Rebuild Valve Set

[Bookwus]

Hiya All,

So......I've pretty much arrived at the longblock stage of the rebuild and I'm wondering what to set the valves to. I'm fine and good with .006 but it seems that I've read (somewhere at sometime) that it's a good idea to initially set the valves at .007. Then tighten 'em up to .006 after the first run in.

Any opinions/ideas on this?

[vdubyah73]

Just speculating. Engines running in place for 20 minutes at around 2000 rpm on initial startup get HOT. All the parts getting used to each other,etc.. I've been there for several cam breakin runs, 3 that have been mine. They can get uncomfortably warm to stand next to and fiddle with. Maybe that is why the suggestion has been made. You wouldn't want the valves to become too tight due to over expansion of parts at the higher than normal operating temps..

Suggestion, before start up have a way to hold throttle where you need it to maintain the rpm. Be it someones foot or a pair of vice grips. 20 minutes is a long time to hold the throttle with a foot while standing still, even longer if holding it by hand. Have someone with you for start up so one can start while the other watches for catastrophe. Have a fire extinguisher handy. Good luck and remember that 2000-2500 RPM standing in the driveway sounds horrible, like a million sewing machines. Listen for screechy, grindy noises, probably tin.

[spiffy]

The idea also might stem from folks that want to ensure "soft" stress on the cam during break in. In other words, the extra .001 may give the cam a little "cushion" from the hell it gets put through the first 20 minutes. Or as mentioned before prevent the tolerances from tightening up too much.

Not that I suscribe to the idea but .007 would be better then .005, yes?

[Bookwus]

Hiya Mike,

Well, that aspect makes sense to me. I was just concerned with the other end of system, the valves. I'm a little paranoid about valves these days!

[spiffy]

I guess the extra space may clatter for a few minutes which may or may not chew the valve stem or adjuster up...but I doubt it. I am planning on running mine the first time with .006, I think if an engines parts can be damaged by 20 minutes of break in temps then one might question other things other then valve adjustment options.

Crazy how you can research these things and there are SOOOO many opinions out there. I have noticed that if you read up enough a common "middle ground" starts to form and the outliers just loose their traction in yer head space. I guess if I were an engineer or metalurgist I could confirm or deny said opinions....until then....who am I kidding

[Amskeptic]

Hiya Mike,

Well, that aspect makes sense to me. I was just concerned with the other end of system, the valves. I'm a little paranoid about valves these days!

If you are going to be adjusting your valves the very next morning, why not keep them within factory settings while parts are not bedded in?

Your clearances are likely to drop as the heads seat and the valves bed into their seats. So by all means adjust the next morning to a nice easy .006. The next valve adjustment, you make a judgment call. Did some valves close up a lot? Did they all close up a little? Did some actually open up? If they closed a lot, you will want to reduce the interval to your next valve adjustment, like at 100 miles instead of 300 miles. If they opened up, counter-intuitive, check them in 50 miles, because you may have a cam or lifter issue. If just one valve shifts its clearance, that is more troublesome than if all did. Don't second guess the factory settings right here. I have run loose clearances on broken-in engines in extreme heat, yes, but I have enormous elephant feet swivelfoot adjusters that are a piuece of cake on the valve stems. You may remember I did not set my valves loose on the Squareback when the seat was failing, because the hammering would just hasten the failure. What I did do, was adjust my valves every three days. So you may not mess with clearances, but I invite you to monitor closely amd adjust frequently until your sense of trust has developed.
Colin