timing, TDC and distributor rotor

[swilliams]

Hello. I have a 86 c10 350 Goodwrench crate motor I am adding MSD 5520 ignition box, cap, rotor and HEI coil. What I am trying to find out today... I have my engine between 10 and 12 deg before TDC.



My rotor is pointing like this



even if it is 180 off it will not be pointing at where the #1 plug was before I replaced the cap. Please tell me what I have over looked or have wrong. Thanks

[bd]

Are you saying that the engine doesn't start?  Does it backfire?  Did it run properly before adding the coil and MSD box?  Did you remove the distributor for any reason?

[swilliams]

All I have done is remove original cap, rotor and coil. It ran before that. No backfire. I am just trying to understand the set up and how it works I have not put it back together and tried it yet. The reason for moving to TDC is that the location mark to reinstall the cap came off so I was trying to figure out where to put it.

[Terryr85]

Roll the motor over 1 time and put it on zero. If u didn't pull the distributer then your good. You're 170* off I think

[bd]

All I have done is remove original cap, rotor and coil. It ran before that. No backfire. I am just trying to understand the set up and how it works I have not put it back together and tried it yet. The reason for moving to TDC is that the location mark to reinstall the cap came off so I was trying to figure out where to put it.

The distributor cap cannot be installed incorrectly since it is indexed by a tab on the cap that mates with a notch in the distributor housing - the cap will fit onto the distributor only one way and clamp down.  Align the cap, finish putting it together and start it.  Then check your timing using a light after you disconnect the vacuum advance and plug the hose.

Roughly how many miles on that crate engine?  Did you install it yourself?

[swilliams]

The engine has 30 to 35000 miles. The PO installed it.
So do the spring clips of the cap go here?



I thought putting engine at TDC the rotor should b pointing at or even near the #1 of the firing order.

[swilliams]

Ok I just checked the original cap and was able to determine where MSD cap (which does not have locating tab) should go. I will finish tomorrow and then I will have more questions. I still would like to know about the TDC and rotor location.

[Terryr85]

Being that you didn't take the distributor out, the engine is still in time. The rotor isn't pointing where it should because you are at TDC...just not on the right stroke. You can set it to have #1 be wherever your heart desires. I was taught to put #1 on the driver side of the front two closest to the carb. If your cap has no locating tabs then the side of the cap with the power and tach plug in will go on the driver side, opposite the vacuum advance side. Hope that covers it for ya

[swilliams]

Thanks for your help

[bd]

...I still would like to know about the TDC and rotor location.

The small block Chevy firing order is 1-8-4-3-6-5-7-2.  The crankshaft makes two complete revolutions for each cylinder to complete its intake-compression-power-exhaust cycle - the piston makes two complete down-up strokes per cycle.  As the crankshaft rotates, piston top-dead-center (TDC) occurs between the compression and power strokes, and between the exhaust and intake strokes.  Piston bottom-dead-center (BDC) occurs between the intake and compression strokes, and between the power and exhaust strokes.  The piston stops and reverses its direction of travel at TDC and BDC.  Ignition occurs directly between the compression and power strokes...

...intake stroke-(BDC)-compression stroke-(TDC)-ignition/power stroke-(BDC)-exhaust stroke-(TDC)-back to intake stroke, repeating cyclically...

Reiterating, a piston comes to TDC twice (two crankshaft revolutions) for each complete cycle. 

------------------------

Engine cylinders fire as opposing pairs or "running mates," as follows:

1 - 8 - 4 - 3
6 - 5 - 7 - 2

So, cylinders 1 and 6 are defined as running mates.  When cylinder #1 is at TDC compression/power, cylinder #6 is at TDC exhaust/intake, and vice versa.  In your posted images, cylinder #6 is near TDC compression, just beginning its ignition/power stroke; whereas, cylinder #1 is near TDC exhaust, just beginning its intake stroke.  Similarly, cylinders 8 and 5 are running mates, as are 4 and 7, as are 3 and 2.

Conceptualize the preceding description with a piston moving up and down in its cylinder to get the idea.

[swilliams]

That is good information to know. I got it all back together and running. My timing light was dead so I have to get a new one to do fine tuning. I followed instructions with MSD 5520 ignition now when I drive normally all is good but if I get on it my gauges fuse pops. Any ideas

[bd]

When the fuse pops, does the engine die?

• Yes - You may have tapped ignition power for the MSD box from the wrong ignition circuit.
  
  
• No - Look for an ignition wire that is getting pinched or arcing to ground when the engine torques over under load.
  

[swilliams]

More wiring... Yeah I did not expect this I have taped everything up I cant even think of where it could be there is only 4 wires and the 2 to the coil. The engine does not die I here the pop and gauges don't work. the first time I thought wires arced that is why I went ahead and taped it all up. I will have to go through it again. Thanks

[bd]

It could be coincidental - perhaps engine compartment wires or wires under the dash were moved just enough to chafe and start arcing as the engine/frame/cab flex.  So you don't spend a fortune in fuses, make up a 10-amp or appropriately sized test breaker with a couple of attached test leads and clips then substitute it for the 'popping' fuse in the fuse box.  Make sure no wires were pinched under the distributor cap.

[Greybeard]

MSD actually makes a cap with NO locating tab? Weird.