Hi,

I have the cam timing set properly on my 71 240z, but I have run into what I see as an unusual problem. The head has recently been machined. After doing a cold adjust on the valves, the cam would not turn through a full rotation. After alot of investigation, it was found that the cam was trying to compress a couple of the valve springs further than they wanted to go.

Has anyone here had a problem like this. What is the easiest fix?

Thanks

After giving a simple answer in a previous thread, I'm treading carefully here.

It appears that the cam towers may need shimming, most machinist's usually set up the valve train after machining. YOurs may not have.

There is no simple answer as you may need to adjust the valve train geometery using cam tower shims and different size lash pads.

Have you changed cams, this may have contributed to your problem?

Or perhaps your timing is not actualoly right, and the valves are making contact with the top of one or more pistons. I'd re-check the timing to make sure it's really as accurate as you believe.

The timing is right.

when looking at the pistons, none of them are up when the valves are down. The problem is that the springs are being compressed too much, as in the rocker arms are going too low.

How much did the take off the head?

I wish I knew how much came off the head.

The story on this car is that I bought it off someone in a non-running condition. The guy was selling it because of the classic wife and kids story. He had blown the head gasket, removed the head and had it remachined.. and that's where he stoped the work. So I guess is there an easy way to fix this without knowing how much was taken off.... . or should I be investigating that?

What about the lash pads . Are they correct thickness . The towers only would need to be shimmed if more than .030'' was milled from the head. I am not sure what you are experiencing. If you adjust the valve with the cam lobe straight up and the setting is correct then when you rotate the engine . The rocker over compress the valve ?? Gary

What abou rised

Yes this is what I do not understand If adjusted in the proper position and the lobes are up and it's the right cam and valve components it can't push them down too far unless they go going down at the wrong time. The can only go as far as the height of the cam lobes. I would realy suggest making sure the timing is right and the right parts are there. I am not even sure that this is a interference engine. (meaning that it is possible for the valves to hit the piston if they go down at the wrong time) Good luck.

The standard head thickness is 4.218". (I believe) Grab a set of calipers and measure the head. As mentioned before .030" under this needs to be shimmed.

You are using stock components right? If not, that might be the problem.

I'm just grasping at straws but is it possible that something came loose down low? (Tensioner)

Stock head thickness is 4.250

More technical info is needed to diagnose your problem. Also note, a head with valves/cam etc. can be set up on the bench to eliminate all or most of the unknowns you list.

Phred

After reading this, and what others have written, I figure I'll have to shim to cam towers. I'll keep posted as to how it works out.

Any suggestions on a good supplier for shims?