byebyeL98

when adjusting hydraulic lifters / setting rockers, i've read how important it is to be on the base circle of the cam, and to get to "zero lash" (and not go too far past it and completely collapse the spring in the lifter).

what exactly is the definition of zero lash? is this the point when the push rod would JUST start to move the spring / plunger assembly in the lifter after tightening down the rocker arm?

and once zero lash is reached, 1/4 turn past that should do it, right?

as always, thanks for the education!!

Corvette Kid

With the rocker loose, begin turn the adjusting nut slowly while turning the pushrod with the other hand. At one point, the push rod will cease to turn easily. This is zero lash.

CFI-EFI

Zero lash is when there is NO play in the valve train and before the plunger in the lifter moves.

RACE ON!!!

JAKE

Yea, but don't forget that the lifter MUST be on the base circle (sometimes referred to as he "heel") of the camshaft lobe, or all bets are off.

If the lifter is on the ramp of the cam lobe, you'll get an erroneous reading.

Since the lifter and cam are buried inside the engine and can't readily be seen, you have to watch the pushrods of the cylinder you're working on to determine when it's on the base circle.

You watch the intake pushrod/rocker to set the exhaust, then watch the exhaust pushrod/rocker to set the intake. It's the same procedure used to set the lash on mechanical cams, except instead of preload you'll be setting lash.

The Tech Tips Section has a step by step, but if you can't find it, email me and I'll send it. jakejr266@sbcglobal.net

Jake

byebyeL98

thanks for quick responses and helping me to understand

i've got a new 383 in my '87 (mini-ram, afr 195 heads, about 10:1 comp, 30lbs accel injectors, fuel pressure set at 40 psi w/out vacuum, timing initially set at 17*, heated O2 sensor) that i'm having a little trouble getting tuned just right. it has no trouble starting, and after it warms up will idle ok. but it does have a hesitation, and will occasionally back fire when the plugs get really fouled. under a load during acceleration, it stumbles and does not rev up smoothly. it seems to run pretty rich, and some of the plugs get carbon fouled a lot more than others.

could poorly adjusted valves cause a condition like this? when i initially did the adjustment, i followed the procedure doing the intake and the exhaust at the same time (at tdc for that cylinder). since then, i have read Jake's, CFI's (and other's) about the method Jake mentions below.

i will also be doing a real-time scan this weekend with the Auto X-Ray tool to see what the computer is seeing, so be prepared for a lot more questions!!

thanks so much!

dan

Corvette Kid

Okay. I only answered part of your question, sorry about that. The absolute easiest way to determine that a given cylinder's valves are in an optimum position to adjust is to watch the valve operation of the opposite cylinder in the firing order. For the Chevy these pairs are 1-6, 8-5, 4-7, 3-2. When the exhaust valve is closing on that opposite cylinder, let's say you're watching #3, continue to turn the engine by hand (in the correct operating rotation) and when the exhaust is nearly closed and the intake just begins to open, you are ready to adjust the valves for #2 cyl. Both of these cylinders are at approximate TDC. #3 has just finished it's exhaust stroke and is ready to get the next intake charge. #2 (the one that's ready to adjust) is in firing position with both of it's valves completely closed. This method works for any engine for which you know the firing order and direction of rotation. When a cylinder is in the adjusting position, then you can determine zero lash as I mentioned above. Then just go 1/4 turn or whatever you've determined that you will go past zero.

CFI-EFI

I don't think your valve adjustment has anything to do with it. Do you have a custom chip? Is that 17* base timing? That is an awful lot unless the prom is set up for it. Same with the injectors. Those 30 pounders are HUGE. Again, unless the prom is set up for them, that thing will run pig rich.

RACE ON!!!

byebyeL98

i do have a custom chip - it was burned by the guys who built the engine, (hopefully while it was on the dyno) with the 30 lbs injectors.

i set the timing at 17* at idle with the EST disconnected. does that seem high? maybe i misunderstood what my engine builder told me to set it at for best results. i've read a lot of posts where 6* seems to be a good place to start. i should probably give that a try before messing with the valves. would that be enough to cause the condition i'm describing?

i'm running stock AC Delco plugs (41-629) with .035 gap. is that appropriate for my set up?

CFI-EFI

The stock base timing is 6* btdc with the ESC disconnected. 17* seems like a lot to me, but it all depends on what the chip was set up for. Hopefully the prom is set up for those 30# injectors. They are bigger than necessary for a 383.

RACE ON!!!

byebyeL98

they are on the big side, but hopefully the chip was properly tuned for use with them.

if the chip IS properly tuned, would my plugs/gap and/or the timing cause what i am describing?

by the way Corvette Kid NC - thanks for the clarification.

JAKE

I can see that you really do have some tuning issues to deal with. But it's not much different than many others have had to go through with a new setup; sorta like teething pains.

First, you need to check with whoever burned the PROM to make sure he modified it to work with 30 # injectors. I've never gotten into burning PROMs, but from what I've read there is something, (I believe it's called the Injector Constant) that has to be changed.

I agree, to, that 30# injectors are BIG for a 383.

If the PROM wasn't properly modified to reflect the 30# injectors, the engine's not going to run right. It'll always run rich. See, the ECM can only tell what size injector is in the engine by what's programmed in the PROM. If he didn't change the injector size in the PROM the ECM still thinks you're running stock size injectors, so it'll be sending injector on-time pulses that are much too long, causing a rich condition. Lowering the fuel pressure is going to cause the loss of atomization.

This too rich condition can foul the 02 sensor and damage the CAT, too, if your running one.

Second, I agree that 17 degrees is too much initial ignition timing, unless some serious changes were made in the timing maps in the PROM. Even if the PROM was modified, that much lead should cause slow, labored cranking, especially when the engine's hot. That's if you set it at 17 degrees with the EST disconnected.

If, on the other hand, you set 17 degrees or are reading 17 degrees WITH THE EST CONNECTED, then it's too low. You don't have enought timing. With the engie idling and the EST connected, the timing should be in the low 20s.

Based on those issues and based on what you've posted about how the engine is running, my suspicious meter just went off the scale. Suspicious that the recommended settings, injectors and PROM burn aren't right. Together, those issues are really radical and unconventional ways to set up a 383 TPI engine.

Third, 40 # of fuel pressure with the vacuum hose off isn't in the ball park either. That would put it around 32 to 33 with the vacuum hose connected. Fuel atomization from the injectors is going to suffer with fuel pressure set that low. When the pressure falls below 35 psi, the atomization suffers a lot. It begins to dribble rather than spray in a fine mist spray.

Fourth, yes a misadjusted lifter, one that't too tight, can cause idle and backfire problems. One that's too loose is noisey and, over time, can damage the lifter itself, but the engine won't backfire. so back-firing could be a lifter set too tightly or a ignition timing issue.

I'm a firm believer in not re-inventing the wheel. Those who've gone before me already invented it. They've ironed out the best procedures and settings to use. If, or when, someone deviates drastically from those, he enters new territory that can result in all sorts of unexpected problems.

So, as far as initial timing, 6, 8 or, at the outside, 10 degrees BTDC is the norm for our engines. The computer does the rest.

When it comes to fuel pressure, you should look at it this way, for every 2 degrees of vacuum your engine pulls, fuel pressure will decrease by about 1 psi WITH THE VACUUM HOSE CONNECTED.

So, if you set it at 40 WITH THE HOSE OFF, and if your engine pulls 16 inches of vacuum, that 40 psi will drop to 32 psi when you connect the hose. At WOT, when vacuum falls off to nearly zero, fuel pressure goes up. Remember as vacuum goes up fuel pressure goes down and as vacuum goes down fuel pressure goes up.

When it comes to adjusting lifter preload, you'll get different responses; primarily based on what procedure the poster is comfortable with. (Maybe I should have written "with which the poster is comfortable" but that reads sorts dorkey, doesn't it?)


Anyway, the procedure I use and recommend is the way the PROs do it at the track. Rather than sit in the stands watching a lot of smokey burn-outs, I spend my time in the pits watching the Big Boys work on their cars. It's amazing what you can learn just by paying attention - attention to detail.

If you take the time to do the same you'll see that they set valve lash using the exhaust opening/intake closing method; one cylinder at a time. All of the race engines I track-tuned had a starter button bolted to the firewall for JUST that purpose. In fact, with a tunnel ram intake manifold, you can't even see the other side of the engine to see what the other rockers are doing.

As I've posted many times before, the procedure you find in some manuals is much too prone to error. I wish I'd kept a listing of all the guys on this Forum who have tried using it, only to have problems. Take a look at the procedure recommended in CompCams', Crane's, TPIS' catalogs, etc.; the differ slightly as to how much and when to set the preload, but all recommend the EI/IC method.

Let's be frank about it, a guy who has to refer to a manual to adjust lifter preload isn't going to be comfortable trying to remember which cylinder is which, which rocker is intake and which is exhaust, which to set at the same time you set another, etc.. Just too darn prone to a mistake, and it doesn't take but ONE mistake to cause the engine to run terribly.

There are some very knowledable guys on the Forum, but one of them installed the spark plug wires on the wrong plugs and another installed the distributor wrong. Even knowledgabe guys make mistakes (yes, een me!); just think how complicated it must be for someone not so knowledgable.

So, a guy does the best he can, using the manual's procedure, then he fires the engine and it runs like crap, where does he then look? Which one is misadjusted? Really no way to tell. So it's frustration time and back to square one.

In another of my previous posts: "Ever try setting valve LASH with the engine running"? Don't! The same procedure used for setting LASH is used for setting preload. The only difference is that with mechanical cams you use a feeler gauge to establish the clearance between the roller tip and the valve stem tip but with a hydraulic cam you make a certain amount of turns to preload the lifter.

I hate to use cliche's like Trust Me; whenever someone says that to me, I immediately don't. Instead I'll just say, I don't believe in re-inventing the wheel. If it works for guys who know a he** of a lot more than I do, why wouldn't I use and recommend the same. They've obviously scienced out the procedure or they wouldn't where they are.

What you're experiencing isn't unusual though, actually it's rather common, based on the posts I've seen on this and other forums. Straightening every thing out is only a matter of getting the correct burn in the PROM and getting all the sensors to operate within their design ranges.

Feel free to email me and I'll do the best I can to help you out. jakejr266@sbcglobal.net

It's like I constantly tell a friend of mine that I built a 434 for, "There can be too many cooks in the kitchen".

I hope this helps.

Jake

byebyeL98

that helps a LOT - thank you!!

i'll post again this weekend after i go over everything one more time.

by the way, after i set the fuel pressure to 40 psi with the vacuum hose off, i reconnected the vacuum hose and pressure only dropped to about 36 psi. does this seem right?

dan

JAKE

It depends on what amount of vacuum the engine is pulling. Did you have a chance to plug in a vacuum gauge yet to see?

Jake

Ramanstud

of course an obvious flaw to the fuel pressure drop is whether or not there's an intake leak. Grab a can of carb cleaner and see if it surges at idle...

byebyeL98

Jake - not yet. I'll check the vacuum on a gauge this weekend. where is the best place to plug in the gauge? or does it matter?

Ramanstud - excellent idea. should i spray it where ever there is a seam (around the throttle body, intake gaskets, fuel injectors, etc.)?

thanks very much, guys. i know i haven't provided enough quality information for you to work with, but i really appreciate the troubleshooting help. i'll go over everything this weekend, then put the scanner on it so i can give you better (more) information to work with.

JAKE

My power brake booster has a little unused and plugged nipple. I connect my gauge there.

If you're still running the emissions stuff (I'm not) many of the vacuum hoses go through all sorts of 'T's and check valves and other bewildering fittings that could effect the reading. I don't know if they would or not, but figured why chance it.

Since the booster nipple is tied right into the plenum, I chose it. It's downstream of all that other 'stuff'.

BTW, I just went downstairs to the garage to do another check on the amount my fuel pressue changes. I have the pressure set at 41 psi with the engine warmed up, closed loop, idling @ 800 RPM
and the regulator vacuum hose CONNECTED. When I used a pair of pliars to squeeze the vacuum hose at the regulator to cut off the vacuum, my pressure increases to 50 psi.

Jake

byebyeL98

thanks again for all of the help. i definitely have a few issues to sort out this weekend

or i'll just "accidentally" let it roll out of my garage into my neighbor's rock wall...

JAKE

Naw, don't do that. LOL

I know, right now, it seems like there's no light at the end of the tunnel, but hang in there. We'll solve this.

Jake

byebyeL98

thanks Jake!!!

i've already made a list of things to check / verify this weekend, so at least i feel like i'm heading in the right direction (thanks to you guys!)

smacko

Interestingly, my HAYNES manual says once you get to 'zero lash' you then tighten the nut 1 complete turn (360') - but I read here that 1/4 turn is correct...

MIND YOU; Haynes is referring to COLD adjustment