L84 Valve lash adjusting clarification

[Edward G.]

I am adjusting the valve lash on my 63 L84 engine with the original Duntov cam. I am referencing the John Hinckley and Duke Williams cam valve adjustment article dated 9-23-2008. I have indexed my harmonic balancer in 90* intervals and verified that the timing marks are accurate at 0* TDC #1 piston. I am using the factory settings of 8 and 18 thousands.
My confusion is that I am assuming that when I go through the steps of of adjusting each valve as listed on the article, TDC #1 - 8E, 2I then 90* and adjust -4E,1I and so forth, I am assuming that each valve listed in the sequence will be set at the lowest point of each cam lobe. Then after going through the complete sequence I should not have more clearance on the valve lash at any time during the cam rotation than I set during the initial adjusting sequence.
So to clarify, if I complete one adjustment sequence and I am back on TDC #1 and now search for any rocker arm other than 8E-2I that is loose and check the clearance on that rocker I should not see a greater clearance than I initially set on the first go around.
Is this correct?

Ed

[Timothy B.]

Re: L84 Valve lash adjusting clarification

Ed,

I don't want to get in front of anyone responding to your question but "one adjustment sequence" would be two complete revolutions of the crankshaft. At that point you are correct in that the adjustment on any valve should not be greater than the feeler gauge setting you used but keep in mind there are other valves that have a little lash in those crankshaft positions but they are not on the base circle of the camshaft.

[David M.]

Re: L84 Valve lash adjusting clarification

Your over thinking this. Run each valve individually until you get the feel for it. Then move to the fancy time saving moves as you build confidence.

I will rock the engine back in forth with the feeler gauge under the rocker until I get the slightest drag. Lock that rocker down recheck then move on to the next.

When done spin the engine over on the starter for a sec or three and recheck if you think you need to.

[Duke W.]

Re: L84 Valve lash adjusting clarification

Adjusting all the inlet valves at 90 deg. ATDC and the exhausts at 90 deg. BTDC of the compression stroke is absolutely REQUIRED with the 30-30 and LT-1 cams to ensure that the lifter is on the lobe's base circle due to their very long clearance ramps, but as I stated in the paper with a Duntov cam you can adjust both valves at TDC of the compression stroke on that cylinder.

From the beginning of the 30-30 lobe opening clearance ramp to the end of the closing clearance ramp is 540 crank degrees! That's 270 on the cam so the base circle only occupies 90 degrees or one-quarter of the lobe. At TDC both the inlet and exhaust lobes are about nearly three thou into the clearance ramp so if you adjust them at this point the actual clearance is about three thou more than your feeler gage thickness. At 450 crank degrees the Duntov cam at TDC has both lifters on the base circle. The LT-1 cam (L-72 lobe for the inlet and 30-30 lobe for the exhaust) is in between. At TDC the exhaust lobe is into the clearance ramp. The inlet isn't, but just barely.

So if you are absolutely, positively certain that the installed cam is a Duntov... My recommendation is to use the 30-30/LT-1 indexing procedure to adjust all 16 valves. Then bring it back to TDC #1 and check clearances, which should be as you set them. Then do one or two more cylinders as a sanity check.

Also the paper recommends different that Chevrolet's recommended clearances for reasons that are explained in the paper.

Duke

[Edward G.]

Re: L84 Valve lash adjusting clarification

Thank you all who responded.
That's what I thought but I had looser clearances on some valves than I had set using the every 90* method. I just wanted to verify that by using the every 90* rotation method the indicated cam lobes were there lowest base point and not on the lobe ramp.

Ed

[William F.]

Re: L84 Valve lash adjusting clarification

Duke,
I've read you valve setting article several times but still a little confused about settings with a Duntov cam. Excuse my slowness. Are you saying with #1 cylinder at TDC on compresssion you CAN adjust both the intake and exhaust valve of #1 cylinder and the move on to others at TDC doing both E and I or do you adjust 8e and 2I on #1 and follow sequence you have given for the more aggessive cams?
Thanks

[Duke W.]

Re: L84 Valve lash adjusting clarification

The answer to your question for the Duntov cam ONLY is yes. Or you can also use the "all inlets at 90 deg. ATDC" and all of the exhausts at 90 deg. BTDC method, which is REQUIRED for the LT-1 and 30-30 cam, but NOT for the Duntov cam. So for the Duntov cam, assuming you are absolutely, postively certain that was manufactured to the GM print, you can use either method.

I also recommend the second method for any cam that you don't know the "full" duration as measured from the beginning of the opening clearance ramp to the end of the closing clearance ramp.

I don't know how I can explain it any better than in post #4.

Duke