C1 Solid Lifter Valve Adjustment

[ROB DAME MEM# 36211]

The ST-12 list two different valve adj. specs for 1956 225hp.
Section 6-3 shows .008 & .016 hot while section 14-5 shows
.012 & .018 hot for Dual 4 bbl.
Which specs should be used?
Also can the valves be adjusted cold by adding .001-.002
to the hot specs? Thanks in advance Rob

[John H.]

Re: C1 Solid Lifter Valve Adjustment

Rob -

I have several other period Chevrolet Service references (dealer Corvette Tune-Up filmstrips and Corvette service pamphlets, etc.), and they all recommend .012" and .018" hot, and state that the intakes can be closed up to .008" for extreme duty situations of "extended high output operation" (racing) to get slightly more effective duration. I'd stick with .012"/.018", set them hot as specified, then measure them cold and use that measurement to set them cold from there on out as necessary.

[Duke W.]

Re: C1 Solid Lifter Valve Adjustment

The .012"/.018" is based on the "theoretical" rocker ratio of 1.5. Based on my measurements it is 1.37 at the top of the ramps and 1.44 at max lift.

Being as how this is the case I "factor" the OEM recommended clearance by 1.37/1.50 and truncate, which yields .010"/.016".

If the valves are looser than this they will be set down on the seat at greater than clearance ramp velocity, which will acclerate valve seat recession.

The .008" inlet clearance was recommended in a fifties vintage Corvette News as a inlet setting for "weekend competitive events" and was adopted as the standard setting for for '63 for the same reason - to achieve a bit more effective inlet duration.

You can adust the valves cold at TDC on each cylinder with the pre 30-30 mechanical lifter cams.

Duke

[ROB DAME MEM# 36211]

Re: C1 Solid Lifter Valve Adjustment

Thanks John And Duke. I'm going to use a valve adjustment chart
I printed from this board. I think Duke posted it a while ago.
It goes with #1 cyl Int valve at full valve lift adj #6 int valve
and so on through the firing order.
Duke, so if I adjust the valves cold, which is what I'd rather do
as I've just now finished cleaning valve covers from the last time
I messed them up.
How many .001s should be added to hot specs?
BTW the aluminum jelly worked best for me thanks Dale.
Take Care, Rob

[Clem Z.]

Re: C1 Solid Lifter Valve Adjustment

the way to check between hot and cold lash is to do 1 cly. hot and leave the engine cool over night and check the setting the next day. i have found unless you have aluminum heads,rockers or block there is not enought difference to worry about. JMHO

[James F.]

[Duke W.]

Re: C1 Solid Lifter Valve Adjustment

As Clem pointed out, I, too, have noticed little meaningful difference between hot and cold clearance. Since cast iron and steel have very similar thermal expansion characteristics, there is little measureable difference between hot and cold clearance.

When you run the engine real hard the exhaust might tighten up a bit, and that's why exhaust clearance ramps are typically a little higher than inlet clearance ramps.

Jim's method will work on the Duntov cam because the overall lobe including the ramps is of a "normal" duration, but it won't work for the 30-30 or LT-1 cams because they have unusually long clearance ramps.

I recommend that you set the cold clearance two thou TIGHTER than spec - .010"/.016" - to account for actual rocker arm ratio, and you will notice that the valvetrain is quieter.

Duke

[ROB DAME MEM# 36211]

Re: C1 Solid Lifter Valve Adjustment- Rob

Thanks Jim, I'll adjust your way seems like less motions.
If it's worked for you for 40 odd years who am I to question
Never knew off the go-nogo gauges just called Autozone
they have em in stock I'm on my way
You'll have mail in a bit. Take care Rob

[ROB DAME MEM# 36211]

Thanks guys for your time & knowledge NM *NM*

[Dale Pearman]

Right On The Money. Furthermore

good technique in the use of a feeler guage is something that almost none of us have. Typically two or three thousandths of an inch error and inconsistancy from valve to valve is NOT uncommon.

Dale.

[Dale Pearman]

Re: C1 Solid Lifter Valve Adjustment- Rob

Short of a dial indicator that's the only way to go. The traditional "how tight is the drag" way of using a standard feeler guage is not accurate.

Dale.

[Dale Pearman]

Re: C1 Solid Lifter Valve Adjustment

You will also notice a slight decrease in bottom end torque. But then again, we always go for groceries at 6500 RPM and 120 MPH!

Dale.

[Duke W.]

Re: C1 Solid Lifter Valve Adjustment

I doubt if the difference in low end torque between adjusting at .010/.016 and .012/.018 is measureable. The important issue is to lift and, in particular, set the valves back on the seat at ramp velocity.

When I realized 25 years ago, after taking meassurements on my engine that the rocker ratio is a good deal less than the 1.5 that has always been gospel, I wondered why Chevrolet never took this into account when specifying clearances just as I wondered why Chevrolet installed a 16" vacuum can on an engine that idled at 10-12'. Of course, the latter they fixed in '64, at least on small blocks.

Duke

[Duke W.]

Re: C1 Solid Lifter Valve Adjustment- Rob

Feeler gages give you a range of values. For example, the exhaust valve clearance should be .018 (1.36/1.50) = .1644". If a .017 gage does not slide in, but a .016 gage does, then the clearance is somewhere between .016 and .017.

For the Duntov cam inlet cleraance should be .012 (1.37/1.5) = .1096.

I would shoot for a smug .016 on the exhausts and a loose .010 on the inlets.

The reason why mechanical lifter cams have clearance is to insure that the valve fully seats under all operating conditions. During normal driving the exhaust valve is relatively cool and the stem does not get much hotter than the surrounding cylinder head material because about 80 percent of heat transfer is conducted through the valve seat. During sustained hard running the exhaust valve heats up and the stem expands enough to close up the clearance a bit. That's why exhaust valve ramps are typically higher - to provide more margin to keep the clearance from closing up completely and hanging the valve open. If the exhaust valve doesn't seat properly, it will quickly burn.

Inlet valves run much cooler because they are cooled both by heat transfer through the seat while they are closed, plus the convection cooling from the incoming fresh charge while they are open, so they don't need as much clearance ramp because their running clearance will be more consistent during all operating modes from idle to sustained WOT.

Duke

[Clem Z.]

back when the 55 chevys came out there

was a valve gapping tool that use a dial indicator that snapped to the valve spring retainer and had a camera type cable that you pushed and it stopped the dial indicator needle movement as the valve went up and down. and you read the valve lash in .000 of a inch. that was one of the tools i lent out and never got back.