Locating TDC : dumb questions
 

Couple dumb questions about the procedures I've been reading (e.g. Clark's) to locate TDC for cylinder 1:

Does the starter have to be out to perform the procedure to locate TDC?

Is the crankshaft bolt the only one that's 24mm?

:)

starter can remain
the steering wheel nut is also 24mm :)

I usually pull the distributor cap and turn the motor until the rotor is short of facing the #1 spark plug wire terminal and then, (spark plugs removed), turn the crankshaft slowly until I see the cam gear timing mark lines up (viewing hole) and then verify it in the bell housing hole.

No, only to install a flywheel lock if for instance you are removing the crank pulley bolt etc., as would be needed to replace the balance shaft seals...

Thanks this helps - I'm not interested in TDC cylinder 1 per se for this post, but turning the engine. It just occurred to me that the TDC procedure in Clark's was a good start.

What should it feel like to turn it?

You can also use 15/16.
As for what it feels like when you're turning over the engine... Well It sorta feels smooth, then rough, then really rough, then smooth again. Sorta like that first time.

The rough resistance is the compression stroke.

Just like AZ_porschekid said. But if you take the spark plugs out, you won't have to content with the compression and it should turn pretty easily. Just be sure to put it in neutral.

It looks like the belt cover can stay in place - true?

Also looks like you can just leave everything as-is when you feel like it and resume driving - nothing special to do except put spark plugs, belly pan back?

belt cover can stay in place. the crank bolt and the associated pulleys are exposed outside of the plastic cover.

If you haven't take out the starter but only the spark plug, yes. You can resume driving after putting the spark plug and wire back in.

I think that Clark's also says that you can put a wooden dowel in #1 cylinder and watch go up and down as you turn the crank. But don't do it if you're easily hypnotized!

Clearance between the radiator and the pulley is minimal, so you need the correct socket and ratchet combo. I use a 3/8 swivel head ratchet, a 3/8 to 1/2 converter and a 3/8 24mm standard socket.

Thats pretty close to what I use, except I think you mean 1/2 24 mm socket. I use a 1/2 extendable ratchet from harber freight with a 1/2 to 3/8 adapter and a 3/8 in 24 mm socket. Fits perfect. You can crawl on the fender, turn the ratchet with one hand, hold a flashlight with the other, while looking in the clutch housing for the TDC mark.

Just tried it out - must say again, thank you all - I'm happy :) this was an epiphany for me.

A few last questions :

What should I be listening for?

Is the engine essentially operating like normal (minus electric/fuel) during this method - valves opening/closing, oil/water pump going,...?

Does the 24mm bolt get rotated clockwise to avoid loosening it? What happens if rotation is counter-clockwise - i.e. can the engine go both ways (not that I want to try it!)

You ain't gonna loosen it by turning the engine over either way. It's tighern**** and you'll need a flywheel lock to put enough torque on it to loosen it. However, the correct rotation of the crank is clockwise so no worries.

Why are you doing this anyway?

Well, now that you ask, ... short answer is - want to test the engine gently before issuing an "all systems go".

A lot of work was done, over a long period of time.

You can back it up a little if the crank bolt is proper tight, but it goofs up timing belt tension measurements and stuff like that since it shifts the belt tight spot around. It's probably not a good idea to rotate the engine backwards significantly but it is often done if you are doing a leakdown test or the like.

The oil and water pumps will pump when you do this. Listen for compression I guess, I dunno. You should feel the compression.

Ahhh. I see. Take the spark plugs out to make it easy to turn over and you should not feel any increases in resistance (compression) as the pistons get to the top of the cylinder. Get it on TDC using the mark on the flywheel visible down behind the Oil Fill cap. Once you get it at TDC on the crank. Look through the inspection hole next to the distributor and check to make sure the cam is timed. If it is.. Rotate it over slowly a couple of more times and get it back on TDC at the flywheel. If the cam gear is still in time. You're good. You're not going to be turning the engine over fast enough to feel the oil or water pump. IF you have a HARD stop with the plugs out, it could indicated a mechanical interference somewhere. This is NOT what you want. You need to figure out what it is before attempting to fire the engine.

However, I highly recommend pulling off the front top timing belt cover and visually inspect the belts for cracking and make sure the idler pulleys are not locked up. Make sure the water pump pulley is turning with the belt. It runs on the smooth side of the timing belt and if it's locked up, it will smoke the belt. I'm working on an 88S model and the water pump was locked up (trashed). I had taken the timing belt covers off to check the belts and fired it up. I noticed a little smoke coming from that area and immediately shut it off. Grabbed a pair of channel-lock pliers and tried to turn the pump and could not. That would have not ended well had I let it run for several minutes with the covers on.

I tried this again. Spark plugs were out - if I recall correctly : still felt some resistance periodically. Is that the springs? Could also hear squeaks coming from cam tower at that point.

car is in gear :rolleyes:

go off of the flywheel mark. You should be able to rotate the engine while looking at the bell housing while using a ratchet...

Pull out the 6 plugs on top of the cam tower and drizzle some oil strategically. see if that changes anything.

Also keep in mind that a four stroke engine has two TDC per cylinder, hence the suggestion mentioned early on in this thread to take the dist cap off so you can figure out if you are at TDC exhaust stroke (i.e. exhaust valve closing, intake valve opening) or TDC compression stroke (i.e. intake valve closing, spark about to fire).

It's good practice to keep in mind which TDC you are trying to reference. What I do to find TDC compression stroke is take the spark plug out of #1, put a piece of tissue in the spark plug hole (enough that it doesn't fall in of course!) and when the tissue blows out while rotating the motor, you know you're on the compression stroke. Then a screw driver or fancy dial feeler gauge will get you to TDC. If you're looking for TDC exhaust stroke, then of course you go round one more time. Then you can verify that your cam belt and distributor rotor are on correctly.

Maybe it's overthinking it a bit on a SOHC engine...I'm used to working on quad cam V-6's

Interesting comments - I thought the rotor comes off/on only one way or something like that - IOW ignorance is bliss for replacing the rotor?

@sausagehacker : I'll have to understand those bolts first before I drizzle.

I'm confused by that post. lol
Simple rule, cam goes twice as fast as the crank.

@ Bukowski: You're correct of course, the pin is slotted, so the rotor only goes on one way. Apologies for the confusion. Again, I'm more familiar with engines where the distributor is geared off the cam, or for added fun, off an auxiliary shaft. In that type of arrangement, knowing which TDC you are at in the engine stroke is important because it is very easy to install the distributor 180 degrees wrong. Anyhow, let's just say working on a 944 8V NA motor has been pleasant compared to a Maserati V-6 with about 6 feet of timing chain: http://tinyurl.com/hbk5ju7

The cam rotates half as fast as the crank. So every 360* of the crank, the cam only moves 180*.

He is saying that if you use the mark on the flywheel you may be on the exhaust stroke with the cam 180* out. You will then need to rotate the crank another 360* to get the engine to TDC.

there are 6 plugs, 8mm allen head. Go slow and be careful, they strip. Happened to me twice now. now, just pour some oil in each hole (they're just access holes, the inner cavity only contains the cam and its journals/bracing). You want to have some oil present on the cam lobes and lifter faces as you turn it, ideally.