TDC / Rotor Mis-alignment

[Lorne G.]

My 300hp 67 vette is reading 30 degrees initial timing and will not run at anything lower. I assumed the balancer spun so I replaced it with a correct replacement. I then used my TDC tool to confirm TDC at No.1 piston.

At top TDC my rotor is pointing half way between No.1. And No. 8 on the distributor cap. I know it should be pointed directly at No. 1 so what is causing this?

I recently purchased the car which has pertronix 111 installed. I am not sure if previous owner had distributor out or did any modifications to it.

any suggestions would be appreciated.


Lorne

[Patrick H.]

Re: TDC / Rotor Misalignmenti

At top TDC my rotor is pointing half way between No.1. And No. 8 on the distributor cap. .

Lorne

Can't you just loosen the retaining bolt/clamp and rotate the body of the distributor so that the rotor points approximately where it should?

Don't forget that initial timing is done with the vacuum disconnected and plugged on the engine side.

I usually set the balancer at 8 degrees BTDC, rotate the distributor to aim the rotor at the #1 plug wire location, and start the car. It's usually very close.

Patrick

[Michael W.]

Re: TDC / Rotor Misalignmenti

At top TDC my rotor is pointing half way between No.1. And No. 8 on the distributor cap. I know it should be pointed directly at No. 1

Actually it doesn't point directly at the tower, nor does the position tower affect timing.

[Lorne G.]

Re: TDC / Rotor Misalignmenti

The timing was done with vac line disconnected and plugged. The car starts great, accelerates great but has a low speed surge. The 30 degrees initial timing is puzzling so that is why I initially thought the harmonic balancer had spun.

Lorne

[Patrick H.]

Re: TDC / Rotor Misalignmenti

How are you measuring 30 degrees initial?

The other possibility is that the springs are so weak that your centrifugal advance is "in" while at idle.

[Edward J.]

Re: TDC / Rotor Misalignmenti

Lorne, check to male sure the mechanical or vacuum advance is not stuck. the mechanical advance is a common issue. another issue sometimes is if the camshaft has been replaced with a aftermarket type, sometimes there not pinned as the factory. and will require rotating the Distributor gear 180 degrees. to correct this. I ha a similar issue when I rebuilt my engine and could not position the Dist.to get the timing set correctly because of limited movement.

[Lorne G.]

Re: TDC / Rotor Misalignmenti

I measured the initial timing with vac line disconnected at 750 rpm idle ( seems to like this rpm so perhaps a mild replacement cam ) and got a 30 degree reading. When I tried to retard the timing the car would barely run.

With the rotor pointing between N0.8 and N0.1 towers, it appears to be out one tooth but when I moved the distributor over one tooth the vac canister hit the intake manifold.

The current orientation appears to be factory correct but the rotor location is puzzling as is the amount of initial timing even though the car seems to run, idle, and accelerate well. Just some low rpm and low speed surging which I assume is due to timing issue.


I will put a rubber band around the weights to see if the springs are weak and try timing the car again around 600 rpm to see if this changes anything.

I am out of ideas to try and seriously thinking about replacing the distributor.

[Patrick H.]

Re: TDC / Rotor Misalignmenti

I measured the initial timing with vac line disconnected at 750 rpm idle ( seems to like this rpm so perhaps a mild replacement cam ) and got a 30 degree reading. When I tried to retard the timing the car would barely run.


I am out of ideas to try and seriously thinking about replacing the distributor.

Perhaps I was not clear. Did you get your timing reading from the balancer? A dial back timing light? What was your procedure you followed to determine your number is 30?

I'd send it to Bill Clupper and have it rebuilt and tuned. It's less expensive and you get a better result than buying a new one of unknown origin.

[Lorne G.]

Re: TDC / Rotor Misalignmenti

I used a Dial Back Timing light initially and thought is wasn't working correctly when I got the 30 degree initial timing reading. I had my mechanic look at it and he also got the same reading with his two timing lights and it was his suggestion that the harmonic balancer had spun.

I know the cam was changed at one point so perhaps I need to rotate the gear 180 degrees which I will try as a last resort. Failing that I will replace or rebuild my distributor.

[Michael W.]

Re: TDC / Rotor Misalignmenti

With the rotor pointing between N0.8 and N0.1 towers, it appears to be out one tooth but when I moved the distributor over one tooth the vac canister hit the intake manifold.

The 'one tooth off' thing is a red herring in all cases as is the 180* off, unless the distributor cannot be rotated sufficiently to set timing without the housing hitting something. This is not your problem.

I'd stop worrying about the rotor to cap tower position as this varies tremendously (almost 50 degrees) while the engine is running with the effects of mechanical and vacuum advance.

Let us know what happens with the mechanical weights restrained.

[Edward J.]

Re: TDC / Rotor Misalignmenti

I used a Dial Back Timing light initially and thought is wasn't working correctly when I got the 30 degree initial timing reading. I had my mechanic look at it and he also got the same reading with his two timing lights and it was his suggestion that the harmonic balancer had spun.

I know the cam was changed at one point so perhaps I need to rotate the gear 180 degrees which I will try as a last resort. Failing that I will replace or rebuild my distributor.

If you have not done a visual the mechanical or vacuum advance check those first. with the dist. rotor removed you should be able to rotate the shaft and the springs and fly weights should return back to normal. another item is the vacuum advance can sometime fail in the fully open position and the breaker plate will not return to normal position