Valve Adjusting? You won't believe this...

[Turbo1dr]

...on second thought maybe you've seen this happen. I have the latest and the greatest GN1-R's (full race ported 2.0 & 1.6 valves), T&D roller rockers and SOLID roller cam. Brief history: On the engine stand, I adjusted all rockers to .013. I installed the engine in my Malibu and I heard them clicking... normal I thought, no big deal. It runs fine and I've even drove it about 50 miles.

Fast forward to today:

I decided to check the lash so I pulled the valve cover on the drivers side and started adjusting them. The engine was about 120° when I started. Before I put the valve cover back on I cranked the engine and let it idle for about 2 minutes to check for tapping. I then rechecked the lash and it increased about .003. So, I re-adjusted them again and restarted the engine. Ran it for a few minutes and I cut it off. I re-checked the clearance again and the same thing happened. There was more clearence. Puzzled as to why this was happening (actually scratching my head), the engine had a chance to cool off but not totally cool. I then decided to set one rocker at a tight .006 lash and then started the engine. I run the engine for about 3 minutes and turned it off. I immediately got the rocker back to the same location to where I set the lash except this time the lash was .009! I stayed there checking & re-checking the lash with the feeler gauges as the engine was cooling down. As the engine was cooling down the clearences got tighter. You could actually feel the .008, .007, .006 feeler gauges get tighter between the rocker tip and the valve stem.

Everyone knows that metal expands when heat is applied so the gap should decrease but it's increasing instead. My diagnosis is the combustion chamber is actually "expanding" as it heats up and in turn, this causes the valve to become farther away from the rocker arm tip. If ANYONE near me would like to come see for yourself and confirm with your own eyes PLEASE DO SO! If you have a simular set-up as mine please post your experience. I'm an ASE Certified Master Technician so I have seen lots of unusual things in the automotive world. I have never seen this happen before on ANY car.

All the guys with the simular combination please post.

 

[wbrophy]

Aluminum heads on a cast iron block will expand more than the block therefore most experts recommend setting valve clearances .002/.003 tighter than spec. when using aluminum heads to allow for the expansion. It's .002/.003 if I remember correctly.

 

[Turbo1dr]

I didn't think the whole head would expand that much with only 2 to 3 minutes of running. If that's the case, then I can just set the rockers at only .003 when totally cold and after it heats all the way up maybe they will increase to .010.

 

[Turbo1dr]

UPDATE:

I set all the valves to .004 when the engine was 55°F. I started it up and it was so quiet I was amazed. After it warmed up more I could hear them start tapping again. Fully warmed up it sounds like a secretary typing 200 words a minute. This is my first aftermarket aluminum headed car with solid lifters. I guess you learn something new everyday.

 

[wbrophy]

Checked the spec. iron block/aluminum heads= .006 tighter for cold setting, (ex. Hot setting= .018, Cold setting= .012) rule of thumb, some iron block/ aluminum head combos may need a little more or less to get the hot setting right on.

 

[Mike Licht]

Best thing to do is get the motor good and hot and set one cylinder that is easy to do. LEt it sit overnight and then check the same cylinder cold. This will give you a "cold lash" that will be easy to get when the engine is cold
Mike

 

[65vette396]

Yes, I can believe this. Actually quite normal. I typically just find out where the car runs during normal driving say 180 or so water temp. Then to adjust the valves, start the car and warm it up to 15-20 degrees above where it normally runs. The adjust one bank of cylinders. Re-warm to 15-20 above opperating temp and adjust the other bank. Works out well everytime, Drew