1968 GMC Inline 250 Valve Adjustment
 

Hi All...
I have a slight clicking/clacking noise so I'm thinking the valves may need adjusted. I found some older posts I've been reading but I saw conflicting information. Some say to tighten the nuts an additional 1/2 half turn after reaching zero lash and some say to tighten 1 full turn. Also, some say to tighten the additional turn with the motor running and some say to tighten after turning to motor off. With that being said, the GM shop manual says to tighten each nut four 1/4 turns, 10 seconds apart (for a total of 1 full turn) while the engine is running. That was back in 1968 so the thinking may have changed. My motor is all original with 55k miles. Looking forward to the advice.

Re: 1968 GMC Inline 250 Valve Adjustment
 

I've always adjusted hydraulic lifters as the manual you cite specified.

Re: 1968 GMC Inline 250 Valve Adjustment
 

I've always used the "one turn" method on new lifters and "half turn" on used lifters.. Never had a problem with either method...

Re: 1968 GMC Inline 250 Valve Adjustment
 

X2, 1/4 turn at a time.

Re: 1968 GMC Inline 250 Valve Adjustment
 

They so seldom loose that adjustment, you may want to do a little investigation to determine the cause.
Several years ago I had a problem with the stock push rod ends. Cam is considered mild and rocker geometry is good. I replaced the rods with ones that had what I think have a nicer machined end. Similar to ones in the 2nd image from the web.

Chevy inline six rockers are 1.75 compared to SBC 1.5 ratio.

You can't go wrong with the manual method of cold adjustment with the engine stationary. Half at TDC and the rest after rotating 360*. One half turn below Zero lash

Re: 1968 GMC Inline 250 Valve Adjustment
 

I once talked a Junkyard Guy out of an L6 Valve Cover, saying I was going to cut out the top of the piece and have an open slot so I could adjust the valves while running and keep oil splash to a minimum. Those little clips they sell at the hot rod store to clip on the end of each rocker may work on V8s, but they slip right off L6 Rockers in less than 2 seconds.
Still have the extra Valve Cover -- never did the modification because I've had good luck setting the lash while the engine is still and cold -- once TDC has been found.

Re: 1968 GMC Inline 250 Valve Adjustment
 

I did the valve adjustment yesterday. Did it with the motor running. Found an old valve cover that I cut out and used as a splash guard. No oil splashed anywhere. Ended up adjusting them three 1/4 turns, ten seconds apart. The motor didn't seem to like the fourth 1/4 turn. Put the valve cover on with a new gasket and let it sit overnight. Took for a ride today and all seems good. Sounds better too. Thanks for everyone's advice!

Re: 1968 GMC Inline 250 Valve Adjustment
 

Glad that worked out for ya.