DJH

I’m the original owner/purchaser of a 66 roadster (watched it being unloaded from the car carrier) and twenty five plus years ago I put the original matching numbers engine in secure storage and built essentially an LS6+ as a driver engine using the original TI distributor.

Recently I’ve incurred some problems with carburetion. (Idle and off idle issues) but I’ve learned to insure the ignition is solid before messing with the carburetors ( 3 x 2 ). During my ignition checks I find the timing mark very unsteady. I set timing in the usual manner (vac advance disconnected and hose plugged.). The timing mark will remain consistent for a few flashes then suddenly jump towards retarded by 4-5 degrees a moment than go back again. It’s randomly unsteady. I use a near new Innova Equus 5568 digital dial back light and believe it to be accurate as it’s steady on my Model A, tractor and other engines. I removed the centrifugal weights and installed strong springs to insure the rotating pole piece was staying locked in position relative to the distributor shaft-no joy. The only way I know to measure the cam gear to distributor gear clearance is by the amount of free play at the rotor and this is less than 1 millimeter measured at the discharge tab. This leaves me wondering if I have cam walk or a really sloppy timing chain or something I’m entirely missing such as cross firing inside the dist cap.

This engine I built as a driver is using the original T.I. distributor but with a new reluctor and a new epoxy encapsulated circuit board in the amplifier module-the spark is strong. I’ve rebuilt what’s mechanically needed on the distributor according to Lars’ pictures and suggestions. The housing was machined in a bridge port mill and a mild steel button installed for the cross gear to push against. The shaft and the sleeve bearings checked for wear, which was virtually none at all, and a new drive gear was installed as a matter of course. I think the distributor is good to go. On the other hand I’m left with this timing variation. This engine has around 18-20K miles on it, the cam is a Comp. 292 with roller rockers and the timing chain is a Cloise True Roller with a cam walk button. Idle has always been very rough due to serious valve overlap. FWIW, I had this spark timing issue before restoring the distributor but I had to start somewhere. I would have thought that since the timing chain, cam gear and distributor gear are driving the high output Melling oil pump any slop in components would be taken up by the force necessary to drive the pump.

Tell me what I’m missing before I have to mess with pulling the pan, pump and timing cover to have a look at the chain.


Minor second question: The two raised metal tabs or buttons on the distributors rotating pole piece, on which the centrifugal advance weights rest, have worn down considerably. What’s a good way to build these back up to original height?

Cheers to all and comments please.

62Jeff

Do you have any plug wires crossing the #1 wire?

You can check the play in the timing gear by moving the crank pulley back and forth while watching the distributor rotor to see how delayed it is in responding.

midyearvette

i would start with the breaker plate in the dist.
see if it is loose or too loose as you suck or put a vacuum gauge on the vac can port, if you are losing 4 deg at idle or when setting the timing, a loose plate will back off slightly and give an erroneous reading or missing or loose screws will let the plate retard somewhat
read 62jeff's post on the easy way to check for a sloppy chain

DJH

62Jeff and Midyearvette those are both good suggestions for me to recheck. While there is no breaker plate there is a reluctor coil that rotates via the vac can and I will check that again. Thanks guys, I'll do some more sleuthing and get back to you later.

Chuck Gongloff

FWIW.....Totally different car, but similar symptoms.

Had the same trouble with my old 54.

Long story short...the distributor shaft was bent ever so slightly. Also, the upper distributor bushing was worn.

That allowed the dwell/gap to change as the rotor turned, thus the timing jumped all over the place.

A distributor rebuild and a new shaft cured my problem.

Remember the old adage: "Dwell changes timing, but timing won't change dwell".

Chuck

Donald #31176

Also on the line of Chucks suggestion is the end gear play. Excessive play will cause an up & down motion on the shaft that affects dwell. Check the end play to a tolerance of .005"- .010 ".

DansYellow66

If you elevate the idle until the engine smooths out somewhat (1200 rpm or so) does that make any difference?

larrywalk

Like midyear vette says, check the magnetic stator (reluctor) for
freeplay - if there's any way the reluctor can drift around, the
timing will vary.

Checking for distributor driven gear to cam drive gear slop by
checking the slop at the rotor tab is valid as long as you aren't
into the centrifugal advance.

When you say you removed the fly weights and used strong springs, did you replace the weights before checking the timing - the preload of the springs must hold the centrifugal advance against the flyweight
cam to hold them steady. If the weights are not there, the position
can vary, subject to the frictional hysteresis of the rotating pole
piece on the dist shaft.

Here's some pictures of a TI distributor I rebuilt awhile back...




If your rotating pole piece tabs/buttons are worn down that support
the fly weights (my rebuild had nylon buttons), I'd just TIG a couple of new support spots and file them flat to the proper height.

Although it sounds like your cam timing chain is good, it may be worn and loose causing the problem.

Hope this helps

DJH

Thanks again guys for even more suggestions. Yes there is a bit of slack in the cam drive because I can move the crank about 1 inch measured at the end of a 16" breaker bar before the rotor starts to move. Haven't done the math but thats probably 3-4 degrees right there. The distributor has been completely rebuilt and the end play is a tight .005". The reluctor is tight to the vac cannister with no discernable motion there. No other plug wires cross #1 plug wire.

Lastly, I respectfully disagree that the weights have to be in place for the springs to pull the rotating pole piece back to the 0 degree advance position. In fact those springs have to pull the rotating pole piece PLUS the weights back to 0 position. Taking the weights off and using heavy springs was a quick and dirty way to lock those two components together for testing. (I could have left the springs out and simply locked the two components together with a piece of tight wire and gotten the same effect.)

I'm open to anyone telling me I'm wrong on removing the weights for testing. I know without them installed there is no chance that the weights are causing any fluctuations in base timing. I'm thinking the "premium" Cloyse TrueA roller chain I put on this engine is the primary culprit with possibly a bit of cam walk to boot.

rongold

I have a Snap-On dial back timing light, and I find if I leave the dial back on "0", the timing jumps quite a bit. If I set the dialback up 1 or 2 degrees, it steadies it right out. I then read the manual that came with the light and it says to do that if the timing mark jumps around. Try it with yours before you start to rip things apart. Just remember that your timing is going to be low by the amount you dialed back.

DJH

Hey Larrywalk,

You're a prince for the pictures. Would you hazard a guess those are NYLON buttons supporting the weights? That would be a simple fix compared to tig welding and polishing and they likely never need lubrication. My originals, worn as they now are, were stamped in from the bottom and I even used to put a bit of lube on them at each tune up and they still didn't last.

Cheers.

DJH

rongold,

Interesting the mfgr. would know the light could give fluctuating readings in the zero position and not resolve the issue. If that is the case with my light it's going back. HS, could it be that easy? As I mentioned in my original post I'm using an Equus 5568 digital but I'm going to give it a shot in any case. For all anyone knows they're made in the same factory.

Thanks

DJH

DansYellow66

Yes it does settle down a bit with higher RPM but not until I get up over 2500 or so. I'm guessing the oil pumps load at that speed is keeping the chain and cam from dancing around.

David

larrywalk

Yes, they are nylon buttons which snap into the existing holes.