Adjustable ignition timing

[Creative Engineering]

As some of you may have discovered, not all of these engines perform the same.

I've found that bogging, 2-stroking, and a lack of overall power, can be traced back to ignition timing that is incorrect.

You can have your carburetor mixture adjusted perfectly, install a tuned pipe, and/or high compression cylinder head; and still have very poor performance due to incorrect ignition timing.

From the factory these engines are, typically, set-up with the timing 2-5 degrees advanced...which is about 15 degrees retarded from ideal.

The PK-80 engines that Pirate Cycles had last year were noticeably more powerful than all of the others we tested...the ignition timing was 12 degrees advanced on these engines. The engines were night and day; more torquey than any of the others.

Interestingly enough the Chinese do understand that 20 degrees advanced is a good starting point...The crankshaft key slot is cut at 20 degrees from T.D.C...Unfortunately the magnet guy ran his broach through at, (you guessed it), approximately 20 degrees...which completely nullifies the 20 degrees of advance that the crank maker built in. It’s like they couldn’t agree who was going to create the off-set key…so they both did. Do it twice just to be sure!

There isn't enough room inside the case to allow for any sort of backing plate that would allow for rotating the coil...an adjustable magnet is the only way to easily alter the timing.

Slightly advancing the ignition timing makes a HUGE difference in the performance.

Obviously you don't want to go too far advanced...too much isn't good either.

A retarded ignition causes bogging, misfiring, (four stroking), poor fuel economy, and fouled plugs.

Too far advanced and you risk overheating, detonation, and piston seizure.

The photo below shows the fix.

Jim

 

[corgi1]

good deal,must remember that

 

[culvercityclassic]

I like the fix, is that something you offer to purchase? btw CE that's some good information to know.
ccc

 

[2door]

I've always maintained that this is the key to good performance. I've posted this info a couple of times and gotten arguments or no response about my findings. The best engine I've ever had was a full three (3) degrees advanced over the second best running one. Just to prove my findings to myself I cut a new keyway in a rotor (magnet) and physically advanced the timing on my worst running engine. The results were dramatic.
If you have more than one engine, especially one that runs noticably better than the other one/s and if you have a means to check, like a camshaft degree wheel, you can prove this is not just a theory. The trick is to find what works best. It isn't exact science and takes some trial and error to find. Jim's tapered bore idea might make it easier to get the right combination of advance verses crankshaft/ magnet indexing. You'll need an accurate way to determine top dead center of the piston stroke, a dial indicator is the best method and some means of indexing just where the magnet is in relation to the crank at that point to make any adjustments. This is not something for the beginner to try. It takes a full understanding of crank/piston/rotor understanding to see what happens with an advanced or a retarded ignition timing.
It is my belief that the factory's idea of quality control has something to do with the variance we see in the performance of engines. Whoever cuts the crankshaft key ways or the ones in the rotor are just getting in the ball park, so to speak, and not concentrating on maximum power output. That's the problem.
Tom

 

[cannonball2]

Lapping the magnet rotor to the crank will also work. Properly lapped and tightened it will stay where you put it with out a key. If you have ever seen an old 2stroke outboard, the first third of throttle advance is just timing, the carb begins to open after that. Timing is crucial on a 2 stroke.

 

[2door]

Lapping the magnet rotor to the crank will also work. Properly lapped and tightened it will stay where you put it with out a key. If you have ever seen an old 2stroke outboard, the first third of throttle advance is just timing, the carb begins to open after that. Timing is crucial on a 2 stroke.

Never tried that. It might be worth experimenting with. Thanks.
Tom

 

[Goat Herder]

One can raise or lower the jug too. I think of some motors that may have come with thinner gaskets on the jug but fixing it at the magnet might just be better all around. I can think of some base gasket material that some folks will not be able to easily make.

 

[timboellner]

How about a degree wheel mounted on the right side small crank gear,
with a fixed pointer mounted to the crank case.

You could use a dial gauge to calibrate and set to TDC.
Use Jim's adjustable magnet idea advance to 12 degrees or better.

Is there anyway to use the old school timing light we all used to use back in the day?

The whole idea of being able to adjust the timing seems the most logical thing to do in order to tune for performance. It's a major player in the motor's
ability to run right.

Cool ideas fellas

 

[Creative Engineering]

From a pure mechanical standpoint, the taper lock design for attaching parts to a shaft is old...real old, and proven to work.

I've been doing this for the past 6 months on my builds, and I've never had one slip.

The difference in performance can be night & day.

As soon as I can get one of my dealers to ship me 100 magnets, they will be available, and announced in the swap & shop forum.

How to set it up:

With magnet, split collar, washer, and nut installed: you can not see the keyway…in other words you will not be able to use the keyway as a visual reference. It doesn’t matter. You can still, with confidence, get a good base point. For most users with a stock engine, this will be a set it, and done, procedure. Fine tuning within a degree or two is pointless until you add additional performance items that truly change the nature of the engine.

The CAD graphics below show the relationship of the magnet relative to the crank.

The first graphic shows the typical “stock” set-up with 5 degrees of advance.

The second and third graphics show what I consider to be a good starting point…as you can see the timing is off by about ½ the key width. This is only a baseline, as I have had engines that were more or less degree-wise when looking at the magnet “clock” position relative to the crank.

In the second graphic you can see the piston position relative to T.D.C. when the crank keyway is in-line with the cylinder…The keyway in the crankshafts have been consistently checked at a clock position of 20 degrees from T.D.C. +/- one degree.

As shown, you could simply rotate the crank so that the crank keyway is, (vertical), inline with the cylinder...then attach the magnet so that the poles are, (horizontal), perpendicular to the cylinder. On most engines this will be about one half the key widths.

When attempting to set it up this way, the poles of the magnet are constantly trying to attract to the frame of the coil. i.e. the magnet wants to spin 90 degrees.

An easier way:

As shown in graphic #4, rotate the crankshaft clockwise 90 degrees and mount the magnet so that the poles are in-line with the cylinder.

You can, of course, scribe witness marks into the end of the crankshaft so that you have a reference mark as to where the crank keyway is located. This must be done precisely though, and isn’t necessary to get a good base point.

The instructions will elaborate on all of this further.

Jim

 

[oldtimer54]

Why not just make a magnet with the keyway at a good offset with out the adjustment. Seems like it would be way better then the stock magnet and it would be WAY easy. The poorly setup HT magnet work ok with no adjustment these would probably work great with out the adjustment. What do you think Jim? Thinking out loud here.

 

[timboellner]

Those graphics and your explanation make it very clear how easily this could
be done.
As usual you are on the cutting edge of bolt on engineering.
I hope this idea can come to fruition.
Thanks for your dedication to "advancing" the hobby.

TIM

 

[cannonball2]

Cutting a new key way might prove difficult for some folks. Lapping the magnet is simple, and doesnt take too long IF the maching is a pretty good match between the crank and rotor. If you are real good with "hand machining" making an offset key is also possible. I raced karts in the unlimited class for awhile and the lapped flywheel was the way to go. We used "in the hole timing" set with a dial indicator. A degree wheel was used to verify the amount. using a degree wheel for these engines would work fine. An easy way is with an extended piston stop. Set the degree wheel, rotate the piston to the advanced side of TDC, screw the stop down until the desired setting is met and simply tighten the lapped rotor in place. The trick is determining where exactly the rotor triggers the ignition.

 

[Creative Engineering]

cannonball2,

I'm going to assume that the engines you are talking about had tapered cranks where the mag was attached...in addition to a key. This was typical of the Suzuki and Yamaha MXer's I had years ago.

Lapping a tapered crank to achieve a spot-on fit would, of course, work fine as you pointed out.

The problem is:

The HT cranks, and the bore of the magnet, are not tapered. It's a straight 8mm, (.315"), shaft and bore. Lapping would do nothing but produce a sloppy fit.

Jim

 

[Creative Engineering]

Those graphics and your explanation make it very clear how easily this could
be done.
As usual you are on the cutting edge of bolt on engineering.
I hope this idea can come to fruition.
Thanks for your dedication to "advancing" the hobby.

TIM

Thanks Tim!

Jim

 

[oldtimer54]

So Jim do you think it would work to make a magnet with the keyway in the (close) to the right place? Seems it would be much better then stock? I know I would buy one.

 

[cannonball2]

Youre right I didnt realize it was a straight shaft. WOW even the throw away weedeaters have a taper shaft! The offset key might be a posibility, easily made from a larger key. Are they straight or woodruff type? All my bikes are 4 stroke, I have only owned 1 of the 2 strokes. Due to the vibes I soon moved to the 4 stroke so never really became really familar with these engines. One possibility might be an ignition system from an R/C engine. Requires the use of a small battery but will run for many hours. You would simply drill the rotor for a small rare earth magnet and mount a small sensor. The beauty of these systems is they are auto advance. They start at around 5 degrees for easy starting and great idle and advance to the uppers 20s. The R/C gas engines operate in the same basic rpm range as the bike engines. I have used many of the systems converting chain saw engines to aircraft, very reliable.

 

[Creative Engineering]

Youre right I didnt realize it was a straight shaft. WOW even the throw away weedeaters have a taper shaft! The offset key might be a posibility, easily made from a larger key. Are they straight or woodruff type? All my bikes are 4 stroke, I have only owned 1 of the 2 strokes. Due to the vibes I soon moved to the 4 stroke so never really became really familar with these engines. One possibility might be an ignition system from an R/C engine. Requires the use of a small battery but will run for many hours. You would simply drill the rotor for a small rare earth magnet and mount a small sensor. The beauty of these systems is they are auto advance. They start at around 5 degrees for easy starting and great idle and advance to the uppers 20s. The R/C gas engines operate in the same basic rpm range as the bike engines. I have used many of the systems converting chain saw engines to aircraft, very reliable.

Other than these...I've never seen one without a tapered shaft either. At first the taper may seem redundant, but there is a sound reason for doing it this way...concentricity...I don't know why the Chinese didn't do it this way. The crank is tapered at the opposite end where the pinion gear is attached.

The key is a woodruff type. On some of these engines, there would be very little left of the key if it were filed down to get the correct timing...doable yes...but there would be the chance that the remaining key may shear.

This end of the crank is small and totally soft...It's not a typical 4130 crank heat treated to 42-45 rockwell...it's dead soft.

The split collar secures the magnet without having to put excessive torque on the nut that holds it on.

You're right...it would definitely be beneficial, and possible, to adapt a different ignition system.

Jim

 

[Creative Engineering]

So Jim do you think it would work to make a magnet with the keyway in the (close) to the right place? Seems it would be much better then stock? I know I would buy one.

Yes it would...

The problem is volume vs. cost vs. value...

Although the effect is dramatic...this is not a fix that will have a perceived value of $45.00, which is likely what it would cost to make a new magnet.

It is very easy to set-up the modified factory magnet, and some builders with tuned pipes and other upgrades are going to want the infinite adjustability.

Jim

 

[oldtimer54]

Yes it would...

The problem is volume vs. cost vs. value...

Although the effect is dramatic...this is not a fix that will have a perceived value of $45.00, which is likely what it would cost to make a new magnet.

It is very easy to set-up the modified factory magnet, and some builders with tuned pipes and other upgrades are going to want the infinite adjustability.

Jim

Right got ya. Well when you get these made Ill buy one for my dead motor lol. (ill get her going). I know your work and I dont want to miss out.

 

[Goat Herder]

Youre right I didnt realize it was a straight shaft. WOW even the throw away weedeaters have a taper shaft! The offset key might be a posibility, easily made from a larger key. Are they straight or woodruff type? All my bikes are 4 stroke, I have only owned 1 of the 2 strokes. Due to the vibes I soon moved to the 4 stroke so never really became really familar with these engines. One possibility might be an ignition system from an R/C engine. Requires the use of a small battery but will run for many hours. You would simply drill the rotor for a small rare earth magnet and mount a small sensor. The beauty of these systems is they are auto advance. They start at around 5 degrees for easy starting and great idle and advance to the uppers 20s. The R/C gas engines operate in the same basic rpm range as the bike engines. I have used many of the systems converting chain saw engines to aircraft, very reliable.

It would be awesome to have a automated system. The old Russian engines did. Granted they were points they still had automated advance.