Guys, I have a 56 Chevy that has a early 60's sbc in it. The motor has an unknown amount of miles on it. It has about 70-80 compression in each cyl. Car usually starts fine and runs well. The past two times I took it out for a drive everything was fine for a few hours then I stop and turn the car off. When I go to restart it will crank, has fuel but wont fire. Two times I fixed it by advancing the timing and it stumbles to a start, then I set the timing by ear( by idle rpm) then drive it home. I have tightened the bolt, but it still does it. Car has new: edelbrock carb, new fuel pump, new pertronix dist and ext coil, new wires and plugs. I have bypassed ballast and wiring is correct. It is not the starter, that works great. Today car started, warmed up, then died and will NOT restart. Has fuel and power to the coil. Thoughts????
shit can the pertronix. or at least remove it and replace with points or hei to see if thats the problem. Could be coil or module breaking down with heat.
You say that it cranks and has fuel,does it have spark? Is your timing chain in good shape? Since you say it started when you changed the timing I'd suspect that the timing is changing, either by the distributor or the timing chain jumping. When you time by ear, you usually have it advanced.
You may be having a flooding problem. Push foot feet all the way to floor hold it down and try it again. Just something to try.IMO
Wonder how bad the timing chain is if the rest the engine is worn to the point of only 80 lbs. compression? I'd stick a screwdriver in the end of one of the plug wires and see what kind of spark you get to ground.
I thought you had to run a Ballast resistor with the Pertronix..? Why did you bypass it? That might be your problem..
I've got Pertronix in both my SBC and BBC hotrods and no ballast resistor. The instructions don't call for one. The BBC has had the Pertronix for over 10 yrs. so far and works great without it.
I'm kind of suprised that it runs at all with 70-80 lbs. of compression on each cylinder. It's been my experience that an engine needs around 100 lbs. of compression for a cylinder to hit. Might be a coincidence, but advancing the timing has the same effect as boosting the compression (kicking back on starting and detonation). Just something to think about. Larry T
I'll go with the others most likely the timing chain. When it jumps a tooth by moveing the dist you get it going again,it must seem to have less power now.
check that you have the correct ohms and coil for the Petronix. i believe on the Ignitor you need 2-3 ohms for the coil/ballast , on the ignitor II i think less than 1 ohms. it's been a while since i messed with one , so double check that
yeah, have always heard 85 lbs the minimum for a motor to run........you have 70 to 80 lbs cold or hot, bet it gets lower hot, so after you warm it up its down to even less and doesn`t wanna run, going throught that right with on eof mine, only have 50 lbs in 2 cyl and a huge miss and doesn`t wanna stay running......time for a freshen up....
So, if it's the chain and I need to install a new one and re-time the cam. I can handle the install, however is there a special procedure to re time the cam? Any links to a tech article is much appreciated.
first off if a timing chain jumps, they run barely if at all. Your compression is so low it's amazing it starts ever. I have seen tired engines wash down the cylinders and never restart again with 75 pounds compression. As mentioned you need to check for a good spark before you start throwing parts at it. Maybe it's your coil breaking down, they usually tend to be more problematic hot than cold when they start getting bad. Also if you have a test light (I'm assuming you do if you checked for power to the coil) try checking on the other side of the coil while cranking. The light should blink on and off.
You can check and see how much slop is in the chain. Get the timing mark up to the pointer, pull the dist. cap. Now rock the engine back and forth on the crank and see how many degrees you move the crank without the rotor moving. I have seen as much as 22 degrees of slop in sbc engines that still start and run ok. Is your compression gauge a screw in one or the old cheapo hold it in the hole kind? Maybe those numbers aren't accurate. Installing a new chain isn't hard. Just use a small straight endge and make sure the marks on the cam gear and crank gear are lined up with the imaginary line that goes through the center of the crank and cam. If you put it on top dead canter with the rotor pointing to the #1 cylinder before you take it apart, it will be real close, only off as much as the slop in the chain or however much it might have jumped, which I still seriously doubt it has or it wouldn't run at all or if it did it wouldn't have enough power to move the car.
Sounds good. I'll check for slop tomorrow. Car won't run at all. I'm gonna recheck the compression as well. I checked the compression when I first bought the car. It hadn't run in 30 some odd years so the numbers may no longer be accurate. Btw, it's a snap on screw in style compression set. Thank you all for the advice.
I agree with Larry T that the compression is way too low, and that fiddling with the timing is temporarily raising the compression ratio. My guess is that once the motor has run, and built some heat in it, something in the cylinder is expanding, causing clearances to loosen up even more, and causing even more compression leak. Then no startey. Cools down, clearances close up, then it starts. Just a guess. Good luck. No sense doing anything else without an accurate compression test.
If it hasn't run in 30 years you might have some stuck rings. You might try pouring something down the spark plug holes and letting it sit a while. Marvel Mystery oil works ok. I heard an old timer once say ammonia did the trick but I can neither confirm nor deny it's effectiveness.
I agree that compression is too low. I've got a Weedeater with 70 PSI that won't start either. It's worn out.
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