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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: buddy84GMC on May 04, 2008, 07:20:48 pm
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I have been trying for a half hour to find TDC on my small block 400 and the rotor keeps pointing to the drivers side firewall and not cylinder 1 when the rotor points to 1. Any ideas on what may have happened or how to fix it. I am trying to replace my pick up coil and need the distributor off so I tried doing it right by finding TDC on cylinder 1 and its in the wrong direction. Is this an advance or retard problem? Truck ran fine for 2 years with this problem. Thanks
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Put your finger over the #1 hole to make sure it's on the compression stroke
Remember there are two tdc's on a 4 stroke
If the TDC is wrong
then fix it when you pull the dist (actually when you put it back in)
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Thanks. I have tried it numerous times each time it comes around knowing about 2 TDCs. Each time its pointing the wrong way. So I can pull it and be ok? I wanted to make marks so I know where to put it back in, but I should I just pull it and treat it like its a new distributor installation? Thanks
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Once your find your TDC make sure it aligns with the "O" on the timing tab or at least somewhere close
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If it was ok before, and you didn't pull the distributor recently, you may have othe issues. It is possible to install the distibutor 180 out. Now this comes to another issue. I may have missed it, but have you recently changed the plugs and wires? I had to help a friend of mine in a similar situation, he changed the cap and wires on his truck, and unknowingly, the previous owner installed the dist. 180 out, but instead of correcting the problem, they just rotated the wires on the cap. We moved the wires around the cap, and it fired right up. Now, I can't leave it at that, ( too picking) so we clocked the dist right and fixed the wiring right. If you have changed the wires lately, then just for a check, when you get the no.1 at what you know is TDC, the put the wires starting with one right there, and work around. This is just a test, so please if it works, fix it right. Now, if you haven't done anything, it just changed, you may have a bad timing chain, stripped distributor gear. Are you sure you are at no 1. Picture from the drivers seat facing to the front the rotor should point at the left front corner. Please dont take offense to this part, but even I have gotten messed up by having to work on the occasional Ford. Hope this helps. Sorry so long
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Start from scratch. tdcc #1 cyl point the rotor @#1 on the cap and rearrange your wires.
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If it was ok before, and you didn't pull the distributor recently, you may have othe issues. It is possible to install the distibutor 180 out. Now this comes to another issue. I may have missed it, but have you recently changed the plugs and wires? I had to help a friend of mine in a similar situation, he changed the cap and wires on his truck, and unknowingly, the previous owner installed the dist. 180 out, but instead of correcting the problem, they just rotated the wires on the cap. We moved the wires around the cap, and it fired right up. Now, I can't leave it at that, ( too picking) so we clocked the dist right and fixed the wiring right. If you have changed the wires lately, then just for a check, when you get the no.1 at what you know is TDC, the put the wires starting with one right there, and work around. This is just a test, so please if it works, fix it right. Now, if you haven't done anything, it just changed, you may have a bad timing chain, stripped distributor gear. Are you sure you are at no 1. Picture from the drivers seat facing to the front the rotor should point at the left front corner. Please dont take offense to this part, but even I have gotten messed up by having to work on the occasional Ford. Hope this helps. Sorry so long
Thanks. I have not changed the plugs and wires recently, but did about 2 years ago when I bought the truck and noticed this problem then. Had a friend come over and he got it running and the timing corrected. It does seem 180 degrees off and I never had the dist. pulled myself. TDC at cylinder 1 has the rotor aimed at the middle of the passenger's side and to the driver's seat as well on the next rotation to TDC at cylinder 1. I have cylinder 1 correct as the plug closest to the front bumper on the driver's side. That would put this thing at 180 degrees off. I remember it being like this 2 years ago when I tried to start the truck up for some reason the timing just was off completely after being parked and it ran fine. At the time I had changed plugs and wires and dist. cap. I know I had the wires hooked up right since I numbered them and had the firing order diagram. Thats when a friend came over and fixed the timing and advance, but has ran fine since then till now. I had no spark and found the pick up coil to be bad but wanted to take the dist out marking everything and then remembered my problem I have now. How can I take the dist out and reinstall without making a huge mess. I was told by Blue 82 to take it out when its at TDC and lined up at '0' but it does that 2 times...both incorrect so which one is the one to use. This is beginning to be a nightmare. Thanks
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If you were 180° off it wouldn't run. If you are 180° off yould be pointing at #6
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Start from scratch. tdcc #1 cyl point the rotor @#1 on the cap and rearrange your wires.
I understand what you are saying, but I have 2 TDCs and neither point to cylinder 1 when cylinder 1 is at TDC and the '0' on the tag lines up with the mark on the balancer. Should I loosen the dist. bolt and rotate the rotor to cylinder 1 while its at TDC then fix the wires?
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It will if you move the wires around. you want the one with the compression coming out of no.1, the look for th timing mark, but your balancer ring may have moved.
If you were 180° off it wouldn't run. If you are 180° off yould be pointing at #6
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If you were 180° off it wouldn't run. If you are 180° off yould be pointing at #6
It does aim for #6 and the oil sending unit behind #7 when the '0' lines up with the mark. It always has and did run! I have never messed with it except to adjust the timing that once 2 years ago.
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I think I would set it at no6 where you know it is tdc now, pull the distributor, and when it is put back in, point it in the right direction, and correct the wiring.
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I think I would set it at no6 where you know it is tdc now, pull the distributor, and when it is put back in, point it in the right direction, and correct the wiring.
I think I can do that without screwing it up. I understand how changing the wiring could make it run 180 off. I barely remember, but that may have been what we did to get it running. How it came off in the first place is a mystery to me. Thanks again
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TDCC means top dead center COMPRESSION. Then R&R the distributor and put it back in with the rotor pointing @#1 tdcc
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Another thing you should verify is TDC on your balancer is actually TDC. The outer part of the damper can spin on the elastomer.
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Another thing you should verify is TDC on your balancer is actually TDC. The outer part of the damper can spin on the elastomer.
Almost like it wore out or deteriorated. Whats the best way to check it?
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pull #1 spark plug and verify the piston is all the way up
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Another thing you should verify is TDC on your balancer is actually TDC. The outer part of the damper can spin on the elastomer.
Almost like it wore out or deteriorated. Whats the best way to check it?
Yep, I found out after much frustration that a "new" engine was about 6 degrees off. Sure fire way to make everything right is to remove the valve cover, find TDC by making sure #1 cylinder is at the bottom of the compresssion stroke (exhaust valve closed), line distributer up with #1 then check or remark timing on damper.
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Quote from Leevon
"find TDC by making sure #1 cylinder is at the bottom of the compresssion stroke (exhaust valve closed), line distributer up with #1 then check or remark timing on damper. "
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I believe the piston needs to be at the top of the compression stroke, with the exhaust valve closed. I.E. Top Dead Center Compression (TDCC
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Thank you guys. I need to know which rocker arm to watch on cylinder 1 when I pull the valve cover. There is info online, but I never believe it till I hear it from a real person. I need to spin the engine to get TDCC stoke. I know thats when the exhaust valve is shut, but wanted to know which valve on cylinder 1 that is? The one closest to the front of the engine or the second one. I may be able to see the smaller diameter rod for the exhaust but have not had the covers off in a while and cannot remember if its easy to see or not. Thanks
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Found my old photos from getting the heads rebuilt and the exhaust port is on the outside on both ends so that was easy even if the photo was upside down. Hope I can get this truck running.
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Make sure both valves are closed on number one to help verify tdcc #1
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Make sure both valves are closed on number one to help verify tdcc #1
Just to verify, both are closed when the valve springs are compressed (for cylinder 1)? I am 99% sure on that since I know how the engine works, but I am no pro mechanic; just need to make sure. Thanks a lot.
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Neither valve spring should be compressed. The end of the rocker that hits the valve, should be at the highest point of its travel.
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It is much easier to pull the plug on cylinder 1 and cover the hole with your thumb. When the engine is rotated (by hand), you will feel and hear the air being forced out past your thumb. Then slowly rotate the engine until the cylinder is at the top.
I guess if you want to watch the rockers, that's ok. Just seems like a lot of extra work to me.
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yep, and just look in the spark plug hole. You'll be able to see the piston at TDC
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It is much easier to pull the plug on cylinder 1 and cover the hole with your thumb. When the engine is rotated (by hand), you will feel and hear the air being forced out past your thumb. Then slowly rotate the engine until the cylinder is at the top.
I guess if you want to watch the rockers, that's ok. Just seems like a lot of extra work to me.
Thanks a lot. I know that works, but I am usually alone when working on this truck and turning the engine by hand and putting my finger over the spark plug hole is almost impossible on my truck! I do not want to take that cover off if I do not have to, but might if I do not get any help. My buddy is as busy as I am these days. Thanks again for all the help. Hopefully I can get to the truck within the next day or 2. If anything goes wrong after all this...I'll be back on here asking away! Dang rookies huh?!
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ok, an easy way I found, and im sure alot do it this way. Put a rachet on the damper bolt (i think its either 5/8 or 3/4) have all the plugs out since its easier to start from scratch. Rotate the engine with the ratchet till you feel and hear air com out of the #1 cylinder. I had no problem with mine with room. Hope this helps ;)
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If you routinely can't have a friend helping, Take an old sparkplug & break out the porcelain, get a round whistle & epoxy,glue, what have you, it into the base of the plug. When it stops whistling, look at the timing tab, your wanting to stop soon. As I mentioned in previous posts, I like to set the balancer on 8-10 BFTC & put the rotor on a line drawn on the distributor base in line with the #1 post. I feel this makes it easier to fire, then reach for the timing light & fine tune from there. To each his own. No real reason to take the valve cover off, it's just extra work, not that it's that hard to do, just not necessary for what you need to accomplish. Hope this helps, Lorne
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The dang thing was 180 degrees off so I fixed that reinstalling the dist. correctly. The new pick up coil is in and the old was badly deteriorated. The tape that holds the pick up wires was completely dried out and flaked off when I look at it crocked! Tested the old one and no reading either. Everything else looked great like the bearing and gear so I put it back in and ran out of time to give it a start and do the timing. All and all, the ESC was bypassed, new pick up, and corrected the distributor. heck of a project for a guy who had never done this before...but now I have and thanks for all the help! I make body parts from scratch pretty well, but when it comes to mechanics..I need help every now and again, but I always do it myself with help from people like you and friends of my fathers who have a lot of experience. I will post and success and if it still does not run...there will be a new post with this smiley all over it ???
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Got spark now..but no start. I have the coil cover off while trying to start and there is a blue spark right over the coil where the 2 wires are for the BAT and the other one. I looked for bad wires, all look good and I replaced a few just in case with some extra wires that were good as well. I held a screw driver up to distributor and had the other end on the intake and it did spark. Thats when I saw the blue spark on around the coil like its grounding out. Any ideas? Thanks
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How are you checking this? Do you have an HEI? If so the coil needs to be mounted on the carbon button and the coil housing needs to be grounded. the primary should receive b+ from the bat terminal and the - terminal is connected to the ignition module. Check for spark from one of your wires.
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I checked for spark from the wires and no arcing onto the block or headers where I tried. The coil is mounted on the button and it is grounded and hooked up correctly. The only thing I can think of right now is that the button is surrounded by that round rubber spacer with a hole in it to let the button through. The new coil cam with one and I used it but its a tad bit too small but from what I can see it still lets the spring loaded button touch the coil. I can check it and try the old one again if you think its not making contact. It is HEI by the way. Thanks and let me know if that button not making contact would cause a spark on top of the coil itself. I had the coil lid off to check so maybe it just arced off the nearest wire on the distibutor?
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I see it's already been discussed but I thought I'd add in about when my mechanic was doing my heads and cam I was talking to him about finding TDCC and he showed me an easy way to tell is to see that both rockers are in the up position (valves closed) and the rockers will wiggle a little as there will be no pressure on them. I thought that was kinda neat.