timing a 1924 j.d. mag engine. need help.

[John Mertens]

I need help timing up my 1924 j.d.#74 WITH A BOSH ZEV mag.i have tryed timing on the rear cylinder top dead center. to fire on the front cylinder just after the front cylinder intake closes. but im not getting a pop out of it. I just installed a m51 linkert rebuilt by Mikes linkerts so i know that that ok. the mag is a new rebuilt . and fires real good.i belive my problem is in the timing of engine.could someone give me a step by step instructions on timing a mag j.d. engine. thanks guy. call me stumped. Johnny.

[rwm]

how many teeth do you have on the mag gear?is your timing mark always in the same place when you recheck it?.are you sure you have a spark in the cylinder? a weak mag will zap your hand but not your plug under compression. call and ask ed strain.
813 521 1597.

[Tommo]

John,
I thought someone may have given you more detailed advice by now so here goes
Firstly set the mag at FULL ADVANCE. That is with the interupter ring rotated as far as it will go in the direction opposite to the rotation of the magneto.
Then make sure that the pick-up marked 1 has its HT lead connected to the rear cylinder. This usually means that the rearmost pick-up HT lead will go to the rear cylinder and the front pick-up HT lead to the front cylinder
Set the mag points at 15 thou.
I find a bit of cigarette paper between the points is about the best thing to determine when they are just starting to open. You'll feel the cigarette paper release if you're lightly pulling on it as you rotate the mag.
Now set the rear cylinder at 5/16 of an inch before TDC on the compression stroke and then rotate the mag, ensuring the engine stays stationary, until the points are just staring to open.
Now tighten the nut holding the mag drive gear to the mag armature just enough to hold it firmly in place.
You now need to turn the engine over in it's correct rotation until the front cylinder is 5/16 of an inch before TDC on it's compression stroke and check that the contact points are just starting to open.
If they are you've timed your engine. If they're not you've timed it on the wrong breaker ramp so go back and repeat the process but time the rear cylinder on the opposite one you used the first time.
When you think it's right rotate the engine in it's running direction and stop when the pionts open, cigarette paper releases, and measure where your piston is. 5/16 BTDC.
By rotating and checking you take all the backlash out of the gear train and get a more accurate setting but it does mean you may have to adjust things more than once.
Some mag drive gears are keyed and some are not but I prefer to leave the key out of any that are keyed as I find I can get a lot more accurate timing setting.
If you prefer to keep the key you may find you need to advance or retard the mag drive gear up to as much as 3 teeth from the factory marks to get correct timing.

[koanes]

That's good stuff Tommo. Printed off and filed for future reference. Thank you for taking the time.

[John Mertens]

Thank you very much Tommo. is it best to remove the engine from the frame to get the 5/16.or is there a better way to find the 5/16 with the engine in the frame.what is the best way to do this.. the mag has a repop gear and it dozen't have any timing marks. i like your idea of removing the key im sure that i can get a more acccurate timing. i'm sure a lot a guy out there really appreciate your step by step instructions very easy to fallow.again i really appreciate you time. thank you very much. Johnny.

[kg993]

All you need is a depth guage or a narrow scale to measure from the piston to the top of the plug hole or a head fin (something in a fixed position). I prefer a degree wheel on the sprocket shaft and a pointed rod fixed to a motor or frame bolt. If you don't have a degree wheel you can adapt a protractor to work. You will have to determine what 5/16" of piston movement is in degrees of rotation first.

[Tommo]

John,
I prefer to do it before I install the engine in the frame and use the holes the two cylinder steady studs are screwed into. As they are directly over the piston they provide a ideal place for accurate readings.
Get a pair of old steady studs and drill 1/4 inch holes in them so that they can be screwed into the tops of the cylinders and have lengths of 1/4 rod dropped down them so that you have something that rests on the top of the piston and goes up and down as you rotate the engine.
Make sure you put a nut or something on one end of the 1/4 rod so as you don't lose it down inside the cylinder.
The rod that protrudes out the top can then be used to accurately measure where the piston is and thus help in getting the timing right.

[Tommo]

Here is a selection of my timing tools which may give you a better idea of what I'm talking about.
Sorry about the picture quality but my camera doesn't have a close-up facility.
I'm sure the Harley one is easy to pick.

[kg993]

still learning

Timing tool 001.jpgTiming tool 002.jpg

This is one of the adapters I made to attach a degree wheel to the output shaft. If there are a couple of threads showing on the shaft it will go on and hold just fine.

When I posted that about using the plug hole I never considered the location of the spark plug in that model and know it won't even work on a flat head. I also would never imagined there would be a through hole into the combustion chamber. I learn something new every day, and just wish I could rember it the next day.

[Chris Haynes]

Tommo,
If you open a free account at photobucket here is how your photos will appear on the boards. No resizing necessary. Simply upload your photo then copy the IMG Code for the photo and paste it here.

[John Mertens]

Thank you guys for the great information. it makes me proud to be a menber of amca. it truly has some very good members who truly want to help other members reach there goals . with all of this info i am sure i will have the old girl on the race track at Davenport.#24. again thank each and everone of you for your help. Johnny.

[Tommo]

Johnny,
As you're playing with a race bike does your cylinders have Ricardo chips in them?
If they do don't remove the steady studs unless you are prepared to take your cylinders off.
There is another way to measure the 5/16 BTDC but it is not as accurate and at this stage it will only complicate things if I try to explain it.
No "Riccy" chips just go for it but if you do have them you better contact me.

[John Mertens]

Hi Tommo. thanks for all your help. no i am running the stock Harley Davidson cylinders. standard bore and stroke. however i wish i had Ricardo jugs.are Ricardo easy to find in New Zealand. we pay big money hear in the U.S. for them if you can find them. some of the guy i race against are very serious about racing and run very high compression cylinders . port the intakes. larger valves . grind the cams . stroke them. etc. my bike is a very much stock #74. with very little mod.i race to have fun and let the fan of board track racers injoy them. we are trying to bring back board track raceing.and the history behind them. to keep it alive so the younger people has a sence of history. it's a great thrill to leave the pits and hear the fans cheering.that in it self is worth it for us. o did i mention i'm 67 years young. my wife said she hopes i never grow up. me to. thanks again Tommo for all your help. Johnny.Mertens.#24

[John Mertens]

I have a question on the braker ramps on a zev bosch mag.there are 2 of them. is the ramp at abourt 4 oclock for the rear cylinder and the other at 9 oclock for the front cylinder. and do they fire also on the exhaust.seams years ago i was told that older harleys fire on intake and also exhaust. thanks Johnny.

[Tommo]

Johnny,
Wasted spark is on the electric models that have what is known over here as the "Two spark coil". Mags are not "Wasted Spark."
It's very hard to describe things when there are so many variables in play and you have never seen the thing you are trying to describe but generally a Bosch ZEV 45 degree twin mag will have the points ramps at about 2 o'clock and 4 o'clock in the fully advanced position so long as a standard interrupter ring is fitted.
Some 45 degree interrupter rings have advance slots in two places at 180 degrees to one another to enable you to choose which side you want the advance lever on and others have no built on advance lever and instead have a band with the lever attached so that you can position the lever where you want it.
The most important thing for you is to make sure you have a 45 degree interrupter ring as there are 42, 50, 60 and 180 degree rings that will fit but will give you all sorts of trouble if you try to use them on a 45 degree machine.
It's also important to ensure you have a 45 degree armature in your magneto.
The easiest way to decide which ramp is firing which pick-up is to remove a pick-up and turn the mag to which-ever ramp you choose and look to see if the brass strip on the slip ring is visible or not.
If the brass strip is visible that ramp is firing that pick-up. If it's not visible then the chosen ramp is firing the other pick-up.
Does this help?