TDC adjustment for Setting Ignition Timing

[posplayr]

What is a reasonable way to make adjustments to ignition timing given that I am using a degree wheel to set cam timing?

I started off writing this thread assuming I did not want to upgrade to a new timing light. After all my $10 unpowered timing light (purchased 30 years ago) with the paper towel roll taped to it (also has the feature that it only works in low light levels) probably has a few more years of life.

Oh well times change and technology marches on. I just ordered this....

http://www.amazon.com/exec/obidos/tg/detail/-/B000BSY9JE/ref=ord_cart_shr?%5Fencoding=UTF8&m=ATVPDKIKX0DER&v=glance

So the question just gets down to this:

Since the first step to degreeing the cam is to establish TDC, I should also make sure that my ignition timing is also accurate. I should also degree in the timing marks and figure out how much error there is relative to the calibrated degree wheel.

Finally when actually measuring/setting the timing, I can dial in the timing mark error into the timing light and get an accurate timing adjust.

With this adjustment I can verify initial advance and total advance using the built in Tachometer.

Does this sound about right?

Posplayr

[lecroy]

I don't see anything wrong with what you wrote. I have never checked the tick marks on the rotor (advancer) and timing plate to see how accurate they are. I just assumed the factory had them close enough and set them with them with my 20 some year old Sun light. If I was off a half a mark one way or the other, I guess I didn't care too much.

However you made a very good point "Oh well times change and technology marches on.". How true this is. If your still working with your stock ignition from 25 plus years ago, your safe. But if you've pulled all those old stock parts and are using some high performance sht, like I assume you are because your in the performance mods area, then this may not be such a good idea.

Some of those newer technology ignitions are normally setup a little different. The MSD type ignitions can fool a timing light into giving a false read. Many of the newer ignitions have an LED that will tell you when the ignition detects the trigger. Everything is setup with a degree wheel. Some of the more complex ignitions like the MC-4 can be a real undertaking to try and understand if your new to this sort of thing.

Me blabing to a friend about setting the MC-4's timing........

So, call it overthinking or being thorough, I decided it was best to see how it really works. I set up a little test using a spare harness, coils, wires and a few pieces of test equipment. I have a computer program that simulates the ignition trigger. There is a little current transformer that is stuck on #1 plug wire to see when the ignition fires the plug relative to when I tell the ignition to fire. This data is captured using a scope. I first set the RPM to 1000 and looked at the waveforms.



The rising edge of the green trace is telling the ignition to fire, the yellow is the plug fireing. You can see the second spark from the MSD. This time is 1.350mS. So a little math,

1000RPM = 16.666667RPS
1/RPS = 0.06 seconds for 1 rev or 360 degrees of crank rotation.
So 1 degree = 0.000166666 seconds.

0.001350 / 0.000166666 = 8.1000000 degrees.

I had set the ignition to 36 degrees BTDC using the little LED. So, 36 - 8 = 28 degrees.

It works!!!

I then did the same test at 10,000 RPM, and you can see the ignition delay is now 131uS. So, again 28 degrees.

[posplayr]

Lecroy

I only bought my 83 GS1100ED in January and rode it 100 miles and pulled it a part to get it into shape. The ignition is stock except the Accell coils/wires the PO put on. No MSD. I had not considered the timing much as I think on my 81 GS750EX has fixed timing??? Anyway when I pulled off the breaker plate on the 1100 I saw it was slotted and I would have to get it back on and properly timed.

I was mentioning to another memeber how sensitive my 327 small block Chevy was to initial advance. By limiting the total mechanical advance, an inclease from 4 degrees to about 12 degrees initial BTDC made a huge difference in off the line pep even for a basically stock engine with just headers.

Given that these GS cams are degreed because of the possibiity of +/- 5 degrees of production variation, I suspect the same hold true for timing. Got me to thinking how to adjust the timing mark using the degree wheel measurements. Rapid Ray said he used an adjustable Snapon timing light ($400).

I have new webcams and slotted gears so I'm going to do the compulsory cam degreeing. While I'm at it I'll note how far the timing marks are off as well. Without even worrying about the timing mark of a timing light, I could just use the degree wheel to get the motor to the desired timing mark and then static time as I had done many times on my Chevy.

Well the newer light seems would allow me to use Rays proceedure.

Anyway thanks for the scope outputs. Apparently the new ignitions maintain an estimate of RPM and adjust the delay to match the desired angular delays. Your scope displays demostrate this. I'm assuming that the double spike on the secondary is what throws the timing lights for a loop ???

Thanks

Posplayr

[lecroy]

Ah, I'm with you now. Only problem with static timing is it has an inductive pickup and I am not sure that you could adjust it slow enough to get a good reading and still get the ignition to see the trigger. The inductive pickup works like a small generator. Slower you turn the less voltage it outputs. Then there is the mess of where the ignitions threshold is and I doubt they compensate for this with the stock units.

The reference plate isn't slotted (or at least on any I have seen) and this should give you the a good starting point. 10 degrees of crank error on the pickup? Well I'm not so sure about that. I would guess maybe 2, but have no proof. The dents are pretty large on the stock advancer from what I remember. Won't hurt you to check and give you peace of mind. Heck, just check the marks with the degree wheel and see.

I thought there were a few differences between where the bikes were sold to meet emissions. Hard to belive that the Japs couldn't set timing on the cams or ignition better than this with all the other precision parts and setup.

Man Ray, what you doing with stock ignitions? Thought your shop was building drag bikes.

MSD (not the company name) stands for Multi Spark Discharge and that is the second pulse you are seeing. Sorry for the poor color choice. The slower the crank turns the more pulses.
The MC-4 is the timer from hell. You can play with timing until your blue in the face drawing cute little pictures with the PC. I am not sure if the multi-spark is the problem with the timing lights but would guess this is the case.

[posplayr]

Inductive ???

Good point on inductive pickup. I was using an stock mechanical points system on my Chevy but the static timing worked very well (checked with a timing light).

As mentioned previoulsy I came into the 90's err maybe even 2000's by buying the adjustable digital timing light. Supposed to be basically a handheld distributor machine.

Should work well with stock GS breaker plate and I can dial in the TDC error as Ray dose.

Posplayr

Product Description
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[rapidray]

Ah, I'm with you now. Only problem with static timing is it has an inductive pickup and I am not sure that you could adjust it slow enough to get a good reading and still get the ignition to see the trigger. The inductive pickup works like a small generator. Slower you turn the less voltage it outputs. Then there is the mess of where the ignitions threshold is and I doubt they compensate for this with the stock units.

The reference plate isn't slotted (or at least on any I have seen) and this should give you the a good starting point. 10 degrees of crank error on the pickup? Well I'm not so sure about that. I would guess maybe 2, but have no proof. The dents are pretty large on the stock advancer from what I remember. Won't hurt you to check and give you peace of mind. Heck, just check the marks with the degree wheel and see.

I thought there were a few differences between where the bikes were sold to meet emissions. Hard to belive that the Japs couldn't set timing on the cams or ignition better than this with all the other precision parts and setup.

Man Ray, what you doing with stock ignitions? Thought your shop was building drag bikes.

MSD (not the company name) stands for Multi Spark Discharge and that is the second pulse you are seeing. Sorry for the poor color choice. The slower the crank turns the more pulses.
The MC-4 is the timer from hell. You can play with timing until your blue in the face drawing cute little pictures with the PC. I am not sure if the multi-spark is the problem with the timing lights but would guess this is the case.

I don't do ANYTHING with STOCK ignitions. Where did you get that idea? He asked about setting the timing & I told him I use a Snap On light with the dial for finding the exact amount of timing at full advance, I set all my stuff up so it has full advance in by 2000 RPM. What part of the country are you in Mark & why do I need a website? I stay more than busy without one. Ray.

[lecroy]

I don't do ANYTHING with STOCK ignitions. Where did you get that idea? He asked about setting the timing & I told him I use a Snap On light with the dial for finding the exact amount of timing at full advance, I set all my stuff up so it has full advance in by 2000 RPM. What part of the country are you in Mark & why do I need a website? I stay more than busy without one. Ray.

Figured anyone setting timing on a race bike was using a degree wheel, but guess not. Have you tried it with any of the MSDs? Not sure why you care but I am from Michigan. Not that you need a website, I just wanted to see what your doing in your shop. If this is how you earn a living, must be a pretty nice setup. But I can't seem to get you to post even the basics of what your doing for some reason. Oh well, I'll stop asking. It's obviously a sore spot with you.

[rapidray]

Mark, first, he wasn't asking about setting the ignition timing on a race bike. I time all of my race motors with my degree wheel. It is the 18 inch Moroso wheel with the marks 1/4 inch apart. GREAT wheel! Yes, I have tried the light on an MSD system & it doesn't work. Somehow it screws up the signal & reads WAY advanced. I asked where you are because I was going to issue an invite for you to come check out the stuff I do. As far as what I do, I do a LOT of cylinder heads & run my flow bench about 6-10 hours a week. I also do frame raking, body mounting, & all types of fabrication. I have a chassis jig & am in the process of my first full chassis bike now. I am just a small shop trying to make a living while having fun. Hope this helps, Ray.