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How to find Top Dead Center and set your distributor and rotor when it has been out

01-13-2008, 11:56 PM
Here’s a how-to that will help you align your timing (distributor, rotor, No. 1 cyl. at Top Dead Center (TDC) on a 1997.

This will be most helpful when:

1) your distributor has been out it’s housing and it wasn’t marked properly for re-installation
2) you cranked your engine while the distributor was out
3) you think your distributor may have jumped a tooth

*Top Dead Center refers to when your No. #1 piston in the firing order is at the top of it’s compression stroke – when the piston is furthest from the crankshaft. http://en.wikipedia.org/wiki/Four-stroke_cycle


Disconnect negative battery cable. **This is not just a precaution. If this is not done, you might actually crank and start your engine manually when turning the crankshaft ---- very dangerous.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding015.jpg

For extra precaution, disconnect the ignition coil.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding016.jpg


In my case, I thought my distributor had jumped a tooth after replacing my lower intake manifold gasket (turns out it did, due to a loose hold-down bolt). I was determined to pull the distributor without taking off the air-intake and the whole top of the engine to access it.

It is possible. I was able to pull out and re-install my distributor with this special socket I made without removing all the stuff on top.

As you can see in the pictures below, there is not much clearance between the distributor housing and the hold-down bolt. To loosen and tighten the hold-down bolt, I made my own shortened socket by sanding down a sacrificial 10mm socket. See the pictures below.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding025-1.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding006.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding008.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding007.jpg


Now on to setting TDC ...

Looson wheel lugs on front drivers-side wheel. Jack up the left front of the truck. Remove wheel lugs and tire.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding026.jpg


Remove your #1 sparkplug (drivers side front-most plug). If your air intake is still on (like mine was), this is best done from the front wheel-well. Wobble extensions are extremely helpful here.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding017.jpg


Now, get under your truck and look at the harmonic balancer behind the crankshaft pulley. You should see two white marks. Both of these need to line up – on at about 4:00 o’clock on the balancer which lines up with on the plastic, and another one on top of the balancer at about 1:00 o’clock which lines up with a notch (see pictures).

Put a ratchet and socket on the crankshaft pulley and rotate the crankshaft to make them line up.

Now, the marks can be lined up and still be 180degrees off which means -- your truck still won’t go. Everything has to be lined up on the compression stroke. To do this, you’ll need to put your finger or thumb into the open No. #1 cylinder spark-plug hole while turning the crankshaft (an assistant can help but I was able to do this easily by myself). When you feel air coming out of the cylinder, that means it is on the compression stroke. At that point, you know you are on the compression stroke – begin to watch the marks and align them slowly.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding010.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding011.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding012.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding013.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding014.jpg


You are now at TDC. Time to line up the distributor shaft and rotor.

Here’s the distributor

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding001.jpg

Two small Torx screws hold the rotor to the distributor. This picture was taken on reassembly.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding020.jpg

The rotor only fits on one way. It’s not possible to attach the rotor 180degrees off. Here’s an underside picture of the rotor. Note the dimples next to the screw holes. They are displaced – one is closer to the screw-hole than the other. This is why it’s only possible to attach the rotor to the distributor in one way.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding009.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding009a.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding028.jpg

Step 7:

Now attach the rotor to the distributor and rotate to the number 6 which is embossed on the plastic distributor housing (there is a number 8 as well for eight-cylinders – us 4.3 guys want the 6 of course).

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding029.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding031.jpg

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding002.jpg

Here’s the 8 – don’t align with this though

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding030.jpg


Now you are at TDC, your rotor is attached to your distributor properly. Now, the trick is to slide the distributor back in (use a gasket if you have one) so that the hold-down bolt lines up and the rotor stays lined up with the number 6 embossed on the plastic distributor housing. If you don’t get it the first time, you’re probably off by just a few teeth – pull the distributor out and try again.

Here’s a picture of everything lined up.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding019.jpg


Re-install hold-down bolt

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding021.jpg

And distributor cap

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding022.jpg

STEP 10:

Now re-connect ignition wires. Note the order on the cap (3, 1, 5 front-to-back).

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding024.jpg

Reconnect the harness electrical connection on the distributor. Re-connect coil as well.

STEP 11:

Re-connect spark-plug and wire.

When I reconnected the spark plug, my socket got stuck on the tightened spark plug. I had to use a pair of channel locks to grab it and pull it out.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding018a.jpg

Next time I’ll use a longer socket that extends farther than the exhaust manifold heat sheild like this one on the left.

http://i23.photobucket.com/albums/b390/drdd/Jimmy%20Top%20Dead%20Center%20Distributor%20and%20 Rotor/Wedding023-1.jpg

STEP 12:

Put your tire back on. Re-connect your negative battery cable and you’re good to go.

01-14-2008, 06:42 AM
Excellent, Write up drdd... (Life Saving for some)
This should end up in the DIY Section...


01-14-2008, 10:06 AM
moving to FAQ section

05-08-2008, 10:17 AM
Great write up..
Thanks for taking the time to do it...
You & this thread just saved me a TON of $$$$$$$$$$$
I almost gave up hope on the Jimmy until I "Stummbled" on to this site!!!
Again Thankyou.. :biggrin:

10-29-2008, 02:55 PM
WOW, i can't tell you how much i appreciate this how -to!! You saved me a ton of hours and money! Tried it and got it the first try with your instruction...2 big thumbs way up!:iceslolan

04-24-2010, 10:39 PM
I just wanted to say thanks for the step by step and pics about the 4.3l dist. and timing. I have been working on my 02 chevy silverado 1500 for about a week trying to get it start after someone pulled the motor out and did not mark the dist. location after i rebuilt it and put it back in. Then i went to start it and nothing could not figure it out my book did not explain nothing about the #6 or #8 location on the dist. once i put it on the 6 cranked it over and it fired right up. So thanks again to see it help out so much. Thanks aging Tony Rogers Rochester Indiana

04-26-2010, 01:08 AM
glad the forum could help! it has def helped me. the guys on here are great!

09-19-2010, 01:42 PM
looks like this info will fix my '96. just curious why you have to pull the distributor all the way out? why not just lift it out of the cam gear, index it, and drop it back in? thanks for the info!

09-19-2010, 09:58 PM
looks like this info will fix my '96. just curious why you have to pull the distributor all the way out? why not just lift it out of the cam gear, index it, and drop it back in? thanks for the info!

Correct. No need to completely remove the dist.
With the cap off as it should be when sinking in the dist., the mark (6 pointer) is clearly evident when approaching the dist. on the passenger side (RH). Also, we need not be concerned of the exact rotative position of the distributor because of the simple fact that it does not rotate (while it is clamped, anyway). Note that the odd bank ign. wires are NOT in consecutive order although the even (RH) side is. (2,4,6,coil. & 3,1,5 for the LH bank) Vortec engines are nice servicing in my opinion. Unlike so many car makers, for the most part the design does include some provisions, with less pompous in opposing fact that will always apply which warrants that the vehicle actually might have to be worked on someday.

What an excellent post this is. Better than the premium content you have to pay money for. GREAT photography too. The poster is an asset to the site, irrefutably, if that is an example of his posts!

Best to all! - Pete

VEH: '10 -C6

09-12-2011, 01:40 AM
Hello All,

Does this procedure work on 1991 4.3l S10 Pickup?


09-12-2011, 04:33 PM
Hello All,

Does this procedure work on 1991 4.3l S10 Pickup?


No. This procedure is for the 4.3L 1996 and newer engines only.

1991 only has one timing mark on the damper. No need to remove the #1 plug on either engine, (The piston will push air out of the spark plug hole on both strokes when approaching TDC). When the TDC timing mark on the damper lines up with the index on the timing cover, #1 piston is at TDC. There are two ways to determine if you are at TDC of the compression stroke, (not exhaust stroke) on the 4.3L engine: One is to remove the driver side rocker arm cover and check that both valves for #1 cylinder are closed. The second is much easier and done by using a timing light after the distributor is installed. The rotor and distributor are different on the 1991, (no "6" or "8" on distributor housing). On your 1991, when the distributor is fully seated, the rotor must point to the #1 plug wire in the cap. Connect a timing light, disconnect the EST wire, and crank the engine. If the timing mark is visible while cranking, adjust the timing to spec and tighten the distributor hold down bolt. If the mark is not visible, the distributor was installed on the exhaust stroke and must be removed, the shaft rotated 180 degrees, and reinstalled, then check and adjust timing.

04-22-2012, 11:52 AM
thanks... workin' on my 97 s-10 i just bought a few months back for $700 w/ over 200k miles on it, and ran into just this problem... very helpful, though i wish the pictures were still available to aid even further in the trouble shooting... just a minor issue though, as the step by step was very clear and concise... thanks again.

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