Slop in original timing chain on 78k 430

Unit is definitely stuck. But bushing is still in great shape! So now where can I get a nice correct unit cheap and fast? vc24a?

 

I think just the vacuum advance for now

 

Summit has a few different adjustable options. That seems like it would be neat to try.

 

I ordered the vc24a

 

I have always read that vacuum advance was for fuel economy only but I hope it helps my issues. Idk

 

You vehicle will definitely run better with more initial timing. Vacuum advance provides that in a stock setup.

 

Someone correct me if in wrong. Or if I missed a previous post . Sorry.
Chain slack check.
1. Dist. Cap off.
2. Turn crank clockwise with big wratchet
Or breaker bar and line balancer mark up to 0* on timing tab.
3. Watching Dist. rotor turn crank counter clockwise till you see Dist. rotor just start to move.
If timing mark moves 6* or more the timing chain should be replaced.
Consideration should be considered for wear on distributor gear. Verify its ok.
Ide guess tolerance should be closer on performance applications.
Ie. Cam Degreeing

So 69 WILD is over 6*. .
8 to 9 Lot to me.

 

It's on my list of things to do but it would be nice if a working vacuum advance fixed my issue. I'll keep you posted. Thanks to everyone for their input!

 

Likely...but not absolutely. As has been discussed, the breaker-plate could be seized. Seems unlikely that the vacuum advance unit itself could be seized--I don't know how the rod could be prevented from moving.

Since he says it holds vacuum, a seized breaker-plate is worth investigating. And since there's no way to know--yet--just where the plate seized, the plate may be permanently holding some amount of "vacuum advance" that then gets adjusted-out by turning the distributor.

I'm also suspicious of having 25 degrees of advance "all in" at a mere 2500 rpm. That's not the way GM tuned those distributors. GM held-off the max-advance RPM way too long, over 4,000 RPM, then kinda compensated with too much vacuum advance. Someone may have modified the centrifugal advance. A heavy car with "highway" gearing would probably be better-off with a slower advance curve, and maybe a bit less centrifugal advance so the initial can be adjusted "up". Probably needs some--but maybe not OEM-quantity--vacuum advance. Depends on cam and compression and about a dozen other things.

You may not want a "correct" unit, because the "correct" unit may not be optimum for your application.

In general, engines seem to like additional initial advance, somewhat faster centrifugal advance, and less vacuum advance; which leaves the actual timing about the same but with improved driveability. Everything depends on the engine in question, and the compromises GM made when selecting the "correct" parts. THIS engine has too-fast centrifugal, and zero vacuum advance.

Makes a big improvement in fuel economy.

ALSO makes an improvement in part-throttle efficiency--improved power on less fuel, better throttle response, reduces potential stumbling. Less carbon build-up in the combustion chamber. Can lower engine coolant temperature, increase exhaust valve and seat life, and lower exhaust manifold temperature (reduced exhaust manifold cracking.) It's NUTS to disable the vacuum advance on an engine primarily run at part-throttle.





Putting this all together, I suspect an engine with too much timing-chain slop that retards the cam timing. This leads to low-rpm torque deficit. Also running with too-fast centrifugal advance curve. That would slightly but not totally offset not enough (zero) vacuum advance. The lack of vacuum advance potentially leading to excessive combustion-chamber and engine coolant temps along with carbon deposits. Yeah, I bet it "pings" and "stumbles".

 

Thanks for your suggestions. My breaker plate does move freely. I thought it might be binding but no. My va unit is garbage. I applied 25 in of vacuum and it didn't move but as soon as I helped the rod move it lost the vacuum immediately.
I plan to install stiffer springs to delay full centrifugal advance.

 

When you have the new VA hook it up to ported and manifold vacuum and feel the difference. My factory original 430ci runs better and smoother via manifold vacuum.

 

From your pic it looks like it’s been replaced.
Looks like an iron cam gear.

 

I would have bet it had not been replaced because my grandmother bought it in 69 and our family maintained it for her. But I was only 4 years old when she got it. My older brother did most of the oil changes. I could ask my brother and pops again if it's possible it was replaced. I'm not sure what the original nylon cam gear looks like. Would anyone have a picture or drawing? Thanks in advance

 

Here you go:

(A 1967 though)

https://www.ebay.com/itm/302524001431?epid=660781894&hash=item466fd5ec97:gJkAAOSwARZXn5rp&amdata=enc:AQAIAAAA4OOjj7xl6cIdtLRp4zPOgVG/3HHHTPb6uOeuDkHZUrmv6vYE3JmmOW2cbRJgkBCQF33EsdWAGzpfaWWEdBsYnqYYQ7kR2TS39lD/BYwMqdchurs4K3FMyOh9TaNfCE8okpyuakw4DttP0Bt2HkIFiADBGdlRNz85vNT03ad45tIdLZKtHbXMRxwdg4EX292uFOkCsAd1g/arAp4SPNpXYC5TRFVjUEDaBiaoTkf2F8kzaNnonxml3dMqbduIAmaH7ApwLVtFX8/H1RJI4cFGOgdRWRCrGXZyMmReaFbKSPwY|tkp:BFBMlMS70rxi

 

Lol that’s the same pic I was going to post

 

Sorry Mark!

 

It’s cool, I’m slow
As long as the pic helps a member!