View Full Version : can valves hit piston

05-19-2008, 07:01 AM
I messed up the alignment of my cams with the crank so I'm planning on redoing it all. Can the valves hit the pistons? I've heard people say so but I've been thinking about it and the piston is flush with the block, and the valves are up there in this dome shape so how can it? and my cam is off by alot, almost 3 or 4 teeth. Is it possible for me to put it back together and just time it with a gun?

05-19-2008, 07:50 AM
Yes, valves can hit the pistons.

There are no valve reliefs in the stock pistons.

What you need to do is:

1) Remove cams

2) Get the motor to TDC on #1

3) Reinstall cams properly

...and a timing light will only be of use when it's back together, and you're checking the base timing.

- Brian

05-19-2008, 12:28 PM
A timing light is used to set your ignition timing via the adjustment of your distributor/cam angle sensor.

Your cam timing is set mechanically and cannot be adjusted after the engine is assembled.

Being off 3 or 4 teeth is more than enough to cause the valves to hit the pistons. You have to understand that even though the valves are up in the dome of the head, when they open the protrude down into the block. If the mechanical timing of the valves is not set correctly, the valves and pistons will try to occupy the same space at the same time, with dire consequences.

If you know your cam timing is off, do not even attempt to turn the motor over by hand. Fix the problem and then get on your way.

P.S. - Since I know someone looking to start something is going to chime in. If you have a motor with VVT, the cam timing can be adjusted electronically once the motor is assembled. However, that is out of the scope of this quesiton.