Help with TDC

[Chimi]

Hi,

I'm in the middle of the timing belt, water pump, cam seal, etc, and so right now, my car sits with all the belts removed. I'm having some difficulty finding TDC; any advice would be appreciated.

For the cam shaft, I have two questions.
In the first attached picture, I see the mark that I have to line up, but how do I actually rotate it? It is very hard to turn by hand.

Second, I need to do the cam seal; what size bolt is that? My manual says to use a hex 7mm, but that looks like a strange star type bolt.

On the crank side, the only mark I could find is the one shown in the second picture. What does this align with for TDC? Also, for the crank, I cannot rotate it freely for an entire revolution; I am guessing this is because the valves are in the way? How am I supposed to line up the marks then.

Thanks in advance

[arch4ngel]

Woah stop right there.
You have to find tdc and line up the marks BEFORE removing the belt.
If you havent already bent valves you will if you keep trying to turn the crankshaft like that.
At this point youll have to remove the head to look for damage.

Not sure what manual you have but it should have told you all of the above.
If you insist on continuing to work on yout car get a bentley manual.
That said you may be better off taking it to a mechanic.

[Chimi]

Hey, thanks for the heads up. I was just following the steps in the DIY thread here and didn't notice any explicit instruction about lining up TDC or not before removing the belt -- looks like a mistake on my part. So what can I do about it at this point? Hopefully... I didn't damage the valves. Otherwise, I guess I'm in the market for a new head.

[Andy.B]

OK. Take a deep breathe. All is not lost here, and there is no need to take the head of just yet...

First, carefully find the point where a piston is hitting a valve and can't rotate anymore. Don't try and force it.

Then rotate the crank back about 20 or 30 degrees. This will pull all of the pistons down away from the head.

Then, with the pistons safely out of the way, rotate the camshaft to its tdc marking.

Now, you should be able to spin the crank to tdc as well. If you end up getting contact, back off on the crank, rotate the cam 180 degrees, and try getting the crank closer to tdc.

Basically, you are going to have to move one shaft at a time, a little bit at a time, until you get them both to tdc. By making sure none of the pistons are at their tdc, you can safely move the camshaft. Just don't ever force either one.

If you carefully get them rotated to cylinder 1 tdc position, and get a belt on, you can do a compression test to find out if you have any bent valves.

It would take a decent amount of force to bend the valves with just a wrench on the crank bolt. I suspect that once you get the timing straightened out, it will be fine.

[arch4ngel]

I havent read the diy so not sure what they do/dont mention.
Theres no way I know of to line everything back up without removing the head.
I suppose you could index the valves and crank and slowly rotate everything back into place but I wouldnt risk it personally.
Besides at this point there may be bent valves.

[Chimi]

OK. Take a deep breathe. All is not lost here, and there is no need to take the head of just yet...

First, carefully find the point where a piston is hitting a valve and can't rotate anymore. Don't try and force it.

Then rotate the crank back about 20 or 30 degrees. This will pull all of the pistons down away from the head.

Then, with the pistons safely out of the way, rotate the camshaft to its tdc marking.

Now, you should be able to spin the crank to tdc as well. If you end up getting contact, back off on the crank, rotate the cam 180 degrees, and try getting the crank closer to tdc.

Basically, you are going to have to move one shaft at a time, a little bit at a time, until you get them both to tdc. By making sure none of the pistons are at their tdc, you can safely move the camshaft. Just don't ever force either one.

If you carefully get them rotated to cylinder 1 tdc position, and get a belt on, you can do a compression test to find out if you have any bent valves.

It would take a decent amount of force to bend the valves with just a wrench on the crank bolt. I suspect that once you get the timing straightened out, it will be fine.

Hi Andy,

Thanks. I'll try this and report back; I am worried I have bent a valve though. I did pull pretty hard on the crankshaft while turning it

[arch4ngel]

OK. Take a deep breathe. All is not lost here, and there is no need to take the head of just yet...

First, carefully find the point where a piston is hitting a valve and can't rotate anymore. Don't try and force it.

Then rotate the crank back about 20 or 30 degrees. This will pull all of the pistons down away from the head.

Then, with the pistons safely out of the way, rotate the camshaft to its tdc marking.

Now, you should be able to spin the crank to tdc as well. If you end up getting contact, back off on the crank, rotate the cam 180 degrees, and try getting the crank closer to tdc.

Basically, you are going to have to move one shaft at a time, a little bit at a time, until you get them both to tdc. By making sure none of the pistons are at their tdc, you can safely move the camshaft. Just don't ever force either one.

If you carefully get them rotated to cylinder 1 tdc position, and get a belt on, you can do a compression test to find out if you have any bent valves.

It would take a decent amount of force to bend the valves with just a wrench on the crank bolt. I suspect that once you get the timing straightened out, it will be fine.

Hadnt thought of this, definitely worth a try.
When replacing the head turning the crank back is one of the recommended steps to avoid damaging extended valves.
Good luck and let us know how it goes.

[Andy.B]

As for finding the timing marks:

For the camshaft, the divot on the cam belt gear tooth lines up with a line on head (offset towards the intake side of the head, about the 2 o'clock position).

For the crank, that line in the picture you took on the hub lines up with a corresponding notch on the aluminum piece between the hub and the idler gear (it is just about the 12 o'clock position on the crank).

[digger]

might be an idea to remove plugs if havent already and will make it easier to rotate so you have half a chance to feel any interference. might be too late though

[Andy.B]

If you did manage to bend a valve by hand, I would consider just having a local machine shop replace the offending valves. Since it didn't happen with the engine running, the forces involved were limited, and it would likely cost much less than going out and purchasing a new head.

If you do go the new head route, I recommend BimmerHeads. I purchased my last head from them after having had a previous head for another e30 rebuilt locally, and the cost for what you get with BimmerHeads is hard to beat.

[Andy.B]

Good luck getting your timing straightened out, and let us know how you make out. Like I said, I doubt you bent a valve by hand, but it is a possibility.

[Chimi]

I'll probably take a look at it tomorrow evening after work, but one more question. Is there an easy way to turn the camshaft? I just ran out real quick to test your approach. I moved the crankshaft til it came into contact with something then backed it off. Then I tried to turn the camshaft by hand; is there somewhere I can just attach a wrench like with the crank? I'm having trouble getting any leverage to turn it.

[TurboJake]

I highly, highly, HIGHLY doubt you did any damage to the valves. They are very sturdy and made of a very strong alloy. The pistons are pretty damn sturdy too. It would require you to put a breaker bar on the crank, and force it nearly as hard as you can to overcome the obstruction to do any real damage. Even if using a 3/8' ratchet, you will have to put pretty much your entire body weight into it to cause anything, which I highly doubt you did.

Don't worry about the head, get the pistons to be away from it, rotate the cam TDC, then rotate the crank to TDC, then continue on your way. If you can't get them both to TDC, slowly shuffle them along until you can.

[Andy.B]

To turn the cam, you can use an inverted torx socket on the torx bolt that holds the rotor mount on (but can only turn it clockwise, otherwise you'll just loosen the bolt), or use a pair of vice grips set to kind of awkwardly clamp onto the rotor mount to turn it. Just don't go too tight or crank it too hard and risk damaging the mounting tabs on it.

[goldenbb]

Take a breather--you can get it all lined back up with the belt off, but you have to follow the advice on here and turn the engine and the cam together and do little fixups until they line up right.

You need a torx socket* for the cam sprocket, do not try to use a regular socket. Use a 22mm on the crank bolt with the transmission in neutral (e-brake and block the rear wheels!!!!). You can pull the plugs if you like, but the engine can be turned pretty easily regardless. You have to make sure the timing marks line up perfectly and that you check again when you get the belt on and tensioned, and then it is a good idea to turn the engine by hand after that to make sure it all lines back up the next time it comes around.


*(I think it's the E12, but it might be the E14, I'm in the middle of a top-end rebuild and I have all that stuff floating around in my head right now)


By the way, to do the cam seal, you will use that E12 torx socket and you can use the old timing belt with some vise grips to hold the sprocket so you can loosen the bolt. If that doesn't work, an impact ratchet will work, or any small impact driver with the air turned down.