Slop in original timing chain on 78k 430

I'm afraid I already know the answer but asking here.

My 69 wildcat has been pinging and stumbling at WOT off the line for about 25k miles now. Carburetor rebuild and adjustments don't help. Power timing procedures don't help. Doesn't use any oil and no other engine troubles. Meticulously maintained.

I checked the slop in the chain by turning the crank back and forth observing slightest rotor movement. Seems like about 8-9* of crank movement before rotor begins to flinch. I should probably compare to my fresh 350 chain slop.

Would this slop in the original nylon gears and chain after 78k be causing these engine performance troubles?

 

I would check the distributor the advance stop bushing as there made of rubber and deteriorate. If it is missing will let the mechanical timing go way over 28-30 total, causing severe pinging eventually destroying the pistons. I personally seen it happen to many 400-455 engines through the years. A $1.00.part ruining the engine.

 

Yes I did that on the 350 but can't remember if I did on the 430.

 

Timing seemed pretty steady. Using vacuum advance. I'll check timing again and note the numbers.

 

Checked timing just now. 3* initial and 28* total at 2500. vacuum advance is inoperable. It holds vacuum pretty well but doesn't move when i add vacuum with my mityvac. I will leave it disconnected for now. Timing advances smoothly with throttle. If I advance distributor more it pings a lot on all premiums I've used. It would just be nice if it didn't stumble off the line.

 

Thats not enough timing. Set it at 8 initial and test drive it.

What octane are you running?

 

30-34°?? My 430 distributor had 20...

 

My vacuum advance is inoperable. Doesn't budge with mityvac. Must be stuck. 18 inches of vacuum at idle off large port of carb in front.

 

I think of fuel first in this scenario. If you haven't tried it, run some racing gas in there and see if it still pings.

I see you have identified an issue with your vacuum advance.

Fix that first. Perhaps the diaphragm is leaking. Or as you said the mechanical bit could be stuck.

 

Just checked. 1111260.. transplant from a later year?

 

Diaphragm is not leaking but is now disconnected because it doesn't advance at all. I confirmed total advance is 28 or 29 tops with 3* initial. All in at 2500. Maybe that's to early and should have stiffer springs. So I guess I will do some work on the distributor this winter.

 

1111335 on my wildcat

 

Mityvac holds steady with vacuum applied. That seems to be not leaking or possibly plugged!
Distributor is out now. I peaked at the timing gear and chain. I'm guessing it's original?

 

You should see the plate move when vacuum is applied. Either the plate is stuck or the unit itself is stuck.