Is something horribly wrong with the timing on my SBC? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-23-2012, 05:02 PM
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Is something horribly wrong with the timing on my SBC?

I had a quick couple minutes in a long while to mess with my ratty 240Z with a SBC 350. It has set over the last couple months after developing some sort of issue not allowing the car to start. It is getting fuel (new carb) and would try to start every so often, but would spit/backfire ect horribly before petering out.

I suspected some sort of timing issue and ordered a HEI distributor to replace the stock dizzy and coil, as this would most likely solve 80% of the issues pertaining to spark. Today I went out to get my bearings straight before the installation, I am a very amateur mechanic at best. Right away I went to find top center and found an issue, or at least a circumstance that had me confused. When I got the timing mark on the balancer to match the static pointer for TDC center the distributor rotor was facing what I believe to be cylinder 7 (farthest back cylinder on driver side, picture #1).

Just for poops and giggles, and to make sure that the everything was turning correctly I turned the motor over one more turn and the rotor was then pointing 180 degrees at what I believe to be #4 (2nd cylinder from the front on the passenger side, picture #2) which may not be correct but at least correlates correctly with the first reading.

Do I have something horribly wrong with my timing here? Should I just disregard this issue and start from scratch when installing the new HEI distributor by manually finding the compression stroke on cylinder #1 (which I believe to be the front the cylinder on the driver side) and go from there?

Also need to note that when I try to turn the motor over by hand the harmonic balancer nut just spins. I have to turn the motor over with the starter, and then put the car in gear and rock it back in forth to get it exact. Does this mean perhaps that the harmonic balancer may be loose and hence the timing mark could be rendered completely useless at this piont?

Any help would be greatly appreciated.

****note the pictures were taken from above and from the front of the distributor so it reads as a clock would.
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Last edited by Fenderbaum; 02-23-2012 at 05:26 PM.
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Old 02-23-2012, 05:48 PM
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Pull the plug on #1 cylinder and turn it until you feel air being pushed out, then rotate it some more, slowly until the pointer is at zero or say 8 degrees before TDC. Wherever the rotor is pointing, make that your #1 plug wire and go from there in the firing order around the distributor, in the direction of rotation, it should start if you have fuel going into the motor and spark at the plug.

The disadvantage to not having it in the "normal" 5 o'clock position is having enough room to rotate the distributor without possibly hitting the intake.

Tha balancer is keyed, is it rotating on the snout? Not a good idea to turn the motor with the bolt. It sounds like the bolt is stripped, not good! There are fixes for that, do a search here.
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Old 02-23-2012, 06:19 PM
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I appreciate the response.

I forgot to add that the plug wires are connected correctly as per the diagram so when the timing mark is at TDC, and with the rotor positioned as pictured at that point, that the spark is indeed going to cylinder #7.

With that being said are saying to completely disregard all this, and just start from scratch with cylinder #1 and go from there? I'm not sure if the timing mark can be trusted at this point and the car has run in the past.

Also, and you may have already picked up on this, but when I said the harmonic balancer nut what I was actually referring to was the bolt that goes through the belt pulley in front of the harmonic balancer and that was what is actually spinning freely. If this is not the proper way to turn the motor over what is the appropriate way? The balancer seems to spin correctly when using the starter to turn the motor, but when wrenching the bolt the bolt spins while the balancer remains static.

Thanks again.

Last edited by Fenderbaum; 02-23-2012 at 06:24 PM.
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Old 02-23-2012, 10:03 PM
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Wow! don't break off that bolt on the flywheel! I still have one broken off in
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Old 02-23-2012, 10:41 PM
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Quote:
Originally Posted by Fenderbaum
I appreciate the response.

I forgot to add that the plug wires are connected correctly as per the diagram so when the timing mark is at TDC, and with the rotor positioned as pictured at that point, that the spark is indeed going to cylinder #7.

With that being said are saying to completely disregard all this, and just start from scratch with cylinder #1 and go from there? I'm not sure if the timing mark can be trusted at this point and the car has run in the past.

Also, and you may have already picked up on this, but when I said the harmonic balancer nut what I was actually referring to was the bolt that goes through the belt pulley in front of the harmonic balancer and that was what is actually spinning freely. If this is not the proper way to turn the motor over what is the appropriate way? The balancer seems to spin correctly when using the starter to turn the motor, but when wrenching the bolt the bolt spins while the balancer remains static.

Thanks again.
Use your #1 piston as a tdc reference, and I would also see that #1 valves were both closed as well. I would re-insert dizzy to get 5oclock as well for adjustment room. Your pics don't show HEI.
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Old 02-23-2012, 10:50 PM
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Quote:
Originally Posted by Fenderbaum
I appreciate the response.

I forgot to add that the plug wires are connected correctly as per the diagram so when the timing mark is at TDC, and with the rotor positioned as pictured at that point, that the spark is indeed going to cylinder #7.

With that being said are saying to completely disregard all this, and just start from scratch with cylinder #1 and go from there? I'm not sure if the timing mark can be trusted at this point and the car has run in the past.

Also, and you may have already picked up on this, but when I said the harmonic balancer nut what I was actually referring to was the bolt that goes through the belt pulley in front of the harmonic balancer and that was what is actually spinning freely. If this is not the proper way to turn the motor over what is the appropriate way? The balancer seems to spin correctly when using the starter to turn the motor, but when wrenching the bolt the bolt spins while the balancer remains static.

Thanks again.
If the engine has run good previously w/the wires in the cap as they are now, here are two possibilities:

The timing chain has skipped some teeth on the gear.

This causes an "out of phase" condition where TDC as seen at the damper line and timing tab no longer corresponds to cylinder #1 and #6 being at TDC.

You see, when the timing line on the damper and timing tab on the timing cover are saying "TDC", BOTH #1 and #6 are supposed to be at TDC, but only one cylinder will be ready to fire, w/both valves closed. This is if the timing chain and gears have not slipped. If they have slipped, when the damper line/timing tab say TDC, the rotor could be pointing anywhere, but it won't be pointing at (or very near to) #1 or #6. And the engine won't run, and can pop through the carb or exhaust pipe when you try to start it.

OR

The damper might have broken the key that locates it in the correct position on the crankshaft snout. The bolt being loose/broken could have allowed the damper to hammer away at the key until it finally gave. If that happened, the damper line used to time the engine and to locate TDC will no longer be correct- but the engine would have still run the same as it did before as long as the timing wasn't changed using the now-incorrect damper line. The only real difference would be there's basically no damping of the harmonics that is provided by the damper when it is tight. This will cause damage over time, but as I said, the engine would still start up and run.

Also, if the damper bolt is broken, you should be able to pull it out by hand.

Some links that may help:

DETERMINE TDC. This will also allow you to be sure the timing tab and damper are correct for TDC.

MAKE A TIMING TAPE. Useful for determining total timing, etc.

There were three different combinations of damper lines and timing tabs that go together. THIS page describes them.

Last edited by cobalt327; 02-23-2012 at 11:03 PM.
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Old 02-23-2012, 10:51 PM
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Easy SBC timing. Only things you might not have in yer tool box might be a broom stick and a TDC bolt.
1. Pull spark plugs, all of em. Easier to turn engine by hand.
2. remove left (driver side) valve cover
3. turn engine by hand until #1 at TDC. (I like to use a TDC stop) and Mark It on harmonic balancer and block. This is going to be your timing reference.
4. turn the engine (by hand) until #1 intake valve opens and closes. continue around to TDC and stop. Go get a cup of coffee.
5. Drop distributor in so that gear line rotor up with #1 post. If the distributor wont seat, and it probably wont cause been turning the engine with it up and oil pump hasn't been turning.
6. Use broomstick w/slot in end to turn oil pump to line up with distributor.
7. tighten Distributor hold-down bracket so you can turn the distributor, but it won't pop up out of the manifold on you.
8. reinstall plugs.
I like to set the distributor a little retarded when initially timing, and move it forward until the engine fires and move it forward till I get a nice even idle, then go from there. I almost have to use a timing light as my hearing is shot.
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Old 02-24-2012, 08:01 AM
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Appreciate the further responses.

I have not started the install of the HEI as of yet. I stopped in my tracks when I noticed the timing issue with the original distributor.

If the timing chain skipped some teeth, or the damper lost its reference on the crank, these types of issues were what I was worried about when I started the thread and seem the only plausible type of explanations as to why the car did run but won't now, it seems like the only appropriate course of action at this point is to diagnose if either of these issues are indeed the case and address them before initiating the install of the new HEI.

I am aware that I could probably just start from scratch by finding top dead center of #1 anew by disregarding the timing current timing marks and correlate with the new distributor and work my way around from there, but it doesn't seem prudent if there is an underlying issue (which seems to have to be the case) which would either result in the timing skipping again, or the engine slowly consuming itself with an out of balance harmonic balancer.

My next step will be to pop the valve covers off and find were top dead center is on #1 in correlation to the timing mark on the balancer. That should tell me if my timing is off, or if the balancer is off.

If anybody disagrees with this logic please feel free to chime in.
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Old 02-24-2012, 08:32 AM
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Broken Bolt ?????

Hi,IF the bolt that holds the balancer on,is broken,STOP,you MUST get that broken bolt OUT,BEFORE you try to start the engine,OR,if the balancer is loose,you MIGHT be buying a new crank.(if the balancer comes off)...
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Old 02-24-2012, 09:29 AM
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The bolt is not broken at this point. In fact it takes a 1/2 ratchet to provide enough leverage to even get it to turn, but once it starts to turn it just spins. It has gotten to the point though where I don't feel comfortable spinning it anymore.
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