Other than a loose distributor clamp, What causes timing to move? I set it to 12 degrees BTDC. When I started the engine, and took a timing light to it, the mark had moved completly off the timing tab (ATDC side). My engine misses badly, when I rotated the distributor back up to 12 degrees, the engine idles high. Must also mention this vehicle has an electric choke (not installed yet). Can anyone give any advice? I'm atempting to download a video/sound file on this forum so anyone can check it out.

 

Is this an engine I might be familiar with? :D

The woodruff key for the balancer wasn't installed or came out and the balancer is moving on the crank.

The outer ring on the harmonic balancer could have slipped.

The mechanical advance in the distributor could be sticking open.

Or the distributor clamp could just be loose.

 

Afraid not Steve, the engine you gave me is still on the stand, covered with two plastic bags. (also have .060, 4-bold main block within the confines of my small garage) Gotta keep engine blocks on standby :D will look at these possibilities. Thanks again for that engine, I really appreciate it.


[Modified by Oldguard 7, 9:31 PM 1/25/2004]

 

It may be that you have a vacuum hose off. If the engine has a vacuum leak, it runs rough. Also if you have an elctric choke on the carb but it is not hooked up, the engine will run rough. When you set it to 12 degrees and it idels high, it sounds like that's where it should be and the idle screw needs to be set down IF the choke plate is open. Are you sure the timing light is conneceted to number 1 plug wire?? If timing is moving just a little, it may be distributor creap due to hold down bolt not tight or there may be a problem with the vacuum advance or centrifugal advance mechanisms but if the change is huge there is another problem.

Try a step by step approach. Step #1: Pull #1 spark plug out. Hold tip of finger in the spark plug hold while someone turns the ignition key to start for just less than a second. When you feel the pressure on the tip of your finger check where the the crankshaft dampner is relartive to the timing mark on the timing cover. If the TDC line on the dampner lines up (or very close) to the TDC mark on the timing cover, there is no problem with the crank key or dampner. You might try bumping the starter several times with your finger in the spark plug hole just to get a sense of where everthing lines up.

If you feel the pressure build up to maximum (it'll blow your finger out of the hole) and the timing mark and dampner are no where close to lining up, STOP here, you have a problem with the dampner. crank key, or camshaft. If they line up (or very nearly line up) continue to step two as the proble, is not with the dampner or crankshaft key

Step #2: Make sure all vacuum lines to the engine are connected or plugged. Disconnect the vacuum line to Dist advance and plug the line. Hook timing light to Plug #1. Make sure choke is open. Block it open if necessary (carefull here (do not put anything in the carberator that could fall down inside. You can usually pull on the accererator pedal once to un lock the choke and then use Duct tape on the side of the carb at the chocke control rod to hold it open. This would work so much better if you would just hook up the electic choke even if temporarily ( you just need 12V to pos term and Grd wire to neg terminal. After one minute the choke will open. Now with choke open, Timing light connected, start engine and check timing. The engine should run faitrly smooth with 8 degrees or so BTDC. If engine runs OK, tighten distributor lock down bolt. Unplug distributor vacuum hose and hook it back to distributor. If engine advance goes up more with hose attached, rev engine and check that timing goes up to 35 to 40 degrees estimated unless you have marked this on your dampner.

How do you mark 40% on your dampner? Jack car up so you can get under it, wrap a tape around the dampner to measure it. Divide the measurement by 9 (360 degrees /9 = 40 degrees) and mark this number of inches above your TDC mark with white paint or shoe polish. You now have a 40 dergee mark. If this mark lines up with the TDC mark on the timing cover at 2500 to 3500 RPM during very breif trttle snap, the total engine advance is 40%. If all this works stop here.

Step 3: If you have to go way out of wack on timing to get the engine to run smoothly, the distributor gear has sun on the distributor shaft. Pull the distributor out of the engine. If the distributor gear is still locked in place with the cross pin and has not spun, you have a mopre serious problem somewhere whith either the timing chain or the camshaft.

Remember, the timing light does not lie. It lights up when the spark is detected in the wire. It will light the dampner at the precise moment it detects fire in the wire. Wherever the dampner is when it lights is where that particular plug is firing. Plugs 1 and 6 will both light up the dampner near TDCat whatever advance you set the distributor at. It's just that plug six fires 360 degrees after plug number 1. Plugs 8 and 5 fire 90 degrees later (although they are 360 degrees apart). Plugs 4 and 7 fire 180 degrees after number 1 and 6 respectively and plugs 3 and 2 are at 270 degrees. SWo if you attach a timing light to any wire, you can detect if it is firing at the proper location. It's just that the timing mark is setup to work with the line on the dampner at plug 1 or 6. Since the timing light does not lie. Whatever shows up on the dampner under the light is where that plug is firing. If it is way off, there is a serious problem in the timing chain, cam, distributor gear.

 

I agree with Marioncole except for the total amount of mechanical advance. It should be 36 degrees (360/10 instead of 9). Just ask Lars on this. Total advance should be 52 degrees including vacuum.

 

Look closely at your harmonic balancer. It can slip at the rubber if it is old, and this will show up when you put a timing light on it. Your timing won't change, just the mark. I hunted this problem for two weeks. When you attempt to reset timing, you will be off. Mine would move back and forth, making it hard to diagnose. This could be your problem. I replaced the balancer and cured it on my 72.

 

also slipped timing chain

 

:iagree: the chain was my 1st thought probably broke a tooth and it changes the timing with every rotation of the crank