Ford 289 with 302 heads, Edelbrock performer carb, verified spark and timing and compression, fuel fills float bowl, engine won’t suck through intake all valves are opening and closing properly, will not crank with fully closed choke and starting fluid, could this be a huge vacuum leak?
Cam timing has to be off to not have suction at carb base. You would hear a vacuum leak that big sucking air.
Do you have to have intake to have compression? Isn’t compression just the piston forcing air through the cyclinder?
@BenWY Intake manifold not required for compression test. However you would have to have correct valve timing and push rods/rocker arms installed. If you do have the intake in place and are not developing vacuum at intake, I agree with others that cam timing/operation is likely the problem. Edit: by the way.....I think you meant to say “engine will not fire” vs “ engine will not crank”. Those are two different things. “Cranking” is usually understood to mean the crankshaft is being rotated by the starter. “Firing” means the spark plugs are receiving high voltage and igniting the fuel mixture....or not......while cranking (aka ‘turning over’) “compressing” isn’t just the piston pushing air through the cylinder, it is what the term implies, ‘compressing’ the air which requires a closed and sealed chamber so the air is ‘squeezed’ into a smaller space as the piston pushes the air. Ray
I think what he's saying is that if the cam timing is off, at least to a specific degree, you could end up with an intake stroke occurring with little or no intake valve opening or an exhaust valve not completely closing. And you could also have a compression stroke with either or both valves not completely closed. Either way it makes for little or no cranking vacuum or insufficient or no compression pressure.
Yes sir understood compression isn’t reading at normal but each cylinder close to the the same pressure, I have noticed that when you try and crank it it’s slower than normal on the rotation which would explain the bad timing ?
@Hnstray, great explanation for those that don’t always know the proper terminology, and/or just how things function.
Just pull a valve cover for #1 turn the engine watch the exhaust valve close and when the intake just starts to open look at the timing mark it should be very close to TDC.
It would help to know if this is a fresh build or an “experienced “ engine with an unknown history. Fresh build and the cam could have been installed incorrectly so the valves aren’t opening at the proper crankshaft/ piston position. Old engine and the nylon teeth could be shelled from the cam gear, allowing the chain to jump a few teeth. Same result: no compression. I would go back and verify spark, though. The distributor may be installed incorrectly so it’s not firing on #1. Pretty easy to be off a tooth when trying to insert the distributor and line up the oil pump drive.
It’s an experienced engine I would say, pick this up from sitting for about 15 years, distributor timing is correct and verified spark, I pulled valve covers and can physically see the valves/springs opening and closing, I’m sure this motor has ran before not how long and to what extent etc
Ive seen engines that for some reason wouldn't hit on one cyl. due to a bent rod causing the piston to be down in the bore. maybe you have 8 bent rods? or 302 pistons on a 289 crank? Maybe its simply worn out?
Almost certain that everything is from a 289 but a 302 head swap.....dumb question and usually the simplest things are what’s wrong....if a battery isn’t big enough as far as the CCA goes van is cause low compression and lead to some of these issues? If it’s not strong enough to turn the motor over fast enough to create enough compression and vacuum ?
Check to see if your exhaust pipes are completely plugged up. It’s a long shot, but possible for an engine that set around for 15 years. Bones
So pulled timing cover off and it is in time with the crankshaft, I pulled a vacuum test on I take port and literally read zero, it’s just not drawing in
Squirt some oil down the bore and do the vacuum test on the intake again. After that, back off the exhaust valves and vacuum test the intake again (maybe add some oil down on the exhaust valves as well)
And then there is the occasional marine reverse rotation cam or even entire engine that has snuck over to the automotive side to ultimately have more than a few scratching their heads over the years....... Ed
Possible stuck valves from sitting so long? Wouldn't have to be stuck very far open to destroy the combustion chamber seal. Ray
You might also try to apply some air through the spark plug holes and see if it is escaping through the valves. Are you here in Wyo somewhere?
Since you have a mis- match of parts, are you sure the intake is seated well on the heads? Have the heads been milled or the intake been cut on the port side? Are you sure of the parts you have are unmolested? They might not seat properly Do you have the right intake gaskets?
Leak down, leak down and a leak down test. Did I mention do a leak down test? Sent from my iPhone using H.A.M.B.
I’m leaning more towards an intake valve, when you turn the motor over the intake/carb will whistle air, this evening I’ll put compressed air in the cylinder and see what I get
Wouldn’t I have to much vacuum with a stuck open intake valve? Because it literally has no draw on a vacuum gauge right now
Should still have vacuum with a stuck open intake valve, the pistons “pull” against the throttle plate, the reason diesels don’t make vacuum. If the throttle is closed and you have zero vacuum there is a big leak somewhere or there are no rings in it! Sent from my iPhone using H.A.M.B.
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