C2 Distributor - Can't rotate....

[Jim V.]

I know, I know..check the archives...(been there got it) but.... what if the drive gear IS indexed correctly (dimple and rotor) and you are still banging up against the intake or the coil trying set initial timing? Reindexing the distributor gear and cam gear gets me banging the coil on one tooth and the intake on the next. It appears the only solution (Bubba or not)is to move distributor wires. Other strategies?

I also noticed the points seem to open and close before the rotor points to the wire tower. I thought the points should just be opening when the rotor is indexed to a wire tower There's no other way to mess-up distributor assembly besides indexing the drive gear since the cam can only be installed one way on the main shaft. Is this normal?

Motor runs but seems to lack power.

Thanks
JimV

[bob downs]

Re: C2 Distributor - Can't rotate....

try it the other way.

[G B.]

There is more to check

Your timing light is showing you where the #1 piston is located when that plug is firing, not where the rotor is located in relation to the #1 terminal on the cap.

There are several components between the piston and the distributor rotor. Any of them could be causing your distributor to have a phasing problem. For example, slack in your timing chain could require you to rotate the distributor excessively to get the spark timing back to spec. Think what that does to the position of the rotor with repect to the #1 terminal in the cap.

Here's where I'm going with this. The physical relationship / condition / quality / compatibility of the crankshaft, harmonic balancer, timing set, cam, and distributor shaft all play a role in positioning the vacuum canister midway between the coil and intake manifold when you have the timing light indicating the specified initial advance.

[Donald O.]

Re: There is more to check

Jerry,
If the timing chain has too much slack in it, it either grew or ( more likely) the plastic teeth on the original gear sets are too worn. When it happened to me, the timing could vary by 20* to either direction.
Don

[Donald O.]

Re: There is more to check

Jerry,
If the timing chain has too much slack in it, it either grew or ( more likely) the plastic teeth on the original gear sets are too worn. When it happened to me, the timing could vary by up to 20* to either direction.
Don

[G B.]

I would do this next

I would use a TDC tool (piston stop) to confirm that the timing mark on the balancer matches the O position on the timing tab.

Chevrolet used several positions for the balancer timing mark over the years. For example, there was a subtle 10 degree move in 1969. With each move of the balancer mark, the timing chain cover tab scale had to be moved too. It is fairly common to find a pre-'69 timing chain cover mismatched with a post-'69 balancer on a mid-year Corvette.

[Chas Kingston]

Re: I would do this next

Also, the rim of the balancer can become displaced WRT the center hub and keyway. A slight shift here can cause performance and timing problems. Been there, done that, on the very first Corvette that I owned, back in '68.

Geezer

[Jim V.]

Yeh.. but

Thanks guys..
I have verified TDC on the balance using a piston stop. Timing chain is new.
Let me rephrase my questions..
1) can somebody verify that points should just be opening when the rotor is pointing to a distributor terminal?
2) After reading all the stuff on indexing the drive gear to the rotor I am hesitant to do it otherwise. In order to center the vac can mayber the best shot is just move the plug wires over from the standard.

Thanks again
JimV

[Mike McKown]

Re: Yeh.. but

1. Yes

2. No

[Mike McKown]

Re: Yeh.. but

1. Yes

2. No

[G B.]

Well, I'm stumped.

Turning the mainshaft gear 180 degrees will in effect relocate the canister by half a distributor gear tooth. Jumping terminals on the cap will move the canister a whole tooth. In other words, your canister will still hit if you move the wires.

I'd be suspicious that something else is off within the engine if it still has no power after you set the timing. Did you use an aftermarket sprocket chain kit with three different keyway positions for the crank snout? Are you running an aftermarket cam? Has your distributor advance spring plate ever been off the mainshaft? Is it a reproduction mainshaft? It's embarrassing to admit how I know all these things can cause problems, but they can. Maybe I read about them somewhere. Yeaaaah... that's it.

[Richard S.]

Re: Well, I'm stumped.

Jerry, thanks for two very informative posts. For those having post 69 blocks (BB 512) and all other original 67 internals can you provide any more guidance with respect to possible variations. Your expertise is very much appreciated.

[Jim V.]

Re: Well, I'm stumped.

Hi Jerry,
Lots-o-variables .
1.) chain kit original
2.) aftermarket Competition Cam 12-212-2
3.) advance spring plate can only go on the mainshaft one way
4.) mainshaft appears stock...how can you id?

Thanks for you help!
JimV

[G B.]

My money's on the cam

The cam grinder doesn't have to be off by much indexing the distributor drive gear teeth on the cam to the front chain sprocket bolt holes to cause the distributor orientation to be slightly different from the factory position at TDC.

My reference to the distributor "advance spring plate" means the small oval shaped metal piece brazed to the top of the mainshaft. I'm not talking about the separate point cam / rotor stand part. I apologize for not using the proper GM terms for these two parts. I am too full of grits this morning to go look them up in the P&A Catalog and educate myself.

The reproduction mainshafts have longer tach drive gear teeth and odd shaped "advance spring plates" that are welded (not brazed) on the shafts. If you compare them to a similar GM part you will appreciate these visual differences. The budget mainshaft reproductions sometimes don't have the top plate indexed properly to the pin hole for the bottom drive gear.

I've also found that the reproduction mainshafts tolerate very little lash with the tach drive cross shaft teeth. You either set up the tach drive gear mesh dead-nuts, or you have binding teeth. The GM teeth will stay intact with up to 1/16" end play for the cross-shaft. The reproductions will usually bind with this much lash. But, once again, I digress...

It must be time for my nap.

[G B.]

To feel the power of that cam...

I suggest you keep the engine above 5,000 rpm at all times.

That grind used to be called Comp Cam's "280H Magnum". With specs only slightly milder than GM's #754 2nd design off-road mechanical cam, I would call it an...ahem...unusual choice for a street-driven car.

No offense meant. Perhaps you vintage race your car with a 4.56 rear.