Tttiger

1976 L82 motor. Bone stock. Ran great but leaked oil and was time for a clutch.

Took it apart and had the machine shop do a valve job (with new springs) and bore the block .020 over.
Used the original stock cam and crank, journals were fine.

New double roller timing gear set. Punch marks dead nuts on. Crank at 12 cam at 6. #1 at TDC. All looking good.

After final assembly we verified TDC #1 compression stroke by looking at valve movement We put distributor in with rotor pointing to #1 wire on the cap.

Car wouldn't start. moved dist to full advance and got it to run, like crap, but it ran. We got the timing mark to 12m degrees before TDC (factory spec) and it dies. There was zero inches of vacuum when the car was running.

We double checked valve adjustment, all good. Took front cover off and checked timing chain punch marks. They were right on. Checked for any vacuum leaks, none.

Tried rotating the dist 180 degrees just for grins, nothing.

Put the dist back with rotor pointing to #1 again but one tooth advanced. Car started and runs pretty well, but not perfect. Can't see the timing mark. If we put the timing light pickup on the #8 wire, we can see the mark around the 0 degree mark. We get around 11 inches of vacuum.

We're thinking the timing chain may be a tooth off? Everything we've read points to that even though the punch marks lined up dead on.

Thoughts?

TimAT

Pull #1 spark plug, have someone bump the engine until it blows your finger out of the hole. THEN look and see where the rotor is pointing and adjust accordingly. If the dots on the gears are lined up, and the crank gear has ONE slot, that's not the problem.

Tttiger

DId that. And yes, crank gear has one slot.

kossuth

Did you degree the cam? If not you have no idea if your off or not or by how much. In short everything has some manufacturing tolerance in it. The cam sprocket, crank sprocket, keyway in the crank, and the cam itself could all be off X amount. While each might be within their respective tolerance combined together if everything is off in the retarded direction then your motor could be out of tolerance.

This is why you should always degree the cam in any build/rebuild to ensure your combined tolerances don’t throw your timing way into left field. You could probably degree it with the motor in the car but that would be tough. The driver side head should be off when you degree a motor. Personally I would pull the motor, throw it on a stand, pull the driver side head and degree it. If your pretty sure it’s cam timing this is the only way you’re going to know. Sucks but that is the truth of it.

FYI super advanced timing and a lack of vacuum are classic symptoms of retarded cam timing.

kossuth

Just to make sure though before you go bananas on this thing are you certain your lifters are not pumping up and leaving the valves open or something crazy like that? I’m sure you’ve gone through all that stuff but figured I would ask.

derekderek

Pull #1 valve cover. Crank motor until #1 exhaust valve is just closing and #1 intake is just opening. Timing mark will be lined up with tdc mark. This is the overlap point between exhaust and intake strokes. Dist pointing to #6.

jim2527

With crank gear at 12 and cam gear at 6 the engines at TDC firing for #6. Engine needs to be rotated 360 to get #1 at TDC firing.

Lots of good advice above.

jackson

OP Tiger
Did you replace original damper/balancer in course of rebuild?

If so, there're several versions which look virtually same but (in relation to keyway) have a range of timing mark locations.

Similarly, did you change the timing TAB/cover itself?

HeadsU.P.

360 degrees = right back where you started. I think he means one sprocket 360, not the whole engine.

But, Dots across from each other / near each other, is firing on # 6.

And NO you don't need to pull the engine or degree the cam unless you are all-out-racing. You can work this issue out by thinking clearly, back-tracking, one step at a time.

cv67

w/heads up. Call Summit and get a tdc locator rotate the engine by hand, see where your rotor is oriented to go from there.

Jebbysan

If you believe the dots were perfect then they probably are.....although you were on #6.....most common chevy mistake on the planet 50 years running......
Now get a piston stop and verify TDC....is the balancer showing zero at true TDC.....forget the cam at this moment.....if it does show dead nuts TDC......do as suggested above....blow the thumb and install the distributor.
If it does not line up on #1....buy a new balancer and a premium timing pointer (Moroso or Allstar).
Also......you are looking for total timing at 3000 rpm or more......forget the initial timing...not important here....and make sure the vac advance is unplugged when checking......
If you have timing marks on your balancer, cool....if not....buy a digital dial back timing light.....mine has the RPM on it as well as timing degrees.

Jebby

kossuth

Ummm. Degreeing a cam isn’t a performance thing. It’s to ensure that ALL your valve train components have been manufactured and work together in tolerance for your motor. Yes, pro builders use what they learn during the degreeing a motor to advance or retard a camshaft. But they don’t do anything until they figure out the exact timing.

kossuth

As for what information you would need beforehand is what the specs are for your camshaft. In this particular case you are looking for the intake centerline of the camshaft. It should be in degrees ATDC (after top dead center).

First you you need to establish 100% true TDC on the number one. This doesn’t mean bring the piston up and that’s it. Basically the piston has 3-4 degrees of crankshaft rotation where the piston doesn’t move but it’s transitioning to a downward motion. Once you establish this zero out the degree wheel.

Next at you want to have a dial indicator setup with a magnetic base and measure the camshaft lift on the intake. Always rotate the motor in the clockwise direction. You don’t want slack in the timing chain to screw up your readings. The duration and lift numbers aren’t important here. What is important is that you specify a number (I would say .050” lift) and stick with it. Roll the motor over a few times and establish where MAX lift is on the camshaft and zero out your dial indicator.

Once you have that done roll the motor over clockwise again until you have the intake valve opening again. Watch the dial indicator and slowly rotate the motor until the lift is -.050” below the max lift. Look at the degree wheel and write that number down. Keep rotating the motor until you hit max lift, go past it, and are on the closing event of the valve. Again watch the dial indicator and rotate the motor until you are again -.050” below max lift as the valve is closing and write down the number on the degree wheel. Add the two numbers up and divide by 2 and you should have your AS INSTALLED ATDC measurement of your camshaft.

I don’t know the specs for your cam but if your specs are supposed to be 114 ATDC and you find the measurements are giving you 122 degrees then your cam is 8 degrees retarded and that will cause problems.

If all you can find is the cam centerline (difference between intake and exhaust lobes) the you would need to do similar but on the exhaust valve and divide by 2 and go from there.

With all of the parts being outsourced to China (and we know what their QA process can be like) you have to check these things. Maybe you have a bum timing set. Maybe the issue is elsewhere, but degreeing the cam is the only way to rule out cam timing.

OP I also misspoke on having to pull the head. There is a way to do it with the head on.

jeffwebley

Since you re-used the OE cam, and the crank and can were dot to dot, I would suspect the damper ring has turned.
If you have the timing cover off (again) when the cam and crank are dot to dot, turn the crank 1 full revolution, that will put number 1 tdc compression. Stuff the distributor pointing at #1 and it will run.
If the cover is on, a piston stop is your best friend. Turn the crank till the piston touches the stop and mark the damper at the zero mark of the timing tab, then turn it the other way till they meet again and make another mark on the damper. Then split the difference and you will have #1 tdc. Compare it with the timing mark on the damper, they probably won't line up, as my guess is the damper ring has turned.
Just my opinion, I could be wrong.
And scads of sbc's have left the factory with dot to dot timing, so I wouldn't worry about degree-ing the cam until you step up the hunt for performance.
Good luck.

Sky65

I agree with first verifying balancer timing mark and pointer are correct. Use a piston stop to confirm. Then check dist installation. You don't need the eng out.


Tom

HeadsU.P.

I agree Jeff, poor guy doesn't need or want to spend another $100 just to get it running: degree wheel, dial indicator, etc.

I think everybody missed one sentence in the original post:

Ran like crap with ZERO VACUUM! Somethings amiss elsewhere.

jackson

At first crap running & Zero vac ... but later found running pretty well @ 11 inches ... once true TDC & timing's sorted I expect vac will rise.

jim2527

Help me out here then..... timing sets assembled with crank dot up and cam dot down as per instructions. That would be firing on #6. 2:1 ratio with crank turning 2X and cam turning 1x. If crank turns 1 full turn them cam turns 1/2 turn.

Turning crank 360 or 1 full turn gets engine on #1 firing like this:

HeadsU.P.

You are right. I misunderstood your statement. That photo is for numero uno TDC. But it can be difficult to get a visual on the dots alignment when the cam dot is so far away. So, people will put the dots across from each where its easier to line up, and hopefully realize that is for #6.

derekderek

Also, when timed at 6, watch rockers on 1. Work engine back and forth so the 2 rockers are moving together. 1 closing and the other opening. This SHOULD happen right at or very near TDC mark on balancer. Not scientific, but decent eyeball check of cam timing and TDC mark. Also, how many teeth on cam gear? I think they are 36 or 44 teeth. 36 is 10 cam degrees a tooth. 20 crank degrees. 44 teeth is 8.2 or so.16.5 crank degrees. So 1 tooth off is hugely retarded or advanced. Will run, but like crap, and intake valve is about to hit the piston if 1 tooth advanced.