lost my cam timing, grrrrrrrrr!!!!!!! HELP!

[Jared at Pelican Parts]

so last night, im doing a valve adjustment and installation of the carrera tensioners. did a partial engine drop, tins off, muffler off. I clamp the chain around the sprocket, and remove the mechanical tensioner and idler arm.

As I go to put the idler arm back on, I put the hydraulic tensioner and idler arm on and as i pull the pin for the tensioner, after pumping it up, I see the chain tighten up, and the cam sprocket moves about 1/4 inch. (Im screaming at this point.) I havent even touched the other side.

Can ANYONE offer advice as to what to do here? at this point, Im almost thinking of dropping the engine and taking it to someplace to have the cams re-timed. Any idea what it would run to just have the one cam re-timed and nothing else at a shop?

I dont think I want to handle re-timing this on my own.

[yelcab1]

You know, it is really not that bad to re-time your cam in the car, if you have the right gauge. Where are you?

[Jared at Pelican Parts]

thousand oaks. Can you help? I also have the later style cam bolt on there as well. As I understand it, it's a matter of getting it back to Z1 on the crank, making sure the writing on the cam is facing up and then use the gauge to approximate the position, then you check the rotation and re-adjust as needed...

[ChrisBennet]

Are you saying the chain slipped over the teeth of one of the sprockets? Unless it slipped teeth, your cam timing didn't change.
-Chris

[RoninLB]

I'm with Chris on this one.

But under the circumstances it would be a good idea to recheck the cam timing.

[MotoSook]

I see the chain tighten up, and the cam sprocket moves about 1/4 inch.

I don't think you have a problem unless the chain actually skipped a tooth on the sprocket like the others said.

[Jared at Pelican Parts]

Is there any way to confirm that the chain didnt skip a tooth? Like is there supposed to be more or less slack on one side of the sprocket? I imagine putting it all back otgether and very carefully, rotate through 720 degrees, and check to see that both tappets are loose on no. 1 cyl and check the other two on the same bank through rotation? Or am I grabbing at straws? As least it gives me a reason to now drop the motor and fix some oil leaks and replace the vacuum hoses.

You know, (realizing now in hindsight that I did this on TDC for no. 6, forgetting to set no. 1 back to Z1 after the valve adjustment, stupid) I'd have to incrementally advance the cam and crank independently back to Z1 and re-time it anyway. Right Could the lift on the cam lobes cause the cam to rotate when tension was applied?

Chalk this one up to another learning experience, i'll figure it out. just need info on how to re-time the cams now I guess.

[RetroSC]

I can't imagine it skipped a tooth unless you lost alot of tension on the chain. Even if it did somehow skip a tooth, you could easily set the engine at the Z1 mark, release chain tension on that side that skipped and turn it back a tooth, or however many is needed. Since your cam-nut is already holding the cam sprocket and cam in the proper location (this is where cam timing is set) you'll be able to tell which tooth it needs to be on by simply looking at the mark on the cam while it's at Z1.

Anyhow, I think somebody with more experience could explain this a little clearer than I can, but I'm pretty confident you should be fine.

Bill

[RoninLB]

Originally posted by Jared Fenton

. just need info on how to re-time the cams now I guess.

"How To Build & Modify Porsche 911 Engines" by Wayne R. Dempsey p163

[RetroSC]

Maybe this will help a bit more. I'll explain the basics of cam timing and maybe you'll understand better why you should be ok. It's been awhile since I've done this, so bear with me..

When setting cam timing, you start by static timing them using the ZI and small dimple marks on the ends of the cam. This gets it pretty close, then you use a dial indicator, loosen the big cam nut, and this lets the cam rotate on the cam sprocket to make the small, but very important adjustment.

That being said, you've already got the important adjustment done... it never changed! You never loosened the cam nut or anything, so you can simply get the cams back in the proper orientation with relation to Z1. This should be pretty easy since one tooth the wrong way, and it will be pretty obvious that you're too far out of wack.

[wilke3169]

I do believe you would know if it "jumped" a tooth. mine did during cam timing after rebuild and it was very noticable when it happened. If it has gotten out of time, like the others have said, it isnt as horrifying as some make it sound. Critical yes but complicated no. Think of it not as broken just out of adjustment.

Kevin

[Jared at Pelican Parts]

Originally posted by RetroSC
Maybe this will help a bit more. I'll explain the basics of cam timing and maybe you'll understand better why you should be ok. It's been awhile since I've done this, so bear with me..

When setting cam timing, you start by static timing them using the ZI and small dimple marks on the ends of the cam. This gets it pretty close, then you use a dial indicator, loosen the big cam nut, and this lets the cam rotate on the cam sprocket to make the small, but very important adjustment.

That being said, you've already got the important adjustment done... it never changed! You never loosened the cam nut or anything, so you can simply get the cams back in the proper orientation with relation to Z1. This should be pretty easy since one tooth the wrong way, and it will be pretty obvious that you're too far out of wack.

Thanks, that really clears it up a bit. So basically, Just use a c-clamp to hold the idler arm against the case, advance to Z1, and check that the marks on the cam are at 90 degrees relative to Z1.

If they arent, slip the chain back a link at a time til it does line up, right?

Looks like I have to change the chain ramps as well. A whole chunk of one of them is broken off, laying at the bottom. Those inside ones look like a *****, should I grab them with a pair of needlenoses and hold them as i remove the retaining bolt?

Oh man, makes me much happier. This board never ceases to amaze me.

[Jared at Pelican Parts]

where are the dimples on the cam for the SC, on the face of the sprocket?

I've got a pin lined up in one of the holes, that it?

[ChrisBennet]

Originally posted by Jared Fenton
where are the dimples on the cam for the SC, on the face of the sprocket?

I've got a pin lined up in one of the holes, that it?

The dimple is on the end of the cam. It also has writing on the end. I think it reads "930" just below the dimple and "147" or "148" below the that.
Not to alarm you but you're kinda scaring me a little with the talk of removing the pin and apparently not knowing the orientation of the cam. Maybe I'm just not understanding you.
-Chris

[Jared at Pelican Parts]

I meant the pin on the inner sprocket being used as a reference mark, setting the cam in a relative position to the Z1 mark

[ChrisBennet]

Originally posted by Jared Fenton
I meant the pin on the inner sprocket being used as a reference mark, setting the cam in a relative position to the Z1 mark

Aha! The "pin" you are refering to is called a (Woodruff) "key" and the slot that it fits into is called a "keyway" (or is it "key way"?). AFIK, the keyway is at the top just like the dimple and is much easier to see.
-Chris

[Vipergrün]

Jared, BE SURE TO TURN THE MOTOR OVER BY HAND FIRST. I have pics on the board somewhere of what happens to valves and pistons when the timing chainn jumps a tooth during ramp installation. It ain't pretty.

[Jared at Pelican Parts]

Ok, I turned the motor over by hand and felt no resistance.

Engine is back at Z1, however woodruff key is at roughly 80 degrees from the top? am I 180 off? stick a pencil in the cylinder to check for the piston? If this is right and I'm 10 degrees BTDC, does this make sense, considering the cam rotated the opposite way?

I checked the intake and exhaust valves clearances and they are exactly how I set them earlier.

[john walker's workshop]

the only position the engine should be in when the tensioner is removed is #1 TDC (Z1). any other position, and the cams won't stay put when the tensioner is removed. sounds like what happened. the cam flops one way or the other and the chain jumps a tooth on the intermediate shaft. don't assume all is ok. you need to get hold of the proper dial indicator and go through the procedure to see for sure where the timing is. wayne's $29.95 engine rebuild book would be a good investment right now. barnes and noble, etc.

[Jared at Pelican Parts]

Yeah, I know, I made a huge mistake here....