Loud “Pop” after priming oil pump

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JAndrea

JAndrea

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okay... in Minnesota right now.. pretty chilly, but garage is moderately heated. Break-in Oil is most likely pretty stiff.

My engine is in a “built” state, but waiting to be mated with tranny and installed in car. I hadn’t primed the oil pump since last Fall (everything went well in the Fall... lots of good oil passage leakage as I rotated engine), so decided it was time to do it again. I pulled out the distributor and oil drive gear (paying attention to orientation from when I installed) and primed counter clockwise (383) with a battery impact driver to the point where it got very stiff, then kept going a little more. I could hear lots of good suction and dripping, etc.

I reinstalled distributor, then wanted to just rotate the engine a tad. All was going well...good sounds, dripping... then, as I slowly rotated some more, I heard a loud “POP”, as if I stomped on about a 6” balloon.

Anybody know what that might have been? Maybe oil passages simply lining up in crank/cam/bearing journals.... maybe a valve, etc??

I rotated the engine a little more and all seemed fine, but that freaked me out a little (first time building an engine), so didn’t do too much more.

Thanks for any info!

Jason

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Thick oil & air pocket in oil passage maybe?
I like to hook up a mechanical gauge when priming a new engine so I can see whats going on. I would suggest hooking one up and verifying you have plenty of oil pressure. Hope it was not a oil passage plug blowing out.
 
I second a sticking valve.
Has a fuel pump on block?
Maybe it made the noise?
 
Fuel pump is in the block. I’ll not worry too much just yet and get a mechanical oil pressure gauge. That was not a good feeling.
 
Yeah that sounds like a valve hitting the seat. You better pop the covers and make sure the pushrods/etc are still where they belong. Then I think a compression test would be a good idea, in case the piston bent that valve
 
JAndrea said:
primed counter clockwise (383) with a battery impact driver to the point where it got very stiff, then kept going a little more.
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If you didn’t make a mistake in your post, I would not be using a battery impact driver to prime the oil pump with. If it gets to the point where it’s actually using the impact it will shock the parts in the system.
 
Good point, we used a cordless drill on ours. An impact wouldn't be good.
Dubob said:
If you didn’t make a mistake in your post, I would not be using a battery impact driver to prime the oil pump with. If it gets to the point where it’s actually using the impact it will shock the parts in the system.
Click to expand...
 
4spdragtop said:
Good point, we used a cordless drill on ours. An impact wouldn't be good.
Click to expand...
Havent tried it to run an oil pump,but i have a few impact drivers, the percussion is different than that of an air impact and will destroy fasteners and sockets in very short order.
 
I was very careful with it and didn’t go balls out by any means. But thanks for the good point. I probably knew that last year but forgot.

I popped off the valve covers and inspected the push rods. All looked normal. Then I hooked up a mechanical oil pump and used a regular cordless drill.l to bring he pressure up. It hovered at 50 psi when I was drilling. I then installed the distributor and rotated the engine again. All seemed totally normal as far as the engine revolutions, with good leakage of oil all over the top end, with no crazy sounds, binding etc...

I’ll keep researching and see what else it could have been. I’m assuming it was a lightly stuck valve in compression stroke. I didn’t feel any noticeable resistance.

Thanks for now everyone!
 
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I don't even use a drill motor, I just use a 1/4in drive speed handle with a socket. It really takes very little hand cranking to prime an engine.
 
I would be taking the springs off to check for a tight valve. U don’t want it to seize when u fire it up. U may be able to get some lube down the guide. Kim
 
Sorry you are dealing with this. I had a fresh motor I built sit for a while- 1 year. I did the same thing... turn the motor over by hand while a friend ran a drill on the oil primer shaft. Sadly I heard the same “pop”.
I removed the heads / intake and all looked good. It sounded like a valve closing so i sent the heads to the machine shop. It seemed one of the valve guides stuck to the valve and pulled its way out. The spring closed it but the guide was moving in the head. The machine shop repaired it with an oversized guide. They checked them all but said even with break in oil on everything- don’t let them sit for more than 6 months before repriming the engine for 20 mins while turning over. ( a bit much I thought)
Anyhow that was a 318 complete rebuild.
Not sure if different with a 383. But gaskets and time is cheap if something is really wrong.

Good luck and I hope all is well with your engine.
Joe
 
JAndrea said:
..............and inspected the push rods.....
Click to expand...
Location, location, location......
Did you happen to notice or hear the area of where the pop sounded?
I had a stuck relief valve on a SB oil pump causing zero pressure that released as soon as I broke one pump mounting bolt loose. It made a pretty good hollow sounding pop. I knew right away where it came from. No way I was using that pump again.
Other than that, IMO, it's pretty easy to "miss" the rocker cup when bolting down rocker shafts if you're not continually checking them during tightening. This "could" cause a pop as it springs into the cup if one wasn't in and the valve seats. I'd go through them again at least tension, TDC for each pair. Spin 'em to see if one may have bent.
If your fuel pump misses the pump rod I'd think a pop might be possible.
 
I'm thinking this is a likely scenario... I remembered I had my exhaust ports pretty tightly taped with painters masking tape, so I went and checked to see if one was blown out. Sure enough... cyl #3 had tape that appeared to have been blown out from the inside. All other exhaust ports remained tightly taped. Also, as I was rotating the engine, I could hear the flexing/wrinkle sounds of the tape, so I knew air could slowly leak through as I was rotating.

If i was rotating through the exhaust stroke, and I had a lifter that wasn't fully pumped yet, thereby keeping that valve from opening, and air from escaping... then finally pumping up and opening that valve.... that would totally cause that popping balloon sound, as well as blowing out the tape.

Seems pretty likely to me. I think I'm still going to try a leak down test to see if there are any valve train issues. I'm assuming I'll have a certain % of leakage past the rings, since they are unseated, but I would think a valve issue would be exposed if there was one.
 
yep... Same thing happened to me. Startled me it was so loud !
And I was turning it over by hand...
 
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