[Shotimes] +20 cam valve noise

[Mike Bruce]

Bruce,

I did the install on my own set of +20 cams, and chose to set my gaps at .006" and .010" for intake and exhaust.  As soon as I had the car running, I notice more valvetrain noise than normal.  After 2000 miles, I checked the valves to see where the gaps had moved and found that they had opened up .002-.003".  They were all still in spec and making as much noise as when installed, but I chose to tighten them back up to the lower limit.


My belief is thatv you should check your gaps after a couple thousand miles just to be safe.  The extra valve noise, I think, comes from the change in profile over the stock lobe.  The longer distance from the base circle to the lobe tip would have more impact than stock.  The tip of the cam lobe hits the shim like a hammer hits a nail.  Think of two hammers with different length handles. The "+20" hammer would hit the nail, or shim in this case, with more force.  

Mike

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anyone want to confirm for me that when cams are 25% to 50% out of spec on the valve lash they will sound like a sewing machine? Got a friends car in the garage that makes a racket, and I'm finding intake valves in the .008 to .013 range and exhaust valves in the .011 to .016 range. These were a SHOnut +20 set of cams installed by a trusted New England SHO mechanic, so I know they were installed right. 

I thinks I need to look at my own cams and see if they have opened up in my car. 

Before I go tearing into this engine to reshim the motor I wanted to make sure I wasn't missing anything else.

So, outta spec valves sound like a sewing machine? Anyone. I've only seen a few cars with a valve or two just barely outta spec, and never heard these kinds of noises.

Thanks

Bruce