Hello everyone... I picked up a halfway decent 1969 350 H.O.?.. And seller told me engine was rebuilt...
Well first thing is very rough idle and veh has spark knock bad with 93 octane..
So since im new to this engine i got some numbers off Heads's ,,Intake,,Carb,, Block...
Heads are Cast number 48,,
Block Date code looks like L288, which means the block was cast on Dec 28, 1968.
Block casting number is 9790079 -So it looks like its not the orig block, but that fine by me...

So after chasing spark knock and rough idle and 15 inch manifold vacuum and i then find initial timing at 4 degrees ATDC ..(mallory Uninite Dist)
So i pulled the Mallory Distributor out and put in old reliable G.M. HEI.. Set initial timing to 8, and i see a max timing of 35 degrees with vacuum advance unhooked..
So im still chasing 15 inch of manifold vacuum and rough idle and spark knock... Then out of no where i see vacuum gauge bouncing very fast at idle but not going over the 15 mark...
So im assuming i have worn out valve guides ??????????

Thoughts guy's... Im thinking my best bet is to get rebuilt heads they may lower compression or new ? But gotta same some money so rebuilt may be my option.

All the codes point to a '69 350 HO

Normal Engine: On a normal engine, accelerate to around 2000 rpm and then quickly release the throttle. The engine should snap right back to a steady 17- 21 "hg vacuum.
Steady low between 5-10 "hg vacuum: This indicates that the engine has a leak in the intake manifold or the intake gasket. This leak should be easy to find because it would be making a loud hissing noise.

Steady low between 10-15 "hg vacuum: This reading indicates late valve timing. There's a good chance the vehicle has jumped timing. Check the timing belt or chain depending on the application.

Steady low between 15-18 "hg vacuum: This just low reading indicates retarded ignition timing. Advance the timing on the distributor to correct this problem.

Fluctuating Needle: A fluctuating needle indicates there's a problem with a valve or a there's an engine misfire.

Needle drops during acceleration: If the needle drops steady during acceleration there's a restriction in the exhaust or intake. This is typically due to a clogged CAT or muffler.

also see: https://www.motor.com/magazine-summary/mastering-the-basics-reading-a-vacuum-gauge/


one clue is " seller told me the engine was rebuilt".......when? by whom? any receipts?........something could have been put together wrong or the intake gasket is screwed up

The clue to me is that you found the initial timing retarded by 4 degrees, so somebody was trying to get it running right without pinging by backing the timing down.

First I would make sure you have the distributor stabbed correctly. Set no. 1 at TDC compression and make sure the rotor is pointed toward the no. cylinder (at the cap).

If not, the camshaft timing may be OFF, which can also account for you low vacuum readings. You'll have to pull the timing cover to verify that.

Could have just been a poor rebuild job as well.

excellent point on the camshaft, I'm suspecting the "rebuild", but I wouldn't panic, could be somewhere they made a mistake like the camshaft not properly lined up with the crank, intake gasket not sealing, etc etc etc

all of my Pontiacs have had excellent vac so soemthing is amiss

Was able to look at car some more and here is what i see know.. 15 max vacuum on gauge , but its Fluctuating very fast,....
So i let the car cool off again, and then went and started and waited till choke came off. And then i removed one plug wire at a time and when i do the rough idle smooth's out .. and it did it with every cylinder i pulled a wire at.. ???....
So decided to drive veh, and try to get it at its worst for rough idle.. Now when i pulled all the wires one at a time, i found that number 5 and 8 seem dead at idle..And the rest were firing.
They seem to come alive the second you bring it off idle..

Oh and i have searched till im blue in the face for any vacuum leaks.... But power bakes will go hard at times

The Mallory Dist was the issue with timing set at 4 ATDC.. For some reason i was getting way to much total timing. (total timing was over 40 when i set initial correctly) And harmonic balancer has not slipped.
So i droped in a G.M. H.E.I. i had here, and set it up with initial at 8

If you've got no change in running at idle when you pull wires off of 5 and 8, those cylinders are not contributing. Next thing to do is run a compression test on ALL the cylinders.

Pull all the plugs out and hold the throttle wide open when you do it.

Could have burned valves (would account for the low vacuum and needle fluctuation)

Sounds like you may be getting close to an answer.

Thanks... What throws me off was engine smooths out with each wire i pulled one at a time right after the choke was off ....
Gonna hope its just a valve(s) or valve springs...as i do get a little breathing heavy thru breather tube at air cleaner.

I pulled drivers side valve cover today only to find that a few of the valve springs have broken.. The piece under the retainer that covers upper part of spring...and the others are cracked...

Also inside the chrome valve covers are what looked like glued on cork material which i wasn't sure if that's nomal,, but i could see where rockers had been hitting in that location on cover..

So since i had a few Comp Cam springs here 988-1 , i removed number 5 springs and then spun the valves with a drill (lol yes) and then installed new springs and assembled..

Started car and number 5 cylinder was back alive .. whoo hooo.... So i buttoned up car and let it set for cool down of 2 hours...

On restart number 5 cyl is dead again....

Without a leak down tester , i would have to assume burnt valve ..

But if someone had put a big [censored] cam in, will the stock rockers and studs work and have valve lash correct ? - as i stated earlier that rockers showed they had been hitting inside of valve covers a tiny bit.

Carlbird, way do case this down.

I’ve never seen valve covers with addled “insulation” on the inside. Based on that alone, I’m suspicious of the so-called rebuild.

Re vacuum: you can’t be sure if your 15” reading is good or bad without knowing your cam specs. I have a 10-11” with a quivering needle...and power brakes. Obviously, my can ain’t exactly stock.

Others more knowledgeable will off more detailed advice, but you need to pull the heads for a fresh valve job, and while you’re in there, might as well yank that cam. You know you want too...

Thanks... Well with mine at 15 vacuum and quivering needle, i end up loosing all my power brakes at times and never know when... Scary when it happens..
Last thing i wanted to do , is pull these heads and cam right now... But will do leak down test before i do that...
Im still gonna attemp to get to cylinder number 8 and replace the springs -- but car has factory air and will be a tight squeeze to get in there with spring tool...
Also gonna try chevy rocker nuts and do manual adjustment since i dont know for sure what previous owner(s) might have done with engine.

hmm

not sure about your situation but Pontiac stock heads won't take high lift cams, which sounds like what you have,, RAI & III style, 068 cam etc yes, but something like a RAII or IV, no, the factory used different heads with different springs, your push rods should be bent too if this is the case, Crane makes what they call Blueprint cams which are indentical to the factory, the 068 or 744 cams are great cams, the 041 which is the RAII & RAIV cam is too radical

it sounds like your top end has to come apart, sorry

hmmm again

they also may used the wrong push rods, I would check that too, that would create a hell of a bind and breakage if they're too long

also high lift cam Pontiacs used a higher valve cover gasket to clear the higher lift, Ames performance has it, I use it with my 068 cam just because it makes a better seal, it also requires taller bolts

this person may not have rotated the engine when they set each rocker nut to 20ft lbs, if they even did that, it's possible that is what caused the breakage and other issues, if the nuts were screwed down too far it would hold the valves open or one or two and break things

Car has orig heads cast number 48..(350 H.O.). But when i get back to the car to replace the rest of the springs (Comp Cam 988-16) ill look for bent push rods...
So will i be able to try 3/8 chevy rocker nuts on studs to adjust ???...
I have a set of 7/16 studs and ball's and nuts but was unsure if the rocker balls will fit the stock rockers.

"... but you need to pull the heads for a fresh valve job, and while you’re in there, might as well yank that cam. You know you want too..."

Do it right. Do it once. You'll save money. (ask me how I know...)

the 48 heads were originally made for the 350HO for the original Judge which never happened because DeLorean didn't want a 350 in a GTO, the heads then became the 400 RAIII available in the 69 year I believe, I'm not sure if you have a 350 or 400 based on this thread but I would check to be sure, a 350 would never take a big cam, neither would the 48 heads in a 350 or 400

verify what block you have, the 48 heads are great heads, take all of your pushrods out making sure to locate them where they came from, I use a drilled block of wood, roll each one on a plate of glass to see if any are bent and replace those, get the heads fixed, while the heads are off check the pistons for dents or worse, pop'er back together with a 068 cam

68, there was also a 350 "HO" which had increased power with the addition of higher compression #18 heads (#17 and #46 were the most common 2-barrel heads), a four-barrel carburetor and matching intake that was also used on the 400 and 428 engines. There was also the addition of dual exhaust, and in the case of a stick shift car, a slightly more aggressive cam.

In 1969 the 350 HO was upgraded again with the addition of the 400 HO cam, commonly referred to by Pontiac hobbyists as the 068 cam. Also added was the #48 casting number heads with a 68 cc (4.15 cu in) chamber for higher compression, along with larger 2.11 and 1.77 in (54 and 45 mm) valves. Free-flowing exhaust manifolds from the 400 RamAir were used late in the model year. This was underrated at 330 hp (246 kW). Many of GM's other divisions' 350's like Chevrolet, Buick and Oldsmobile and even the base SS396 were handily beaten by this little 350 "High Output" (HO) Pontiac.

Decode the production number and engine code. According to Pontiac Power, the production number for both 1968 and 1969 350 HO engines is #9790079. Between Pontiac Power and Firebird, the two-letter engine code is either "WK" or "WN.", in the first post it sounds like you do have a real 350HO, HOWEVER that engine is supposed to have the 068 cam, nothing else would be wise, these engines beat the hell out of chevy big blocks with the 068 cam, they flew, set it back to stock config, best of luck

https://itstillruns.com/identify-1969-pontiac-350-ho-7423834.html

Ive verified most of what you said..
Block casting number is 9790079 ?. But it shows wrong stamp number below pass cylinder head in front.. But past owner said block wasn't orig, but it is a 1969 block.

the 9790079 number is telling, sometimes some numbers are funky, for instance my 400 does not have the 400 in the block under the drivers side like it's supposed to, all other numbers including the carb check out

good luck and please keep us informed as to what you find as you dig,

A few thoughts.
First If I had broken pieces of anything under my rocker covers I wouldn't even start it until I was sure there is no debris anywhere in the oil system. Any little pieces of fragments of metal that get into the bearing areas and you can start saving for a complete tear down. Draining the oil through a paint filter and opening the filter to check for metal is the very least I would think needs to be done.

Replacing broken components the running the engine without first determining the cause of the original breakage is another thing I would avoid. Those components broke for a reason, replacing them without rectifying the initial cause is asking for more broken parts.

Idle smoothing out when pulling a plug wire may be due to a screwed up valve timing, firing the cylinder when the increased pressure slows the rotation rather than increases it.

If it was mine I'd pull the engine and do a complete teardown and inventory all the component specs just to see what's there to start with. At the very least I suggest pulling the heads and camshaft. Until you know what you have in there it'll be a bit difficult making an informed decision as to the best course of action to rectify your malfunctions. With the heads off you can measure the chambers, inspect the pushrods, guides, seats, cylinder walls, lifters etc, You can also measure the stroke to see if someone dropped a larger or smaller stroke crank into the block as well as determine the deck height, measure bore, measure the camshaft lobe lift, check if the camshaft has any lobes worn right down, etc.

Vacuum gauge needle will always drop during acceleration. At idle or cruise the throttle valve is almost closed or only slightly opened. The area above the throttle valve is at atmospheric pressure and the area below is at a reduced pressure due to the downward movement of the pistons on intake stroke. When the throttle is opened the pressure differential is reduced and the vacuum reading drops.

Back in the good old days when the lifters were solid, guys used to glue pads to the underside or the rocker covers to dampen the valve train noise cause by valve lash. I kinda like the sound of mine. Also It's easier to hear any changes in sound due to an increase or decrease in lash without the pads.

Just my opinion, I'm not an expert.

Well since money and time and a place to do a complete tear down is impossible right now , im going to replace the stock springs,Rocker studs (adjustable),and rockers and hope that is reason the oil slingers caps on spring were broken,
Found one bent push rod so far and also seem to be aftermarket as they have writing on them of 4127 .
Now that i got over to the right bank and on to number 4 cylinder i found broken cap like the rest, but now i see the spring seat in head is a little damaged where old spring had worn off the edge and had slipped off some..
.. So where i am now i guess i need a valve spring type shim as i dont want the new spring to do the same..
Any idea of the shim inside diam i need to get. ????.... I do know my new springs have a outside diam of 1.384 - ( comp cam 988-16)

[quote=Bartbird]hmm

not sure about your situation but Pontiac stock heads won't take high lift cams, which sounds like what you have,, RAI & III style, 068 cam etc yes, but something like a RAII or IV, no, the factory used different heads with different springs, your push rods should be bent too if this is the case, Crane makes what they call Blueprint cams which are indentical to the factory, the 068 or 744 cams are great cams

So what cam then was in the 1969 350 H.O. automatic .. the 068 ?
I have the cast 48 heads and matching intake and carb,, and also the ram air exhaust manifolds.

The only time I've personally seen pushrods bend was when the timing was off. As in timing gear installed in the wrong position. Probably not your issue but you definately having a timing issue of some sort. Could be as simple as being wired up in the wrong firing order or a slipped balancer. Pull the timing cover and start at the beginning by lining up the marks. Until you do you won't know it's right.

Yes, the 350HO used the 068 cam. unless it was auto

found this on hemmings--

Differentiating the 350 H.O. from its base two-barrel counterpart, however, was–first and foremost–its four-barrel intake and corresponding 750-cfm Rochester Quadrajet, as well as a dual exhaust system. Less perceptible visually was the change in cylinder head design, the ’69 edition making use of “#48” heads (a reference to its casting code) with enlarged 2.11/1.77-inch intake/exhaust valves. Also referred to as “big-valve heads,” the D-port units feature 66-cc chambers and are the same as those bolted to the manual-shift Firebird 400 (335 hp) and the manual-shift GTO and Ram Air III engines. On the 350 H.O. engine, they contributed to a 10.5:1 compression ratio.

Complementing the fuel delivery and breathing components was a hotter camshaft. Engineers fitted two different cam profiles depending upon transmission selection. Owners who preferred to retain a manual received what has become known as the “068” cam, with its .414/.413-inch intake/exhaust lift and 288/302 degrees of duration. An automatic transmission meant the “067” cam was installed, it’s profile being .410/.413-inch intake/exhaust lift with 273/289 degrees duration. These same cam profiles were utilized in select Firebird 400 and GTO engines. Regardless of which camshaft is inserted, the collaborative effort yielded an official output of 325 hp and 380-lb.ft. of torque. No other engine was offered in the Firebird H.O.


and on a lighter note, these were 14 sec cars with standard gears and cheapo bias ply or polyglas tires that had no traction and went up in smoke like most cars of the day

Also your block should have one of these numbers punched in the front right below the passenger head-- the Firebird’s 350 H.O. should have either “WN” (manual) or “XC” (automatic)

right where this one says WW

http://www.pontiacpower.net/numbers/

Bartbird ,, On the letter stamping below passenger head in front it say's Y.U...But my block shows its a 1969 version by the numbers on the back.. But i do know its not the correct code for a 350 H.O. . The block is a 1969 tho but seems to show it came with #47 heads, a 2-barrel carb, & was rated at 265hp and Date code looks like L288
But when i get timing cover off this weekend i'll look for that other number near timing cover (vin) i guess they stamped into block but hard to see.

The guy i bought it from said the block was changed and he has the orig if i want it.


I have the new valve springs on now and new seals and 7/16 rocker studs,, and i'll be taking the cam out by this weekend.. Very curious of what someone has stuck in there and if marks are lined up..

A YU means it's not a 350HO, but your block ID has the correct number, weird, perhaps they used the block ID on many 350's, maybe not

the only 69 350 I find with a YU block is identified as a YU F-body 69 350 265hp Powerglide trans 1×2carb block ID 9790079

Yes thats what i came up with. That it was a 1969 block but 2 bl carb. The guy i bought it from said block was changed and he has the orig and i can have it,, but i havent found a place to store it yet tho..(live in apartment) ( guess i could wrap it up and stuff in corner- ?.)
. But i guess as long as its a 69 block im fine with that..

[quote=Carlbird1], but i havent found a place to store it yet tho..(live in apartment) ( guess i could wrap it up and stuff in corner- ?.)
..[/quote

Just put on a Harbor Freight engine stand and use it as a night stand next to you bed.

LOL

Update of what i replaced.. To try to get running better ..



1 = New valve springs and seals

2 = Cam and lifter's. ( Summitt Cam = 2801) Cam i took out ended up being a Comp cam 252h

3 = Timing Chain

3 = New screw in 7/16 rocker studs, so i can adjust rockers. (1/2 turn down from zero lash)

4 = Comp cam roller tip rockers 1.5 ratio

5 = New Melling stock length push rods. ( one of the old one's was bent)

6 = Carb kit from Cliff with new bigger primary jets and power piston rod's.



Well car is better,, still chasing spark knock which gets pretty bad in hot city driving,,Have initial set at 8 and i backed down my adjustable vacuum advance to 6 inch to help.. Think its coming on to easy and fast... But plan on pulling out the Chinese Distributor and put a better one in that is on order.

Today car was not to bad after i put in the correct carb jets , but after a hour of sitting and i go back out and start car its just the opposite = rough idle,.. Ended up readjusting mixture screws again and had to raise idle speed up. 1/8 turn on screw...

Car is very touchy and a mind of its own...

At this point im not sure yet if im still chasing a carb issue or engine issue. = breaths hard out tube to air cleaner..