Removing Distributor - Why Needs to be at TDC?

[the-glove]

I'm going to be putting in new lower intake, upper intake, and valve cover gaskets. Because I'm removing the lower intake, I need to take out the dizzy. From surfing around for information on how to do this, most posts I've seen say to mark the rotor location on the lip of the distributor and also mark the shaft where it goes into the block so it all goes back in without messing with your timing. A lot of posts also say that you should find TDC of the #1 cylinder on compression stroke before doing all this. I'm trying to understand why you need to do this if you're already marking the rotor location and the distributor body location. Aren't those two marks what helps you get it back in correctly? What does having crankshaft at TDC do? Is it just another way to check it's going back in correctly because you're looking to see that the rotor is pointing at the #1 lead? But isn't that just the same as making a mark on the lip and aiming the rotor for that mark when putting back in? Can I just make the two marks and skip the TDC part?

Also, people warn against accidentally pulling up the oil pump shaft and dropping it into the oil pan when pulling out the dizzy. How do you avoid this? How do you tell if it is stuck to the dizzy gear? If you see it coming up, isn't it too late?

Thanks in advance!

 

[jckkys]

It makes the whole process easier and less likely to go badly if you get the crank and cam timed to TDC of cylinder #1's compression stroke. This should coincide with the rotor being pointed at the #1 post on the distributor cap. With no reason to turn the crank while the distributor is out, things should be right when you reinsert the distributor. The exception is the oil pump drive that usually needs the crank to be bumped a little, before the distributor fully seats. The same pump drive has a spring clip on it to keep it from coming out with the distributor. So you shouldn't have to worry about that.

 

[the-glove]

It makes the whole process easier and less likely to go badly if you get the crank and cam timed to TDC of cylinder #1's compression stroke. This should coincide with the rotor being pointed at the #1 post on the distributor cap. With no reason to turn the crank while the distributor is out, things should be right when you reinsert the distributor. The exception is the oil pump drive that usually needs the crank to be bumped a little, before the distributor fully seats. The same pump drive has a spring clip on it to keep it from coming out with the distributor. So you shouldn't have to worry about that.

Jckkys, when you bump the crank a bit to seat the dizzy onto the pump drive, won't that throw the alignment of your markings off? Sorry, this is the first time I've done this. Thanks.

 

[Steve83]

No, it will just move the marks temporarily. Their alignment will reappear, as soon as you bump the crank back to #1TDC. Click this & read the last section of the caption:

 

[blubuckaroo]

Unless you'll be rotating the crank before reassembly, putting the crank at TDC doesn't matter. Just make the marks and pull out the distributor.
When reinstalling the distributor, distributor shaft rotates when engaging the helical gears, so you'll have to lead that rotation a bit so your marks will line up.
The oil pump drive shaft may keep the distributor from dropping in all the way. Bump the starter while pressing down on the distributor housing and it will engage the oil pump shaft and drop down.

 

[Ourobos]

Use a ratchet to turn the engine on the balancer bolt, not a hit and miss engine bump.

 

[jckkys]

Sure you can just mark the direction of the rotor and replace the distributor in the same orientation. The use of TDC works when installing any distributor on any engine and takes only a few seconds. I've reoriented the distributor housing to get the vacuum advance in a better position to clear other components or simplify plug wire routing.

 

[brianstrange]

Don't be fooled by TDC, it happens twice every engine cycle. Although it's tricky, you can install an intake with the distributor in place. If you're not up to that task (risk of moving the gasket if not done perfectly) Just mark the base of the dist in two places, and find an alignment point between your rotor and a spot on your motor. Use a straight edge for exact placement. Don't touch the crank, and you should be good. Just line up as it was.

 

[brianstrange]

Sure you can just mark the direction of the rotor and replace the distributor in the same orientation. The use of TDC works when installing any distributor on any engine and takes only a few seconds. I've reoriented the distributor housing to get the vacuum advance in a better position to clear other components or simplify plug wire routing.

Some (or most) fuel injection distributors have a #1 specific firing position on the cap. I think it has more to do with telling the computer when to fire the injectors than spark plug firing. I've never had an issue, but some have said you can get a rough idle if they are off.

 

[the-glove]

Thanks for the input everyone.