bshaw

I'm working on setting up the cam timing and am having some trouble. I have the 2 dial indicators set up, one on #1 intake follower and one on #1 piston. I set the crank to the position specified in the wsm, 45 degrees before #1 bdc, apply 45 psi of air to the tensioner air fitting, then rotate the crank looking for my .39mm on #1 intake. As soon as I start rotating the crank the tensioner moves up, messing up the setup. Apparently the air isn't holding the tensioner in the down position properly.

When I rotate the crank, with or without air pressure in the tensioner, the tensioner moves up and down a few times per rev. This doesn't seem normal, does it? Is there a problem with my tensioner?

RajDatta

You should be sholding the pressure. You are losing that pressure somewhere. ou need to simulate 3 bar of oil pressure. Do you have the metal ball in the tensioner where the j-tube meets it?
Raj

bshaw

Yes, I used the wrong terminology but set it up per your directions (and the WSM). As soon as I roll it forward to get the 0.39mm the tensioner moves up. Have you seen this behavior before?

jgporsche5

I just went through this a few weeks ago. I had taken my cylinder head off looking for bent valves and didn’t mark my cams. I’ve only worked on 911’s prior to my 968. I was going to go through the cam timing thing also, but I noticed that the grime behind the timing gear that connects to the exhaust cam had imprinted a shadow that I marked with an engraver, I believe there is nine holes. I then cleaned it up and filled in the engraved circles with a permanent marker. It was obvious to me that if I lined up the holes in the timing gear that the little key was near the middle of the adjustment key way. I then put the gear back on and lined up the holes. Car runs great. Our PCA club is having a dyno-tune day in a few weeks and I will see if it’s putting out the right HP. Seems the same as before.

Also, although I replaced the cam chain due to age I did it with marking the 12 links on the new and old chain and just matched them up. I didn’t disturb the cam timing. I imagine this would be useless advice if you stripped a cam or broke a cam chain, but if you just broke a timing belt like I did it would give you a good place to start from. If you took off the big bolt holding the timing gear off with out marking anything and no realizing that we are suppose to put bolts through the timing gear to keep your cam setting.

I did notice that the variable cam chain tensioner raised and fell as I hand cranked the engine via the crankshaft bolt, just figured that was normal.

bshaw

We went through the timing process at least a dozen times last night until we were sure it was dead nuts on. Although the instructions in the wsm aren't crystal clear it's actually pretty straight forward once you do it.

The tough part is holding the exhaust cam while turning the cam sprocket. It's right at the top of a lobe and wants to jump off once the sprocket is loosened. That accounted for at least 3 of our attempts at setting the timing. Got the intake opened to 0.39mm, loosen the sprocket bolt to bring the piston up to tdc and whoops, the cam jumped again!

It is normal for the tensioner to raise and fall as the motor is turned over by hand. With no oil pressure to hold the tensioner in one position or the other it just kind of flops around as the cam lobes present varying amounts of tension on the chain. When the #1 intake lobe is about to start pushing on the bucket the tensioner can be pressed down and held in place pretty easily, so it all works out OK.

We're done with this step now, time to put the motor back in. Thanks for all your input guys.

RajDatta

I guess if you have steady air pressure into teh tensioner, you should be fine.
Raj