Cam ignition timing 'deflection' (wobble)?

[dan filipi]

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?

 

[flash2002]

It seems to me that, if your cam is moving to that point from wear, you have a lubricating problem or not changing the oil at the right time causing wear. One more thing, if the belts are too tight it might cause the cam to wear faster, maybe. my two cents, Canadian. LOL

 

[Steve83]

Each tooth on the cam sprocket is 9 degrees (360 divided by 40), so a 9 degree variation of cam-driven ignition timing is the same as being 1 tooth off in cam timing. If your heads/cams/cam supports are so worn that this much play is present, more than likely the rest of the engine is not very healthy either.

Also, the 1000 uses a centrifugal advance ignition, so any weak springs, or play in the advancer plate or shaft, will cause variations in the ignition timing, even with rock-steady cams.

Just my humble opinions... :BigGrin:

 

[mcgovern61]

I always preface my posts with "I'm no expert", but if the cam shaft was moving around enough to cause timing issues on a 1000, I would suspect there is a more serious problem going on there! I've seen how the cam shafts on my 1100 are installed and if they could move in any other direction other than rotating about their axis, other damage would be taking place. Also, for sure the cam seals at both ends of the cam shaft would be leaking if there was any axial movement outside of shaft rotation.

 

[joedrum]

to me you guys have nailed it ..ill just say the cams are well supported and very short ... ideal conditions not to have this problem ...

 

[ekvh]

[video]https://youtu.be/357YpRfUKiE[/video]
Watching an idling Gl's belts you will see the belts fluctuate a little. Might be from a bad sync, but the ones I have watched you can see the belt go from some slack to none. I'm thinking the timing has to be a little off?? Since the cams pulleys control the timing and the timing should be tight. I could be wrong, wouldn't be the first time. Don't know if this video will come through or not, but watch the belts vary in slackness. This is my hybrid with 1000 heads and it is the first start. Good for a laugh of me jumping when it sprang to life. From looks, I would guess that the belt is fluxuating a bit at idle. Is it enough to cause the lumpiness of an early gl?? Once under load, the belt stays tight, but at idle, it looks to me like it would be enough to cause a more difficult idle. Flopping back-and-forth only a few degrees. It might be a bad idle that causes the belts to wobble too. This is why I was hoping C5 would come with a crank mounted version, but I now see Paul's point for ease of installation.

The wobble term originated years ago describing the slight flexion of the cam under the pressure the valve train. With proper equipment, it is/ was measurable. This was the explanation of why some bikes varied from the F1 or F2 marks.

Like Dan, I'm just looking to learn.

 

[dan filipi]

Great video eric :smilie_happy:

I've jumped too is why I'm laughing.

 

[Ansimp]

joedrum » Fri Feb 13, 2015 7:26 am[/url]":mon0bcjp]
to me you guys have nailed it ..ill just say the cams are well supported and very short ... ideal conditions not to have this problem ...

Subaru ran the ea82 engines with distributors run off the rear LH cam without any problems, they also used the same ignition drive on the EFI version. This series engine is also a two timing belt system like the GWs.

 

[ekvh]

Perhaps I didn't have my belts timed right for that video, but you can sure see the one side jumping, and that is the side that should stay tight. Subarus are known for their lumpy idle's too.

 

[mcgovern61]

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]

 

[joedrum]

welll that proves it to me all the flop is on the tension side of the belts ...slower the rpm the worse it is

that has to paly hovac on mechanical advancer...especially and idle

 

[dan filipi]

I can see some minor flap of the belt as I've seen on mine but nowhere near any degree that would be of any concern in ignition timing more than a degree or 2 at most, and even at that they tighten with rpm under load.

So how about more input about the topic of this thread, cam wobble on the rear end of the cam.

 

[ekvh]

How about combining it with Steve83's info. It looks to me like it jumps almost as much as a tooth, which is 9 degrees. Again, I am not sure my belts were tightened properly in that video. I lack the tools to check the cam wobble on the other end.

 

[dan filipi]

Well keep in mind the topic of this thread, 'cam wobble' which 'wobble' implies moving off it's center axis, not rotational.

 

[joedrum]

there is no cam wobble it is advancer gone wild from belt shutter ...that was so obviously put this all to rest in gerrys video ... eric theres no way the belts are off a tooth just seems so but it enought to cause unsmooth centifical force ... witch the advancer cant deal with witch throws timing the 6-9 degrees off ... on my bike with the c5 theres no advancer to go wacky and the timing is stable ..the belts if put on right and tension right can lessen the flop hugly as hooch is done and there is simply no ignition issues and it is in a great spot for user friendly .... the oldwing motor when tweaked to replace it faults is a mighty motor ....personally i am not in these waters at all on my bike ... with the timing that wont set right be it points or dyna and the advancers they use

 

[dan filipi]

I just looked up the word 'wobble' to see what could apply here:

1. To move or rotate with an uneven or rocking motion or unsteadily from side to side.
n.
1. The act or an instance of wobbling; unsteady motion.

So unsteady motion could apply to the belts' shutter action being discussed?
Could it be THIS 'wobble' being referenced in the past and not an off center wobble?

 

[joedrum]

:builder:

 

[Ansimp]

ekvh » Fri Feb 13, 2015 7:43 am[/url]":860fnzye]
Perhaps I didn't have my belts timed right for that video, but you can sure see the one side jumping, and that is the side that should stay tight. Subarus are known for their lumpy idle's too.

The lumpy idle is more about their firing order and design :yes:

 

[ekvh]

VW, Porshe, not to disagree, but some had different firing orders, but all have the putt-putt sound. At idle. I always figured it must be the flat or horizontally opposed nature of these beasts. Not being argumentative, just would like to know.

 

[dan filipi]

dan filipi » Today, 3:08 pm[/url]":34una1ng]
I just looked up the word 'wobble' to see what could apply here:

1. To move or rotate with an uneven or rocking motion or unsteadily from side to side.
n.
1. The act or an instance of wobbling; unsteady motion.

So unsteady motion could apply to the belts' shutter action being discussed?
Could it be THIS 'wobble' being referenced in the past and not an off center wobble?

Wait, what was told to me was "On high mileage 1000's" this 6-9 degree variation (wobble) is found.
This would imply the finding (or theory) is not belt related.