Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor per

[William H.]

Hello Guys,
Im looking for some fresh Ideas here about my tow vehicle.
Mostly stock 69 GMC 396 ,A/T, P/B, P/S, A/C Original Motor and trans Heads exaust manifolds. Edlebrock Performer intake. Quadrajet carburetor. 3" exaust from manifolds back. gets about 8mpg around town maybe 12 or 13 highway. Idles with just a very slight miss in drive and pretty smoth in Park. Hei ignition with MSD 6al box. plugs gapped .035. Had to turn up initial timing to 30 deg in order to get the throttle plates in the right relationship to the curb idle ports and so there would be no vacume at idle on the dist vacume port.
Engine has extremely low vacume. I ran the valves on the stock hydraulic cam ( I think ) and i backed them off until they clattered and then in till they stopped and then 3/4 turn more 1/4 turn at a time. I thought I might have weak valve springs which would have made the idle drop and not come back after tightening the 1/4 turn but instead the engine rpm didnt drop at all as it tightened the nut to about 1.5 turns in!I did this on several cylinders and it was the same.( After that I adjusted them correctly)
So now Im wandering if the valves are not seating well. Ran some water in the carb at fast idle and drove 10 hwy miles at 75mph and the vacume readings went from fluttering 1-2" to being steady. I ran a compression check dry and got
1-175 3-175 5-170 7- 170 2-172 4-165 6-167 8-165 have not had time to run leakdown test. also wandering about cam timing being retarded.

here are current vacume readings

vac = vacume advance connected
t = timing
RPM
VR= Vacume reading
TR=Trans position

VAC T RPM VR TR
N 30 800 16" Steady Park
N 30-32 625 12-13" Fluct Reverse
N 32 1350 18" steady Park
Y 38 1425 19.5" Steady Park
Y 30 800 16.5" Steady Park
Y 30-32 625 12-13 Fluct Reverse
Y 48 2050 20.5 steady Park
N 40 2050 20.5 Steady Park
N 44 2500 20.5 Steady Park


Seems to me like eithjer valves not closing tight or cam retarded or
not hydraulic cam or HP cam. But doesnt idle like HP cam?
I verified TDC mark on Balancer and have checked timing light against another. Also centifical advance is all in at 2500 and there must be some advance between 0-650 rpm because it doesnt fight the starter unless its hot and it always starts even when hot. It doesnt overheat unless around town with the a/c on.
Any way to tell if hydraulic or solid lift without removing lifters?
Any way to tell if cam gears alighned withhout pulling cover?
Anyone have cam specs for the stock cam for this engine so I could degree it? Does the compression check values seem ok the motor is supposed to be 9:1 and my 87 jetta with 9:1 pumps about 190-200psi.
Thanks in advance for any suggestions,
Bill

[Gene M.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

William,
if ya are talking high miles the numbers sound about right. I suggest ya set the lifters the right way and go by the book. I'm assuming the camshaft is stock and not some hot rod thing, so you can set it on #1 and #6 firing sequence listed in the manual. high miles has a way of loosing up the timing chain so you are always a couple degrees cam retarded.

[Terry D.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

If the valves were not closing you would not get the compression readings that you have. What is the total timing above 2500? Agree with Gene on setting the valves according to the book if indeed you have the stock cam. Don't understand the intial timing at 30? Why?
Terry

[Domenic T.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

William,
The timing mark on those big balancers can move as the rubber gets old and not be correct.

I have seen it many times and you can check it with the plugs out and have someone turn the crank till #1 is exactly on top. When it is exactly on top the crank can be moved a few degrees either way without the piston moving.

Also, we found that 1/4 turn works great, but when you hear the clack give it a few seconds as it needs a few seconds to fill again to make sure you were backed off all the way.

I agree with the non messy#1 & #6 that Gene recomended. You can get the feel of the rocker touching the valve stem, but remember that when you back them off the lifteris not full of oil and will be mushy , so you need to keep your eyes on the lifter and make sure you arent depressing it into the mushy area before you turn it down.

DOM

[William H.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

Hello Terry,
The total timing above 2500 rpm is as I stated 44 deg there is 8 more vacume as shown so vacume and mechanical is 52 deg. There is 30 at idle because when it is set at 4 like the book says it will barely run. at 12 it will run but you have to open the throttle blades so far to get the idle right that the throttle blades are not alighned to the idle transfer slots like they are supposed to be. then the idle mixture screws do not work. This is a problem that you get with a really big cam with lots of overlap. the normal way to fix it is to drill holes in the throttle plates until the idle speed screw can be backed out to where it is supposed to be. But I shouldn't have to do this with a stock cam. Also when timing set at 12 deg then the throttle plate is open far enought that the disributor has vacume at idle it is not supposed to. I have set the valves like this on many cars without any problem it is just a little messy. but really i dont think much different than what you are saying. One has the motor running one does not. But Ill give it a try. I always did it the way you are saying when putting the motor together to get it started than do it with the motor running as a final adjustment. By the way on page 6-6 and 6-7 of the 63 vett shop manual it tells you to adjust the lifters the way I did it with the engine running. Turning the nut down 1/4 turn at a time and pausing to alow the engine to run smoothly before going another 1/4 turn until one full turn has been made. The way you are saying is listed on page 6-15 after removal and repair of the lifters and then has a note that if they are noisy after this meathood you should adjust them with the engine running . Anyway I will try to do it with the engine off and see what happens. Also I forgot to mention that the timing cover gasket has been replaced recently so I am pretty suret that the timing chain was replaced so that makes me wander if they got it retarded by one tooth. What I dont understand is why as I tightend the nut down past zero clatter the engine did not run rough for a few seconds untill the lifter pumped down. Thanks for the input and Ill let you know what happens.
Bill

[William H.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

Hello Dom,
As I stated I did check the timing mark on the balancer it is right on. Scred a stop into the spark plug hole and turned the motor over both directions until it stopped made marks on the balancer the factory mark is right in the middle.
I dont exactly understand what you are saying about the mushy area. can you exppound on that sentence a little and how can you keep an eye on the lifter can you see it?
Thanks
Bill

[Domenic T.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

Hello Dom,
As I stated I did check the timing mark on the balancer it is right on. Scred a stop into the spark plug hole and turned the motor over both directions until it stopped made marks on the balancer the factory mark is right in the middle.
I dont exactly understand what you are saying about the mushy area. can you exppound on that sentence a little and how can you keep an eye on the lifter can you see it?
Thanks
Bill

Sorry it took so long to respond but the mushy area is when you back the push rod out and the lifter plunger is in the area that hasn't filled with oil yet leaving air in the lifter.
I watch the lifter as I tighten it back to 0 and make sure I am not compressing the air in the lifter before it fills with oil.

If you back off the rocker arm to get 0 (with engine not running) there isn't oil pressure to fill the lifter leaving air in the lifter (mushy).

The hydraulic lifter adjusts every revolution because it has a required bleed off of oil so it won't hold the valve open. With no lifter bleed off of the oil pressure would fill the area (3/4 turn) and the valve would not touch the valve seat.

You mentioned adjusting 1/4 turn at a time so you know that 3/4 turned rapidly with engine running would hold the valve open making the engine run rough till the bleed off of oil out of the lifter was completed.

DOM.

[William H.]

Re: Slightly off topic sorry need help 69 GMC pickup 396 low vacume readings and poor

Ok Dom,
I think that I get it. You are saying to make sure that you are just taking up the slack and not pushing down on the lifter plunger or else you would really be going past the 1 turn preload? As I understand it the 1 turn is supposed to put the lifter plunger in the middle of its travel. I think this is important so the lifters act correctly at high RMP and you get the max rpm before valve float.
Thanks for the help,
Bill