Geo

John, you've got this backwards. If you line up the cam you have 100% chance of lining up (roughly - needs fine adjustment), but if you line up the flywheel you have a 50/50 chance of having the cam line up. You said it yourself, the crank turns twice for each turn of the cam.

I just did a belt job a couple of weeks ago and we briefly had the flyhwheel lined up with the cam 180* out just demonstrating how lining up on the cam first is the way to go.

Saying this another way, the flywheel will line up twice for each time the cam lines up.

Again, line up the cam and you will be roughly lined up with the flywheel (mark should be in the window). Then it's just takes a small bit of movement to get it exactly lined up.

Geo

Nope. EVERY rotation of the cam when the marks are lined up the flywheel will be lined up. I positively guarantee it.

Geo

Think about what is happening at the cam and at the crank with each stroke. John described it correctly, but then got the lining up of the marks backwards.

The following ignores overlap and duration as well as ignition timing.....

At TDC all valves are closed.

Stroke 1 (intake): The cam rotates and opens the intake valve during the stoke - exhaust valve remains closed. When the piston reaches BDC the cam rotates enough that the intake valve is closed.

Stroke 2 (compression): The cam rotates but there is no bump (it's on the base circle) to affect the valves on either lobe. - all valves are closed. The piston rises to create compression. At TDC the spark plug fires.

Stroke 3 (power): The cam rotates but there is no bump on either lobe to affect the valves - both are closed.

Stroke 4 (exhaust): The cam rotates to open the exhaust valve - the intake remains closed. The piston rises to TDC and the cam roates enough to close the exhaust valve at TDC. We are back where we started and the cam is in the exact location it started in. The crank however has rotated twice (as evidenced by the piston twice being at TDC).

Thus.... Each time the cam lines up at the marks, the flywheel MUST line up at the marks. As a corallary, the flywheel lines up twice for each time the cam lines up.

Yabo

OK i got a question now geo.

I have the engine on a stand with no flywheel right now because I'm getting teh flywheel machined. I also have the head off, and i've had to tturn the crank so its no longer at TDC.

Upon reassembling, can I just:
Put the head on,
Then before putting the cam tower on, turn the cam tower to TDC
Put cam tower on
Take engine off stand, put flywheel on
Line up flywheel to TDC

?? Or will I damage something in the process of lining up the flywheel and must I do it before putting the cam tower on?

Geo

1) I would install the flywheel and line it up at TDC before installing the cam tower. This will ensure no valve to piston contact.

2) The only possible wrench in the works that I see here is if there is any tension on the valves with the engine (cam and flywheel) at TDC there may be some difficulties installing the cam tower. Maybe John can shed a little light on this.

You're certainly on the right track. As far as the bottom end goes, TDC is TDC. you just don't want to line it up with the cam installed.

KuHL 951

Mike,
If you haven't pulled your old timing belt yet and your car was running correctly before, then setting at TDC at the cam at TDC should give 2 good references. One at the sensor housing opening (OT) and one at the slot at the bottom of the bellhousing. The one at the bottom wasn't marked on my 83 but has been on every other late car I've worked on. You might need to shine a light into the sensor window opening if you are working in a dark garage. If the cam and sensor opening aren't lined up then your car might be off a tooth on the TB but you would feel it as the car would run poorly but it will run. More than one tooth and you can enter valve-to-piston contact.

Yabo

sounds good geo,thanks. I do understand what you are saying about the tension thing, I think there was some when I took teh cam tower off, as I would undo bolts the right side was getting pushed up and I thought it might be a little tricky to get back on. may just need an extra hand to help push down.

MM951

Ok. Found the mark. Only problem is the notch on the cam sprocket is about 3 teeth away from the notch its supposed to be lined up with.

Is that normal? The car ran fine...

KuHL 951

Is the flywheel OT line at the reference mark on the sensor hole housing? Sometimes if you are not looking squarely over the sensor opening the OT line can look off due to the angle. I doubt you can be 3 teeth off on the timing belt, you would have felt it for sure, and I mean felt!

MM951

Hm. What I did is use the notch in the bottom of the flywheel (I cannont see the OT in the window. Its too filled with crud and stuff)

Thats what I thought...I'd know it cause I wouldn't have a runnin car

What do you reccomend I do?

KuHL 951

The reference mark on the bottom of the bellhousing should be just as accurate but I still prefer the OT mark on the sensor hole. Set your cam at TDC and spray some brake cleaner into that hole and see if the mark shows up, it virtually has to be there. All I know is after I do belts I hand turn the engine to get TDC on the reference marks and recheck everything. If the belt was installed right it the cam should all line up as before, if off one tooth it's usually the TB wasn't pulled tight enough from the crank pulley when slipping it over the cam gear.

MM951

Alright. I'll do that and try and make my hand fit down there so I can clean it

but..why how could the motor be @ TDC with the cam THAT far out and still run??

EDIT: Brought the cam to TDC and when I put in my dowel I noticed that tdc for the cam had the piston at the top of its travel. I spun the motor a few times (back and forth about 5 teeth in each direction) and when the notch on the sprocket was aligned with the notch was right before the piston started going back down.

Am I at TDC for #1 now? I know its bad - espically to rush, but I gotta drive this car in 3 hours or else I'm not gettin to work lol

Thanks
Mike

KuHL 951

Like I said if the OT mark is seen from the side at the sensor hole it can look on the money and still have a good 1/4' to 3/8" rotation to be right. Good luck with cleaning up that OT mark, use a small pint brush with the brake cleaner if you have to. I not sure how a car would run being 3 teeth off but mine and others experiences seem to say it would be very noticeable, maybe not fatal though. The TDC mark on the cam sometimes doesn't line up exactly, Serge showed me that if the crank is TDC and locked, if the cam gear doesn't line up perfectly with the new belt on it, he would rotate the cam gear mark just barely to the right of the mark on the rear belt cover to set the belt teeth. Everytime we would rotate the cam gear to the left to seat the belt it would be off one tooth after tensioning and rotating the motor. This is just my experience and might not agree with methods used by others but it's worked fine for me.

RedlineMan

Ummm...

So I get confused easily! I usually don't even bother to check the flywheel. If the cam is aligned, it is aligned... you know?

If you suspect anything funny, I like to use the top "OT" mark too just to be sure. I'm with KuHL on this one. I've never actually used the bottom mark. Never even seen it to be honest.

You can sometimes get valve spring tension that will make the cam rotate a bit when you loose the t-belt, but it is not a problem. Just turn it back by hand.

For engines that are apart, it is important to not install the cam housing if not at TDC. Damage will likely occur! Yes, you can bend a valve this way!! I place #1 at TDC with the head off since it is never easier, then install the head, then the cam housing set to the mark. I start with a central cam housing bolt to draw it down evenly, and do it in stages to boot.

To make sure you have the cam and crank properly aligned, it is important to install the belt properly. It turns clockwise. Therefore, I install the belt such that it is stretched completely tight on the cam-to-crank side. If I cannot get it completely tight, I tweak the cam gear back a tad to get it taught. That way it will hold position while you fiddle, and not be off a tooth on you. The belt from the crank-to-adjuster-to-pump-back-to-cam side has all the left over slack, which is then duly taken up by the eccentric/tensioner. I do the same thing with the balance belt too.

MM951

Alright, I'm gonna try and uncover that "OT" mark for the next few minutes and if I cant get it...I will just go on. Piston is at the top of its travel, cam says TDC...car ran..

I'll just turn the motor over a few times before I crank and see if I feel any resistence..

Sound like a bad plan??