NassauL79

Trying to start newly rebuilt L79 in our 66 after priming the engine.

1st attempt it didn't even try to start and backfired thru the carb.

I thought the distributor might be off 180 degrees. so I ;
-pulled #1 plug, bumped it over til felt air coming out, moved the balancer to 10 degrees advanced and looked at the rotor, its pointed very nearly right at the #1 plug tower (pointed just a touch midline of it). So that seems right, if dist was off 180 the rotor would be pointing at #6 tower, right ?

-Also took the driver valve cover off to make sure I was on compression stroke. The rocker arms at #1 were even with each other.

-double checked the plug wiring, its all correct.

So I'm wondering if the dist could be off 1 tooth ? Even if it is that wouldn't cause the backfiring would it ? As mentioned it didn't even try to start, didn't sound good with the turn of the key.

Should I remove the dist and walk it around to see if that helps or do you guys have another idea ?

Thanks-

SS409

Just a thought here, but your cam doesn't have a 4/7 swap does it? I would pull the distributor and do a 180.

66jack

Do you have the 'correct' HB on?

I tried using a 350ci HB on my L79, wont work it is 'clocked' differently making the tdc off...

the L79 HB is different...the keyways are different allowing the timing marks on the HB to be off...

65tripleblack

IF THIS IS A CAM BREAK-IN START FOR A FLAT TAPPET CAM THEN DO NOT MESS AROUND TOO MUCH. A NO-START CONDITION WILL RISK DAMAGING YOUR NEW CAM LOBES AND LIFTERS.

Your rotor position says it all. At 10 degrees advance on the balancer it should be pointed right at the #1 plug electrode in the cap. With the balancer at TDC, then the rotor should be pointed 5 distributor degrees clockwise of (rotated beyond) the #1 electrode.

PUT A PAINT MARK ON THE BASE OF YOUR DISTRIBUTOR WHICH CAN BE SEEN WHEN THE CAP IS INSTALLED. POSITION THIS MARK AT THE #1 POSITION. INSTALL THE CAP AND MAKE SURE THAT YOUR #1 WIRE IS IN-LINE WITH THE PAINT MARK ON THE DISTRIBUTOR BASE. Afterwords, the wires should be 1-8-4-3-6-5-7-2 going clockwise.

Make sure that the float bowls are full and that you're getting a pump shot when you blip the throttle.

You want to fire this fresh engine right away, so why not temporarily bypass the ignition switch, ballast resistor, and wiring between the starter and ballast resistor, just to simplify things for now. USE A 18 GA OR THICKER JUMPER WIRE DIRECTLY FROM THE POSITIVE BATTERY TERMINAL TO THE POSITIVE COIL TERMINAL.

If it doesn't start at that point, then it can only be 3 more things:

1. Points not opening enough. Check for .028 - .032 dwell; .018 - .020 gap.
2. Highly unlikely shorted or open points capacitor (condenser).
3. Broken breaker plate ground wire. You can effect a temporary fix by removing the points door and jumping the breaker plate to the negative coil terminal.

Make sure that you have excess cooling capacity on hand. Anything "off" by the slightest amount can cause the engine temp to rise to the boiling point during the 20 minute break-in cycle. You might use box fans and have the car (chassis?) outdoors in a shady spot. The best thing to do is to feed cold water from a garden hose directly into the reservoir tank if it starts to get too hot.

Mike Ward

Not ranting at you, but this 'one tooth off' silliness is really out of control. It doesn't exist, period. If an engine can be timed to the correct setting, the distributor cannot be 1 tooth, 2 teeth or all the teeth 'off'.

The ONLY relevance it might have is if the distributor housing cannot be rotated sufficiently to achieve the desired setting without mechanical interference between the dist. housing and the intake manifold or other external components.

-Check again that the #1 piston is at TDC on the compression stroke meaning that both valves are closed, not just 'even' with each other

-with a timing light and the ignition on, turn the distributor back and forth to ensure that the #1 plug fires somewhere close to TDC.

-make sure that the other wires follow the correct sequence and in the correct direction from the dist. cap.

-fire it up.

thoyer

Mike has made some very good points, especially about the distributor teeth.

FWIW, My procedure:

A few assumptions: Valves have been set and double checked and the timing mark vs TDC has been verified during engine build.


Prime oiling system. (distributor out, rotate oil pump with drill and adapter until gauge shows good pressure reading for a minute or so)

Set point gap with feeler gauge.

Set timing: Compression stroke, timing mark at preferred timing, in your case 10 deg BTDC. Turn ignition on, Verify battery voltage at coil (9-10 volts with ballast resistor) rotate distributor back and forth. Stop when light fires. Snug distributor hold down. This will put you very close to your desired timing.

Fill float bowls with fuel, verify good squirt with throttle actuation.

Give everything one last once over, water level, all vacuum hoses attached or plugged so there are no vacuum leaks (could cause backfiring...) Verify firing order. Verify belts, hoses, etc are secure. Also make sure fire extinguisher is within reach and if you have helpers, they know what to do if a fire occurs.

Get in and fire 'er up.

Run at RPM specified by cam manufacturer for proper break in. Check dwell once it is up and running. You can fiddle with the timing if it is way off, but leave the fine tuning of the timing for after breakin

Keep an eye on oil pressure and water temp and water level.

I may be missing a few minor things, but this general approach has never let me down.

Tom

MikeM

On the exhaust stroke, the valves will be even with each other but both will be slightly off the seat.

ryan22

Didn't get to mess with the 66 today but did do some reading in the forum. I'm wondering if the following post from JohnZ could be the problem i'm facing since our engine has its original dist. & an aftermarket camshaft.

JohnZ's post about the indexing of the dist. and the cam;

"The helical distributor drive gear on factory cams is specifically indexed relative to the dowel pin hole in the front of the camshaft, and the driven gear on the distributor mainshaft is specifically indexed relative to the rotor position so the distributor housing will end up in its correct position.

Aftermarket cams generally don't have the drive gear indexed to the dowel pin, and aftermarket distributor mainshaft driven gears don't have a "dimple" and aren't indexed to the rotor (it only matters on Corvettes); if either the cam or the distributor is aftermarket, you may have to re-orient the driven gear on the mainshaft 180* in order to get the distributor housing (and vacuum advance can) properly located with base timing set."

"Thoyer" wrote to "make sure all vacuum hoses are attached or plugged so there are no leaks which could cause backfiring."

Our 66 is a 4 speed, No A/C, No PB. I did put PS on it since this engine was rebuilt. Correct me if I'm wrong but the only vacuum line it has is just the one from the vac advance to the carb right ?

I appreciate everyone's input, please keep it coming.

69z28&ss396

Not to scare you, but I destroyed a 30/30 lash cam in my Z28 the first time I tried to start it.. Very much the same issues you described. It turned out that the double roller cam alignment "dots" were no **** 180 degrees off.. Its still installed like that to this day and once I figured out that was the problem, new cam, 180 off of dots, fired right up. If you still cant figure it out, check that!! Intrigued at what fixes it..

midyearvette

read again post #5.......good luck....

Tampa Jerry

Vacuum leaks can come from many areas. Look at intake gaskets or improperly torqued intake bolts at the manifold, carb gasket or warped carb base, bad seal or hose in the PVC system, or hose in the dist. to carb for vacuum advance or any nipple used on the carb for ports not used. Once the cam is broken in, I like to use a vacuum guage for carb tuning and to determine the general wellness of the engine, Lastly, if you have a few backfires through the carb and it is a Holley, check the power valve. An old valve could easily blow with an engine backfire. Good luck. Jerry

Powershift

Excellent comments from previous posters. I would follow their advice.

What cam are you running?? Is it flat tappet or roller, hydraulic or solid?? A solid cam requires vlave lash, a hydraulic cam should have the lifters pre-lubed. Do you have a good dose of assembly lube on the cam and lifters??

Did your timing chain set have various keyways for different advance/retard settings?? Did you set them correctly?? Many don't.

At this point, I would probably mark down the actual/installed cylinder firing order on the distributor (check that each plug wire also goes to that cylinder) and then remove the plugs and do a complete 720 degree engine rotation verifying that each valve set open and closes correctly and in the proper sequence.

Then reconnect the plugs wires, fill the carb with gas, bypass the ballast resistor, and try another start.

If you have not prelubed the engine and lifters with oil, you need to do this before any restart. If you are unsure about this, do it again.

Larry

NassauL79

Powershift, to answer your questions-

What cam are you running? - a flat tappet

Do you have a good dose of assembly lube on the cam and lifters? - Yes the rebuilder assured me of this.

Did your timing chain set have various keyways for different advance/retard settings?? Did you set them correctly? - I don't know if the timing chain has keyways or not.

I tried something in regard to the timing that was suggested in another thread. Took the #1 plug out and put it in its wire, loosened the distributor, turned the key on. Turned the dist. as far clockwise as it would go then rotated it back counter clockwise while holding the plug against the exhaust manifold to ground it. Watched for a spark at the plug which never came.

There is very little room to rotate the distributor, about 10 degrees, before the vac advance hits either the coil or the #8 intake runner.

Mike Ward

The engine has to be at TDC on the compression stroke.


That's correct. You should be able to achieve correct timing without the advance hitting anything.

NassauL79

The balancer is at 10 degrees BTDC now...so it needs to be right at 0 in order to get a spark at the #1 plug when I rotate the distributor ? i'll make that adjustment and try it again.

midyearvette

it should fire and run anyway.....

Powershift

You answered about 1/2 of the questions. If you are not sure what is going on and what you are doing, I would have my engine builder come to the house to assist you. Hopefully he has built and run many engines before, and can provide the guidance that you need. He will also be there if there are warranty issues.

If you don't do things correctly, you can damage a number of engine components. Then you have to replace and redo. It sounds like you need on-site help.

Larry

Mike Ward

No, you keep skipping over the important bit being on the compression stroke.

Sounds like you're at the top of the exhaust stroke.

thoyer

One thing I did many years ago when I was just starting out playing with engines, was to take an old dist cap and cut a hole in it directly below where the #1 plug wire attaches. This way I could see the rotor and verify that it was pointing at the #1 plug on the compression stroke, at the desired timing for the #1 cylinder.

If you are trying to see the spark by using either a timing light or a plug inserted into the #1 wire and grounded, you should only have to rotate the distributor enough to open the points. Once the points open (assuming you have voltage to the coil, a good coil, the rotor pointing at the #1 terminal and the balancer set at the desired timing on the compression stroke) you should see a spark or trigger the timing light.

Tom

thoyer

If you do this, your timing will be set at 0 BTDC. Not where you want it to be............

You need to be on the compression stroke for #1 with the balancer set to 10 deg BTDC, then try the spark test.

Tom