Ignition timing and cam timing

When a cam chain wears on most bikes, all the slack is taken up at the rear of the engine - as a consequence of the wear,, the cams become progressively more and more retarded from their factory settings. The intake more than the exhaust - this impact the duration, and opening / closing of the valves. I've noticed on bikes with high mileage, changing the ignition timing by a couple of degrees seems to helps them run better.

Should it though?

I've struggled to get my head around this. thoughts? LarryC - others?

If my rough calculations are correct, a worn cam chain will impact the exhaust cam 2-3 degrees and the intake 4-5 degrees - potentially more with severely worn chains.

Wow, Jeff do you like lay in bed at night staring at the ceiling thinking of this stuff?

Jeff.Saunders wrote: When a cam chain wears on most bikes, all the slack is taken up at the rear of the engine - as a consequence of the wear,, the cams become progressively more and more retarded from their factory settings. The intake more than the exhaust - this impact the duration, and opening / closing of the valves. I've noticed on bikes with high mileage, changing the ignition timing by a couple of degrees seems to helps them run better.

Should it though?

I've struggled to get my head around this. thoughts? LarryC - others?

If my rough calculations are correct, a worn cam chain will impact the exhaust cam 2-3 degrees and the intake 4-5 degrees - potentially more with severely worn chains.

A worn cam chain will not affect duration one bit. It will only affect the open / close values. Lash, to a minor degree will affect duration, every so slightly. I've seen chains with stretched spots so bad that the chain falls away from the top idler in certain spots.

Back in 1985 I ported a head for a 900 with 1015 Wisecos and installed used 2x Andrews. It already had 29 Mics on it. The guys cam chain was severely stretched. At the time I was working at a dealership. On a Saturday the guy came to my house and I checked his cam timing. His lobe centers were up aroun 118 degrees :ohmy:

The bike didn't idle well at all. What it did do was pull very, very hard from 4000 RPM on up. I pulled the cams out, slotted the sprockets and set them to 106 centers. It fired right up. A few adjustments and it idled like it should. When the guy rode it he came back and said it's much improved in the low end but that crazy top end pull was not the same.... Well....which do you want? With what you have you can take your pick but you can't have both :sick:
There's only one good solution for a stretched out cam chain. Call Jeff for a new one

Jeff.Saunders wrote: When a cam chain wears on most bikes, all the slack is taken up at the rear of the engine - as a consequence of the wear,, the cams become progressively more and more retarded from their factory settings. The intake more than the exhaust - this impact the duration, and opening / closing of the valves. I've noticed on bikes with high mileage, changing the ignition timing by a couple of degrees seems to helps them run better.

Should it though?

I've struggled to get my head around this. thoughts? LarryC - others?

If my rough calculations are correct, a worn cam chain will impact the exhaust cam 2-3 degrees and the intake 4-5 degrees - potentially more with severely worn chains.

Jeff
you are better off to use adjustable cam sprockets and correct the cam timing changing ignition timing is in my opinion a bandaid but does help somewhat but getting the cam timing correct is way more effective hope this helps.

Many claim even the factory cam timing is not exactly correct. Degreeing the cams is a PITA, but at least you know the timing is spot on.

It doesn't seem like cam timing should affect how the ignition timing makes the motor run. But here's some info on the KZ550D:

The Kawasaki spec for the cam timing is 270 deg duration, with intake opening at 31 BTDC, and closing 59 ABDC.
However, that is with using .012" lift as the threshold for open or closed.
If I use .000" as the threshold, the duration goes way out to about 388 degrees duration (with zero lash).
That puts opening at about 69 BTDC, but more importantly, it puts closing at about 138 ABDC.
138 ABDC is the same as 42 BTDC.
At full advance, the ignition sparks at about 35 BTDC.

So that only puts about 7 degrees between when the intake closes and the ignition sparks, but only under extreme conditions, such as when the valve lash is down near zero, and at full advance. But if the intake was retarded 5 degrees, now you only have a 2 degree gap between valve-closed and spark.

That's close, but still seems dubious as the cause since that is really pushing all the numbers to their extremes.

I have also noticed that adjusting ignition timing off of the spec makes it run better on a really worn engine, but have not figured out why.

Things change when running under op temp ...........Although most substances expand when heated, not all expand at the same rate. Aluminum, for example, expands twice as much as iron when both are heated the same amount.

loudhvx wrote: It doesn't seem like cam timing should affect how the ignition timing makes the motor run. But here's some info on the KZ550D:

The Kawasaki spec for the cam timing is 270 deg duration, with intake opening at 31 BTDC, and closing 59 ABDC.
However, that is with using .012" lift as the threshold for open or closed.
If I use .000" as the threshold, the duration goes way out to about 388 degrees duration (with zero lash).
That puts opening at about 69 BTDC, but more importantly, it puts closing at about 138 ABDC.
138 ABDC is the same as 42 BTDC.
At full advance, the ignition sparks at about 35 BTDC.

So that only puts about 7 degrees between when the intake closes and the ignition sparks, but only under extreme conditions, such as when the valve lash is down near zero, and at full advance. But if the intake was retarded 5 degrees, now you only have a 2 degree gap between valve-closed and spark.

That's close, but still seems dubious as the cause since that is really pushing all the numbers to their extremes.

I have also noticed that adjusting ignition timing off of the spec makes it run better on a really worn engine, but have not figured out why.

I guess my question is....WHY would anyone want to attempt to fine tune an worn out engine? I stand by the old saying... "Only a farmer can start with $hit and end up with something good"

I've never really thought about it...but...As for why it seems to help...I would suggest that cylinder pressure comes into play and that by advancing the burn you may increase the cylinder pressure somewhat.....which in turn will help gain back some of the performance lost through poor cylinder sealing that usually accompanies the worn out rings and valves....

Other than that, you've done nothing else to restore the efficiency lost from worn out components.

I question that 388 degrees of duration number...There are only 360 degrees in a one revolution of the crankshaft. How are you borrowing time from the next cycle? There is no time for the compression stroke??

Essentially I believe the compression degrees are being included into your total

I believe what's happened is you've set up a dial indicator and degree wheel but not taken into account the number of degrees the valve is motionless on the seat. ie, from closing point where Zero lift is recorded to the opening point where you are just seeing movement.....let's say .0005" of lift on the opening event.

Ultimately, it's neither here nor there in the grand scheme of things....it's all in how you look at the dynamic vs the static events. All 4 cycle engines are multi taskers....4 strokes need both valves open together at TDC overlap to both evacuate and refresh the charge.... It is the reason they are so complex in things that affect their performance. We try to single out events for improvements but sometimes fail to consider the basic principle that more than one thing is happening at the same time at some point during the process

You are one of the very rare group of people that knows to use .3mm for the checking lift for OEM cams

:whistle:
cam-degreeing-for-zombies

A little off topic but sort of related....

There have been debates about flow importance at various valve lifts in other forums. It's well known that the exhaust system will pull a stronger vacuum on the cylinder than the piston can pull. Hence the supporting argument that low lift flow is of significant importance.

The unfortunate things about that are:

A] The piston is in the wrong position
B] Much of the charge gets sucked out the exhaust valve and exhaust system wave activity is heavily relied upon to stuff the lost charge back into the cylinder before the exhaust valve slams the door shut. [ 2 stroke expansion chamber Deja Vu :laugh: ]

So assuming exhaust scavenging rules the day....why bother to lift the valve more than a stock cam. Instead let's just increase duration a whole bunch? ...After all, that is a reasonable conclusion based in implications...

In the real world, if you want high RPM power....you need to lift that valve....in spite of the implication :side:

LarryC wrote:

loudhvx wrote: It doesn't seem like cam timing should affect how the ignition timing makes the motor run. But here's some info on the KZ550D:

The Kawasaki spec for the cam timing is 270 deg duration, with intake opening at 31 BTDC, and closing 59 ABDC.
However, that is with using .012" lift as the threshold for open or closed.
If I use .000" as the threshold, the duration goes way out to about 388 degrees duration (with zero lash).
That puts opening at about 69 BTDC, but more importantly, it puts closing at about 138 ABDC.
138 ABDC is the same as 42 BTDC.
At full advance, the ignition sparks at about 35 BTDC.

So that only puts about 7 degrees between when the intake closes and the ignition sparks, but only under extreme conditions, such as when the valve lash is down near zero, and at full advance. But if the intake was retarded 5 degrees, now you only have a 2 degree gap between valve-closed and spark.

That's close, but still seems dubious as the cause since that is really pushing all the numbers to their extremes.

I have also noticed that adjusting ignition timing off of the spec makes it run better on a really worn engine, but have not figured out why.

I guess my question is....WHY would anyone want to attempt to fine tune an worn out engine? I stand by the old saying... "Only a farmer can start with $hit and end up with something good"

I've never really thought about it...but...As for why it seems to help...I would suggest that cylinder pressure comes into play and that by advancing the burn you may increase the cylinder pressure somewhat.....which in turn will help gain back some of the performance lost through poor cylinder sealing that usually accompanies the worn out rings and valves....

Other than that, you've done nothing else to restore the efficiency lost from worn out components.

I question that 388 degrees of duration number...There are only 360 degrees in a one revolution of the crankshaft. How are you borrowing time from the next cycle? There is no time for the compression stroke??

That measurement is only an academic value, and would almost never happen in real life. I figured while I had the test rig in place, why not go to the extreme, so I measured where I could detect any significant movement of the bucket.

That measurement was taken from the very first angle the bucket moved at all, to the very last angle where the bucket moved at all (the degree wheel was on the cam itself, then converted to crank degrees by multiplying by two). I measured at least two, and possibly four cams and took an average. The bucket was in contact at all times, and I measured bucket movement with a dial indicator. This is not an easy measurement to make since the opening and closing ramps are so gradual near where they transition to the base radius, so there may be some error in the numbers, but I did the measurements many times.

My mind was a little blown by this result as well. But it actually falls in line with all of the other results I got that day, and those fall in line with the specs that Megacycle has posted for those cams.

LarryC wrote: Essentially I believe the compression degrees are being included into your total

I believe what's happened is you've set up a dial indicator and degree wheel but not taken into account the number of degrees the valve is motionless on the seat. ie, from closing point where Zero lift is recorded to the opening point where you are just seeing movement.....let's say .0005" of lift on the opening event.

Correct, for that one extreme measurement.

I also took duration readings using different amounts of lift as the threshold.
At .000" lift, the duration is 388 deg.
At .006" lift, the duration is 324 deg.
At .012" lift, the duration is 270 deg.
At .040" lift, the duration is 230 deg.
At .050" lift, the duration is 226 deg.

Notice the numbers are quite reasonable until you go all the way down to zero lift. That is because the transition is apparently very very gradual. This also means the lobe occupies more than half of the cam, but it doesn't appear that way to the naked eye.

And when I say zero lift, I don't mean actual zero lobe lift. Duration at actual zero lobe lift would be theoretically 720 degrees of crank rotation (or infinite, really). (Think about that ) At all crank angles, the lobe lift has be theoretically zero or greater.

So if actual zero lobe lift is essentially infinite (or 720 degrees) duration, one would expect that just slightly greater than zero lobe lift will be a pretty large duration angle.

(I realize Larry knows all this, but for the benefit of others...)

I measured the duration when there was any significant movement of the needle, so it was probably somewhere under half a thou, as Larry predicted (.0005").

Kawasaki stated 270 degrees of duration, but did not state the amount of lift for that duration (using zero lash). I measured the amount of lift at 270 degrees duration, and I came up with .012" (.3mm).

I also took the duration at .040" lift, since that is what Megacycle used to measure those cams. They measured 233 deg and 234 deg at .040" (they should be the same for intake and exhaust, but no two cams measured exactly identical in my limited experience). I averaged mine, and got 230 degrees, but my cams are old. I assume they made their measurements on new cams.

I have the details on this page for any 550 owners who are interested.
home.comcast.net/~loudgpz/GPZweb/CamsKZZ...KZZXZR550500400.html

LarryC wrote: Ultimately, it's neither here nor there in the grand scheme of things....it's all in how you look at the dynamic vs the static events. All 4 cycle engines are multi taskers....4 strokes need both valves open together at TDC overlap to both evacuate and refresh the charge.... It is the reason they are so complex in things that affect their performance. We try to single out events for improvements but sometimes fail to consider the basic principle that more than one thing is happening at the same time at some point during the process

I agree. I realized that after getting near the end of my original post, but I hit the submit button anyway. Hated to throw away all that typing.

LarryC wrote: You are one of the very rare group of people that knows to use .3mm for the checking lift for OEM cams

Now that makes my day! :blush:

Believe me...when you post something, I take the time to read it because it's always good stuff

Cam specs can be very misleading because having only two points, an open and close will never yield the picture of what the lobe profile is providing. Here's a list of Kawasaki Cams with durations at 3 points each. As you look through it you'll see a better picture of what I mean.

Master #
Lift
Duration
@ .020
Duration
@ .050
Duration
@ .100

45 .415 268° 244° 220°
110 .395 284° 256° 228°
118 .365 283° 246° 216°
119 .384 276° 240° 210°
146 .420 288° 258° 232°
208 .408 282° 258° 233°
218 .418 280° 242° 218°
227 .383 276° 253° 228°
483 .395 266° 242° 216°
493 .415 276° 252° 229°
536 .378 268° 244° 218°
539 .400 280° 256° 230°
540 .384 272° 248° 222°
549 .369 280° 252° 226°
613 .381 266° 240° 218°
715 .408 283° 256° 228°
797 .410 277° 252° 224°
813 .388 268° 244° 218°
814 .402 279° 251° 223°
830 .383 272° 244° 217°
931 .380 280° 258° 232°
961 .400 282° 256° 228°
968 .386 274° 248° 220°
1002 .379 274° 248° 221°
1029 .381 263° 240° 218°
1043 .400 268° 242° 216°

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