need a little help with locating tdc

[chris_8222]

i have a 95 lumina with a 3.1L engine i replaced the timing chain and am having a hard time finding tdc.do i just bring the number one cylinder all the way up?i was told that it may have to be turned until the number one has gone all the way down and back.is this true?to many people telling me how to do this.can someone tell me the proper way?

[jeffcoslacker]

If you can't find a mark and have to static time like you said, you need #1 piston at the top with both valves closed (compression stroke), because at TDC on exhaust stroke the exhaust valve is open, and you'd be 180 degrees out of time. that's where the twice around comes in...the crank goes around twice for one complete cycle, coming to TDC twice, once on compression, and then at exhaust stroke.

I guess the chain is off and you are just looking to set the crank, you have located a mark on the cam? If so, and you are just looking to set the crank to TDC with no chain on, then just bring #1 to TDC, forget the other stuff.

Did the old chain slip or break?

[chris_8222]

Originally Posted by jeffcoslacker

If you can't find a mark and have to static time like you said, you need #1 piston at the top with both valves closed (compression stroke), because at TDC on exhaust stroke the exhaust valve is open, and you'd be 180 degrees out of time. that's where the twice around comes in...the crank goes around twice for one complete cycle, coming to TDC twice, once on compression, and then at exhaust stroke.

I guess the chain is off and you are just looking to set the crank, you have located a mark on the cam? If so, and you are just looking to set the crank to TDC with no chain on, then just bring #1 to TDC, forget the other stuff.

Did the old chain slip or break?

the old chain slipped.so how should i find tdc?also how can i tell if both valves are closed?would the car still run if it was at tdc on the exaust stroke?if so what would happen to the engine(any damage)?

[john51md]

Originally Posted by chris_8222

the old chain slipped.so how should i find tdc?also how can i tell if both valves are closed?would the car still run if it was at tdc on the exaust stroke?if so what would happen to the engine(any damage)?

They make TDC finders that screw into spark plug hole on No.1 cylinder, if you could get one of those its easy, you screw it in, turn engine by hand till piston contacts the finder, and you put a mark on the damper wheel, then you turn engine the oppsite direction till piston hits finder again, put another mark on the wheel, TDC is mid way between these 2 marks.
I like this way as you can use any point on the wheel to do it as long as you have/make/use a stationary reference point becuase faCTORY reference points arent always easy to see.
Heck, you can put it on the bottom of the wheel if you want.
This may be confusing to someone who has never done it tho.

[jeffcoslacker]

You have me confused as to what you are trying to do. You said you put the chain on...but you are trying to find TDC...you have to find TDC and get the timing right BEFORE putting the chain on...so if you slipped you have to bring the cam and crank to proper positions before putting a new chain on, right?

You won't hurt it with incorrect valve timing, it won't crunch like some motors...but it won't run either.

Are you using a manual that tells what reference marks you are looking for on the gears?

[jeffcoslacker]

Here is the timing marks on the 3.1...align them as shown, that all you need to do.

[jeffcoslacker]

Notice it is the mark, not the keyway on the crank gear that indicates TDC...and you look through the hole in the cam sprocket for the timing mark on the block...

With the chain on, if the marks are still aligned, you're set...

[chris_8222]

Originally Posted by jeffcoslacker

Notice it is the mark, not the keyway on the crank gear that indicates TDC...and you look through the hole in the cam sprocket for the timing mark on the block...

With the chain on, if the marks are still aligned, you're set...

i have run into a problem.i can only turn the crankshaft about 1/4 of a turn then it will not go anymore.is this a crank problem or a timing issue?i even had someone else try to turn the crank and he couldnt do it either.i can see that the mark is not lined up but cant line it up because the crank wont turn.could this be something inside the engine that is broken?

[jeffcoslacker]

1. Did the starter turn the motor over or not after this happened?

2. What are you using to turn the crank?

If the chain is still off, try rotating the cam a bit and see if anything changes. Like I said, this motor isn't supposed to interfere. If it is, something else has gone wrong inside.

Give me a little background on how this started and what happened and what led you to the timing chain.

You're starting to scare me, wondering if something came apart and jammed and stripped the timing set...maybe the chain problem is symptomatic of something else that came unglued inside it...

Gotta know if it cranked by starter after whatever happened. Was the car running down the road when it failed, or idling, or just wouldn't start one day, or what?

[chris_8222]

Originally Posted by jeffcoslacker

1. Did the starter turn the motor over or not after this happened?

2. What are you using to turn the crank?

If the chain is still off, try rotating the cam a bit and see if anything changes. Like I said, this motor isn't supposed to interfere. If it is, something else has gone wrong inside.

Give me a little background on how this started and what happened and what led you to the timing chain.

You're starting to scare me, wondering if something came apart and jammed and stripped the timing set...maybe the chain problem is symptomatic of something else that came unglued inside it...

Gotta know if it cranked by starter after whatever happened. Was the car running down the road when it failed, or idling, or just wouldn't start one day, or what?

the car was running down the road and then it just died.what made me think timing was my buick did the same thing and the timing chain had broke.i still have the chain off and yes the engine did turn after this problem.i am using the bolt and a wrench to turn the crank.i think you may be right about something else breaking inside because it will only turn so far and then stop.i have tried moving the cam and still nothing.what else could have broken and how can i find out?

[Blue Bowtie]

Only Superman can turn a camshaft by the snout once the valve springs are installed. You can "cheat" by installing the old cam sprocket and using a strap wrench or large pair of Chan-Nel-Lock pliers (like #460s) to turn the cam into position. If you cannot turn the cam with a strap wrench on the cam sprocket (it's still going to require some effort to fight the valve springs), something may be wrong in the valve train or oil pump.

Don't ever use the balancer bolt to turn a crankshaft. I know there are a thousand of you out there who will reply "I've done it a hundred times..." but I've never broken a bolt in the crank snout by using a crank socket. The only way to break that bolt is to turn the crank with it. Then again, when you pull the crank to get the bolt out, you'll find out whether there is some other interference problem, I suppose. Use a crank socket or install the old sprocket and use pliers.

HINT: It helps to remove the spark plugs so you're not fighting compression and vacuum. Remember - The VALVES are not opening. That may be what is preventing turning the crank right now.

Since it's a wrong-wheel-drive, using a flywheel tool to turn it is probably out of the question.

You're making this more difficult than is has to be. Just get the crank sprocket marker pointed in the right direction, and turn the cam sprocket to align with it, Forget about finding TDC any other way. You cannot look at the valves because they won't move WITHOUT A TIMING CHAIN installed. Besides, it doesn't matter anyway. Just install the chain set dot-to-dot and forget it. If it looks wrong, turn the crank one more revolution and it will look perfect. And it really just doesn't matter because there is a CAM POSITION SENSOR to determine which half of the phase the cam is in at any given time. There is no distributor, so forget about getting the cam "in phase" by worrying about compression stroke.

[Blue Bowtie]

BTW - Not to pick nits, but are there ANY punctuation keys on your iPhone keypad? Your posts are difficult for us old farts to read when done in "text message" style, fwiw & imho.

[jeffcoslacker]

Originally Posted by Blue Bowtie

And it really just doesn't matter because there is a CAM POSITION SENSOR to determine which half of the phase the cam is in at any given time. There is no distributor, so forget about getting the cam "in phase" by worrying about compression stroke.

Forgot about that...that's been part of doing this for so long it didn't even occurr to me.

Even with the valve train not moving, it shouldn't prevent him from being able to turn the crank...I can't believe it has THAT much compression...'specially with the miles we're talking, but taking the plugs out has gotta help....coulda spun a cam bearing and welded itself up or something...

Was there any evidence of sudden trauma in there? When something catastrophic happens, you'll find teeth stripped off and galled up chain links...when they slip from wear they are evenly worn with no large debris found in there...the sprocket just has rounded nubs where teeth used to be...

It's hard to rotate the cam, like he said. I've used a method that's a bit hard to explain, but involves putting your breaker bar's socket through one hole in the sprocket, and using a second socket and extension into one of the other holes to lever against...still requires some strength. The cam's movement is very notchy, it springs from one position to the next as you fight the valve springs...

[chris_8222]

Originally Posted by jeffcoslacker

Forgot about that...that's been part of doing this for so long it didn't even occurr to me.

Even with the valve train not moving, it shouldn't prevent him from being able to turn the crank...I can't believe it has THAT much compression...'specially with the miles we're talking, but taking the plugs out has gotta help....coulda spun a cam bearing and welded itself up or something...

Was there any evidence of sudden trauma in there? When something catastrophic happens, you'll find teeth stripped off and galled up chain links...when they slip from wear they are evenly worn with no large debris found in there...the sprocket just has rounded nubs where teeth used to be...

It's hard to rotate the cam, like he said. I've used a method that's a bit hard to explain, but involves putting your breaker bar's socket through one hole in the sprocket, and using a second socket and extension into one of the other holes to lever against...still requires some strength. The cam's movement is very notchy, it springs from one position to the next as you fight the valve springs...

i have the camshaft lined up where i want it but even with two plugs out the crankshaft will still not turn.should i try taking out all the plugs and see if that helps?someone told me to line up the cam with the crank the way it is now but im unsure if that will work.

[jeffcoslacker]

No that won't work...the cam and crank go around at different speeds (thus different gear sizes) so you could never guesstimate the degree of the crank to cam correctly and be precise....you'd end up a tooth or to off and it wouldn't run, or run like crap..

Take the other plugs out, it's gotta make it easier. You try bumping the starter and see if the crank will move?