old 318 compression problem

[cherokeechief79]

its in a project car I've acquired.
it doesnt have very much power at all aseems like the secondaries arent opening.
a compression test shows 120 to 130 everywhere except #1,3 and 5.
they all have 90 exactly.
i put a new distributer in it and its got an old mallory ignition box that works fine.
the plugs looked good.the timing mark on the balancer is off about 90deg.
he put his own mark in a new spot and that seems to be good at least for how im timing it.
it wont even run with it near the stock timing mark.

do you think the balancer spun?
theres no way the chain could have jumped that much right?
what about those low cylinders all next to each other?
should i be worried about that?

 

[413]

It doesn't have much power, that's the concern.

Balancer marks way off, no the timing chain won't do that. Time it by ear. Advance until it pings and back it off 5-7 degrees. How does it run now?

Does it get wide open throttle with the foot?
Do the secondaries open?
How much vacuum at hot idle?
What is idle RPM?

 

[Professor Fate]

The balancer is probably because of a mix of early and late parts- late timing covers ('70+) have timing marks on the driver's side, and early ('69 and earlier) have them on the passenger side. The balancers are marked differently because of this.
That would account for the timing marks being "off about 90 deg".
Low compression on adjacent cylinders would make me suspicious of a head gasket...
By the way, what's an "old 318"? Early/late LA? Polysphere A318? Heck, even the Magnum 5.2s are a minimum of 25 years old...
What are you working on? Year/make/model...

 

[AJ/FormS]

If that is a 73 and up 318, they were born with compression problems.
About 140psi@sealevel was all they ever made;
if someone swapped the steel gasket out for something around .040, then 135 was about it
And by 800 ft they were down to 131
Your engine, is measuring awful low on the one side. My first guess would be rusty valves and/or seats.

Here's what I would do;
remove the valve cover from the bad side.
Find the GOOD cylinder
and move it's piston to the bottom.
Pressurize the cylinder with shop-air
with a stick of wood or a brass punch on the end of one of the valve stems, start bopping it with a hammer. No don't smash it! Just bop it open about 3/8 inch and let it slam back onto the seat. Repeat a few times.
While doing this
listen for air hissing, and the sound that the valve makes as it slams back onto the seat. Alternate between intake and exhaust. NOTICE that sound; it should make a pretty sharp pop.
Now go do the rest of them;
When the hissing stops, and the valves all "pop", yur done. Reinstall the rockers, with the shaft oriented correctly, and yur ready for a second compression test.
That's what I would do.

 

[cherokeechief79]

thank you guys! not sure of the year but the timing cover tab is on the pass side.
its in a 67 coronet wagon.
makes sense what you said about the mismatch in balancer years.
i just rebuilt a holley 600 that really looked about brand new.it idles fine but i may have gotten something wrong with the secondaries.
its definately not opening when we get on it and i believe i have the trans kickdown set right too.
i saw a vid and the guy did an oldschool trick and put a screw in the scondary linkage plate forcing it to open.
this looked easy and i thought i would try this next.
i did time it by ear exactly as you described.

 

[cherokeechief79]

forcing the secondaries to open
this is what i was going to tyr next.
is this a bad idea?

 

[413]

guys like this is why holleys are all screwed up when you buy a used one. Look how sooted up his carb is, serious tune problems on that vehicle.

Doing that trick will open the secondaries but there is no accelerator pump and your old 318 probably won't like the lean condition it creates. Bog, stumble, die

 

[cherokeechief79]

i know....its just a simple thing to see if they are truely opening.
if they do then ill remove the carb and see what i did wrong rebuilding it.
i thought the same thing you do about that vid.......how could anyone with a carb that black and sooted up possibly be giving carb advice!

 

[TT5.9mag]

Vacuum secondary carbs have a “pitot tube” in the primary Venturi that activates the secondaries. You can blow shop air across that tube with the primary open and the secondaries should open. If you want to tune them, do it correctly with the spring in the vacuum pod, not with a screw.