Timing chain jumped a tooth

[jussumguy]

Hi, new guy here. I have a 1976 911 with what I believe to be a 1979 3.0. I am in the process of getting it back on the road. I am putting the hydraulic chain tensioners on and lost my cam timing on the right side. I jammed wood shims around the cam sprocket thinking that would be safe to remove the tensioner and apparently it jumped a tooth on the crank side.
I see now that I should have put a couple zip ties on the chain and I would probably be done now. Is there any prayer of getting it to pop back or must I dismantle the rear of the motor and deal with it from there. I have some experience with rebuilding motorcycle engines so I don’t think I’m in over my head yet.
Thanks for any assistance or sympathy

[john walker's workshop]

Just retime that cam. If you had set the engine at tdc on #1, the cams would have stayed put when the tensioners were removed.
When you get everything back in order, see what the other cam is timed at and adjust them the same.

[JSV798]

Sounds like the cam nut is till on. Retiming the cam requires that the 46mm? nut is removed with a special tool (I recommend the Stomski tool). Then he will need a dial gauge etc.... It can be done with the engine in situ. Not a job for the faint hearted.

[jussumguy]

Originally Posted by john walker's workshop

Just retime that cam. If you had set the engine at tdc on #1, the cams would have stayed put when the tensioners were removed.
When you get everything back in order, see what the other cam is timed at and adjust them the same.

I had it at tdc when it happened. Do I need to remove the cam nut to get it back a tooth or is there another way

[Nditiz1]

How do you know it jumped a tooth? Also, and I am not as experienced as other engine builders on here, but I'm trying to wrap my head around how it happened. Are you saying the valve spring had enough force that when you removed the tensioner it jumped the chain? As in you saw it do it? I'm pretty sure I can remove the tensioners in my 2.7 and the timing will not move unless I turn the crank and it force the chain to jump.

[jussumguy]

I set the crank at fz and locked the cam chain onto the sprocket with shims then removed the old tensioner and called it a night. The next evening I bled the air out of the new tensioner and compressed it . When I went to install the new one I found it wouldn’t fit. The upper length of chain was loose and the lower was so tight I couldn’t get the tensioner to fit. I’ve now rolled the crank maybe a third of a turn trying to clunk it back but it’s off.

[Nditiz1]

You will have to remove the large nut. Then you can get the pin out and reset the timing and check.

[jussumguy]

Hmmm ok
That’s not what I wanted to hear. Well I guess I’ll be learning how to degree cams like the big boys do! Where do I get the fancy wrench, is there a rental out there somewhere?
Thanks everyone for the support

[dannobee]

You don't have to remove the cam nut if you're only going to reassemble it, since you pulled it apart at Z1 anyway. But you will need a dial indicator to determine valve lift. Assuming you didn't move the crankshaft, put the crank at Z1, then position the cam with the two flats pointing vertical with the numbers up. Then reinstall the timing chain. At this point you can check valve timing with a clamp on the idler gear in place of the tensioner. It'll be as close as it was before you pulled it apart. Spec for a 3.0 is 1.4-1.7mm, 1.55 preferred.

Whatever you do, do NOT rotate the engine or cam if you feel resistance, as the pistons can hit the valves.

You can sneak the chain around the gear to reposition it if you're careful. I've had to do it a few times myself.

[boyt911sc]

Jussumguy,

Do you know and understand how the cam timing is done for your motor? Do you have the right tools to do the cam timing? Do you know how to do the valve’s adjustment? If you know all these questions, you could do the cam timing in a few mins. of work. First thing you need to do is turn the motor 360°. Repeat it a couple of times and prepare to check your cam timing. If the motor will not complete a full revolution, do not force it.

You don’t need to remove the cam nuts at this point. All you want is see what cam timing you have now. A mechanical tensioner is needed during cam timing. Keep us posted.

Tony

[jussumguy]

Originally Posted by dannobee

You don't have to remove the cam nut if you're only going to reassemble it, since you pulled it apart at Z1 anyway. But you will need a dial indicator to determine valve lift. Assuming you didn't move the crankshaft, put the crank at Z1, then position the cam with the two flats pointing vertical with the numbers up. Then reinstall the timing chain. At this point you can check valve timing with a clamp on the idler gear in place of the tensioner. It'll be as close as it was before you pulled it apart. Spec for a 3.0 is 1.4-1.7mm, 1.55 preferred.

Whatever you do, do NOT rotate the engine or cam if you feel resistance, as the pistons can hit the valves.

You can sneak the chain around the gear to reposition it if you're careful. I've had to do it a few times myself.

Well that’s what I was thinking. The chain rolled over on its own , I didn’t move anything on the engine to get it out of sync. It may be trying to tell me the chains are worn out. I have rolled motor about 1/3 turn forward and backwards trying to get the chain back where it needs to be.when it has resistance I stop. Is there a trick to sneak the chain over?

[jussumguy]

Originally Posted by boyt911sc

Jussumguy,

Do you know and understand how the cam timing is done for your motor? Do you have the right tools to do the cam timing? Do you know how to do the valve’s adjustment? If you know all these questions, you could do the cam timing in a few mins. of work. First thing you need to do is turn the motor 360°. Repeat it a couple of times and prepare to check your cam timing. If the motor will not complete a full revolution, do not force it.

You don’t need to remove the cam nuts at this point. All you want is see what cam timing you have now. A mechanical tensioner is needed during cam timing. Keep us posted.

Tony

I have freshened up several overhead cam Japanese motorcycle engines so I probably have enough experience to get in trouble. I have the Bentley service manual and the Dempsey 101 projects book. Also YouTube is helpful.
I am working in a quiet little shop behind my house. I have a pretty complete tool set but no specific cam timing tools. Setting the valves will be my next project if this poor thing survives me. I just got the SIR feeler gauge tool.
As it sits right now the passenger side cam is probably one click clockwise out. I have already put the cover on the left side but will remove it right now

[E Sully]

At least it didn't jump a tooth like mine did, while it was running. I had to replace 3 valves.
Here's a link that may help you along with Wayne's book. I didn't find it that hard.
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/15-Cam_Timing/15-Cam_Timing.htm

[jussumguy]

Originally Posted by E Sully

At least it didn't jump a tooth like mine did, while it was running. I had to replace 3 valves.
Here's a link that may help you along with Wayne's book. I didn't find it that hard.
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/15-Cam_Timing/15-Cam_Timing.htm

Yikes
Did you replace the chains after that ? And if you did chains , sprockets too? How long do these things last? My car has 290,000 miles on the odometer but I think this isn’t the original motor.

[Superman]

Listen to John.

[john walker's workshop]

Ya know, the cam may not have jumped a tooth and you may have been able to just turn it back until the chain slack was taken up and then install the tensioner. But now you've rotated the engine from where it happened, so hard to tell. The flats on the ends of the cams should be at the same angle if you get lucky. I'd still dial gauge the timing.

[JSV798]

I suggest you get the tensioner back on as best you can and then check the cam timing on both sides. You will need a dial gauge for this. Follow the Bentley manual.

[E Sully]

Originally Posted by jussumguy

Yikes
Did you replace the chains after that ? And if you did chains , sprockets too? How long do these things last? My car has 290,000 miles on the odometer but I think this isn’t the original motor.

The original chain tensioners failed at about 140,000 miles.
I didn't split the case, so I used new master link chains, replaced sprockets, updated oil fed tensioners, new valve guides, and new exhaust valves.