richw40

I have read numerous posts on this topic. Just about every one has a different response. I just built a new 350, and am looking for a correct response. Maybe from a true engine builder ???.

I have hydraulic lifters, stock rocker arms, new engine build. Once I get to zero lash, should I turn the nut a 1/4 turn, 1/2 turn, or no turn. Last thing I want is a bent pushrod, busted lifter, or a messed up motor.

Thanks for any info in advance !!!

sofakingdom

iTrader: (1)

No "true" "engine builders" here; all of us that build engines are LIARS.

You will not bend push rods, bust lifters, or mess up motors with any of those settings. All you're doing, is locating the point that the oil pressure holds the lifter guts up to, before the check valve closes.

There is no one "right" number. The reason so many different numbers are tossed around, is because you have A CHOICE, based on the engine's intended use and its expected life circumstances.

For a very high RPM motor that will be frequently torn down, inspected, and otherwise maintained, go as close to zero as you can. (Racing) They may be a bit noisy at times but it will not be possible for them to "pump up" in the event of loss of valve train stability (valve float).

For a factory motor that you are ABSOLUTELY POSITIVE is built ABSOLUTELY PERFECT and you want to gorilla-snot the valve covers on, shut the hood, and not open it back up for 150,000 miles, use 1 turn. (That's where GM set em)

For most of us, we're somewhere in between. Chilton's says ¾ if memory serves (DIY repair late in the engine's life), a lot of the cam mfrs say ½ (user will probably abuse the motor enough that it won't last anywhere near that many miles before this needs further attention) or ¼ (user is willing to frequently maintain it).

Some brands of lifters (Morel notably) REQUIRE more preload. You don't say what you've got but I'll assume that if you had such a one, you'd know it.

½ is where I usually leave em for a street build.

richw40

thanks for that reply......... !!

danclemts

iTrader: (1)

At the car show last night talking to a couple of 30 year plus racers/builders. This very subject came up. They both agreed on basically a full turn and possibly a bit more on most motors that are not going beyond stock redline.

richw40

the cam specs on this motor are : .050 duration
int: 223 ext: 223
valve lift
int. 447 ext 447

9.5: 1 pistons
stock heads, 1973 block, bored .30 over

Timing is set at 12 degrees initial, Edelbrock 600 carb, headers
after I got this together, and started road testing it, it seemed like the power was half there. my vacuum was low at 10-13 psi w/out power brake booster hooked up. I thought the valve adjustment was to tight, not letting the vales seat properly. I did the cold spin the push rod to zero, then 1/2 turn. I went out today and went another 1/4 turn tighter and the engine wouldn't start for nothing. Backed it down to my starting point and it ran ok again.
hmmmmm?

AlkyIROC

Proper adjustment? Anywhere from 1/2 to 3/4 turn from zero lash. If you want to get more technical, 0.030" - 0.060" on the backside of the rocker pushing the pushrod down into the lifter. That's what a hydraulic lifter requires for preload.

sofakingdom

iTrader: (1)

Well, that 151 copy cam won't be in there long enough for it to really matter; you'll HATE IT. It'll never have any "leave" and the vacuum will always be low. It'll seem like it'll wind out forever, but that's only because it doesn't ever make enough torque for it to "feel" like there's a peak. You'll always get the feeling that if you just hold it in gear for a little longer before shifting, the power will eventually "come on"; but it never will. You'll get REAL TIRED of the gas mileage too.

Set it to ½ turn and start looking for a better cam.

Since you say "9.5: 1 pistons" (flat tops) and "stock 1973 heads", your ACTUAL compression ratio, AS BUILT, is probably a little under 8½:1. That's assuming flat-tops w 6cc valve reliefs, .039" head gasket, .045" of deck clearance (the stock .025" or so, plus the added .020" of "rebuilder" clearance), and 76cc heads.

That cam originally came in 11.1:1 motors, and even in 1964, wasn't the best choice there was; people who wanted to go fast used solid lifters back then. Why that thing is still even available mystifies me; I guess it's the romantic "375HP 327" label that sucks in unwary buyers. Be aware though, even though that motor (the L79) ran fairly hard for a stock motor, if you built it today, part # for part #, you'd end up with roughly 275HP according to modern "ratings" methods, i.e. something that involves actual MEASUREMENT instead of just empty-calorie marketing as was the case before the change in 1972. And that's WITH the 11.1:1 CR the L79 had. Putting that cam into a modern motor, running it on modern fuel, on modern roads, against modern cars, with a deep smogger era no-compression smogger motor, is a sure path to disappointment. I've been talking people out of running that cam since the mid 70s.

It might seem to you that it "runs" "OK"; but until you get rid of it, you won't realize how much better almost ANY modern cam (by "modern", I mean, designed in the last 50 years) will run, compared to that old thing.

For such an extremely low CR motor, I'd suggest a Comp XE262, or the Lunati Voodoo that's about the same size, can't recall the # because they just changed em all.