Hi Guys,
Just fired my L48 up for the first time today after a winter overhaul.
Overhaul consisted of;
Rings (standard)
Bearings (standard)
New oil pump
Brand new, "Stock" ,cylinder heads ready assembled.
CompCams XE262H Kit with;
DR Timing chain
Hydraulic Lifters
Valve springs; Seat load 105lbs @ 1.700"
Open load 273lbs @ 1.250"
Plugs ,wires, rotor,and cap.
And all new gaskets.
Engine is a 350 with a stock Q-Jet and a TH350.

Prior to starting.
Primed the oiling system with a drill and primer tool.After the lifters were all pumped I set the valve lash to zero and gave each a quarter crank passed zero.Filled the carb by hand and set the distributor to 0°.
Fired up after 2 revolutions and I brought it up to 2500 right away and kept it there,pedaling up to 3000 and back ocasionally,for about 45 mins.

Afterwards I let it cool for a couple of hours and fired it back up.Set the timing to approx.12° advance without the modulator and set the idle to 800 RPM.Choke is wired open for now.Engine has a rough idle.I don't mean lopey.Vaccum gauge is fluctuating between 12 and 18 inches.So I ran a warm setting on the valves with the engine running. I backed off till the rockers clacked and tighened just enough till the clacking stopped ,zero lash.Checked the v-guage. Still rough.Then I tightened the rockers a 1/4 turn passed zero.Still idles rough.Gave each rocker an additional 1/4 crank.So now I have a total of 1/2 turn passed zero lash,with still no improvement.

Engine still has an inconsistant idle.V-guage is dancing between 12 and 18 inches.
Off idle ,around 1000 rpm and upwards, is fine.V-Gauge nice and steady.I plugged all the vaccum lines to the carb with no improvement in the idle.The thing acts like it's got burned valves.Oh yeah almost forgot,the idle mixture screws are still set as they were ,for the stock cam, before my rebuild.

I have a couple of ideas here of what the problem could be.

1) Idle mixture probably needs resetting.(But until I get the gauge settled down, might not be possible.)
2) The new valves in the new heads haven't seated yet.

I'm open to suggestions.

 

I'm not a professional mechanic, not even really a very good shadetree mechanic, if you want the truth, but several things come to mind here.

1.) Plenty of people set their idle without using a vacuum gauge. Play with the idle screws a little, and see if you can't get it to settle down.

2.) Sounds like it could be a vacuum leak, double check.

Here's a link to a great site about using a vacuum gauge to diagnose an engine:

http://www.secondchancegarage.com/public/186.cfm


Keep the shiny side up!
Scott

 

I agree about looking for the vacuum leak for sure...but I'm also interested in the process you used to set the valves.

 

Hi Billa,
Back in the day,I always set the hydraulic lifters this way.Cold setting after rebuild or cam change.
1) I set engine to #1 TDC on firing position.Install the pushrods and rockers losely,so theres no pressure on the lifter plunger.

2) Prime the oiling system with a drill to get the lifters pumped.Some will say it's not necessary to pump the lifters,but with the lifters pre-pumped the oil pressure comes up faster when you fire it up.Plus it keeps the plungers from bottoming outand /or running dry in the lifters.

3) While turning the push rods with your fingers,tighten the rockers on the intake valves: 2, 5, 7 and the exhaust 3, 4, 8, until you can barely turn the push rod.Should be zero lash.Then I give em a 1/4 turn past zero.
4)Rotate engine 360 degrees and do the same thing on the intake valves 3, 4, 6, 8 and the exhaust valves 2, 5, 6, 7.

It's just a round about ball park figure for the intitial start up.

After the cam is broken.....in,I fine tune em warm, with the engine running, backing off the rockers till they clack,tighten em down slowly till they stop clacking (zero lash) and give em an additional 1/4 to 1/2 turn.

I hear different opinions and have read where it's said one turn past zero is required.Also heard 3/4 1/2 and my 1/4 turn passed zero.
I've never gone more than 1/2 turn myself and never had any problems.

 

O.K.
A little update since nobody seemed to have an answer for me here.



Read more: http://forums.superchevy.com/70/9103...#ixzz1oYQUYaL4

 

The thing that caught my eye is that you did the cam break-in for 45 minutes at 2500-3000 RPM with the distributor set to ZERO degrees advance?

Have you adjusted the distributor since then to see if your idle improves?
If you did and it's still bad, I am wondering if you burnt a valve or something during break in?

When breaking in a cam, you are to keep the distributor advanced (I usually try to keep it at 30-32 degrees mechanical advance at my break-in RPM) or you risk overheating the exhaust valves.

Have you done a compression test after the break in?
Sounds like something may have gotten cooked.

Just my .02
Elm

 

Yep,Yep,and Yep.

I didn't run breakin at 0 advance.I only had it set zero for initial firing, just didn't mention the part about setting it after it fired up.
All in all It's 12° advance at idle,no vacuum advance.Anymore and my starter drags when its warm.All in I'm around 28°/29°.

tHe bottom line is I have hydraulic lifters from comp cams that don't want to do right anywhere except zero lash.Any little bit of preload and the vacuum falls flat .

 

Are you sure they didn't send you solid lifters instead of hydraulics?
I find it hard to believe you can't turn them down from zero lash otherwise.
Elm

 

I know. Crazy right.
No I checked they're hydraulics alright.
It's almost as if the lifters are pumping up so hard , that they are over powering my new valve springs.

 

Umm...seems like the vacuum leak you did find was the begining of finding other things that were contributing. Thanks for the link, some good information there. I didn't see where you finally got the overall performance you were expecting. Did I miss that? If not, did take your timing to the advance that was suggested, did you make that change? I understood the starter issue, but a couple degrees shy of that perhaps?

You might also consider getting Cliff Rugles Q-jet book if you're going to do more carb work, it was referenced in one of the articles your links went to on the other forum. Either way, looks like your zeroing in on it, I hope so!

 

Just pulling at straws at this point but are your pushrods too short to the point that if you try to turn the nuts down from zero lash, it's actually preventing the valves from closing all the way?
I'm wondering if the issue is really the lifters (which just seems really odd for brand new hydraulics) or that coincidentally the valves can't close due to poor rocker geometry right around zero lash?

 

I still think a compression check would be very telling.
Do the check at zero lash and then again at like a 1/2 turn down from zero. If it's the lifters, you shouldn't see the issue with a compression test because you aren't creating any oil pressure to speak of so there should really be no way the lifters wouldn't collapse (unless they are truly bad or solids). If the compression drops at 1/2 turn, you know something is holding the valves open- And that can only be the lifters if they don't compress or valve train geometry.
Elm

 

I don't think so.Theres not anything special about the valve train except the cam.All else,rods and rockers,are stock.I even checked the lifter/plunger height against the originals to make sure during build up.
And I have checked the pushrod to guide hole clearance at zero lash ,1/4 and 1/2 turn.No contact.

One thing.The rockers are stock but not the originals.They came on the heads I 'm using ,from a goodwrench crate motor.Stamped steel, 1:52 ratio,but they have a "tang" on the tip that keeps them centered on the valvestem.I checked them during installation to make sure that the tangs weren't touching the spring retainers at any time during the cam cycle.

 

Worth a try.
At zero lash I have around 160lbs compression per cylinder warm,now.The fluttering from the carb is gone and its runs nice and smooth.Just doesn't show any performance improvement over the stock L48 cam, or maybe I was expecting to much.

 

Yeah, from a performance standpoint, you're really not gonna have a noticeable performance difference with the valves set at zero lash vs 1/2 turn (or whatever) down. But I still think that just for piece of mind, you would want to resolve the lifter/lash issue.

Did you try to compress the plunger on the lifters manually to see if you can move them? With the motor off, you should be able to crank on the rocker arm nut (slowly!) and watch the plunger depress.
If you can't I'm still wondering if these things are solids as they look identical from the outside. You'd probably need to check all 16 because all it would take is one to cause an issue..
Elm

 

Did you have the carb off the intake? Need to be careful when tightening the front bolts fastening the carb to the intake. Too tight, you'll warp the carb causing internal leaks, erratic behavior.

Otherwise I'd check the points, proper dwell, look for vacuum leaks.

 

During build up I installed the lifters dry, not pre pumped.
Before I ever set the initial lash,I pre oiled with an old dizzi and drill.
In there "dry" state I could actually lift up on the tip of the rocker and compress the lifter.After they were primed.I could not.I even tried using a big screw driver back behind the adjusting nut for leverage.No chance.Rock solid.The engine sat for 2 days on the stand,and when I came back and tried agian to compress them,a couple would compress
when I lifted up on the rocker tip,others were still rock solid.
So I'm about 99.999999% sure they're hydros.

 

Except for the ones around my valves,I've ruled out vacuum leaks early on.
Bolts on carb are torqued at 13 lbs all the way around.My Rochester handbook say 15 but I've had warped air horns before.

No Point to checking the points.My problems don't point to the points,cause the point is I run HEI.

 

Weird.. Have you called Comp and discussed the issue?
I would think they should offer to swap out the lifters no charge provided you return the old ones for analysis?

If they compress 'dry' but they won't when full of oil but no oil pressure, something seems off with their bleed down.

 

BRAINSTORM...

Low engine vacuum caused by unseated valves, can only be caused by exhaust valves.In order for an engine to pull vaccum at all,the intake has to be open right?But if the exhaust on that cylinder is also open,even slightly,then I pull air through the pipes,creating a low intake vacuum.
So since my valvespring seats are lower than the intakes on my heads,the seat pressures are also lower ,and it is probably most assuredly,tipping towards definatly that the lifters on the exhaust valves are over powering the springs at 1/2 turn or whatever,keeping the valves open.
Also explains no real power gains.But doesn't explain why I had a fluttering out the carb when the intake lifters were all preloaded.

........ Ouch that hurt.I need to rest now.