SBC timing

[oborowsk]

Just had my 86 Chevy C10 (305) rebuilt. After fixing a "no spark" problem, I have spark now but engine won't start. It is now backfiring out of the carb once in a while but doesn't run. Verified timing again by aligning TOC with mark on damper and making sure cylinder #1 is at TOC. Resinserted dizzy to make sure it points in the direction of cylinder #1 (aligns with #1 on dizzy cap). Hooked up spark plug wires according from firing order (my dizzy has a hold down ring that has them labeled). Unfortunately, I didn't verify that the new timing gear was aligned correctly before I installed the engine. Could that be the problem? How can I verify that it is correct without removing waterpump etc. again? If I take the valve covers off, can I check the valve position? For example, cylinder #1 at TOC, both valves should be closed (since it should be firing). Next, turn the engine 1/4? 1/2? turn and check if valves on cylinder XX are closed?
All the electrical stuff is hooked up but some of the vacuum line are not hooked up. Should the engine at least start without any vacuum lines connected? Do I need to plug any of them for it to start? Can the ECM prevent the engine from starting? Disconnect the ECM? Another thing, I hooked up a timing light and I don't see the marks line up but that could be because there is something wrong with the timing light. The light fires just can't see the marks align. Going to try to hook it up to different cylinders and see if it lines up. Any help is appreciated.

[rich weyand]

It sounds like you are 180* out on the distributor. As you should know, there are two times in one distributor rotation (two crankshaft rotations) when #1 piston is at TDC, but only one of them is the firing position. No run + occasional backfire out through the carb is exactly what you will get when you are 180* out.

You can check the valve position with the valve covers off, as you say. The correct firing position is the TDC position when both valves are closed.

The simpler way to check is to unplug power from the distributor and remove the spark plug on #1, then hold your thumb on the spark plug hole while someone cranks the engine over. The correct firing position is the TDC position where the engine pushes your thumb off the hole as it comes up on the compression stroke.

BTW, the two TDC center positions of the #1 piston occur when the keyway on the crankshaft pulley is in line with the piston rod, at 45* clockwise from straight up (1:30 on a clock face) as you look at the front of the engine.

[oborowsk]

Thanks Rich, what is the easiest way to fix this and try it? In current position, pull the dizzy and rotate shaft 180 degrees? You mentioned that cylinder #1 will have TDC twice. Once, all valvces closed. What are the valve positions of cylinder #1 in the other case?

[rich weyand]

The other TDC is when the piston is completing the exhaust stroke and starting the intake stroke. The intake valve will open before that other TDC and the exhaust stroke will close after that TDC, so they will both be open at least a little. But there won't be any push on your thumb over the spark plug hole for that hole sequence of the exhaust stroke coming up and the intake stroke going down. Only on the compression stroke coming up to the correct firing position TDC will the piston push your thumb off the hole.

The fix for being 180* out is to bump the crank until the distributor rotor points to #6 and the crank is at TDC, pull the distributor up and rotate the rotor 180*, then lower it back down and clamp it. The rotor will move as you pull up because of the spiral gears, and then rotate back as you lower it, but it should end up pointing at #1. The tang on the bottom that engages the oil pump should drop right back in because it is a slot across, like a blade screwdriver.

Actually, you can pull up the distributor in any position, rotate the rotor 180*, and drop it back in, but if you do it with the rotor at #6 and the crank showing TDC with the keyway (or with the timing wheel lined up at TDC assuming it is on right), then you know you are in the right spot going back in when the rotor lands at #1.

[oborowsk]

Rich, that was exactly it. Aligned the timing mark and took the valve cover off. Made sure that both valves were closed. They were....Took the dizzy cap off and???? Finger was pointing at cylinder #6. Took it out, rotated it 180 degrees and put it back in. Put valve cover back on and crossed my fingers. Started right up after a few seconds. Ran a little ruff but had to rev. it up to about 2000 RPM to break in the cam in (for ~20 min.). Need to do some fine tuning but I think I got it solved thanks to your help. It's my 17 year old daughter's first car and she is very happy now. Thanks again. Really appreciate it.

[rich weyand]

Glad to help. I don't know where I would be without the help I've gotten on these forums, so it feels good to pay it back.

You are breaking in the cam, so I hope you are following all the procedures. You know, 20 minutes at 2000 plus drive about 10 miles at varying speeds, then change the oil and filter, at 500 miles change the oil and filter again. No synthetic oil until 3000 miles, which is first regular change. Use break-in oil or oil with high zinc content. Right?

I broke mine in with ZDDPPlus additive for zinc in the oil, and use one bottle every oil change. It's about $10 a bottle and you can get multiple-bottle packs on Amazon. This just makes the oil back like it was in the day before they reduced the zinc content and everyone went to roller cams. Flat-tappet cams want the zinc, though, so I just add it. I switched from dinosaur oil to synthetic at 3000 miles, so I am using Mobil1 10W30 with one bottle of ZDDPPlus, changed every 3000 miles. 2-1/2 years and 12-13 thousand miles on the new engine now with no problems.

For ignition timing, my best recommendation is 16* BTDC, with the stock distributor giving 20 degrees centrifugal advance and vacuum advance giving 15 crankshaft degrees (7.5 distributor degrees) of advance. If you get any knocking you may have to back off that 16 degrees, like down to 12, but it's a pretty safe number and gives great performance.

Also, the engine usually idles better, runs better, gets better mileage, and runs cooler if the vacuum advance is connected to manifold vacuum and not ported (timed) vacuum. Just a matter of which nipple on the carb you connect the hose to, but it makes a difference. Try them both, sometimes you are better off the other way, but my money is on it running better on manifold vacuum.

Also, if you run synthetic power steering fluid, you will reduce steering effort, especially when stopped and the engine at idle, like when parking. Don't overfill the pump or synthetic PS fluid will leak out from under the cap. Keep it down at a quarter to half an inch above the ADD line. But your daughter will probably like the reduced steering effort. To change, drain the system, fill with synthetic, run it for fifteen minutes and move the wheel lock to lock a couple times, then drain it again and fill it with synthetic.

Great dad, getting the daughter a square body!

[dfrank]

To add on to what rich said. Make sure your total timing with vac advance disconnected and plugged is no more than 36° btdc otherwise you risk detonation.

[oborowsk]

Unfortunately, I live in California and have to pass emission. They truck has all the smog stuff on it. Timing is controlled by ECM. No vacuum hose connected to the dizzy. Need to figure out where all the hoses go but I took plenty of pictures before I took it apart so hopefully, that will be a breeze. Thanks again, this forum is great!

[midnight rambler]

good stuff here