425 wont stay in time

ok heres the scenario...66 olds dynamic 88 ragtop, about 15k on rebuild with new mild crane cam. the car never really stayed in time..but has gotten really bad. to the point i have to reset the timing everytime i want to take a short ride and then its off again. i changed the distributor to a rebuilt, tried all differnt sets of points, and have now even dropped in a pertronix electronic kit. its the kit that sits under the cap so it looks stock. the distributor hold down clamp is fine. someone awhile back told me its the gear on the camshaft is loose and the pin might be sheared off that holds it steady. does this sound realistic? are there any other things i should try or check before tearing the engine apart to replace the cam. id like to avoid doing this but if i have to i guess its a good fall/winter project. the car runs and idles fine...but just wont stay timed. seems like its proggressively gotten worse through the past couple of years. grrrrrr! any ideas would be greatly appreciated

[Bluevista]

Gee, that is weird, my timing chain was flopping all over and it still stayed in time, bounced around a little. Is the vacuum advance plate the points or Pertronix trigger sits on free and not sticking somehow? I know it is new but who knows? have seen that a few times. The vacuum advance connected to the right port and disconnected when timing? Only takes a minute to pull the distributor and check it to see if the gear is messed up but you said that was new. I'm not a real experienced internals guy so don't know about the cam gear but I know they can get eaten up. I have heard of the balancer slipping on the rubber ring but it would run fine and just look out of time then I would think?

Allan

it been awhile...but what port should the vacuum advance be using for vacuum?...im pretty sure the pertronix setup is fine. is there anyway to check the cam gear without pulling the cam?

[Oldsmaniac]

There are 2 gears on the cam....the rear one is part of the cam and cannot be changed. It turns the distributor. The front gear bolts to the cam and can cause problems. To inspect you need to pull timing cover. Valve timing is controlled by the timing gear. If balancer has slipped the engine will run fine as long as ignition timing is not disturbed. I cannot say what your problem is being caused by but I would suspect it to be distributor related.

[Run to Rund]

Mark the distributor rotor tip against the distributor housing, and the housing vs. the block. Then pull the distributor and check the gear on the bottom of it. That is the gear with a pin through it and the shaft. If the timing gear on the front of the cam slipped (sheared the alignment pin in the nose of the cam) then valve timing would be way off too.

i figure the valve timing is fine and the timing chain and gear are fine. because i could tune it. the distributor wont stay timed. if it was the valve timing it wouldnt tune at all. the gear on the distributor is new..this is another distributor (rebuilt). i replaced the distributor awhile back hoping that was the problem...no such luck. and then replaced the points and then replaced the point assembly with an electronic setup from pertronix. no luck still.

[Oldsmaniac]

Can you say how you know that the engine timing has gone off?...What happens?...Does the timing get advanced or retarded?....Are you setting timing with a tach so RPM will be the same each time? Is your dwell changing as well?

after you cruise around in it for awhile, when you shut the car off it will keep running a little bit. when i get it timed up it doesnt do this at all. i can get it timed up perfectly, to where it has great response and no hesitation and turns off and starts up fine. ive been timing it right to the manual specs..hose to vacuum advance off and plugged and the rpms at the correct speed. could it be a faulty vacuum advance....i changed that at some point awhile back but i think before the distributor was changed, so i might consider that. does that even matter with the pertronix electronic module? im almost considering picking up an HEI distributor and trying a whole new settup alltogether.

im going to go over the whole thing again..with a fresh head tomorrow. its been sitting awhile. ill try timing it again and check the vac advance and see if i can get a better description of whats going on..ill document my timing settings and whatnot.
another question is...since its not a stock cam..its a mild crane cam..should it be timed to factory specs or should the cam have specific timing specs? dumb question since ive had this cam in it for about 10 years (low miles on it...but 10 years is a long time not to know if i should have it advanced or retarded)

[Danny Wiseley]

Originally Posted by blkmonday

after you cruise around in it for awhile, when you shut the car off it will keep running a little bit. when i get it timed up it doesnt do this at all. >snip<.

When the ignition switch is in the "Off" position, there is no timing, as there is no spark. The only thing ignition timing has to do with "run on," "dieseling," or "keep running a little bit" is the effect it has on the idle speed. Lots of people think they fixed a run-on condition by retarding the timing, when the actual fix was the slower idle speed brought on by the retarded timing. Think about it.
Danny

so in theory...would a slower idle speed get rid of my run-on problem? i do still have the timing walking around...however i did think that the run on was because of the distributor timing. so lowering the idle speed would get rid of the run on?...interesting

[Bluevista]

This is a real longshot but I was talking to an engine guy and he said when you change the cam and have lower vacuum you have to make sure the vacuum advance is fully in at a point lower than full vacuum at idle. The timing will jump around because the advance mechanism is pulling in and out at idle because it is calibrated for the original higher vacuum. It should be changed to one that is all in at a lower vacuum than your highest vacuum reading. I never asked but I think that is if the advance is connected to manifold vacuum. He said some guys use direct vacuum for hot idle problems to advance timing which can make it run cooler, and some just run better that way. If it is connected to ported vacuum I wouldn't think it would do that since it has no real vacuum until the throttle plates open? It may not be the problem but it does sort of make sense, but in my case a little knowledge can be a dangerous thing.


Allan