Hotrodder

Hi
I have changed camshaft, push rods, springs and rocker arms.
Rocker arms are Comp Cams self aligning 1.6 ratio stamped w/roller tip.
Engine is 92 model 350 Chevy factory roller block.

Comp Cams mounting instructions say 1/2 turn pre load after taking up all the slack between push rod and rocker arm.
I's probably best to just follow the recommendation, but I have always heard that 3/4 turn is the recommended pre load.

What do you use? 1/2 turn, og 3/4 turn?

RedLeader289

iTrader: (2)

It's been a long time, but I think I remember 1/2 turn. Besides, that's what the manufacturer recommended so it's probably a safe bet.

86LG4Bird

iTrader: (1)

Either is ok.
The +/- 1/4 turn is far less variability than how well you're able to find the true zero lash.
With factory style lifters, it typically takes over 2 full turns to bottom out the plunger inside the lifter, so anything between 1/2 turn and 1 turn is perfectly reasonable.

sofakingdom

iTrader: (1)

Pure race-only = 1/16 turn
Hot street or street-strip = 1/8 - ¼ turn
Typical street = ½ turn
Typical amateur mechanic (Chilton's)= ¾ turn
Glue the valve covers down and go 100,000 miles (factory) = 1 turn

The single biggest variant in all of this is, finding 0 lash. I have only ever known a TINY HANDFUL of all the people I have ever known trying to assemble engines, that could get it right. All the rest usually get em WWWWWWAAAAAAAAAYYYYYYY too tight. ANYBODY that uses the "spin the push rod" non-method should NEVER be listened to as "advice" and is DOOMED to failure.

The ONLY people I've ever known who could get it right consistently have been, like myself, long-time solid cam users.

Best way for a hyd amateur to get 0 right is, run the motor fully hot; back off each valve one at a time, until it ticks; tighten it until it just barely stops ticking; move on to the next. Do all 16 as fast as you can this way, and don't bother to add preload as you go. Then AFTER all 16 have been set to 0 that way, shut the motor off and add your choice of preload, according to the above table.

Since you're asking, I'd recommend ½ turn. But REALLY, of all the things that make a difference, the ACTUAL # OF TURNS is the LEAST of the variables at hand. What matters MORE is, getting them all THE SAME. Which depends on getting em all to 0 ACCURATELY. If you can't do that, then counting turns is useless, by definition. (as in, random number that's different on every valve + ½ turn = ???how many turns??) Once you get to where you can get em ALL THE SAME, THEN AND ONLY THEN is it time to start splitting hairs about "how much". Meanwhile, learn to find 0 ACCURATELY, and then you'll see that it makes very little IF ANY difference how much you add beyond that, as long as you don't totally bottom em out.

Did I mention finding zero ACCURATELY? that's the key. Far more important than choosing ½ or ¾ turn of preload.

cardo0

If you went to every mechanics shop in your town including the dealership they would say to use the roll the p-rod with your fingers method. Anyone that claims he's the only person that can get it right has a self esteem problem.
Take your lifters and try to get them to collapse with a p-rod. Most likely you can't get them to move/collapse. If you can move the plunger at least you will get a feel for how much pressure it takes to move the plunger down.

For years/decades I used to think the 1/4 turn or less was best. And it is if you over-rev or plan to over-rev the motor as it will minimize holding the valve open from pump up. But the the lifter will still pump up by the amount of pre-load used no matter how small.

The reality is you sacrifice lift by not using as much pre-load as you can. The pre-load limits the amount the plunger can move and the more the plunger moves the more that same distance is subtracted from the lobe lift.
Nowdays I use at least 1 full turn of pre-load and that's what I recommend. There are methods that go further but I won't encourage that to well learners.

Good luck and I hope this helps more than it hurts.

gavin.priestley

OK guy I wanna ask yall. Ok I replaced the head gaskets on my 88 Firebird with a 93 Chevy sbc 350 tbi. I also replaced the cam and lifters and the valve springs as well along with the timing chain too. Now when my dad put the cam sprocket back we noticed that the timing marks on both the cam sprocket and the camshaft gears were both pointing up. So once we replaced the gears and the chain, my dad placed the gear marks facing eachother like on all other Chevy sbc. The engine is on TDC #1 piston up. The distributor rotor is pointing at the number 1 piston. But now the engine won’t start. And me and my dad are baffled

sofakingdom

iTrader: (1)

This applies to ALL SBC motors:

Timing marks both up = #1 & #6 TDC, #1 firing (rotor should point to #1)
Crank mark @ 12 & cam mark @ 6 = #1 & #6 TDC, #6 firing (rotor should point to #6)

The "dots together" position is easier to see and assemble the motor with, but is NOT #1 firing.

Correct build procedure is, install the timing set that way, which leaves the motor at #6 firing; then turn the crank exactly one full turn; THEN stab the dist w rotor at #1. The dots will both be at 12:00, #1 & #6 will both be back to TDC, and the motor will be at #1 firing this time.

The fix at this point is, pull the dist, turn it exactly 180° from wherever it now is, try again.

NoEmissions84TA

iTrader: (1)

What sofa said. Everyone gets this wrong many times and can't understand why.
The dots pointing at each other is actually #6 firing.

gavin.priestley

sofakingdom

iTrader: (1)

Find #1 or #6 TDC with a tie-wrap or the like in the spark plug hole. Make sure that it's the #1 firing spot, not the #6 firing spot (you can look at the valves: #6 exh is just closing and its int just opening, when #1 is firing). Verify the rotor points to the #1 tower (just to the driver's side of straight toward the front) when the engine is at that point. Turn the dist body to align the "teeth" of the little star wheel arrangement down in the center of the dist. Turn it about 1/16 turn CCW from that point. Make double damn sure the plug wires are correct, i.e. the tower you think is #1, has the wire going to plug #1, and then they're in the firing order 18436572 going CW from there. Put in a set of NEW plugs (not, "I just put em in and they haven't run so there's nothing wrong with em"; not "they look OK"; not "clean em with break cleaner"; not anything else besides NEW). Try again.

gavin.priestley

sofakingdom

iTrader: (1)

Not so hard in the end, eh??

NoEmissions84TA

iTrader: (1)

Good job!