online170

I did some searching on how to adjust valve lash.

I plan to use the spinning the pushrod method to find zero lash, then do 1/2 a turn? after it puts up resistance.

Only problem is, im not 100% sure what cam i have, and what the specs for setting the valves are.

What does a stock engine recommend?

1975 Chev 350, supposedly 284H cam, and i would imagine hydraulic lifters.

Also, how would i adjust the valves if i used a feeler gauge? And what spec would i set it to?

Apeiron

With hydraulic lifters you've got a great deal of latitude in how much preload you give it. Anywhere from half a turn to a full turn would be fine.

Feeler gauges are for setting the lash on solid lifters, they're not really useful for setting the preload on hydraulic lifters.

online170

Great thank you!

Ill see how it turns out. I was told the valves SHOULD be adjusted with every oil change, and i havent done it since ive owned the car. Starting to run a little rough, so its probably time.

Apeiron

Whoever told you that is about 40 years behind the times. Did they tell you to burnish the breaker points and set the dwell, too?

iroc.86

if you really want to use a feeler gauge you would use a .001 would be zero lash then a 1/4 to 1/2 turn

Sonix

iTrader: (1)

slide the pushrod up and down, don't rotate it. You can rotate it easily even after 0 lash.
Set it once and forget it. You should never have to reset that. Unless your cam is wearing, or your rocker studs are loosening off.
Use the EOIC method. search for info on it.

TheScaryOne

iTrader: (3)

I always heard rotate until you feel resistance, back off until it just barely has resistance, and then do a turn.

I personally did 3/4 turn, because people were saying 1/2 or 1. So I split the difference. :P

Sonix

iTrader: (1)

only problem is, this is really subjective. Plus it's oily, so it'll just barely drag, you may not even feel it. But moving it up and down will be obvious.

TheScaryOne

iTrader: (3)

True, my valve covers were off for several hours when I set mine, all of the oil had drained back into the pan, so if anything, mine bound up before 0 lash so I'm running less of a preload than I thought I was.

Apeiron

It's absolutely impossible for them to bind up before zero lash.

There are two points where you'll feel resistance. The first is at zero lash when you take up the slack in the valvetrain... the ends of the pushrod are still oily regardless of whether or not the oil has drained back, so it's hard to feel this resistance. If you keep turning it down from this point, you're collapsing the plunger in the lifter, until you get to the next point of increased resistance, which is when you've collapsed the lifter and any further turning starts opening the valve. Most people end up only finding this second point the first time they try it.

Why are you setting the valves anyway?

chaoz28

I set my roller rockers up while running.. tightened them up just to open the valves and then back off one til it chattered closed it barely to stop the chatter and did 3/4 turn from there. its messey if you dont have a sheild for the oil but its always better to set up your engine when its hot.

UNCLE TOM

iTrader: (1)

there are clips you can buy that go over the pushrod end of the rocker arms . makes much less a mess . they keep the oil from squirting everywhere . while you have valve covers off make sure the drain holes on the lwr. front and rear of cylinder head are open . on older engs. they tend to sludge up and slow down oil drainage back into crankcase . good luck .

online170

Wow alot of responses since i last checked in.

Im adjusting the valves because the vacuum gauge is starting to get jumpy, sometimes to the point where the tach will also jump a smidge. Maybe 20rpms or so (you have to look close). I didnt used to have this problem....

Usually the vacuum jumps around within the same unit of in-Hg, but lately it will jump maybe one or two units. This is around 850rpm. It wont happen at or past 1000rpm.

So i should never have to adjust valves? Just one proper install should be good for the life of the motor?

Apeiron

Yes, that's the benefit of hydraulic lifters. You likely didn't need to do it in the first place.

online170

Ill leave it alone for now then. Im not 100% sure it has hydraulic lifters in it, but i dont think it has solid in it either. Just a hunch, it was rebuilt maybe 5 years ago.

Apeiron

If it's a 284H it'd better have hydraulic lifters.

online170

the rest of the parts used were good quality so id imagine its hydraulics.

Moly rings, good bearings, double roller timiing chain, etc...

Apeiron

It's a matter of design, not quality.