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914World.com _ 914World Garage _ How to determine EXACTLY where TDC is?
Posted by: Jeff Bowlsby May 2 2010, 10:34 AM
Eyeballing alignment of the rotor to the tick mark on the dizzy body seems so imprecise...for adjusting valves. Is there a method of locating TDC for each cyl PRECISELY?
1. I thought about making some kind of rotor replacement device with a pointer that could extend down close to the tick mark, but thats only good for cyl 1. All cylinders needed.
2. I thought about making a special trigger point plug adapter with three long wires, and attaching it to me DVM on the buzzer setting. When the trigger points would make contact, then that would indicate...? I am not sure that the trigger points make contact at TDC, I think it is at some different point in the cycle.
Any time proven methods?
Posted by: Tom May 2 2010, 11:02 AM
Jeff,
From reading posts on here, it seems to be more important to adjust the valves based on the rocking method described by the Cap'n. Piston position would not be as important as adjusting the valve opposite the rockin' valve ( on the circle of the cam). Am I misreading something here?
Tom
Posted by: Vacca Rabite May 2 2010, 11:06 AM
Toms right. Due to the cam layout of our cars (the same cam lobe works both sides of the motor) if the opposing lifter is in at all, you know that the one you are looking at is ready to be adjusted. All you need to know is the pattern - which can be found here all over the place after a brief search.
But, if you really much know TDC, put a straw down the spark plug hole, and watch it, As the piston comes up it will move the straw. This is easiest to do with two people. One to turn the motor, one to feel the straw. Just remember that the motor comes to the top of its travel 2X per cycle, and only one of them is TDC. You are at TDC when the piston is at the top AND both valves are closed.
Zach
Posted by: Gint May 2 2010, 11:16 AM
No it isn't more important to do it that way. Krusty's method works fine and a lot of people prefer it, but it's just a different way of getting the same job done.
As for the original question, chopsticks would work great. 
Kidding Jeff...
Really, the distributor mark only gets you close. And depending on how much advance you've dialed in, that mark is going vary.
To find #1 TDC I've always done this: Put the rotor on the dizzy mark and then rock a raised wheel wheel with the transaxle in 5th to find either the TDC mark on the fan or the flywheel (I marked my flywheel so I can see it in the engine compartment). Then I go down and verify that the valves for #1 cylinder are both closed. To further verify I can then rock that same wheel to turn the motor and watch the valves open and close. From there you can just move along in the firing order for the remaining cylinders.
Now that I've done that once for the first time on my 914, I marked my flywheel so I can see it underneath the car also. This makes the entire valve adjustment process very easy and once I've set #1 I don't have to get back up from underneath the car.
I would think your idea would also be somewhat varied based on ignition timing, but then I'm no D-Jet expert so I don't know when exactly those points are closed. I'm sure an expert will pop up shortly...
Posted by: McMark May 2 2010, 11:35 AM
On a running car you can use the rotor to determine you're close to #1 TDC or #3 TDC. Once you're close to #1 TDC you need to look into the inspection hole in the fan housing for the 0* timing mark.
The 'notch' on the distributor is more for getting the static timing close when you're installing a new distributor or have otherwise 'lost' your timing settings.
Posted by: URY914 May 2 2010, 02:12 PM
I found this picture somewhere and thought someone would need it.
Posted by: r_towle May 2 2010, 05:19 PM
Jeff, I can get you onto two.
Via the timing hole in the fan housing, you see the notch at #1 TDC
Crawl underneath and mark the lower window at the flywheel to mark number 3...
Then, if your so inclined...remove the engine and divide the two marks to get two more...
Rich
Posted by: ClayPerrine May 2 2010, 05:41 PM
Just do this the easy way.....
Take off BOTH valve covers. Hook up a remote starter switch. Look at the valves for #2 (front left cylinder). Bump the engine until the exhaust valve opens. Because the engine only has 4 cam lobes, the exhaust valve on #4 will be on the base circle, ready to be adjusted. Adjust that one, and bump the engine until the intake valve on #2 opens, then adjust the intake valve on #4. Bump it again and the intake on #1 will open, so adjust the intake valve on #3. Bump it again until the exhaust valve on #1 opens, and adjust the exhaust valve on #3.
Now repeat front to back on the other side.
It is simple, and it works every time.
Posted by: Dave_Darling May 2 2010, 10:28 PM
Then, if your so inclined...remove the engine and divide the two marks to get two more...
Nope, the crank goes through TWO rotations when the cam (and distributor) go through one. So the two marks on the flywheel or fan are all you need, one of them will always be TDC for both #1 and #3, the other will be TDC for #2 and #4.
BTW, it appears that the fans can be off slightly from example to example. The ignition Tech Article on Pelican's site shows two fans that are slightly off from each other. I would trust the flywheel mark before the fan markings.
But it isn't generally necessary to be right exactly on TDC when you're using the TDC method for valve adjusting. And it isn't necessary at all if you use the opposite-rocking method...
--DD
Posted by: McMark May 2 2010, 10:35 PM
Okay, since Dave upped the ante: 
You should confirm the zero TDC mark by pulling a spark plug and looking into the cylinder with a flash light. You can see the piston as it moves up the cylinder and can visually identify TDC. Then check your fan to make sure the TDC mark corresponds. THEN you can move on. 
Posted by: avidfanjpl May 2 2010, 10:36 PM
And my 2.0 is so early an engine it has a red mark at 27 BTDC and a white mark at TDC, but putting the rotor to the dizzy mark was AFTER I got to TDC by putting it into 5th gear and pushing the car in my very long garage till I saw the red line.
No 0 on my fan wheel, so early ones seem to fall into the Haynes description for the 1.7 engine.
Weird but true.
J
Posted by: Cap'n Krusty May 2 2010, 10:40 PM
Unless you have a VERY unusual fan, there's always a TDC mark, IIRC. The Cap'n
Posted by: charliew May 3 2010, 10:28 AM
My experience is with t1 bugs. It was always real easy to just pop the valve covers with the car up on jack stands a little and jam one wheel so it couldn't turn and put it in high gear. Then you could just turn the wheel as much as you want to determine the base circle of the cam on each cylinder. You don't have to roll all around under the car jumping back and forth between cylinders and maybe forget where you were in the process. The bug was so easy to rotate the starter deal was too hard for me to try and be precise with. You also get used to hearing the compression leaking past the rings as it comes on tdc. THe rocking back and forth to get centered was always easy to do. It's kinda wierd how some things are still the same after 40 years.
Oh yeah, EXACTLY means using a indicator on the piston and moving the piston either back and forth, or actually up and down, to get the exact center of the arc of the crank or running the piston up toward tdc to maybe within 20 degrees, and measuring that point with a dial indicator, marking the pulley, then going on toward down till the same amount that was on the dial indicator before, is reached, marking the pulley, then dividing the two marks on the pulley, and that would be EXACTLY tdc of the piston, or the center of the arc of the crank. But actually that is not the center of the low or base circle on the cam lobes.
Posted by: JRust May 9 2010, 10:49 PM
So when you have top dead center on #1 & have the mark showing in the hole on the fan housing. What is next? Is the rotor supposed to pointing at #1? Or am I confusing that with something else? I'm a little lost on getting my distributor in the right spot. Mine was off a 1/4 turn on my rebuild. My guy had the timing set cold supposedly 
. I'm trying to get my head wrapped around this but struggling 
Posted by: ConeDodger May 9 2010, 10:55 PM
Okay, since Dave upped the ante:
You should confirm the zero TDC mark by pulling a spark plug and looking into the cylinder with a flash light. You can see the piston as it moves up the cylinder and can visually identify TDC. Then check your fan to make sure the TDC mark corresponds. THEN you can move on.
Or, better still - buy or borrow a bore-scope.
Posted by: McMark May 9 2010, 11:01 PM
Yup, when the #1 cylinder at TDC on the compression stroke (both valves closed) the direction the rotor is pointing should be the spark plug wire that goes to Cyl #1 spark plug.
Posted by: JRust May 9 2010, 11:34 PM
Okay here are a couple pics. I believe I am at TDC center. My fan was painted & I am pretty sure this is the mark. I have #1 at TDC using a staw as my guide while looking through the hole in the fan housing. But my rotor is pointing towards the hole
Attached image(s)
Posted by: avidfanjpl May 9 2010, 11:42 PM
Just went through this too. Steve Gaglione set me straight. The rotor must be pointing at #1 when it is tdc, and from there tighten the dizzy when the rotor lines up to the mark on the dizzy, but not too tight. From there, check that the points are at .017 (I had to back up about 5 feet to see the rotor line up with the dizzy mark, but it is possible without removing the engine deck lid.
Then get a dwell meter to read 44-45 degrees and you are ready to start the car and rev it to 3500 rpm, which when at that rpm (use a combo dwell/tach meter set to tach, and if it is a modern one, you have to double the V8 reading, because there are only OLD dwell meters that show 4 cylinder dwell) and turn the dizzy slowly till you get to -27 btdc. If you have the red mark on the fan, you will see it march right to the notch at 3500 rpm, and you will be done!
It was a thing of beauty, as I had the red and white marks on my 2.0, not a zero, so if you have only a zero, you need better directions than I have here.
I ended up marching the dizzy right back to the same grease pencil marking I had noted on the dizzy and the oil neck/vacuum screw lineup BEFORE I changed the points, plugs, condenser and trigger points, so there is some justice in the 914 world of self-adjustment
Good luck. If I can do it, anyone can. I spent years letting others do all the dirty work.
Now I have skinned knuckles and I know more than I should, so splitting another crankcase can't be far off!
John
Posted by: realred914 May 10 2010, 08:29 AM
On a running car you can use the rotor to determine you're close to #1 TDC or #3 TDC. Once you're close to #1 TDC you need to look into the inspection hole in the fan housing for the 0* timing mark.
The 'notch' on the distributor is more for getting the static timing close when you're installing a new distributor or have otherwise 'lost' your timing settings.
how can you view the rotor when teh car is running? clear cap?
Posted by: realred914 May 10 2010, 08:34 AM
for adjusting valves you dont need to be very percise on the cam location, so long as your lifter is off the lobe, your ok to make a valve adjust. near half the cams rotation is over a no lobe zone, for any given valve, so you have nearly +/- 90 degree of cam rotation tolerance for your valve adjustment location. (atcually it may be a little less than 90 degrees due to the width of the lifter) but at anyrate there is a big zone of cam rotation that is acceptable for valve adjustment locations
Using the rotor to eyeball it is close enough in most cases.
Posted by: JRust May 10 2010, 08:36 AM
how can you view the rotor when teh car is running? clear cap?
He does not mean while the car is running. I have my motor out of the car & am getting ready to install it. A running car means your marks should be failry close. A non running motor may be off alot depending on what you had done?
Posted by: jimkelly May 10 2010, 08:47 AM
pic
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Posted by: JRust May 10 2010, 08:51 AM
What I am not seeing is how I adjust the distributor to get my rotor pointed where it is supposed to be? I have top dead center & have my timing mark in the hole. How do I get my rotor to the right position
Posted by: realred914 May 10 2010, 09:50 AM
pic
Gawd, that is horribly complicated. just do one pair of valves at a time, it is much easier, no complex order to remember doing it that way for 30 years and I dont need to remeber any special order.
simply set at TDC for 1 and adjust both number 1 valves, then rotate to number 2 tdc and do both number 2 valves etc..........
this aint rocket science, keep it simple. and remember you only need to be close to TDC for each adjustment, as teh cam has a rather large non-lobe area. the rotor location verses the one number one position mark on the dizzie case is presicion enough for my eyeball.
Posted by: realred914 May 10 2010, 09:54 AM
What I am not seeing is how I adjust the distributor to get my rotor pointed where it is supposed to be? I have top dead center & have my timing mark in the hole. How do I get my rotor to the right position
if the rotor is in the worng location it may be 180 degree off so remove the dizzie and rotate motor crankshaft one full turn, then put dizzie back it should now have the rotor 180degree moved.
if none of these above two posions are correct, then you have the dizzie drive gear in the worn place. for this to be fixxed, you can follow the proceddure in the reapir books for setting up the drive gear. basically you make sure motor is at TDC for #1 (NOT for #3) and set the drive gear in the hole so the dog drive slot is orientated as shown in the pictures most all rebuild books will have. not too difficult to get right, but it is important.
Posted by: McMark May 10 2010, 10:07 AM
What I am not seeing is how I adjust the distributor to get my rotor pointed where it is supposed to be? I have top dead center & have my timing mark in the hole. How do I get my rotor to the right position
You don't change the rotor position, you change the orientation of the distributor body. Loosening this with a 10mm wrench will allow the body to rotate.
If your distributor drive gear was put in correctly, your distributor is pretty close to right. Probably close enough to start.
I can talk your ear off about all the 'philosophy' of distributor orientation at WCR.
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Posted by: vsg914 May 10 2010, 10:30 AM
Dang, there are a lot of different ways to find tdc and adjust valves.
JRust, the two pics on post 17 show the rotor to be pointing toward the # 4 terminal area (I think). The pic of the notch of the van housing shows one of the thick webs. That is not TDC. TDC is about 4 or 5 thin fins to the passenger side of "one" of the thick webs. Either you are not at TDC #1 of compression stroke, or your diz in in wrong. Stick you finger in the #1 plug hole and turn the crank till it blows your finger out the hole. There will be a notch on the edge of the flywheel close to the center line of the crank (assuming your flywheel is so marked). Line up the notch with cl of case (top of engine) and your there. Then make a mark on the bottom of the flywheel. You will have two permanent marks on the flywheel that you can view from the inspection notch on the bottom of the tranni case for future valve adjustments.
Posted by: JRust May 10 2010, 10:30 AM
Okay so I am not off 180 degrees. I am off somewhere in between. My rotor is pointing towards the hole in the fan housing. If I rotated it 180 it would be facing the #3 cylinder?
Posted by: JRust May 10 2010, 10:33 AM
Dang, there are a lot of different ways to find tdc and adjust valves.
JRust, the two pics on post 17 show the rotor to be pointing toward the # 4 terminal area (I think). The pic of the notch of the van housing shows one of the thick webs. That is not TDC. TDC is about 4 or 5 thin fins to the passenger side of "one" of the thick webs. Either you are not at TDC #1 of compression stroke, or your diz in in wrong. Stick you finger in the #1 plug hole and turn the crank till it blows your finger out the hole. There will be a notch on the edge of the flywheel close to the center line of the crank (assuming your flywheel is so marked). Line up the notch with cl of case (top of engine) and your there. Then make a mark on the bottom of the flywheel. You will have two permanent marks on the flywheel that you can view from the inspection notch on the bottom of the tranni case for future valve adjustments.
You are right. It was a little further turn. I have it on TDC now.
Posted by: vsg914 May 10 2010, 10:39 AM
Cool. I haven't seen a rev liming rotor in many years, so I wasn't sure just where it was pointing.LOL
Posted by: SLITS May 10 2010, 10:39 AM
What I am not seeing is how I adjust the distributor to get my rotor pointed where it is supposed to be? I have top dead center & have my timing mark in the hole. How do I get my rotor to the right position
You don't change the rotor position, you change the orientation of the distributor body. Loosening this with a 10mm wrench will allow the body to rotate.
If your distributor drive gear was put in correctly, your distributor is pretty close to right. Probably close enough to start.
I can talk your ear off about all the 'philosophy' of distributor orientation at WCR.
Just to make it more confusing ......
The distributor does not give a crap where it is as long as you have enough "swing" to get the advance you want.
What the engine does care is that the #1 high tension wire, pole on cap and the rotor are in alignment plus the firing order is correct. Moving high tension leads can account for a misaligned distributor drive gear.
Posted by: vsg914 May 10 2010, 10:44 AM
I agree with Slits. Seen more than one car with plug wires one off all way round.
Posted by: McMark May 10 2010, 10:46 AM
Ignore where your rotor is pointing. It's irrelevant. Really. There is a 'but...' that you don't need to hear about right now.
Posted by: ClayPerrine May 10 2010, 10:49 AM
Just to make it more confusing ......
The distributor does not give a crap where it is as long as you have enough "swing" to get the advance you want.
What the engine does care is that the #1 high tension wire, pole on cap and the rotor are in alignment plus the firing order is correct. Moving high tension leads can account for a misaligned distributor drive gear.
Actually that is not quite true. Some of the beetle and 411 distributors have a 2 degree retard on the point opening for the #3 cylinder. This was done because #3 runs the hottest, and that helps to prevent detonation. So if you get the rotor in wrong, and rearrange the plug wires, it could retard the timing on the wrong cylinder.
Posted by: McMark May 10 2010, 10:50 AM
Your rotor is pointing at the line in the distributor housing (arrow). The motor is at TDC. So you should be close enough to start it, then you need to adjust the timing while the motor is running with a timing light.
Your spark plug wires should connect into the cap as illustrated.
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Posted by: underthetire May 10 2010, 10:51 AM
One way to find TDC on # 1 is remove a plug, place finger over hole, turn motor until you start to feel air pressure, then line up the timing mark. My old timer ( he's turning 50 this month 
) neighbor showed me that.
Posted by: vsg914 May 10 2010, 11:40 AM
One way to find TDC on # 1 is remove a plug, place finger over hole, turn motor until you start to feel air pressure, then line up the timing mark. My old timer ( he's turning 50 this month
) neighbor showed me that.I could have sworn that was exactly what I said
Posted by: JRust May 10 2010, 12:21 PM
Your rotor is pointing at the line in the distributor housing (arrow). The motor is at TDC. So you should be close enough to start it, then you need to adjust the timing while the motor is running with a timing light.
Your spark plug wires should connect into the cap as illustrated.
AHHH!
Now that I understand. I was thinking way to much about the rotor. As long as I have where its pointing as my #1 for the firing order. Got it thanks guys. I knew it wasn't as dificult as I was making it 
. Whats with the rev limiting rotor? Any benefits to that over a stock one? I knew it was a different one but didn't know much about it.
Posted by: McMark May 10 2010, 01:01 PM
The rev-limiting rotor has a weight that will disconnect the ignition when a certain RPM is reached.
Posted by: ClayPerrine May 10 2010, 02:10 PM
Whats with the rev limiting rotor? Any benefits to that over a stock one? I knew it was a different one but didn't know much about it.
It prevents testosterone induced brain fade from damaging your motor.
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