Cam ignition timing 'deflection' (wobble)?

[backyardtrouble]

dan filipi » Thu Feb 12, 2015 12:53 pm[/url]":2nf7v08e]
There has been talk that an ignition is better driven off the crankshaft than off a camshaft because of some deflection (variation) in the timing, so I wanted to talk about this because I think there is some misconception of what is actually going on here and may be blown up to be more an issue than it actually is.

Now as I understand it, a variance in ignition timing of 6-9 degrees in a high mileage 1000 is reported.
Where is that variance coming from and is there actually that much variance, is the topic of this discussion.

It was explained to me that in a high mileage 1000, because the cam isn't supported well enough that the cam end where the ignition is mounted can move side to side. This movement has been coined the term 'wobble' (I believe) which changes the ignition timing.
Valve spring pressure effects on the cam can come into play here as well, or may be the root cause, as explained to me.

There has been talk about timing belts causing a variance in timing but I believe now this is not any sort of issue and I'm trying to wrap my head around how on earth can a cam move so much.

Thoughts?

I'm just going to add 2 cents worth. All motors that run have a variance, in the cams, the crank, the rod brgs, main brgs, the valve springs, the whole dang motor.. even the belts when they get hot, they stretch to a certain degree, all these factors are calculated into making these or any motor run at different intervals, so from cold to warm to hot, your going to have a wide range of variance with everything.

 

[slabghost]

All the parts being discussed are mass produced with built in variance. Everything mass produced has tolerances up and down from the designed measure. Additionally only random periodic checks are done on the parts being produced. To think they are all the same is just plain wrong. Even the casting molds change over time.

 

[C5Performance]

My point is that all engines have a variation from cam to crank. What I do not believe without measuring myself is how that "wobble" converts to DEGREES of ROTATION.

If the belts only cause a few degrees of variation (I believe that will prove to be true) then the majority of measured variation would have to come from equipment error and ignition parts such as the timing advance mechanism.

Variations in magnetic pickups has previously been measured in a controlled test and found to be 7 degrees (average) depending on how the magnets were orientated on the rotor. Well take the 7 degrees and add the 2 degrees of belt variation and what do you get? 9 degrees of measured variation! The test was done using points, at engine idle. More measuring will be needed but at least we'd know how much each part of the puzzle contributes to this inaccuracy.

 

[dan filipi]

Boy lot's to think about, and to look at yet.

I'm going to at least check an 1100 and the 1200 I have for any difference in cam TDC and crank TDC in their rotations. I don't have any dial measuring equipment but it's easy enough to mark where the cam end is at crank TDC then rotate the crank 360 and check the cam mark.

 

[C5Performance]

Would an old belt have more "flex" than a new replacement? Just thinking of other variables which could cause one bike to have more timing variation than another.

 

[dan filipi]

C5Performance » Today, 5:03 pm[/url]":2qk7zozz]
Would an old belt have more "flex" than a new replacement? Just thinking of other variables which could cause one bike to have more timing variation than another.

I wouldn't think so but the difference would have to be expansion and contraction either way.

 

[ekvh]

The article I read refers to Robert Overby as the finder and he used the term"wobble." He said it was the end of the cam and due to valve spring tension. Going by memory, what little I have, isn't the center bearing clearance allowance for the camshaft larger than the outsides? If so, this would allow the cam to "flex."

 

[C5Performance]

ekvh » Sat Feb 14, 2015 11:33 pm[/url]":314y0nru]
The article I read refers to Robert Overby as the finder and he used the term"wobble." He said it was the end of the cam and due to valve spring tension. Going by memory, what little I have, isn't the center bearing clearance allowance for the camshaft larger than the outsides? If so, this would allow the cam to "flex."

You might be correct, and I haven't measured it, but the cam would need to "twist" for timing to be messed up, and not just flex.

I immediately think of a car engine and length...

When cylinder #8 fires in a Chevy....it experiences the twist/flex/wobble of the entire crankshaft length. THEN it has chain whip/wobble to the camshaft. THEN it experiences the twist/flex/wobble of the entire length of the camshaft. THEN it has gear lash for the distributor, and finally arrives at the contact points which also have play in the timing advancer.

How does it even run?

My theory is the inaccuracy of the points is probably far worse than all the flex/slop in the rest of the engine. Plus a Goldwing cam is only a foot long. My Hercules inline 6 cylinder engine that operated my crane was at least 4-5 feet long!

The picture shown below uses head mounted distributors but would still be mis-timed to the crank due to gear lash/chain whip?
How much flex is "too much"? Where are the engine designers when you need one?

 

[ekvh]

It is noticed more on points, and some with Dyna. It wouldn't have to twist to throw ignition timing off. That is set by the points and the theory fits in my mind because the wobble or flex occurs at 180 degrees difference of camshaft rotation. (360 of crankshaft rotation) if it wobbles or flexes, it changes the opening and closing time of the points, on earlier than the other. A Dyna wouldn't do it as much because it works with a magnetic field, and your C5 would be pretty immune to it with just one light and 36 teeth to count. Thinking about the belts causing it at low rpm, I'm not sure it would have an effect because it is far enough apart to the next ignition timing event. Valve timing could be off a little though.

 

[Ansimp]

ekvh » Sun Feb 15, 2015 11:31 pm[/url]":3ekje2d7]
It is noticed more on points, and some with Dyna. It wouldn't have to twist to throw ignition timing off. That is set by the points and the theory fits in my mind because the wobble or flex occurs at 180 degrees difference of camshaft rotation. (360 of crankshaft rotation) if it wobbles or flexes, it changes the opening and closing time of the points, on earlier than the other. A Dyna wouldn't do it as much because it works with a magnetic field, and your C5 would be pretty immune to it with just one light and 36 teeth to count. Thinking about the belts causing it at low rpm, I'm not sure it would have an effect because it is far enough apart to the next ignition timing event. Valve timing could be off a little though.

+1 and still manages to run well :yes:

 

[slabghost]

ekvh » Sun Feb 15, 2015 8:31 am[/url]":1vp3wdsu]
It is noticed more on points, and some with Dyna. It wouldn't have to twist to throw ignition timing off. That is set by the points and the theory fits in my mind because the wobble or flex occurs at 180 degrees difference of camshaft rotation. (360 of crankshaft rotation) if it wobbles or flexes, it changes the opening and closing time of the points, on earlier than the other. A Dyna wouldn't do it as much because it works with a magnetic field, and your C5 would be pretty immune to it with just one light and 36 teeth to count. Thinking about the belts causing it at low rpm, I'm not sure it would have an effect because it is far enough apart to the next ignition timing event. Valve timing could be off a little though.

More likely the belts flexing is caused by the ignition than the other way around.

 

[joedrum]

https://www.ngwclub.com/forum/viewtopic. ... 13#p610713
shesh it amazes me what goes on sheesh ....i brought all this up and got slaugthered by idiotic posts from many .....now it seems dyna has jumped on board while trying to cover for dyna problems ...this pretty much tells you .... and its really simple you cant expect to get a good idle from marginal parts combined with the most important adjustment on the motor...looked at as a non isseue like has been touted for yrs to the point of actually convincing people loose is good ....

sheesh in a design that is made for a light spring loads of valves and the belt is not required to stretch to pull load ...the belt can prestress to almost eliminate the belts from bring in any more machanical differences than are inherent to any design ...let me define prestessed ...after belt is timed find neutral spot where not pressure of springs on belt ....take slack out ...without adding extra torque....and the cam wobble is cured ......this will fix all weak flimsy cams .... :smilie_happy: :thanks:

 

[aussiegold]

weelll, heres my 2 bobs worth.
i think the cam movement or wobble is simply that. pressure from the valve train , combined with wear on the cam journals. may explain why it is worse on some bikes than others.
that tiny amount of wobble is enough to open or close one set of points, out of whack to the other. my 75 had it bad, now has a C5,
no problem........
my LTD does not seem to have this problem. it is spot on both sides and has 124,000 klms on it.
the belt " slap " seen some times can usually be put down to being improperly tensioned. we have already seen one example on this thread of belt " movement " . i dont think that poor timing would cause belt " slap "
have a look at the belts on this one. the question that interests me is, why do some GL's have this wobble and not others?

https://www.youtube.com/watch?v=pawfT-res_Y

[video]https://www.youtube.com/watch?v=pawfT-res_Y[/video]

 

[dan filipi]

aussiegold » Today, 3:45 am[/url]":1vqxu5a1]
weelll, heres my 2 bobs worth.
i think the cam movement or wobble is simply that. pressure from the valve train , combined with wear on the cam journals. may explain why it is worse on some bikes than others.
that tiny amount of wobble is enough to open or close one set of points, out of whack to the other. my 75 had it bad, now has a C5,
no problem........
my LTD does not seem to have this problem. it is spot on both sides and has 124,000 klms on it.
the belt " slap " seen some times can usually be put down to being improperly tensioned. we have already seen one example on this thread of belt " movement " . i dont think that poor timing would cause belt " slap "
have a look at the belts on this one. the question that interests me is, why do some GL's have this wobble and not others ? https://www.youtube.com/watch?v=pawfT-res_Y

Doesn't seem to be any belt flop at all on that one I can see.

 

[mcgovern61]

mcgovern61 » Thu Feb 12, 2015 4:50 pm[/url]":26vxdala]
Just for video reference, here is an old video of my now defunct '81 engine. It is a video of the crankshaft pully (which I though was wobbling!) as an explanation for why the engine knocked. At the time I had no idea that what I was looking at "wobbling" was a washer that is installed on the crank pulley. :hihihi: (The washer was obviously not centered.)

But, it so happens that it is a good video to see the tension differences in the timing belts.

[video]https://www.youtube.com/watch?v=0R5Gbo6jO7E&feature=youtu.be[/video]

I know on my bike (in that video), that belt flop was from multiple reasons; improperly tensioned belts, the carbs were in dire need of rebuilding, the engine itself was worn out with significantly worn out bearings, weak valve springs, piston skirts worn down, wrist pins loose and a bit of good old fashioned rod knock.

When I swapped out that '81 engine with my new to me low mileage '83 engine with rebuilt carbs properly set and new timing belts properly tensioned, my belts do not flop anymore!

 

[AApple]

C5Performance » Fri Feb 13, 2015 10:29 pm[/url]":3c3akymr]
What I do not believe without measuring myself is how that "wobble" converts to DEGREES of ROTATION.

I been following this discussion, and Paul finally hit on what I have been wondering the whole time. Sure, you can have cam journal, and cam bearing wear that will cause some MINOR left/right-up/down movement of the cam ends, but there's no way that would change to actual rotational value of the cam. Granted a true "wobble" will mess with a points type ignition, but it was mentioned(if I read it right) that the cam/bike in question was having 6-9 degrees of rotational variance...which in my mind would have more to do with belts than worn cam/bearing journals. "Wobble" indicates something not rotating in a perfect 360 degree circle...not something that is changing the rate of rotation at times. If you have a bent wheel, the wheel wobbles....but it still rotates in the same circle(on the same axis) as a straight wheel. If you have a worn wheel bearing, the wheel can move on both the left/right, and up/down plane, but the center of the wheel would no longer be in the center of the AXLE(cam, if you will)....THAT'S a rotational variance.

I have long said that timing belts can effect timing, whether too tight, too loose, stretched, whatever, BUT...I don't believe any of that will effect it enough to cause a noticeable difference in how the engine runs. You might be able to measure it with some fancy equipment, but in the end, for our purposes, I can't see it making one dadgone bit of difference.

 

[ekvh]

The points don't rotate. They open side-to-side. If the cam moves side-to-side then the opening and closing of the points could be different from one time to the next time.

 

[joedrum]

ok fine tuning is fine tuning and nothing is left out ..that includes belts ..they are the most fluctuating part...... and i think apples post is right things are close enough ... but you cant miss a step or you will have struggles .. to get right ....as radakks says everything effects everything ...on a stock oldwing this is simply fact...carbs that struggle in low in rpm really dont help any miscues in dialing in the timing .. and oldwing super balanced running design can actually cause problems as it so easy to reverse direction if there a backfire or stumble... all these things figure in ..

 

[aussiegold]

dan filipi » Wed Feb 18, 2015 12:46 am[/url]":2e8zxhz3]

aussiegold » Today, 3:45 am[/url]":2e8zxhz3]
weelll, heres my 2 bobs worth.
i think the cam movement or wobble is simply that. pressure from the valve train , combined with wear on the cam journals. may explain why it is worse on some bikes than others.
that tiny amount of wobble is enough to open or close one set of points, out of whack to the other. my 75 had it bad, now has a C5,
no problem........
my LTD does not seem to have this problem. it is spot on both sides and has 124,000 klms on it.
the belt " slap " seen some times can usually be put down to being improperly tensioned. we have already seen one example on this thread of belt " movement " . i dont think that poor timing would cause belt " slap "
have a look at the belts on this one. the question that interests me is, why do some GL's have this wobble and not others ? https://www.youtube.com/watch?v=pawfT-res_Y

Doesn't seem to be any belt flop at all on that one I can see.

yep, that was my point. :BigGrin: the belts on the first video in this thread look loose to me.

 

[julimike54]

Aussigold, thanks for the plug on my belt tension, lots of painstaking adjust readjust, they're running 1/32 over max adjust. As far as the slack in belts affecting wobble (presuming cam journals aren't shot) I can't see it, what would occur is a variation in rotation from belt going from "loose" to a "tighter" condition which would vary rotational speed. We had this problem on cpu controlled motors "hunting" for proper speed in a closed loop control system, hence my familiarity with belt tension along with a host of other occurrences that were unhappy customers & large warranty costs. As Gates (belts) states 60% of all timing belts are under tensioned, they proved it to us as they went to out manufacturing floor & tested out systems as built, we were at 62% too loose. I believe AAple is correct in his post this afternoon.