Slipped timing chain??
 

I was all prepared to do the tensioner upgrade on my '70T today. I thought I would do the ramps at the same time and I was very careful to ensure that the chain wouldn't slip off the cam sprocket. I wedged a piece of wood between the casing and the left sprocket to ensure the chain wouldn't move and then I took off the old tensioner. I was trying to get the lower ramp off and I was pushing on the chain and all of a sudden it slackened up quite a bit.
The chain didn't slip on the cam sprocket but is it possible that it slipped off the crankshaft?? I put the old tensioner back on and then tried to turn the engine by hand but it's meeting some resistance.
HELP!!

a perfectly opportune time to learn more about your engine! search the cam timing archives, and follow the procedure. also in various 911 manuals. there are lots of specs for 911 cams. you need to find your engine type #, and relate that to the proper timing for your engine. that works if nobody swapped cams in the past. the numbers on the end of the cams help ID them also.

Ok, how about this.....
The crank is currently at TDC and the right cam's punch mark is at 12:00 o'clock. My left cam's punch mark is at about 11:00 o'clock so it does look like the chain has slipped at least one tooth on the left side sprocket.
What if I slacken the left chain enough to slip it back one tooth on the sprocket? After I get the cam re-positioned to 12:00 o'clock, I'll rotate the engine (by hand!) to ensure there are no more obstructions.
DOES THIS MAKE SENSE???

If you did not remove the cam sprocket then the cam timing did not change. You are correct: make sure you are at TDC and both cams should be real close to 12 o'clock.
Good luck

not to freak you out, but i've seen cams that did not sit at 12 oclock when the timing was correct. in your case if the cam that didn't slip was straight up, then moving the other one back a link should be ok.

To set your mind at ease I think it would be impossible to get the chain to slip on the crank sprockets unless you had the engine tipped up sideways on an engine stand with lots of slack in the chain. And it would be really difficult to slip a cog on the cam sprocket. You will find out just how difficult it is if you ever decide to (try to) "slip it back one tooth".
The resistance to turning might be caused by something being jammed in there. Did something break off your wooden stick? Are any of your old ramps missing bits? (Look at the bottom where the pins go through.) I would remove the chain ramps one at a time and see if the chain is still stuck.
Once you solve that problem I think the cam timing will be fine. I wouldn't try to "fix" the cam timing if you aren't set up to measure it.
In my own limited experience, when I set my cams they are often not at 12 o'clock but when the top mark "leans" to one side both cams lean the same amount and in the same direction.
BTW: Save your old mechanical tensioners. They are handy for setting the cam timing.
good luck,
Chris

Chris,
I hear what you're saying but how would that explain why my right side cam is sitting with its punch mark at 12:00 o'clock and the left side is at 11:00'oclock (there is a significant difference between the two)? Is this possible?
Thanks

it slipped on the intermediate sprocket. normal.

Thanks John...here's my challenge....
I can't slip the chain on the cam sprocket as there's not enough space between the sprocket and the case to slip the chain off (the case appears to have been welded and has a weld bead on the inside of the case very close to the sprocket).
I'm trying to slip the chain off the crankshaft sprocket but I can't seem to do it. Any suggestions?

To set your cam timing I would not recommend that you pull the chain off the crankshaft especially on the driver side since it can come off or even worse only be on one set of teeth on the double roller and be over looked . You will have to remove the cam nut and do it that way. If im not mistaken the size is 45mm. Also if you changed the ramps make sure they are fully snapped into place. There is no reason however to remove any gears to change the teeth the chain is on. Just remove the nut and large washer then use a small wood screw or a magnet and remove the dowel pin. With a 17mm wrench just turn the cam to 12 o`clock while at tdc (OT) install the pin in any hole that lines up and begin your cam timing procedure. It will probably take you a few hours of trial and error to accomplish this but be sure not to let the chains fall off the crank gear. Make sure the valve adjustment is also in order before you do a final setting. I am not a pro at this but i have changed my chains and upgraded my tensioner recentely so it still fresh in my head.

Kurt Williams

pull the oil drain plate and you will get a better view of the sprocket you need to deal with. with a little ingenuity, you should be able to jump a link there.

Have you fixed the "resistance to turning" problem? You should address this problem before you worry about the timing issue. The timing difference may fix itself when you get things unjammed. You said there was a resistance to turning, do you mean it won't turn at all past a certain point (without forcing it more than you feel comfortable)? If the plugs are still in they will cause some resistance to turning. You might try removing them in order to have better "feel".

I went out and looked just now in the chain boxes of a 3.2 motor that's on the stand. On the left side there is about 20mm between the bottom of the chain ramp and the chain below. On the right side there is about 8mm between the bottom of the chain ramp and the chain below it. If you don't have this sort of spacing perhaps something is making the chain on that side seem a couple of links shorter? That in turn would put the timing off.
-Chris

Chris,
The resistance I'm feeling is very solid...I can definitely feel metal on metal.....it's definitely not compression that I'm feeling. I turn the crank and it gets to a point where it won't turn anymore.
My chain ramps are ok and the measurements you provided are about the same as what I have.
I'm going to take up John on his suggestion to remove the oil drain plate and maybe I'll be able to see if anything is obstructing the chains.
Thanks

slipped timming
 

It is possible to have the chail slip!! While I was timing my new cams. My chain slipped on the intermediate shaft. The chain spun free around and around. Luckely I was able to get it back on correctly.(The way john says) Good luck I know what a hassle it is.:D

Re: slipped timming
 

Wow, I stand corrected!

Success!

I've managed to slip the timing chain back to its original position. It only took me 4 hours of trial and error but I've now perfected the art of chain slipping:)

I used a piece of flexible plastic to slide down the chain so that I could separate the chain from the crankshaft sprocket. I then turned the camshaft back to where it was supposed to be and the chain slipped easily over my plastic "chain slipper tool".

I can't take credit for the idea though.....I seem to recall some other pelicanhead suggesting this in a previous thread :D

Thanks for all your help!

That was me. And im still waiting for wayne to put up that tech acticle on chain replacment.

Kurt Williams

Success!!
 

Just a note of thanks to John Walker, Chris Bennett and Kurt Williams for helping me through my tensioner upgrade adventure. I finally got everything buttoned back up today and she sounds real sweet!
Cheers! SmileWavy