Timing chain and gear set

The first one 66 WT 389  I was going about 70 miles per hour when nylon cover gave way, bent push rods and valves. Next one was my brothers 66-389- tri power,it jumped time as was starting it. Was running great when it was shut off but went to start and could tell when cranking it timing had jumped. Same on 67 Firebird 400.
 Other two were found on teardowns for other reasons. This was back in1966,67,73&84.  

What nylon cover?  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

many years of gm and other cars have nylon toothed cam gears ...  they are cast nylon over an aluminum center... they were said to be silent...  i think they were silent killers...   somewhere between 110K and 145,000 miles the nylon part breaks off and falls into the pan...  the cam timing then jumps...  the valves are introduced to the pistons the hard way...


replacement 3 piece timing chain sets for pontiac motors start at about 20 bucks...   with a cast iron cam gear..


the standard replacement 3 piece timing set will work great for many thousands of miles...

be sure that when you pull it apart... that you inspect the water pump backing plates.. and that you install new seals in the timing cover where the water pump plates line up...  


i cannot imagine how may nylon timing gears are left in running motors..  i do know that some engine builders installed them on reman engines ...

it is also important... that you inspect or replace the oil pump screen..  i have dug a lot of nylon timing gear parts out of the oil pump screen..  

Try to get a hold of a digital read out timing light. Yes, 16 degrees is pretty normal to get the full potential from a 400. Mine is advanced to 18. Once you get it set to where it kicks ass, you can play around with the timing without even disconnecting  the vacuum line. Just make note of the digital reading since it will be way past where the timing tag ends. At that point, even slight adjustments either way will make a difference. If the car suddenly won't start easily, take it back a little. The original manuals were always conservative with their timing suggestions so it would start easy and not drink so much gas.
Experimenting with the springs in the distributor will also change the equation. I get the best performance with the medium size springs.  

Ya the medium tension springs usually work best.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Awesome!  I can't wait to go play with it.  I have a digital timing light.  So, I guess I just disconnect the vac secondaries, and set the timing light to say... 18* for starters, and then turn the dist to line up the tic mark with 0*??  Is that how it's done?

Once I get the timing set, I want to talk about my out of the box Holley 750.  Accelerator pump, power valve, adjustments, etc...  That should clear up the unsteady idle and yield some performance too!  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

I Have seen pontiac engines with the nylon cam gear...  

I set the timing at 18* today.  It was at 29* - much better now!  Then, I turned the carb mixture screws about another full turn out.  They're out about 3 1/4 turns now, and it runs much better with the additional fuel.  It idles very smooth, and the throttle response is much, much better with much less delay!  I am thinking that the floats are out of adjustment too which is causing the modicum of delay that still exists in throttle response.  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

69GTOby,

Glad to hear the 18 degrees helped! I've got my Q-jet mixture screws about 3 1/4 turns out too, and it seems to be the best combination so far. I've been wondering about my float level as well - not because of any delay, but just because fuel keeps seeping through the top gasket and I can't stop it. I don't want to torque the bolts and screws down too tight and crush the gasket, and I've thought about putting a double gasket between the bowel and airhorn. It's running so good that I've opted to let it leak. It's a 1972 Q-jet and the float level should be at 17/32" according to my Haynes manual. I'm wondering if lowering it slightly would stop the leak but I don't want to "fix what ain't broke!" (I usually end up doing it anyway). As a side note, a 12 oz bottle of "Marvel Mystery Oil" in the gas tank every once in a while seems to really keep my carb clean and running smooth.

Brazil  

I think I just answered my own question. I rechecked my raggedy old Haynes manual again and the float level should actually be 1/4". I was going by the 1978 specs instead of the 1972 specs. Hopefully this will stop my fuel leak.

Brazil  

If not, maybe you could try a little RTV silicon gasket sealer stuff on both sides of the gasket sealing surfaces.  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.