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Discussion Starter · #1 ·
Ok. I made a big mistakee when replacing the head gaskets on my GMC Sierra. I Marked the distributor cap location, but did not mark the rotor location. (No laughing please)

How do I find TDC on this truck, without risking being 180 degs. off. If I am 180 degs off, I will have to take the upper manifold off to get at the distributor!

Chuck B.
 

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Do you still have a valve cover off? I usually just check to see that neither of the valves on the #1 cylinder are open, and stick a small dowel rod in the spark plug hole, or wait till my finger gets blown off.

As long as the damper is close to 0°and both valves on #1 are closed, you are at or very close to #1 TDC.
 

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What I did ( and this will only work if you have a cheater switch- I do not suggest trying this even with a friend you trust- just too dangerous) is to pull the cap off, locate #1 cylinder, hook up the cheater switch- this allows you to bump the motor over by youself so you can watch and make sure everything is clear of the belts(had a friend loose the tip of his finger when someone bumped the motor over that he was working on) Pull the spark plug from the #1 cylinder and either use a pressure gauge or your thumb- if you can get a good seal- and bump the motor until you feel/see pressure building up in that cylinder. Then you can take a light and look in the hole for the spark plug until you see the top of the piston. Then using a 1/2 socket and breaker bar you can turn the harmonic balancer until the piston is at the top. You will see it come up, stop, and then start to go down. Don't go too far or you'll have to bring the engine all the way around again. Once it's at the top- check your timing mark on the harmonic balancer to see if the line to set the timing with is near the tab. Then drop the distributor in, and button things up. Leave the distributor loose as you will have to tune it by hand to get it running and then time it with the light from there.

This has always worked for me- wyldman or Fred Pickering might have another better way- this is just how I've done it in my home garage.

Good luck!!

Bill
 

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I am not too sure which engine you have, but assume it is a V-8.

You can pull a valve cover, off and watch the valves come to the compression stroke as you turn the engine by hand... You will need a helper to do this....

Who ever is turning the engine would have a hard time watching.

The helper could place a finger in the #1 plug hole as well and feel compression begin..

You would look for the intake rocker to go down and return upwards and then look to the harmonic balancer (pully where the mark is)

At TDC then you would use a screw driver to aling the oil pump drive to the tab on the dist.

IF for some reason you had the gear off the dist.. be certain it is on the right way... It can get upside down easily enough, and will pop up and out of the cam gear if installed wrong while you are driving! Don't ask how I know, as that is not a pretty story....LOL

A 1 man method is harder but possible. Turn the engine with a screw driver in #1, and watch for it to be as high up in the hole as is possible.. You then are either at TDC or 180 out... But you can tell by the valves... It is harder....

IF you happen to have air you might tell by hooking air to the compression tester something like a leakdown tester does, and if you hear lots of air rushing thru the exhaust you would be 180 out.

Another method might be with a jumper at the starter and you can blip the engine over with your finger blocking the # 1 hole..

With paint marks at TDC you can miss a few times and still tell you missed, and then finding where you are that way and get to # 1.. So one of those ways should work... Mac
 

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start by marking 0° on the harmonic balancer,

remove #1 spark plug and with finger over the hole, tap the engine over until you feel compression blow past, while watching where your mark is. (tap slowly, so your mark doesnt go flying past).

then just turn the engine over by hand, aligning your mark with zero

just be carefull, and stop when you first feel the compression, then do the rest by hand
 

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If you want to find exact TDC(because the 0 on the balancer can be off) you must use a piston stop. Screw this deal into the head and rotate the motor by HAND dont use the starter!!! When it comes to a stop make a mark on the balancer. Now turn it the other way and make a mark. Split the difference between the 2 and you have your real 0. This is helpfull if you think you have a balancer that sliped or the like or you just think the factory 0 is off(is alot of times)

The finger over the hole is a way to do it also that works well to make sure you are on the up stroke and gets you close enough for most stuff.

Make sure you dont have a hot ign, you dont want it firing on you!
 

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Discussion Starter · #8 ·
Ok here is what I did, tell me if this will work.

I can't get my finger in to the #1 spark plug hole, there is not enough room. So I had one person looking at the valves, to see when both came up(closed). Also had someone else watching the 'O' mark on the harmonic balancer, while I cranked the motor by hand.

When both the intake and exhaust valves came up, the mark at the balancer was a 0. I am assuming this is TDC.

Chuck B.
 

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Gotta make sure it was the intake that just closed.Rotate the engine,and watch both valves.The exhaust should open and close,followed by the intake.After the intake closes,then rotate the engine around till the marks line up.

Never hurts to double check it.
 

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Discussion Starter · #10 ·
How do I determine which one is the exhaust/intake?

Thanks in advance!

Chuck B.
 

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Discussion Starter · #11 ·
Using common sense, I should just look at the ports going to the manifold. Those should be the intake ports. So the other is the exhaust. So they intake/exhaust locations alternate for each cylinder.


Chuck B.
 

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If you have a 2 piece comp tester install the first pice and feel or have someone listen for a slight distance.. Might even install the gauge and watch it read a bit.. Don't expect to see full compression turning the engine by hand..

Yes the intake and exhaust ports line up directly to the ports respectivly.

Your term "come up" bothers me as there is slack at the rockers when the valves are closed..

Mr. Wyldman has show a good way to read the rockers, which I can't improve on.

Since the timing marks can only line up 2 times, giving you only a 50/50 chance to be wrong, or correct, maybe having the other valve cover off would be a help.

Once you are there with the crank, and the cam, the valves should be equally slack at #1.

Then with some head banging you need to aline the oil pump drive slot. That is off set, but can be very hard to see and tell which is the off set.

Once the dist is dropped in and IS seated fully down, swing the dist fully side to side, as being 1 tooth off can run the engine but limit the adjustability range due to crowed other parts and brakets. Be sure you are in a range of swing where the rotor will line up with the cap eletrode, and have some room for adjuments.

At times it can appera correct, but as the dist gear winds into the cam gear, the off set screw slot can move, or you can set up the slot so the dist tab will not enter. It can take a few tries to get it right, and this is not a place to call it good enough for Govt work..

I find it most frustrating to have discovered someone has done this very thing and have a running engine which you can not dial in because the dist jams into some other non- related part. Mac
 

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Discussion Starter · #13 ·
Now that I know which valve is which, here is what I did to find to TDC. I cranked the motor by hand and the exhaust valve moved, up and down, slightly. Then the intake valve moved, up and down, with full range of motion. When the intake hit the vary top of its range the harmonic balancer mark was at '0'.

Chuck B.
 

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It should be almost 180 degrees (one half turn of the balancer) from the time the intake closes to TDC.

The valves are arranged like this.

E-I-I-E-E-I-I-E

if you want to make sure,turn the engine backwards 180 degress or one half turn,and install the number one plug.Now rotate it back in the normak direction to TDC.You should feel the compression,and it will be much harder to turn.If it is,you have it on the compression stroke,just like up TDC,and your done.
 

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But isn't this a Big Block Chevy?

E-I-E-I-E-I-E-I [OH, Old MacDon...]

Wouldn't that be the valve arrangement for a BBC?
 

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I think your right,it is a BBC,if it's the same one he was doing the intake gaskets on.

If that is the case,then the valve arrangement is different.

Drivers side - front to back

E-I-E-I-E-I-E-I

Pass side - front to back

I-E-I-E-I-E-I-E
 

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Discussion Starter · #17 ·
Thanks again. - Next time I am taking it to one of you guys to fix!:D

The return fuel line would not line up so I cut it with a hack saw. I picked up some Fuel injection hose and 4 clamps to re-assemble it. The hose would not bend enough to fit properly, so I had to cut the return line past the downward bend. I could not get my small hack saw in to any position to cut the line. So I used my dremel to cut it. In the process I cut the fuel line and 3 wires that lead into the block. Time to crimp wires in an area not larger that 7" wide. What a pain in my [email protected]$%^&*(ss. :D

Chuck B.

For laughs when I cut the return line, there was almost no movement in this line. It would hardly budge, so it didn't line up correctly. I came back to the garage to work on it a couple of days later, after I cut it, and it moved about freely without any problems. The line must have been frozen to the trans or block.

:mad:
 

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Discussion Starter · #18 ·
At last I got this beast running! Had nothing but problems while putting it back together. One question, do I need to set the timing on this truck? A sticker on the truck says it is self adjusted timing. But does this hold true if i take the distributor out?

Once again I would like to thank everyone for their help, in getting this truck back to working order!

Chuck B.:rockonn
 

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You need a scan tool to set it.I think you have one don't you ?

Look for the "Cam Retard Offset" value.If it's zero,your good to go,and don't need to do anything else.

If it's off,you need to rotate the distributor to get it to zero.

Turn it clockwise to decrease,counter clockwise to increase (if it's negative)

You must rev the engine when checking it,over 1000 RPM,or the offset retard value will not be accurate.
 

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Discussion Starter · #20 ·
I do have a Snap-on microscan, but I do not think it has cam retard offset value! If it did, it would be listed in the View Data section. The only thing I get pertaining to Timing is the timing advance data which reads 25.5 degs at 1000 RPM. I think I bought the wrong Scan tool - this one really does not do much more than my MultimeterPlus, besides reading codes. What good is reading codes if you cant diagnose the problem from there. Maybee I will trade it back in for the full set-up!

Here is my newest problem. Truck started fine on the first start up. I let it get warm, then put the motor through higher RPM ranges. No problems, then I go to check the timing, as discribed in the above post, and learn that I can't do it with a timing light. I had turned the distributor a little bit to see if the timing mark on the harmonic balancer would move closer to the 0 mark. It did not appear to move at all, so that is when I posted about how to set timing for this truck. When I turned the distributor the first time, I noticed I did not plug in the connector that goes into the distributor, so I connected it then. (Basically after the truck had warmed up for 20 min.)

Note: all this time with me starting the truck up more that 5 times, and letting it run, and raising the RPM's, the check engine light did not come on.

Then I went back outside to hook up my MicroScan tool, to check the cam retard offset. I started the truck up, it started fine. I proceeded to look for the cam retard offset but could not find it. While searching, I found the timing advance, it was reading 26 deg. at 1000 RPM roughly. So I thought I would turn the distributor a little to see if I could get the timing advance to move. I moved the distributor a couple of times, then the engine light came on. I checked the code, and it said see manufactures manual, or something like that. The code did have a number, but did not describe the problem, like 02, or ECM, or TPS, etc.

Then I put the distributor back in the same spot I originally had it, and started the truck again. It started ok, and I proceeded to rev. the engine. After that the engine died out, and it will not start. I can keep it running for a couple of seconds if I play with the gas peadel a little bit. But it dies as soon as I let off the gas.

Help!!!!!!!!!!!:huh :huh

Chuck B.

P.S. - Could I have fouled out the spark plugs by playing with the distributor? - Thats the only thing I can think of.
 
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