I need a straight answer on performing valve lash adjustment. You see, I did it according to the factory Helm manual at one full turn past zero lash. Unfortunately, the engine cranks but doesn't start. It started for a brief few seconds during the initial startup, but then it just backfired and sputtered out. Now it doesn't start at all. I know the best way is to adjust them with the motor running. However, that's a PITA with all the AIR diverter crap to R&R on the passenger-side. So my question is, how many turns past zero-lash? 1/4turn? 1/2turn? 3/4turn? IMO seems as though everyone here on the board has a different answer. By the way, someone at an engine rebuilding shop told me that they like to do all SBCs at the 4'oclock position past zero-lash. Is he right? Thanx.

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1989 Firebird GTA: black on black 5.7 liter (N10 dual exhaust) with T-tops and leather.

 

try doing it by the book. but instead of tightening them down that extra 1 turn, start the car. then with the car running slowly add the 1 turn.

lemme know if that works

 

When I adjusted my valves I had the same Question. I got answers from 1/4 to 1 full turn. I ended up turning it 1/2 turn past zero lash. 1/4 is used for most race engines and 1 full turn seems like a little too much.

I think the "4 o'clock" method your machine shop is referring to is WHen you take the valve to zero lash then the position your wrench is in is 12 O'clock then your your wrench to 4 O'clock from there. WHich would give you just a little more than a 1/4 turn. I do not belive 1/4 turn is enough.

In my opinion anthing between 1/2 and 3/4 of a turn is fine anything more or less is doesn't seem healthy. Hope this helps.

Later,
Lars

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'92 RS 305 TBI
K&N Open Element
Ultimate TBI mod's (thanks Pablo)
Cam[.442"/.465" x 218*/224* @ .050", 10:1 Hypereutectic Pistons
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Shift Kit, Corvette servo,
and 2800 Stall Trans Specialties Converter,
Gutted Cat, IAT Resistor
MSD Blaster Coil, Accel Cap and Rotor

 

1 Full turn is not to much, but if you don't feel comfortable with it, 3/4 will do. The lifters may need time to bleed down, so you may have to crank it for awhile, but if it doesn't start within a reasonable amount of time, then start searching for possible reasons (unhooked brake booster line, etc...) Good Luck.

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"I used to have a handle on life, but then I used it as a plunger and broke it" -The Wave

ASE Master Tech + L1
Savannah, GA
'87 Trans Am-K&N,Cold air induction, SSM SFC, Flowmaster, 16" GTA rims.
'97 Bonneville SSE
About Me

 

A valve lash set a little bit loose shouldn't be enough to keep your engine from starting. You have other problems which you need to sort out. Check for fuel, spark, etc.

I sort of did an informal survey when I did my valve lash, and the most common answers all averaged out to between 1/2 and 3/4 turn. So I split the difference and gave mine 5/8 of a turn past the zero lash point.

 

I once made the mistake of setting the valve lash for each cylinder, and then cranking the engine over by hand to check each cylinder again. They were all loose, so I adjusted them again. The car would barely run, and it took me a couple of days to realize what I had done. The hydralic lifters bled down when I rotated the engine around the second time and that's why they seemed loose. I backed them off 1 turn and it fired right up. This may help.

89 Transam GTA, a few bolt ons

 

The easiest way I know of to get yourself back in business from where you are now is to back them all off about 1½ turns; start the car; adjust all of them to zero lash with it running; shut the car off; then add the desired preload to all of them. That dodges the issue of killing the motor by tightening them with it running.

As far as the amount of preload to use, that's a highly personal matter. There is about 1½ turns worth of travel in the lifter, so about ¾ turn puts it in the center of its travel. On the other hand, if you want to put it together and not touch it again for 100,000 miles, and you don't plan on ever running it past 5000 RPM or so, you could put a full turn on there. I believe that's what GM does with new cars. But, with that much preload, if the valve train ever floats, the lifters will "pump up" with oil, and you'll have valves that don't close. So for pure racing, people try to get them as close to zero lash as possible (1/8 - ¼ turn typically) for that reason.

For a performance street car, ¼ - ½ turn is usually a good choice. I use ½ on a new motor, ¼ on a broken in one since the lash changes the most during break-in.

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"So many Mustangs, so little time..."

 

I go 1/2 to 3/4 past zero lash.

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ASE Mechanic/Machinist/Smog Tech

RTKTGTR 1999 NBM T/A, flowmaster,FRA,Pro Kit,BMR STB, polished calipers.
1986 Chevy 3/4 ton pick up,flowmasters,4.10s,
1981 corvette FOR SALE
1995 ZX6R,Yosh,D207s

GO #3

 

You've got the settings too tight.

If the engine won't run then the valves are being held open by a too tight setting.

This is pretty common since the most difficult part about setting the proper preload is determining that the lifter is on the base circle of the camshaft lobe.

With many camshaft/lifter/spring combinations, it hard to tell when you're there.

The "twist the pushrod" method is the main reason it's so hard to accurately determine zero.

Guys have their favorite method of finding the spot when the lifter is on the base circle and all of them work when done correctly. I use the system that CompCams and other camshaft companies recommend.

It involves bumping the engine and watching the intake of one valve and when it completely opens the valve and is about 1/2 way toward closing it, you set the exhaust. Then you watch the corresponding exhaust and when it first begins to move to open the exhaust valve, you set the intake.

What I've used with complete success over the years to ensure zero lash is the "up and down" method.

The "up and down" method involves taking the pushrod between thumb and index finger and moving it up and down as you slowly tighten the adjusting nut. When you can no longer move the pushrod up or down, you've got zero lash.

Now you set your preload, and it can be anything between 1/4 turn and one full turn (or more), depending on what you want. I normally follow the cam company's recommendation, which is usually 1/2 turn; but it's really up to you.

I've got a txt file that I send to lots of guys who have had the same problem as you. I you want it, let me know.

Take care,

Jake