Timing issues, Bosch magneto/ laurel cylinder head

[RalphM]

My friend has this setup;
1916 engine, type A laurel head(Roof), Rebuult Bosch magneto about 1918. Plugs will spark with magneto, there’s gas in the Miller type H carburetor(looked rebuilt), but cannot get the engine to pop off. Adjusted magneto several times still nothing. Long reach modern spark plugs.
Pulled around the yard while making adjustments, still will not fire.
Is there a basic setup procedure for the magneto to get it close?
I’m a V8 Flathead guy, so this is all Greek to me.

[RalphM]

Picture

[mercman from oz]

Timing issues, Bosch magneto/ laurel cylinder head - RalphM

[rotorwrench]

I know nothing about this system or application but I've got a long history with all sorts of aircraft, industrial, and motorcycle magnetos. Assuming the magneto is timed internally and makes a spark to each plug in turn, I would be wondering if this mag is fixed for timing during road operation or does it have any form of spark control adjustment for starting and load? Most magnetos are not advance or retard adjustable so they are fixed for running at operating rpm. They will usually have an impulse coupling that delays the spark for starting and then kicks out to full advance after the engine is running by way of flyweights. Other starting aids are also used such as a starting vibrator circuit that provides a shower of sparks but works through a separate set of retarded timing breaker points.

Magnetos will give a spark at low rpm but it is weak until the rpm builds a little. It is still strong enough to light off a good fuel mixture though. If there is no way to retard the spark then the engine can kick back and damage a starter or some poor souls arm.

Internal timing of a magneto will always require the breaker point firing position to be synchronised with the rotating magnets E-gap. This is the point where the magnetic field is at it's stongest in the laminated core of the coil. When the magnet is in the E-gap position, a person can feel it as the magnet is rotated by hand. It wants to stick at this point like a magnet sticks to a piece of iron or steel. As it rotates past the E-gap, the magnetic field collapses which induces the coil to step up the voltage to the primary side and make a spark as long as the breaker points open at the right time.

[RalphM]

This one is adjustable from the drivers seat using the original T Spark advance lever.
The Spark is good, just trying to get the timing correct.

[rotorwrench]

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Does the magneto rotate on its drive axis for advance control? Or in other words, what does the spark control manipulate to retard the spark? Is the mag drive splined, geared, or have an adjustable coupling for timing to the engine? There should be a way to get the distributor rotor timed to the terminal that leads the high tension voltage to the #1 plug when the #1 piston is in firing position. The rest is just making sure the other high tension leads are set up for the proper firing order of the engine. In full retard, the mag should make its spark at TDC or within several degrees after TDC for best starting. Advancing the spark further will be done after the engine starts and is running well.

This would be one of the first application that I've ever heard of that actually has a driver adjustable spark control. Most mags are used for racing so they are set for full advance at all out speed. For starting, which can be difficult on this type of set up, the engine starter is engaged for a bit before turning the magneto switch on. A starting aid is always recommended to prevent kick back and allow for easier starting. The distributor portion of a magneto has to be rock solid with the internal timing of the magneto rotor & breaker points. If the distributor is independently adjustable from the magneto rotor then the internal timing would be off.

Some of the very large radial engines used during WWII and for some time after, had the magnetos separate from the distributors. The magneto would generate the high tension sparks which would then be sent to the distributors by means of two shielded and insulated high tension leads. The high tension voltage was then distributed to each cylinder in proper time. Timing for all this was critical for the engines to run properly. The Pratt & Whitney R4360 radial engine had 28 cylinders that had to fire off of those mags. They had Bendix "shower of sparks" starting aids to retard the spark and get those monsters to start.

After looking at several front plate Bosch magnetos It appears that these units have a rotating coil instead of a rotating magnet. Lucas used these type magnetos on motorcycles but they are a different design. With the rotating coil set up, the points plate can be moved a limited number of degrees before it becomes ineffective but it does allow for some spark timing adjustment. The model T has limitations on how much advance is effective anyway so I can see how it would work.

This info on the DU4 may help you. http://brightsparkmagnetos.com/libra...%20Magneto.pdf

[redmodelt]

If the timing is set to fire just after TDC No 1 cylinder, I would be looking for vacuum leaks or fuel not getting to carburetor. Or possibility that the valves are not closing all the way, or the points are dirty.
This type of magneto is revolving core and is controlled by lever on steering wheel, re advance/retard and uses a flex coupling to drive it.

[RalphM]

I’m waiting on a spark tester to show up to verify the timing, but I think I will do a compression test as well to make sure we’re getting a decent vacuum. May be a little oil in the cylinders to help.
Carburetor throat is wet after cranking. But it is an updraft carburetor and would need a good vacuum to work properly.

[Oldtmtech]

On the tractors that I work on the coupling has a ring of holes on each half
When you have the engine at tdc and the magneto ready to fire in the full retard position you slip the bolts thru the 2 holes that line up

[Oldtmtech]

You didn’t state if this magneto had run on this engine before but they do come in clockwise or counterclockwise rotation there should be a rotation arrow stamped on the outside

[rotorwrench]

In aviation, we use a magneto timing light to set the timing for the exact time the breaker points open. They are made to set two mags at a time so that they can be synchronized. On a single mag set up, only one of the lights would be necessary. It sure makes adjustment a lot easier and more accurate.

https://www.aircraftspruce.com/catal...r_12-16901.php

[RalphM]

Originally Posted by Oldtmtech

You didn’t state if this magneto had run on this engine before but they do come in clockwise or counterclockwise rotation there should be a rotation arrow stamped on the outside

Last ran on this engine in the 1920’s
But when my friend got it it was a box of parts.
I can’t load any pictures of it But if you Google Bobby Sheldon’s race car you will find an original picture from 1917.

[redmodelt]

Compression test will not find vacuum leaks, will tell you if there are valve issues as would a leak down test. Vacuum leaks would be carb or manifold gaskets not sealing or worn hole where the throttle shaft goes through on the carb.

[Oldtmtech]

Great history
Haven’t found the 1917 car yet but here is the 1905 car Sheldon built
And a picture of a river crossing
Wikipedia has information about Sheldon
Good luck and keep us posted

[rotorwrench]

Looking at the diagram from the link in my #11 post, It has a condenser illustrated behind the breaker plate. The technology of that era was such that most capacitors were made using wax paper as the insulator for the wrapped foil internal to the part. Wax paper deteriorates over time to a point that it will no longer insulate as it should. I don't know if there is a company out there that either fabricates a new part or repairs an old part for these magnetos (see link below). I know in the case of the smaller Lucas K2R magnetos, folks substitute a modern capacitor of the same microfarad rating and back voltage absorption capacity as the original but these are a completely different design. This link better illustrates the DU series and also has a better parts break down.
https://oldcroak.com/du1-du2-du4-ad-nauseum-catalog-50/

There is a photo of an old armature in the link where a person can see the condenser housing just adjacent to the gear on the opposite end from the high tension slip ring.

An old magneto may make a spark on the bench with a bad condenser but it would likely break down at higher rpm. I'm not telling you it's bad but after so many years, it would be very likely that it has deteriorated. It would have to be tested with a capacitor tester to know for certain. You might check with this outfit (link).
http://www.mainelymagnetos.com/BoschParts.html

They list a rebuilt condenser for $30.

[redmodelt]

https://www.youtube.com/watch?v=LBWCL52MW3I

[Oldtmtech]

This might help found it on oldcroak.com

[RalphM]

So the magneto was rebuilt by a professional shop. Spark is good, with gear to crankshaft off, my friend spun the mag with a drill(the right direction) and spark to all plugs is real good.
I’m going over there tomorrow to try and help him time it.

[RalphM]

So the magneto was rebuilt by a professional shop. Spark is good, with gear to crankshaft off, my friend spun the mag with a drill(the right direction) and spark to all plugs is real good.
I’m going over there tomorrow to try and help him time it.

[rotorwrench]

Make sure the distributor rotor is timed to fire on the #1 cylinder terminal contact. Make sure the spark advance (magneto cam or interupter housing control arm) is set for the retard position. The engine will start with some advance. Many engines of this size will start around 5 degrees advance from TDC. The model T may start with more advance than that but I don't have the instructions for the model T engine.

These mags can be set for clockwise or counterclockwise rotation so a person has to set the distributor rotor for the proper rotation and observe that the interupter lever is turned the proper direction for advance and retard. It can be set up either way so the installer has to verify that it rotates the correct direction with movement of the lever. The installer also has to verify the the firing order for the other high tension leads is properly set. The mag can rotate either way depending on how it is set up so this has to be observed to get it right.

If the mag is rebuilt and fires on the bench then timing was likely the only problem. From there, it's all about fuel delivery and a proper mixture to start it.