Static Timing Type1 Issue

[hambone]

This is odd, and not sure if I should even post this, but it has become irritating.

Timing my bus statically. Dwell checks perfect, set the timing with a lil' bulb. Perfect.
Drive the bus to get groceries etc. but it's just not quite right. Check timing again, it's off 5 deg. or so. Reset and it stays that way for a while.
This has happened to me the past 2-3 times. What the heck? The endless quest for perfection.

[sped372]

Dwell staying exactly the same or is that also changing? Is your timing advance returning (back to "zero") all the way? I had an ever-so-slightly sticky advance that wouldn't always return to the exact same spot (within a couple degrees).

[hambone]

Dwell stays the same.
Advance, I'll bet that's it. Just slightly askew when I set the timing.
I should probably run the engine for a minute before I set it, I usually do it cold.
Thanks!

[SlowLane]

Vacuum-only advance or centrifugal + vacuum?

I don't think it's possible to reliably static-time a motor with centrifugal advance. The weights, springs and rotor sleeve need to have that slight bit of pre-load that exists when running at idle. Without it, your rotor sleeve could be at any number of positions relative to the distributor shaft. If you manually turn the rotor CCW to the negative stop while static timing, it's unlikley that the weights and springs will be able to return it to that position.

[Amskeptic]

I don't think it's possible to reliably static-time a motor with centrifugal advance.

You can.
A) Statically time engine to "0" (1969 1600 singleport, right?)
B) Start engine and warm up until choke is off. Make sure idle is below 950rpm.
Check timing with light. Same? Of course.
No? wtf.
Colin

[hambone]

Happened again after a rumbly 100 miles down hell roads. It has been speculated that the distributor clamp isn't doing it's job. New German too, what a crock. Betcha that's it though.
Local goons also ensure that aftermarket billet clamps are much better and don't slip.

[Amskeptic]

Happened again after a rumbly 100 miles down hell roads. It has been speculated that the distributor clamp isn't doing it's job. New German too, what a crock. Betcha that's it though.
Local goons also ensure that aftermarket billet clamps are much better and don't slip.

How about miles and miles of end play? End play can move that distributor drive gear a serious bunch of degrees. Statically time the engine with the crankshaft pulley pushed forward. Get an accurate base reading. Now have someone push the clutch pedal down, and recheck the timing. Change?

Holding a distributor in a clamp is not a difficult thing for even a junky clamp. Do a scratch line between the clamp and the distributor. Make sure the clamp is secure to the case!
Colin

[sped372]

Holding a distributor in a clamp is not a difficult thing for even a junky clamp. Do a scratch line between the clamp and the distributor. Make sure the clamp is secure to the case!
Colin

I agree. There's really no torque (reason) for the distributor body to rotate on it's own unless things are pretty gummed up inside. I'd be surprised if a distributor rotated even with a loose clamp. A halfway decent clamp has a serious overkill grip on a part with no real motivation to turn anyway.