My buddy has a '63 Cevy II that he rebuilt a 250 6cylinder for about 3 years ago. All was going fine until recently when it started to run rough. He checked carb, spark plugs, points, vacuum bell...all fine. Checked timing and found it was not what it was originally set at. Reset the timing (with vacuum disconnected and plugged)....two weeks later, timing moved again. Engine has gears, no chain and he had replaced the cam when he rebuilt it. Thought perhaps the distributor gear was at fault but all looked good when he pulled it. Any ideas, we're out of any. Thank you
Probably the first thing to do is verify TDC on the timing pointer. I think the rubber ring on the damper getting old can let the outer ring slip and cause strange readings on those. There is probably something else going on, though.
So if I find TDC by waiting for the pressure to come up against my finger on hole number one, I should see the line on the damper at 0 on the tab....if not, the damper is probably shot, right? Thanks
I had a 250 in my 66 chevy shortbox stepside and I blew a timing gear coming off the freeway one day. The engine just stopped running and I had it towed home after finding the distributor rotor wasn't moving while cranking the engine. Several teeth just sheared off the old fiber cam gear. Your 250 isn't gonna ever jump time, believe me. No way. It can't! The 2 timing gears are allways in constant mesh...If it breaks off a tooth or 2, the cam will simply stop turning...that ain't your problem.
/\ This. Also, don't worry about the balancer pulley just yet. Even if it does slip, that's not going to make the engine run any differently. It will however prevent you from setting the timing accurately. So, if a properly running engine seems to skip time and it has a gear driven camshaft like that Chevy, Id be looking at the distributor hold down first.
I mean a little more accurate than just getting pressure on your thumb....like, put a straw or something in the spark plug hole, and carefully watch it go up as the timing mark approaches TDC, then stop at TDC, and start going down as it goes past TDC, as you turn the engine slowly by hand. The only way the cam timing can slip is if you're missing the key on the crank or cam, where the timing gears fit on.
The stock cam gear is a fiber gear, while the crank gear is steel/cast iron. An aftermarket gear set can be had with an aluminum cam gear. IF it's stripped a gear, it would be the fiber gear, and if that's the problem, and you/your friend has't already gone to an HEI distributor, now would be a good time to do that; there's a huge difference in tunability. JMO. I am Butch/56sedandelivery.
If it's the stock OEM distributor, pull it and check for excessive bushing wear. Common for this style of distributor and can cause erratic timing. The engine may run at high idle speeds and above, but stall out at idle.
Pull the valve cover turn the engine over and watch number six as the exhaust valve closes and when the intake and exhaust are open the same amount you are very close to TDC .
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