Timing Chain Replacement - Trouble Setting Timing

[neeco]

I'm in the middle of a timing chain replacement on a 98 SL2 and everything has gone fairly well except for setting the cam timing. I followed the procedure outlined in the FSM but when I align the cam marks at the 12:00 position, the valves hit the crank (crank is at #1 TDC). I made sure to put the crank 90* past TDC before moving the cams to avoid any piston-valve contact.

Now before I removed the timing chain, I set the crank at #1 TDC but I noticed the timing alignment hole was at around the 2:00 position which should be at around the 8:00 position in order to install a 3/8" drill bit to hold the cams. The cams are now 180* off before I removed the timing chain.

There are several markings on the camshafts. Does anyone know how to identify the intake and exhaust camshafts?


The car ran fine prior to this with the exception of ticking noise coming from the timing cover area. This is the first time I've replaced a timing chain but I've done plenty of timing belts on other vehicles.

This one has me stumped. Any input would be greatly appreciated.

Thanks!

[davorocks]

Did you move the cams after the old chain was off?

[johnny95sl2]

The intake and exhaust camshafts say intake and exhaust on them. Leave cranshaft at 3 oclock, install head, put drill bits in alignment holes(you may have to turn cams), turn crankshaft back to 12 oclock, install chain. Slack in chain needs to be on TENSIONER side before installing guides and tensioner. There are a couple of pip marks on the timing gears that will be "up" when the alignment pins are installed.

[OldNuc]

With crank at the 3:00 position so as to not bend valves. Take the chain off and rotate the cams with a wrench on the cam flats provided while looking for the INT and EXH marks on the cams. It is possible you are dealing with a modified engine. The marks are in the area of #2 and cast into the cam.

[neeco]

Originally Posted by davorocks

Did you move the cams after the old chain was off?

I moved them when I installed the timing chain. I had to rotate them 180 degrees in order to get the alignment holes to line up and the cam marks at the 12:00 position.

Originally Posted by johnny95sl2

The intake and exhaust camshafts say intake and exhaust on them. Leave cranshaft at 3 oclock, install head, put drill bits in alignment holes(you may have to turn cams), turn crankshaft back to 12 oclock, install chain. Slack in chain needs to be on TENSIONER side before installing guides and tensioner. There are a couple of pip marks on the timing gears that will be "up" when the alignment pins are installed.

I did that exactly, but the issue is that the cams are now 180 degrees off by following this procedure. This causes the pistons to contact the valves.

Originally Posted by OldNuc

With crank at the 3:00 position so as to not bend valves. Take the chain off and rotate the cams with a wrench on the cam flats provided while looking for the INT and EXH marks on the cams. It is possible you are dealing with a modified engine. The marks are in the area of #2 and cast into the cam.

I will take a look at the cams when I get home from work today. By the way, the car is completely stock and my mother, who is the original owner, does not have any records of any work being done to the top end. But that doesn't necessarily mean work was never done to the top end, she can't find any receipts for it.


Thank you everyone for your help! I appreciate it!

[OldNuc]

It is possible you took the chain off when you were 90 degrees before BDC. If that is what happened then you would be in the mess you are in now. To fix it you have to carefully and evenly back of all the cam journal bolts so all valves are closed and turn the crank until #1 is 90 degrees past TDC. then set the cams to the pin holes and lock them. Then turn crank counterclockwise to just TDC and install the chain.

[neeco]

Originally Posted by OldNuc

It is possible you took the chain off when you were 90 degrees before BDC. If that is what happened then you would be in the mess you are in now. To fix it you have to carefully and evenly back of all the cam journal bolts so all valves are closed and turn the crank until #1 is 90 degrees past TDC. then set the cams to the pin holes and lock them. Then turn crank counterclockwise to just TDC and install the chain.

Nope, I had the crank at #1 TDC before I removed the chain with the crank keyway pointed at the 12:00 position. I double checked to make sure. I only moved the crank when I had to rotate the cams in order to get the alignment holes on the sprockets to line up with the holes in the head.

[OldNuc]

Before removing the chain you set the crank to TDC and then advance 90 degrees clockwise. When setting to TDC you also verify that the cams are at TDC and Not BDC. The cam turns at 1/2 the engine RPM. It takes 2 turns of the crank to rotate the cams 1 complete turn.

The cams are only at TDC when the timing pins holes line up. Rotating cams with the pistons at any place but mid stroke (90 degrees or 270 degrees past key straight up) will potentially bend valves. The crank must be at 90degrees past TDC before pinning cams and then rotated counterclockwise to exactly TDC, then the chain is installed.

[neeco]

Wow...I thought about this more and I think I figured it out. The camshafts rotate 1/2 the speed of the crank so I needed to turn the crank one more full revolution in order to get the marks on the cam sprockets to line up correctly. So what I'm going to do is position the cams back to their original position (180 degrees off), install the chain and rotate the crank 360 degrees. This should bring the cams to #1 TDC.

Is my thought process correct?

[neeco]

Originally Posted by OldNuc

Before removing the chain you set the crank to TDC and then advance 90 degrees clockwise. When setting to TDC you also verify that the cams are at TDC and Not BDC. The cam turns at 1/2 the engine RPM. It takes 2 turns of the crank to rotate the cams 1 complete turn.

The cams are only at TDC when the timing pins holes line up. Rotating cams with the pistons at any place but mid stroke (90 degrees or 270 degrees past key straight up) will potentially bend valves. The crank must be at 90degrees past TDC before pinning cams and then rotated counterclockwise to exactly TDC, then the chain is installed.

Just saw this post after posting mine.

You confirmed exactly what I was thinking. That's where I went wrong, I did not bring the cams to #1 TDC before I removed the chain. I'm pretty sure that's my issue.

This is the last time I work on any cars late at night

Thank you!

[OldNuc]

There is usually an easy answer to any mechanical timing problem. At least the small 4cyl with a 180 degree crank are easy to sort out.

[jrowley1961]

Is what has been described an issue of bringing it to TDC on the exhaust stroke instead of the compression stroke?

[neeco]

Originally Posted by jrowley1961

Is what has been described an issue of bringing it to TDC on the exhaust stroke instead of the compression stroke?

Yes, you are correct. The engine was at the exhaust stroke and should have been on the compression stroke.

[madpogue]

In short, the cam sprockets can't be "180 degrees off". That'd be like an analog clock (with no AM/PM) being "12 hours off". On a car with a distributor, or a spark system that doesn't fire on both compression and exhaust TDC, yes, that would be described as 180 off. But with our waste spark systems, just turn the crank another full turn and Bob's your uncle.