The Stovebolt Site Forums The Shop Area Engine Shop Valve Adjustment Question

I am going to adjust the valves again in my GMC 228 tomorow. The info I have says the engine should pur like a sewing machine. Some have suggested that I am not getting the engine hot enough. Also I was wondering if a higher octane make any difference?
Any and all advice is welcome as I am still quite a novice!!

IF, (and this is a big one) the camshaft isn't worn, or the lifters don't have cupped-out bottoms, you should be able to eliminate any mechanical noise from the valves with a good adjustment. A camshaft has what's called an "acceleration ramp" that gradually takes up the slack between the parts before the valve is pushed open. Once all the clearance is taken up, the valve is opened, and closed by the movement of the cam, and it slows down just before the valve meets the seat, to prevent battering the seat on closing. The clearance specification just happens to match the height of the acceleration ramps. If an intake valve has a .006" clearance, for instance, the gradual lift before opening is 6 thousandths. Generally, exhaust lobes have more clearance than intakes, to account for the higher operating temperatures, and the tendency for valve stems to "grow" at normal running temps. Hydraulic cams also have clearance ramps, but they're usually much less, normally about .002" for intake and exhaust.

I like to get an engine up to normal operating temperature, shut it down, and do an engine-stopped valve adjustment. Inline 6-cylinder firing order is 1-5-3-6-2-4 on every one I've ever worked on, so write the firing order down in halves:
1-5-3
6-2-4

The nunmbers above each other are "companion cylinders", where both come to the top at the same time. When #1 is on compression, ready for adjustment, #6 will be at the top of the exhaust stroke, with the exhaust valve closing, and the intake opening, getting ready for the intake stroke. This is called "rocking" where the valves, and rocker arms are moving in opposite directions. Turn the engine by hand and watch the #6 rockers. When they're rocking, #1 is ready to adjust, both intake and exhaust. Make 1/3 turn of the crankshaft, and #2 will rock, and #5 will be ready for adjustment. Every 1/3 turn, another cylinder pair will line up. In 2 turns of the engine, all 6 cylinders can be adjusted. No mess, no splatter, and you can get a perfect adjustment the first time!
Jerry

I agree, adjust them after a 5 or 10 mile drive with the engine NOT runing.
on my '55 235 with solid lifters I use 0.008" on the intake and 0.015 on the exhaust. It is quiet but some people might adjust them tighter, I don't really like burnt valves myself...

I use a method similar to Hotrod Lincoln's except I only turn the engine once after the first stop. On TDC of #1 cylinder adjust:
Exhaust valves on 1-3-5
Intake valves on 1-2-4
Then turn the crank 360 degrees to #6 TDC and adjust:
Exhaust valves on 2-4-6
Intake valves on 3-5-6

You won't need anything higher that 87 octane unless you raise the compression ratio considerably. >8 1/2 to one?

HRLincoln: Thanks for the info on cams. I always wondered where they got the clearance specs for the valves. Now I know!

I hate screwing around with a hot motor. If you try to adjust them hot you will have to work fast because the motor cools quickly. I just adjusted mine cold .010 intake / .012 exhaust with excellent results. It makes a slight ticking noise which is expected from solid lifters.