Jump to content

The great fixed spark debate.


Max BURKE
 Share

Recommended Posts

There are many among us who tell the rest of us that fixed spark has advantages. Its advantage to the Hup 20 was in cost. The magneto was cheaper to put on the car as it had fewer parts. The pole shoes were more simple ,No combe, and there was no need to provide a means for the driver to move the cam ring whilst driving. All this austerity just meant a sale instead of the buyer taking up a FORD. If you believe the marks on the flywheel are constant for life, even when the flywheel is not even off the engine it left the factory with, then I salute your good faith. Before committing to these marks of unknown origin please set your engine with the piston 3/8 down the cylinder on the compression stroke. Clearly mark the ign mark with a thin line of white out This is the mark for your engine. The original magneto gear had two keyways but used only one key. Why? To give a half tooth timing variation. Hup instruction called for removing the cover plate and with the armature bobbin past the edge of the pole shoe by .020, this is where the contacts must break. This is said to be the point of maximum flux. Check the ign with a timing light at various speeds. Is it constant to your mark? I have driven many of the Hup 20 s in Australia and have yet to find one not improved by a magneto in which the varying of the spark from the drivers seat was not an advantage. Max Burke Nulkaba 2325 Australia.

Link to comment
Share on other sites

Hupp noted in their advertizing that the fixed spark was 'used with success in France'. My 1921 Peugeot also has a Bosch fixed spark magneto, so they were used for a number of years. My '13 Metz has the same DU4 magneto as the Hupp. This is just to say that they were considered satisfactory. Interestingly, the magneto was the single costliest part in the Metz car (unless you bought an entire engine). I'm not sure how much they saved vs the adjustable spark unit, but every cent was counted in these low-price cars!

Phil

Link to comment
Share on other sites

There are many among us who tell the rest of us that fixed spark has advantages. Its advantage to the Hup 20 was in cost. [...] I have driven many of the Hup 20 s in Australia and have yet to find one not improved by a magneto in which the varying of the spark from the drivers seat was not an advantage. Max Burke Nulkaba 2325 Australia.

(Read to end before getting upset)

Not sure what prompted this but it strikes close to home since Franklin was very up-front about why they used a fixed spark on their small cars from 1909 to 1913 inclusive. Short answer: They did not trust the driver to set the spark properly.

The Franklin of that time was outrageously expensive compared to other small, four-cylinder cars. It cost $1850 without top or windscreen (or radiator) F.O.B. Syracuse. Colors Extra..... This was very high for an 18 HP, 3.375 x 4 car of the time. The larger Franklins had a centrifugal automatic spark advance working on the input shaft on the Magneto so that the points opening-to-flux relation was always at its best to give the hottest spark. All this was before the Bosch DU4/6 Mod 5 was produced which is the first model to have the special-pole pieces give a hot spark over a wide breaker setting.

The Reason for not having a spark control on ANY of their cars was quite simple: Drivers Often ran with the spark set WRONGLY. The error was usually that it was too far retarded so performance suffered and the engines ran hot. The solution to operator error is to remove the operator.

They found that a small engine could be spun over the top with verve on starting so no retard was needed whereas the larger engines needed to be retarded for starting since they were a bit of a struggle to spin. Best of all: the fixed spark on a Franklin works splendidly with no-worries. It may make the car a bit peaky but when you hit the groove (above c.18 mph in top gear), it is just a matter of: If you want to go faster, open the throttle, to go slower close down on the throttle. Nothing to it and almost modern in all respects.

I will admit economy played a part since the automatic spark advance on Franklins is quite complicated and it is also quite large and would not fit on their small car without serious re-arranging. The Mag to Carb distance is frightfully small.

In the Franklin case, it was not Fixed vs Control-lever, it was Fixed vs Automatic

All this does not prevent many people from installing an advance lever since the common notion (as expressed in this thread) is that it is better to have the driver control the spark. But if fixed spark worked well in 1910 and works well now, why change it? What else should we change to make the car run better? Maybe a Vega engine......[i make the joke that the only performance enhancement on my car is: that I generally (but not exclusively) run it on paved roads.]

The Fixed spark on a Franklin G (3.375" X 4") is: 23 degrees. The Full Advance Automatic Spark on their bigger cars (4.25" x 4") is 33 degrees. The OHV hemi-head of the Franklin makes these numbers non-comparable to L-head or T-head engines. In fact, it might be the combustion chamber shape that allows good performance with a fixed spark.

If So: Never mind.:rolleyes:

Link to comment
Share on other sites

F-M, well said, and I agree. It worked well back then, why mess with it now?

It seems that everyone wants to "improve" the old cars, when, as a good friend states, part of the enjoyment of antique cars is driving them as they were, with all their quirks. I've seen a pretty little Hupp that is driven quite a bit on tours, but it's just barely Hupp....two speed rear end, starter, shaved flywheel, different carb, the list goes on... I may not drive mine as much, but when I do I enjoy the originality, and it's just not that hard to hand crank.

Each to his own, of course.....

Link to comment
Share on other sites

I have modified mine so that it does have variable timing. More because my magneto is a later DU4 with adjustable timing and the previous owner had just fixed it where he thought it was best and I wasn't convinced he had it right. I now have it right and I admit I don't touch the adjustment at all -so effectively run with fixed timing. My experience is advancing the timing does very little for performance on my car -perhaps a 10% increase in top speed only. Karl

Link to comment
Share on other sites

G,day to all. Isn,t it grand to have some varied point of view on the fixed spark debate. If we had a dyno we could determine if the point of firing made a real difference or indeed if there is enough increase in power to warrant change. Testing with a stop watch over a fixed distance up a test hill would show results when comparing various advance settings. Just how the Franklin achieved constant flux gap with a centrifugal advance I have not quite comprehended unless a MEA or Dixi magneto was used . The Mason principal used here kept the "gap" constant .Please explain FM for our enlightenment. One of our Hup friends with a model B series 20 has converted his gearbox to five speed. I often tell him to sell the Hup and build a hot rod as he is in the wrong hobby Max Burke Nulkaba 2325 Australia

Link to comment
Share on other sites

[...] Just how the Franklin achieved constant flux gap with a centrifugal advance I have not quite comprehended unless a MEA or Dixi magneto was used [...] Max Burke Nulkaba 2325 Australia

Conceptually, it is Simplicity itself. They used a Fixed Spark Bosch Magneto essentially the same as the DU4 Fixed Spark found on a Hup 20. The centrifugal advance is a spinning mechanism used as the coupling between the engine and the magneto. As the speed went up, flyweights working against springs changed the angle between the Input and Output Shafts of the Centrifugal unit. The Centrifugal advance mechanism is a cylinder about 100 mm in diameter and the whole thing spins at engine speed (or 1.5 engine speed for the sixes). It is quite something to see since you are sure it will catch on a wire or something and throw parts around.

post-91919-143142419829_thumb.jpg

Click to expand

The Magneto in the picture is a Fixed timing Bosch DR6 Dual. The big can on the drive end with screws and "x"s on it is the Franklin centrifugal advance mechanism which spins at 1.5 engine speed (six-cylinder car)

For those who do not know about a MEA Mag. This is a Fixed-Breaker Magneto with the whole Magneto mounted in trunnions so that you could rotate the entire magneto to get advance and retard. I think that Eisemann used the same concept on a few mags. The MEA had the magnets arranged along the shuttle axis which gives it a very distinct appearance. The Dixie mag used completely different system from the MEA to achieve full spark over a wide range of advance.

Edited by Franklin-Madman (see edit history)
Link to comment
Share on other sites

G,day to all. FM you would surely have been interested in a line of Franklins that lay in a wreckers yard in the Newcastle area in the 1950s there were 8,maybe 10 in a line and little had been taken from them. I had never seen one before and was intrigued by the air cooled engine and wooden chassis. They were mostly Horse collar fronts perhaps early 20s. In the 1970s a raging bushfire went through the area and destroyed them all. There was a Franklin in our veteran car club . It was well used, in summer the floor got really hot! It met with disaster and cracked the combustion chamber between the valve seats and eventually the top of the cylinders were parted off to gain access to the problem. In desperation a set of vintage cylinders were fitted and the car sold to an American enthusiast . It went back to USA where it was said to be the last of its type known. It had pent roof combustion chambers and parallel valves. Perhaps you know the car? 6 cyl 6 litre 38 hp @62 developed @2250 revs. Dated 1912 model D. I can give you more on it if you would like.Max Burke Nulkaba 2325 Australia

Link to comment
Share on other sites

G,day to all. [...].Max Burke Nulkaba 2325 Australia

I would like to move this over to the Franklin Forum with your permission since it has gone beyond Hubmobile Related Topics

1912Minerva still has not had a response to how to set the VALVE Timing of a Hub 20. Anyone?

Max: the car pictured with the Advance Mechanism is by strange co-incidence a 1912 D, 38 HP, but not the one you refer to. There are only three such cars in the Franklin Registry and they are a close knit grouping so I am sure someone knows about the car if it is "in the open". Going PM....

Link to comment
Share on other sites

G,day all. First up this is not a redirected thread for valve timing and help? to that question should be offered on that thread. The question has so far been addressed by folk who are happy with the fixed timing as supplied and have no wish to find if change would improve HP . There are other folk who have fitted a magneto with variable timing and noted an improvement, still others have done this and noted no change so they leave the advance / retard in a position that they like. A further group use the variable spark to run on advance with something like 3/8 inch on the piston and use the hand control for starting and to give a very slow idle . Seems from the few comments that each driver is happy with the system that they have. An Impulse attachment stops the cam advancing until the piston is near TDC and can be set to give retard but not more advance. At a speed above cranking the bob weights on the sprags prevent their engagement with the stops and the magneto reverts to its original fixed spark configuration. Flux point air gap remains constant . In our case the difference in performance from retard to advance @ 30 MPH is about equal to one more cylinder. By the way we run modern spark plugs over the exhaust valves. We find they run cleaner when in slow traffic. Max Burke Nulkaba 2325 Australia

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...