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.

So let me get this straight... You're saying that when you line up the marks, coming up on compression stroke, it is not on TDC? It is still before TDC at that point when the marks line up?

I just now found true TDC on my motor using the degree-in-a-cam technique, and then I set my distributor like we're supposed to, and now my P1345 code went away, and it runs really smooth, but it feels really soggy and has less power now. Should I just go by the marks and reset it?

Can somebody verify exactly where the #1 piston is when these marks are lined up as per the diagrams in the DIY tech article? I'm puzzled. I've set up quite a few V-8s and they are straight forward, but I don't know why these 4.3 Vortecs seem so much more complicated to me. I just need to know where the piston is supposed to be when the 2 marks are lined up, so that I can determine if my harmonic balancer ring has slipped or not, or if I sheared my crank key. It shows absolutely no signs of slipping at all on the ring though. Looks tight as can be, and is dry, with no oil or anything saturating it. I had this set up once before at the time I rebuilt the motor and had it all right (back then I also had to make some mark so I remember), but I just replaced the dist. gear this time around and shimmed up the endplay and put the thing back in on the same tooth, but the rotor was pointed slightly different. If I put it a tooth forward or backward, it is way off. I shimmed the endplay down to .015 inch from about .060 inch, and I figured this had something to do with why I had to elongate my holdown bolt-hole to get more movement so I could get my rotor to line up to the proper point with the '6' on it. And also, when I found the true TDC (verified it 3 different times), none of the marks on the balancer line up to anything. This is why I'm so puzzled. I don't have the scan tool to check the cam retard offset, so I have to figure this out the logical way.

I don't know, maybe the soggy feel it has now is because I need to do the CASE relearn procedure. ?

did you ever find a solution?

Well, I left it on TRUE TDC which is where none of the factory marks line up at all, and it ran fine, but felt soggy on acceleration, but no codes. After driving it around for awhile (didn't have time to mess with it after that), after more miles put on it, it seems the soggy feel just kind of faded away. It doesn't feel soggy any more, but I still would like to find somebody who has the proper scan tool so I can check the cam retard offset for real, because I would rather set it with that so I would know for sure how close it is. But it seems to run fine now. You know, with human perception, it is hard to tell if the soggy-ness fully went away or if I just got used to it. This is why I want to check it. But I just haven't had time to get back to it. I may just take it to a local shop and have them check it for me. I have made the distributor adjustable now, so setting it would only take them about 10 mins. But it does run fine on both the CNG and the gasoline, and there are no codes and it passes inspection anyways. I guess stay tuned for part B when I final DO get it checked.

I dont know if this helps or not, but i just worked on a 95 blazer, and judding off the back of the crank pulley was a little mound that indicated TDC, and slightly offset was another mark, to adjust the valves.

Wait this doesnt apply yours is a 96 sorry.

??? ojosch did not get an answer an i want to know also , what do you mean ? "You need to be on the compression stroke for #1 (not TDC #1) and line up the two marks as shown. " are you saying just be somewhaere on the compression stroke on the #1 and line up the marks ?

lined it up and it went right in this time but it wont land exactly on the 6 mark on the dist cup edge . very close but no fire . should i just ply with it ? maybe set it a hair before the mark ?

I think that is exactly what I said... What part wasn't clear? I have used that procedure a number of times and never had the trouble any of you are experiencing... Are you sure you are on the compression stroke? Have you tried rotating the crank a full turn and dropping the distributor in?

yes
 

yes i am sure its number 1 on the compression stroke set to the mark . went ahead and turn it back around one time on th eexhaust set to the mark and the dist wil not fall in all the way , it will ONLY go all the way in when im on compression and on the mark.

i notice the number 6 on the edge is past the #1 post in the cap . why set the rotar to a position past the post ? is this so it fires before tdc?


i also got it one gear back so it lands on the #1 post but that no good either , im %100 sure im doing everything as stated . im going to put a straw or something in #1 sparkplug hiole to see if the marks on the balancer are correct .


i have read a million discriptions and am confused about what mark some say is true

i see 2 grooves in the pully and i see a inverted V at about 1 oclock and a long narrow V at about 5 oclock on the case, when the second grooves lands on the 1 oclock the first lands on 5 oclock , correct ?

Well, I'm still not convinced that my harmonic balancer didn't shear the key, or that perhaps the new distributor gear I installed is indexed slightly different from the original (thus throwing off the distributor alignment). Or perhaps even that the machinist might have exchanged my crank without me knowing it, for a different one when I had mine in getting ground, and maybe had a different keyway position?

At any rate, what I wound up doing way back then was to ignore the marks on balancer, and I made a special bolt that would screw into the #1 spark plug (PLEASE DISABLE THE STARTER MOTOR BEFORE DOING THIS), and I manually with a wrench on the balancer, ran the piston up til it touched the bolt screwed into #1, then made mark on the balancer. Then you reverse, and turn the motor manually with a wrench backwards all the way around, until it again touches the bolt you have in #1 spark plug hole, and make another mark. Then make a 3rd mark exactly in between the other 2 marks, and that is calculated TDC. This spot should be fairly exact. Now, remove the bolt from #1 spark plug hole and put the spark plug back in.

Then line up the new TDC position you just calculated and then modify the distributor so it has more adjustment. I just drilled out the hole on the hold down bracket to a larger size and used a large flat-washer on the dist bolt so I could turn the distributor a bit. Then drop the distributor in and line up the arrows and lock down the bolt. If the distributor doesn't drop down all the way, it is because the oil pump drive shaft is not positioned in the correct spot to line up to the slotted fitting on the bottom of the distributor. You can either pull out the distributor and turn the oil pump shaft with a long flat-head screwdriver (trial and error, til it lines up and dist drops down), or you can bump the starter with a remote start switch until it drops in all the way, and then bump it back to TDC compression stroke and line the marks up again to verify that that your arrows indeed still line up in the distributor, and then lock it down.

It should start, run and be ok, but if it throws a code P1345 then simply adjust the distributor bits at a time, until it doesn't throw the code anymore and that should be within the tolerated spec. As far as I can tell, they designed it so that as long as it runs and does not throw the code 1345, then it is close enough for the computer to be able to adapt it in to run optimally.

I still never got around to manually checking the exact Cam Retard Offset spec, but since mine doesn't ever set the code 1345, and has adapted and seems to run fine, then I just kind of call it 'good' in my mind.

Edit: You probably don't even need to find TDC nearly this exact as I outlined above, as you could probably just have a friend poke the straw into the #1 spark plug hole and you can be underneath, turning the crank little bits, back and forth with a breaker bar on the crank nut until you find a rough TDC location (on compression stroke of course), and drop the dist in, enough to get it running, and then just adjust it so you don't get any codes.

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thanks for the help
 

ok well apon looking into #1 cylinder with my bore light i see the piston is at tdc and the markings on the pully are correct . when i drop in the dist. it lines up with the oil pump slot and fits in all the way , the rotor contact is on the forward edge of the 6 mark , there is a small box around the contact point of the rotor and it is within the box (if this means anything) but the following edge .as to my previous question the 6 mark is in front of the actual post to the #1 wire , and i assume this is so it fires a split sec before TDC ,

the instructions say within a degree or 2 and i am right on the forward edge of the 6 mark so i feel it is safe to say if the 6 mark is in front of the actual #1 cap post and if im landing on the front of the 6 then i am that mutch more early with the spark . givin issues like gear wear, timing chain wear and so on i am going to do the same and make the distributor clamp slightly adjustable so i can move the mark (and contact)forward and have the 6 be dead on with the rotor contact

ll bring photos if this works , this is probably what happens when you try and take the human factor out completely

someones going to get hurt
 

:icon_no: nope #1 tdc on the mark put the dist with the modified lock down on so the contact ws dead on instead of on the forward edge . and all i heard was one flame poof out the exhuast ? coil fires , timing is on, fuel pressure is there , IFL :icon_shrug: it should at least run crappy if im this close . but not one good fire ?

I'm tellin you, turn that crank both ways and 'feel' the piston with your straw trick and VERIFY that it is really at TDC when you do all this. It is not enough to just look at the piston because when I tried that way once, it looked all the way up when in fact it was not.

And if that don't work, then try lining up all the marks and drop the distributor in that way. Remember that there are 2 marks that are supposed to line up to 2 different reference points on the front cover. So if you are lining up the first mark on the right (of the balancer) to the first (and not the second mark) on the front cover then it is almost a quarter turn off, and needs to turn some more until the mark on the right (on the balancer) lines up to the second mark of the front cover (seen from down below).

Also, don't overlook the idea that the timing chain might've jumped and maybe it will never run like this.

i KNOW all this im using the second mark on the left with the top mark on the block and BOTH marks line up on the compression , HOW CAN THEY NOT ? even if it were a ass hair off from TDC front or back from TDC it would still fire . if the timing chain were jumped wouldnt the marks be off ?

The timing chain connects the crank to the cam and through the cam to the distributor. If the chain had jumped a tooth or more, the cam wouldn't be timed properly to the crank even though the distributor may be. The balancer would always line up regardless of the timing chain as it is connected to the crank. The only thing that would cause this to fall out of alignment would be a sheered key.

What have you been doing to make sure that you are on the compression stroke? Have you explored the possibility that you are 180* out (i.e. not on the compression stroke)?

Are you getting a spark?

false pressure reading ,
 

:icon_doh::icon_doh: ok well my pressure gauge was getting intermediate readings as i line dit up agains and shot air in the cylinder it gave back pressure last night and this morning i was going to have someone look at it to see if they saw something i missed so i lined it up and shot air in the hole and it went into the intake ??? WTF so i looked at the distributor it was on #4 so i shot air in the #4 spark plug hole and it was open too ?/ all i did know at this point was it wasnt running and both cylenders read open . so having nothing to loose and nowing it didnt runn with the distributor in this position i fliped it 180 ........:icon_eddie: running like new ... as i turn it off and turn around i smelt and saw a small cloud of smoke , so im guessing when i was cleaning the intake some gun k fell into the #1 (OF ALL PLACES) and was holding the valve from being totally closed and the it got burnt up when i put the dist in the TRUE position . i could have sworn i vacuumed all the intake ports before putting on the manifold . so all this becouse of a interment ant false compression :icon_wink: