Getting engine to TDC
 

Hi, working on 1997 Blazer 4x4 with a 4.3L Vortec. I was looking how to get to Top dead centre for #1. I read the timing thread as posted by the Administrator. The firing order is 165432. 1 & 4 are matched pairs. Could I spin the engine and watch the valves on number 4 or number 1 to see where I am at as far as TDC is? Will the marks on the crank pulley line up exactly like the above procedure would? Also are you able to use a timing light on this engine to fine tune the timing?
Thank you.

Did you remove the distributor at all? If you haven't you can rotate the engine until the rotor is pointing to the #1 plug and the timing marks on the balancer line up. You can also pull the plug and stick like a straw in the cylinder, rotate the engine and when the straw is coming up, and both valves are closed, you should be at TDC.

As far as a timing light goes, I have a 94 and with all the stuff in the way, it would be rough to see without getting hurt. This is one of the things I have yet to do to the little creampuff. I am going to line up the marks at TDC and just make some new reference points at a different location elsewhere on the balancer that I can readily see and use an inductive timing light (still on #1). It's all relative if you follow. I've done this before and haven't had any problems with it. Timing was dead on. My 84 Jimmy, 2.8 is pretty covered up and this is how I do it. As for finding #1 compression stroke TDC, I prefer the "pull the plug and check when the piston comes up" method. If you pop the distributor cap to discinnect the coil wire (inportant) you can hold your finger over the plug hole and you'll hear and feel when it's blowing air out. Now just line up your balancer marks and you can even double check by distributor rotor position. Of course you do have to have a manual that shows you where #1 position is on the distributor. It's really pretty easy stuff. There's always more ways to skin a cat.

No on a 97 you can not adjust the timing with a light. It only bolts down in one position. Unhook coil wire, take out plug one(front driver), put finger over hole. Then have someone bump the ignition till finger blows off hole, use a rachet on the alt. to line up timing marks. Then your at TDC #1 cylinder.

tdc
 

Yes the distributor is out & wasn't marked. I was thinking that the timing marks on the crank & enging cover as noted in the timing writeup should line up. Also check the valves on mated pair #4 to see when exh closes & intake is just about to open. Distibutor will only go in 1 way because of roll pin inside of base of shaft, or maybe 180 degrees from there. Could try long screwdriver to turn oil pump w ay down under where distributer mounts?

I agree you don't adjust timing with a light. You can check it though. Mine is set at "0" degrees with the "Set timing wire connection" disconnected. You can then check the timing and it should be at "0" (or TDC). My factory book describes this method and using an inductive timing light or one that goes between the spark plug and wire. Moot point here.
NOs has a problem. I don't know what the timing specs are for your engine. It should be on the emissions label on the radiator support. You indeed need to find #1 TDC by one of the previously described methods. I would almost bet that your label says to set at "0" (or TDC). If you haven't had the wires off the distributor cap then that gives you a heads up as to which post is #1. You have to realize that the distributor drives the oil pump from the cam gear. When you insert the distributor into it's location, if it doesn't line up then you're right about taking a long screwdriver ro rotate the oil pump shaft so the distributor will slide in. You should not have to force it. Bear in mind these are helical cut gears on the cam and the distributor so a little "Kentucky Windage" will be necessary because the distributor shaft will rotate a little when the gears mesh properly and what looks to be correct to start may not finish that way. The object here is ro get everything synced to #1. If you have removed the wires, then you need to find what post on the cap is #1, put a mark on the side of the distributor where that post is and your turn rotor to point to this and go from there. It's not really that hard. Distributors have been going in engines this way forever. Don't want to confuse you but this probably has happened to anyone who's pulled a distributor more than a few times or they're lying to you. Your distributor might bolt down one way but the principle is still the same. You gotta get the emgine at #1 TDC and the rotor pointed to the #1 post. My 94 doesn't. It still has a clamp. What good it does? I guess you could still rotate the distributor a little.

Gimpy you are odb1 he is odb2 there is no wire to unhook, and as far as pointing the rotor at the number on post that is wrong too. On a 96 and up there is a #6 on the dizzy housing that the rotor points at please make sure you know what you are talking about it is hard enough as a newbe without people confusing you more.

A screw driver should work to turn the oil pump but its gonna need to be a long one.

OK. I stand corected on the 96+. Yes it has to be a lomg one. I'm learning here too. When do we get the full scoop on timing this engine? I just learned that the rotor points to #6. I'm thinking of buying a 98 and like to know as much as possible.
Sorry if I steered you wrong NOs. Just trying to help.

Just to clarify, rotor DOES NOT point to #6 cylinder position in the cap on a 96+, it points to #1 position, but to show you where that is on a V-6 distributor, they molded into the plastic, a pointer, with a "6" cast into the housing. V-8 distributors have a pointer cast into the housing with a number "8" cast next to the pointer. But on our 4.3L engines, this position where the "6" and the little pointer triangle are, is pointing to the #1 electrode inside the cap. Just like it would on most cars that have a distributor.

The other clarification in case it wasn't clear before (was mentioned before). 96+ 4.3L timing is not user adjustable unless you reprogram the computer. The only purpose the sensor in the distributor serves is to provide a #1 reference to the PCM so that it can accurately fire the injectors in the proper order to the firing order, and it also helps the PCM's misfire detection, accurately determine which cylinder is firing at a given time. And once the CASE learn is performed, and if the timing chain stretches beyond spec, or jumps a tooth, then the index between the 2 sensors (crank and cam) will change and thus set the dreaded code P1345 which can help a tech determine that there is a major problem. The timing of the engine is all done by the crank sensor signal. The distributor only has to be close (+/- 2 deg) to provide this reference. The crank sensor is the one that has to be right on. The only other purpose the distributor serves is to distribute the spark to the correct plug wire.

I just wanted to clarify these things.

Now I wish somebody could clarify something for me. On my 96 Blazer 4.3, I put the engine to perfect TDC compression stroke #1 cylinder, and neither of the 2 timing marks on the balancer line up. Another guy on another forum said this same thing. He even showed a picture of this. He had a 4.3 Vortec motor with the head off clearly showing the piston at TDC on #1 and the balancer marks DO NOT line up. Some procedures I've read say to line the 1st mark to the line molded into the cover (approx 5-o-clock position), and the second mark (left of that), at the main marker at approx 1-o-clock position before setting-in the distributor. But if I do that, my motor is not to TDC yet. If I set it to perfect #1 TDC, the second mark (left) is at 5-o-clock position, and the 1st mark (clockwise from the first mark) is close (but not right-on) almost lined up to the crank sensor. I'm baffled, as I just replaced my disty gear, and shimmed up the end play, and I'm trying to figure out if I should index this thing based on the true TDC setting, or if I should line up the timing marks (1-o-clock, and 5-o-clock) positions. Like I said somebody else confirmed this on their 4.3, so I know my harmonic balancer (well, I think I know) it hasn't slipped. But I'm getting code 1345 even though it runs like a top.

By the way, here is the post I was referring to that shows the guy stating that at TDC the marks DO NOT line up.

This is also the case with my 96 4.3L, at TDC the marks are not near where people say they should be:

http://67-72chevytrucks.com/vboard/s...86&postcount=6

I don't know, maybe the balancer did slip on the outer ring? I found another posting here on this forum where it DID slip on somebody.

I think what I'm going to do is find TDC the same way when you degree-in a cam using the bolt in the spark plug hole, and you turn engine by hand until you stop against the bolt, make a mark on balancer, then turn the engine opposite way by hand until you lock against the bolt again, and then make another mark on balancer, then make a mark in the middle between those 2 marks. Then I will actually know exact TDC to a finer degree. Right now I'm just guessing perfect TDC since I just used a tool to feel the piston as I turned the engine by hand. But the concensus from all of the articles I've been reading are saying that it must be at TDC, so I'll just find TDC myself and be done with it I guess. Once I know TDC, setting the distributor is easy. I've done this 1000 times on other GM cars. If it still sets P1345 then I'll know I may need to set the cam retard and/or do a CASE relearn.

On the 96+ engines, just follow the timing procedure listed in the Tech Article (DIY) section and you will be all set. You need to be on the compression stroke for #1 (not TDC #1) and line up the two marks as shown. Then drop the distributor down in lining up the rotor with the molded in pointer in the distributor.