MTFCA Forum

My cover has about .010 oval wear. When I use the centering tool, it has a slop in one direction. Do most used covers have that much wear? Does it matter?
Tool is 3.001, New Day Timer is 2.995

John

John, any amount of slop between the timer and the cover will affect the ignition timing. The question is, how much is too much. I honestly have no idea. The cover on my runabout was all stopped out and replacing it with a better one made a noticeable difference. It certainly was worn more that .010" though. I guess the best thing to do would be to find a cover that your timer fits snugly in and use that.

Stephen

It matters much more (in terms of the difference in timing between cylinders) with an Anderson timer than a roller or brush because of the flapper 'ramp'.
But 0.010" offset of the timer from the camshaft only gives just over +/-1 degree of difference with a brush or roller. You will be doing well to get it that good!

Another good reason to switch to a New Day timer that really doesn't care if the timer is concentric with the camshaft as the brush runs off the timer face, not the circumference.

Sorry Bruce; I beg to differ. If the camshaft is offset towards 12 o'clock, then the brush will be fine at 12 and 6, but will arrive early and late at 9 and 3. Same for a roller.

Chris Barker wrote: ↑

Tue Mar 09, 2021 4:56 am

Sorry Bruce; I beg to differ. If the camshaft is offset towards 12 o'clock, then the brush will be fine at 12 and 6, but will arrive early and late at 9 and 3. Same for a roller.

Exactly!

If the camshaft has a loose or worn camshaft bearing it would possibly cause a misfire or timing issue. But the question to begin with is what to do with a worn timing gear cover not a worn camshaft bearing.
If you have a slightly worn timing gear cover using a flat brush timer would be fine and there won’t be any timing issue. The cover would have to be really be worn out to cause any issues to begin with.
This is another of those ‘over thought issues’. And it’s my very humble opinion.

I agree with Jerry and Chris on this, and I base my opinion on the geometry and alignment of the contacts. However, there have been so many hobbyists over the years claiming the New Day timers run better than original style timers with a centering error that the issue might warrant further study. It would involve building a fixture with a degree wheel and a test light and checking several different timers in the same off-center conditions. ...And also analyzing how that effects spark timing on magneto in relation to the fixed 22.5 degree points that a spark can occur.

If your magneto is operable, all angst over .010 diametral difference between parts is wasted emotion and the car will run perfectly.
If you run only on battery, there is some loss of efficiency, but you'll be hard pressed to detect it.

I agree with Scott. when running on magneto, the timing is most dependent on the peak current output of the magneto. However on battery, it begins to build up immediately after the brush or roller makes contact. Most important thing about timing is to have the coils adjusted evenly whether running on battery or magneto.
Norm

I also agree with Scott......but you do have to be careful with Andersons; they can get waaaay off.

However, the Anderson remains my timer of choice compared with rollers and a different brush timer.

Here is an illustration from the past that is helpful in visualizing the impact of the Timing cover centering about the CAM.
The ID of the roller timer contacts is 2.125" which equates to a circumference of 6.675" and 720 degrees of crank shaft rotation given the 2:1 gear ratio. That means the +/- 1/8" variation indicated in the diagram corresponds to +/- 13.5 degrees of ignition timing variation assuming all 4 coils are adjusted for precisely the same dwell time to fire spark. Note that improperly adjusted coils with varying dwell time to fire spark COULD actually function to compensate for timing error due to timing cover misalignment OR could function to be additive to that error making it even worse. This can explain why differing methods of coil adjustment yield differing results in engine performance. Engine performance should not change depending upon the location coils are installed in the coil box with properly adjusted coils (equal and consistent firing time). If coil position in the coil box Does matter, it may indicate timing cover misalignment And coils with differing dwell times to fire spark.


Note that this analysis does NOT apply to Electronic Timers. They are immune to timing cover misalignment because they use a single CAM position sensor used to determine ignition timing. Spark lever adjustment for optimal engine performance is common for all 4 cylinders.

John, Just another good reason to check out the new I and E timers!
There is a real reason that the guys making the new Anderson will resize your timer to fit your cover and why the Montana guys will work all night to make sure the timing adj is spot on.

Thanks Mike for posting a great explanation!

What Mike speaks of coil timing to fire is all true.

Yet, what is a deceiving in using an example of 1/8" off center and showing 13+ degrees off on firing is that it is for illustrative purpose only. I won't do the calculations and will assume that the author of that old article is correct in their calculations. It does make for an alarming misfire value and I think that's pretty much the point. However, when folks are questioning the size of the timer housing or the fit to the front of the engine, the misalignment is very very small relative to .125" offset of the timer housing to the roller in the drawing. That small misalignment will be a fraction of .125" and thus a fraction of 13 degree mis-timing. It most certainly will not be optimal, though. Very little on a T is optimal anyway and I am not arguing for sloppy work or to disregard it...just to understand the nature of the issue.

Running on battery will take all run-out of the roller to timer body, use it to the worst possible outcome, and cause lower performance but the car was not designed to run on a battery, it was designed to run on its internal magneto. If you are trying to optimize a defective car without attacking the Root Cause, that may be another story entirely.

And again, what absolutely is true, is that on Magneto, the coils are going to fire when they are going to fire and that is NOT at every single leading edge of a misaligned timer, it is when the current to the coil reaches the point to which it was set (or TTF for Mike's method). It would be an extremely unlucky or likely, unconscious individual that would select the very specific point on the Mag node leading edge to leave their timer precisely where the car runs it's worst since that point on the spark quadrant is razor thin within the totality of the range of quadrant that the car wants to run at for that particular RPM.

Chris and Jerry: We're not talking "offset" here but a worn timing cover allowing the timer body to move around in the sloppy hole. Add to this a worn front cam bushing and the roller in an original timer set up will bounce all over the place while the brush in a New Day timer pretty much maintains reasonable contact with the brass inserts. I really don't think it's even possible to install an original timer if the cam was "offset" so much as to create the situation you suggest.

The engine is a new rebuild , so the cam is not an issue. I am going to look at some parts tomarriw,I will see if I can find a better cover.
Thanks for all the great replies, very interesting .

John

Since your engine is a new build the cam isn’t an issue as you said. Find yourself a better front cover and you’ve solved the problem. They are fairly plentiful. Good luck.
A simple question that wound up being a simple fix.