The Stovebolt Site Forums The Shop Area Engine Shop Lash

Ok I am once again a little confused. So I just read a little bit of info that when you remove the rocker arm shaft and rockers for cleaning I should set the lash between 4 to 5 looser than the hot setting. Then after warm up, set the correct lash for your cam. If you use a hot setting to set the lash on a cold engine you could burn an exhaust valve? I am getting ready to test the compression and do a leak down test we were talking about earlier in a different post for an unknown used 235. Now for a freshly built 235 with Patrick’s cam I was instructed set the lash according to the cam card. I ran the engine for 30 minutes at 2500rpm to break in the cam. Should I have started with a loose lash? And if so could I have damaged the exhaust valves, Newby!!
Thank You
Shade Baby

Setting the valve lash for a couple thousandths more than the hot setting should work OK. If you set it at hot lash settings, you'll probably be OK. Since you've already run it at 2500 rpm for 30 minutes, you'll find out if you've burnt an exhaust valve.

Shady, I just did this last week. I was paranoid and anxious that I was going to screw things up because I have never adjusted valves on any engine in my entire life.

It turns out that I was overthinking everything. It went back together perfectly and runs better than it ever has in the last 5 years in my possession and 25 years in the ownership of my friend.

Anyway, I followed Jerry's tutorial posted in the Tech Tips at the top of the Engine Section.

I set the cold lash exactly as he suggested - .008 for intake valves and .012 for exhaust valves. It started right up, ran perfectly and didn't bend any pushrods.

I then did two hot valve adjustments per the manual after several hot/cold driving cycles to double check everything. I quieted down a ticking that was likely due to a worn rocker. I used a tiny feeler gauge in the dead center of the valve stem to get a more accurate adjustment.

The truck has noticeably more power and much quicker acceleration. I'm mad at myself for being too scared to do a valve adjustment earlier on in my curatorship of this truck.

Now you guys have me worried about burning an exhaust valve. I need to stop thinking about this stuff.

How would you know if an exhaust valve is burned? What are the symptoms?

What’s a burnt valve like

I imagine there's be a big loss of compression and the engine would run like crap. I'm still worrying about it now, though.

I always forget to check the Tech tips

Thanks
Shade Baby

A slightly burned exhaust valve will cause a rythmic popping noise at the exhaust pipe- - - - -a little bit of compression/combustion pressure escaping before the valve is supposed to open. A burned intake will produce a rough idle and fluctuating manifold vacuum due to pressure escaping into the intake manifold. A slightly burned valve is sort of like being "a little bit pregnant"- - - - -things aren't going to get better on their own! As valve burning progresses, the cylinder will lose compression and eventually develop a dead miss.
Jerry

None of that seems to be going on with my truck.

Is the .008 / .012 intake / exhaust cold lash good for the 216?

Due to a variety of stovebolt camshaft options that have been available over the past several decades, no hard and fast rules can be set in stone. Of course, the purists who bow down and worship the factory service manuals from 60+ years ago will disagree, since Moses brought those manuals down from Mt. Sinai millennia ago- - - -chiseled in stone!

The purpose of valve lash is to slowly take up the "clearance ramp"- - - -the short section of gradual lobe lift that stacks the cam lobe, valve lifter, pushrod, and rocker arm together before the valve actually starts to lift off the seat. That prevents noisy valvetrain operation and rapid wear from excessive clearance, and also stops valve burning from the valve failing to close all the way at the end of the cam lobe. The only way to be absolutely sure of correct lash adjustment would be to check every cam lobe with a degree wheel and a dial indicator and adjust the clearance according to the lobe profile. That .008/.012 is a pretty good starting point. At least it assures that valves won't burn from being too tight. If they're noisy at normal operating temperature, sneak up on quiet operation a little at a time. The big thing to remember is that there MUST be a little slack on all the rockers with the engine hot.

Now- - - -hydraulic lifters open up a whole different can of worms!
Jerry

Thanks, Jerry.

So to be clear; On a hot engine, if I can reach in and wiggle a rocker arm when its corresponding valve is closed, it's not too tight? It has slack when it's hot. It might be too loose but not too tight?

That's basically correct. You can check both valves on a cylinder at the same time if you line up the distributor rotor with the corresponding wire on the cap.

So it’s best to use the specs for setting the lash per the cam card profile. That is if it’s not stock. Then slowly adjust for a quit operation.

Shade Baby

Yes- - - -the "cam card" should be preserved by the owner/engine builder and its information is gospel for the life of the engine. Anyone with the unmitigated gall to call himself an engine builder should have the ability to degree a cam and duplicate the information contained on the card if he's dealing with a cam of unknown origin. All that's needed is a degree wheel, a dial indicator, and a basic knowledge of how an engine operates. If the cam details are known, it should not be necessary to deviate from the published clearances. For an initial run-in of an engine when I'm dealing with an unknown cam, I gently take out all the clearance on both rocker arms with the piston at TDC on the compression stroke, and back the adjuster screw off 1/4 turn. That assures there won't be any tight valves during warmup.
Jerry