
Tony.

I need the coil outer diameters as well to calculate spring rates, and advance rates from that.

I have a selection of 41589 springs spare, if you want to go standard for the distributor. But they're spare because I am using 41655 springs at least. That's because the stop on my best 41589 appears to be worn, as I measure it to about 12 or 13 degrees. But I have no actual 41655s to spare. As said, the Distributor Doctor has all three types of spring sets. I might be able to compile a set from the oddments I have. But it would mean adjusting their lengths by eye.

Wear in the bob-weight posts seems to be a problem. With the weights pushed out, is there much marking to the baseplate under the moving part of the mechanism, which the bob-weight post stick out of?

One of mine is well-worn in that regard, but okay else. The wear seems to be in the post malone, as swapping the weights with a better distributor leaves them both the same. So I'm looking at reasonable ways to repair the posts.

The posts and baseplate from the 45D are the same and splined on the shaft. So, if the good one I have will press off the 45D shaft and press on to the 44D's without damage, that should fix the problem - have to check it goes on the same relative to the drive gear teeth or the distributor will mount a bit different.

But first I'm looking at sleeving the post and drilling the bob-weight holes bigger to go over the sleeves. Again, the ones from the 45D fit; so spares are cheap and plentiful enough. I've got some stainless tube I thought I'd be able to drill to an interference fit with the posts. But the tube is tougher than I expected, and I wonder if I should get some brass tube for a proof of concept.

It may also be possible to shorten both ends of a 45D shaft, and fit the 44D cam on top and the drive gear at the bottom - the 3/16ths hole for the solid pin to fix the 45D's dog drive will be mostly cut off, I think. The 45D shaft goes in the 44D body, and shows no side play. And the drive gear and cam fit on that shaft, but the wrong distances from the body. So it will need some work on a lathe to shape their ends (rough hew them how we may), which I don't have. I wondered about drilling and threading the cam end for a screw, like on the 25D.

And if all that is possible, then new 45D main shafts are only £30.35 from Simonbbc. And they come with the rest of a 45D, inc., baseplate, points, condenser, arm and (top entry) cap, for free. The new shafts may be a different diameter - but it seems the new dog drives for the bottom of the main shaft fit old and new 45Ds. And if that's true, there's some chance the new shafts will fit in the 44D after shortening - if they are a tad bigger diameter, that might be good for reaming a worn bearing. Even if the body needs a new bearing, it still might be cheaper and better than turning down the old 44D shaft to get it parallel and fitting a new sub-sized bearing for the smaller shaft.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).