SigAlphAdam

Hello all, got a question about turning the crankshaft to TDC. I'm using the Haynes manual, and in chapter 2A, sec 7.4, it says that you can see the camshaft sprocket through the little hole above the distributor cap. I found this. When I turn the crankshaft, I can see the gears moving inside the hole.

But then in sec 7.5, it says that you have to look at the timing mark the flywheel, which can be seen from the rear of the engine. This I cannot find.

My question is this: Which place are you supposed to look to see the TDC position? The camshaft sprocket at the front, or the flywheel mark at the rear? How do you know if the piston is in TDC? (all the teeth of the little gear in the camshaft sprocket look the same)

If you DO in fact need to look at the flywheel mark, where IS it?

Thank you for your help.

PorscheDoc

Ok, first you can crawl underneath the car and in front of the starter you can see a mark on the wheel that turns when you turn the crankshaft. When the mark is between the notch, leave it there...that is going to get you close. Then look on top of the clutch housing through the rectangular hole, you should see 'OT' with a line above it. Line that line up with the knotch, and you are at TDC. I could never use that little hole on the distributor, it just shows the camshaft lining up. I always just removed the metal silver cover, then you can see the white line on the camshaft sproket, and the mark on the rear distributor cover...they should be lined up. Use the top rectangular hole on the clutch housing though for TDC is the most accurate. ALso you can pull the #1 spark plug and insert a wooden dowel, turn the crank and watch the dowel...when it is at the highest point that is TDC.

PorscheDoc

Sorry, the rectangular hole is on top in the back of the engine, down by the reference sensors.

brad-cam

The OT marks on the top of the bell housing is fact the main reference for TDC, but I cannot for the life of me see in there past all the "stuff" on top of that viewing port. I relied on the mark on the bottom of the flywheel and the cam gear marks and everything worked just fine.

Danno

Also due to the distance away and parallax errors, the OT mark isn't very accurate. The distributor hole is only good assuming the belts aren't worn and were installed correctly. The only real way to find TDC is from underneath by lining up the depressed groove on the flywheel with the notch on the bell-housing.

Have someone turn over the engine by the crank-pulley and crawl underneath to find the flywheel, yes you can see it spinning. Then there's a small groove cut out at some point, it's only like 0.5mm deep. That mark needs to line up with a U-shaped cut-out in the bell-housing. Best to look straight up at the flywheel.

PorscheDoc

Danno, i have to disagree with you on this one (not on the mark on the camshaft sprocket, you are correct on that one). Using the mark underneath the car, i could line up the timing belt on 2 different teeth on the camshaft sprocket with this method. That is, either the line would be on one side of the U, or the other, but i could never have it line up perfectly in the middle and still have the camsprocket line line up correctly when putting the timing belt on. So you are like....well which notch do you use? Too big of a notch and too small of a line if you ask me. Also i checked it with a dowel, the OT line is perfect. Oh and to line up the notch below, only takes one guy for crying out loud. You can crank with one hand and have your head directly under the notch....its not that big of a distance where you need two people. I think most people will agree to use the OT line, but then again im not a tuner

Karl

brad-cam

I used the method Danno describes and the mark was perfectly centered while the cam sprocket mark was also perfectly aligned.

PorscheDoc

well there you go. My car must be hosed, cause it sure as heck wouldnt line up perfectly....lol

Danno

"Using the mark underneath the car, i could line up the timing belt on 2 different teeth on the camshaft sprocket with this method. That is, either the line would be on one side of the U, or the other, but i could never have it line up perfectly in the middle and still have the camsprocket line line up correctly when putting the timing belt on."

There are two separate mechanical things going on here.

First is the engine being at TDC. Mechanically, this means the piston is at the highest point in its travel. The mark on the flywheel being centered in the notch is the absolute indicator here. That's why I mentioned to look up at the flywheel, this will guarantee that you're centering the groove on the flywheel exactly inside the notch.

The second factor, completely independent of the TDC mark, is the alignment with the cam. If you can't get the cam lined up with the crank perfectly set at TDC, then your cam-belt may be worn, your head has been shaved for increased compression or the notches in the cam sprocket is off, or the notch in the cam is off, or both! I've seen from a sampling of cam-sprockets, that the notch varies by 2-3 degrees in each direction. So it's possible with two of these sprockets on the extremes of the error to be off by 1/2 a belt-tooth in either direction on the same car! If that's the case, use the more advanced position for more low-end torque, or pick the retarded timing position for more high-end HP.

"Oh and to line up the notch below, only takes one guy for crying out loud. You can crank with one hand and have your head directly under the notch...."

I know, I know. I justed wanted to use the flywheel-motion for people to find it. You'd be surprized at how many people can't find the flywheel. I usually just drop a long ratch down and spin the crank while checking the flywheel mark.

tomc_85.5_944

I had a time finding the notch on the flywheel underneath, because I kept looking at the clutch inspection hole.... There is a cover that is held on by two HUGE bolts that covers the bottom of the flywheel. Once I took it off, I knew what to look for, as it gets real clear then. Once I got the bottom mark close, I could then barely see the OT mark...

PorscheDoc

That is wild. Wierd how they can vary so much. I just find the bottom one hard to use, cause it is just a little line, and a huge notch, so there is room for error on each side.

RSflared72e

I have always gone by the OT line at the sqare aperture without problems. There is a bit of a trick to lining up a flashlight shining through all the wires etc to see the top edge of the flywheel. The first time I tried to show this to a buddy of mine he swore he couldn't find it - took him several times of crawling up on top of the engine peering down in there to finally see it. And some flywheel marks are more vivid than others.

mmmbeer

The easiest way of finding the pistons TDC is:

- Remove the sparkplug on #1 cylinder
- Put a long object (screwdriver etc) throught the hole making contact with the piston suurface.
- Rotate engine using a wrench on the large front pulley bolt.
- Stop rotating when the long object has reached its top position, ie same as the pistons top position.

This is the easy way, not mentioned in any manual.

Regards:
Eirik Kvello-Aune
www.944968.com

SoCal Driver

Ah... there are two places in the four cycle engine where the #1 piston is at TDC and the mark on the flywheel lines up.

Only one is correct.

So using the wood divining rod approach and/or the OT mark is good half the time.

I would remove the cover on the bottom of the bell housing, rotate the engine till you see the OT, clean it with a wire brush and rub caulk into it.

I would also remove the dist cap so you can see the rotor when it moves to the #1 position.

Rotate the engine watching said rotor. When it gets to the #1 position start looking for the freshened OT mark through that impossibly small inspection hole on the top drivers side of the bell housing. Don't blink or sneeze or you will miss it.

mmmbeer

It is the other way around. The piston is at top once per revolution of the flywheel, while the cams move at half the speed. Ie, when the screwdriver reaches the top position you will have the flywheel mark each time, but the cam sprocket will only match up every other time. But that is no problem since the camsprocket is easilly inspectable.

Therefor there is no need to check the flywheel markings as it always lines up when the #1 piston is on top. But you MUST check the cam as it is in the right position every other time. But that is done in a easy way by the rotor.

So the procedure will be very similar to the one Socal just mentioned exept you keep one eye on the cam mark while the other on the wooden stick/screwdriver... Much easier this way.

Edited: the other way around, it is correct now.

Regards:
Eirik Kvello-Aune
www.944968.com