SBC Oil pressure loss.. What the Heck??

I have a new (rebuilt) 355 from a reputable machine shop in my area. Bored, new pistons, bearings, heads re-done....the typical non performance rebuild.
Anyway, when I priimed the oil pump prior to start-up, I got a lot of resistance. the primer (modified distributer, turning it with an air ratchet) was very hard to turn. It was kinda like stirring cold molasses with a stick. Is that normal? It's been years since I've done that so I don't remember. I was able to get about 70 lbs of oil pressure priming it.
Question #2, this is the big one... When I started the car, it started very quickly and I brought it up to around 2000 rpms to break in the cam. After a minute or so I looked at the gauges and saw that the oil pressure was on zero... I immediately turned it off. How is this possible if I had good pressure when I primed it? Has anyone here experienced the same thing?

I had exactly the same thing on breakin, luckily, my Son was watching the oil pressure gauge and we shut it down the second it hit zero. It turned out to be an oil galley plug in the timing chain area that blew out. The machine shop blamed it on "oil pressure spike" :rolleyes: but I think they didn't strake it correctly. I tapped threads and put screw in plugs in their place, no more problems.

Not saying that is what you have (could be a broken oil pump drive shaft or something else), but it is one place to start looking. I rounded off the hex on a drive shaft one time and lost oil pressure immediately too.

Don

That would have to be a huge oil pressure spike.... Get this though..I removed the distributor and put the primer back in...and the pressure started building up again. I'm stumped.

Check the bottom of your distributor?????

Oil drain holes in block-heads open/clear?

Is it pumping the oil pan dry and all of the oil up in the heads/lifter valley?

how soon after oil pressure loss should one hear lifter clatter .. i rarely pay attention to guages till i hear a problem ..

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Originally Posted by cffisher

Check the bottom of your distributor?????

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Bingo. It would appear that your primer is driving the pump but not the distributor when installed. As Charlie suggests, try another drive shaft in the bottom of your distributor while the distributor is out to see if it is tight in there. Inside of the bottom of distributor might be rounded out, or too short to reach the driveshaft.

Don

If I can get pressure by priming, I have to assume I don't have a problem with passages and drains..(but I don't know for sure) The bottom of my distributor looks good, but I'm going to take some measurments and see if the distributor is seating in the oil pump shaft.
Here's a kooky theory...could I have driven the oil pump shaft down while I was priming it? Is that even possible?

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Originally Posted by HOSS429

how soon after oil pressure loss should one hear lifter clatter .. i rarely pay attention to guages till i hear a problem ..

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I wish I had your confidence. I don't want to wait until I hear a problem.

Is this an aftermarket distributor with an adjustable collar?

nope. I didn't even know such a thing existed. It's a factory HEI

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Originally Posted by 65ny

I wish I had your confidence. I don't want to wait until I hear a problem.

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i think i worded that wrong :rolleyes:.. i`ll have to think on what i said and clear it up a bit ;)

No, the driveshaft should bottom out in the oil pump so it will stay at the right length. Is this engine and all the components one that has been together and running at one time, or has it been put togethr from various parts? I'm leaning toward the distributor not indexing on the driveshaft correctly for some reason. Is the distributor taking some effort to get it down over that driveshaft? Usually, you need to play with turning the shaft just a tad at a time until it will index correctly and slip down. If yours just fell into place on the first try, that might mean the insides of the distributor where it goes on the shaft is worn or damaged.

What kind of tool are you using to preprime the engine?

Don

Hmmm.....that has me thinking... I installed an aftermarket intake too. There is a chance (small one) that the distributor mounting surface is higher (further away from the oil pump) than the original. That doesn't sound likely though...just thinking out loud.

Shouldn't be a difference, but anything is possible. Compare it to your old one. Is the distributor seated all the way down?

Don

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Originally Posted by Itoldyouso

Shouldn't be a difference, but anything is possible. Compare it to your old one. Is the distributor seated all the way down?

Don

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That has been my exsperiance too..usually they need shimmed up a tad for proper clearance...I guess its not out of the question for it to be the other way.

I would guess the problem is in the distributor somewhere..not engaged far enuff or broken inside......is there a shear pin inside of those?
Might be sheared off and still binding and spinning the pump some..?

Not sure where the shear pin is or if they even have them in there on that model......or if the shear pin effects the timing gear, rather than the pump rod?

When I install a new oil pump, I check the side clearance of the pump shaft before I torque the pump. I just had a 406 recently with near zero oil pressure. I pulled the eng twice, checked bearings changed bypass, changed cam bearings, changed oil galley plugs...all of which were already new. Turned out to be a bad "new" pump. Installed a milodon STD pump and it idles 40 psi hot. The previous pump was a milodon high vol unit which had a defective bypass piston. Usually when psi near zero it is a oil galley or rear cam bearing alignment to changer issue so I am told.

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Originally Posted by Itoldyouso

No, the driveshaft should bottom out in the oil pump so it will stay at the right length. Is this engine and all the components one that has been together and running at one time, or has it been put togethr from various parts? I'm leaning toward the distributor not indexing on the driveshaft correctly for some reason. Is the distributor taking some effort to get it down over that driveshaft? Usually, you need to play with turning the shaft just a tad at a time until it will index correctly and slip down. If yours just fell into place on the first try, that might mean the insides of the distributor where it goes on the shaft is worn or damaged.

What kind of tool are you using to preprime the engine?

Don

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The engine is a fresh rebuild (first time torn down) from a local (reputable) machine shop. I installed the oil pump though.
I the distributor is taking some effort to seat on the driveshaft, I've never had so much problem with one. The distributor looks good, but the oil pump shaft looks a little boogered up. (technical term)
To preprime it, Im using an old distributor or with the cam gear removed.

Lay your dummy distributor and your real distributor side by side and compare them. Make sure the distance from where it sits down on the manifold to the tip where it goes into the driveshaft is exactly the same. Make sure they are identical in all respects, ie, gear in same spot etc. What I see as a clue to your problem is that the dummy will turn the shaft and pump oil but the real one does not. (apparently, by the lack of oil pressure)

When you say the shaft is boogered up, how so? It could be damaged enough that it just isn't long enough for those tangs to engage the distributor. You might also try a second distributor. The fact you have oil pressure when priming is good, and I imagine you are turning the shaft in the right direction? ( I know, it's a dumb question, but since I play with Chevies AND Fords I have to stop and think each time which one goes which way :D)

It could be that you are going to have to drop the pan and put in a new driveshaft. If it were me, I would spend the extra money and get a good one from someone like Summit, some high performance shaft. I would also be tempted to spend another $ 25 and buy a good Melling standard volume pump and put that in for giggles. Dropping pans or pulling engines to do that are not fun things, so while you are in there.....................just sayin'. I don't think your problem has anything to do with faulty work on the part of the machinist or you putting it together, something is just not turning your oil pump when the real distributor is in place IMO.

Don

Oh, sometimes when you remove that gear to make a real distributor a primer it lets the shaft drop down just a tad more. I have one modified from a Ford distributor to do my Ford engines, and the shaft moves up and down quite a bit. So maybe that slop is allowing your dummy one to click on the driveshaft, but the real distributor doesn't have that slop and won't index on. Something else for you to look at.

take and measure down the dist well till you fall in to the oil pump slot on the pump drive now mark it were the dist seats on the intake .this is the over all the dist need to be to reach the oil drive . the dist gear helps hold the pump shaft so it longer then the over all so you can work out . subtract the over hang of the gear to dist drive or just take out the roll pin .drop the dist in and see it reachs the oil pump drive . so if this make s it to pump then it 3 thing s dist gear is screwed up or cam gear .or the cam is to far front or back in the engine .this can happen if a thrust shim was left off the top timming gear or a thrust shim was added to the timming set and not cut for it. this stuff we have to do all the time on tall deck big engines were i cut the dist shoulder off on the lathe or buy adjustable collar dist. when you get it in ..you do not want the dist bottoming out on oil drive and the gear pattern should be in the mild part of dist gear .use lay to check or red sharpy marker . about all the away down and then 060 up then add gasket gets you close on a good pattern on the gear

hope he did not stick a chevy II v8 oil pump drive in it there shorter then a sbc. bbc are longer then stock sbc. had a customer that did just that . i cut out a stub drive it reach the sbc shaft:HMMM: next day was race day he said no way he was not going.... it work.. told him take it out and not push his luck:D

Very good points, Pat. In fact, I have an MSD distributor for a sbc in the shop that has and adjustable collar. You loosen a couple of set screws to move it up and down. I had never seen that before.

Don

Thanks for all for the suggestions. Sometimes it's hard to see the obvious (for me anyway....) I tend to get wrapped around what I'm seeing instead of what's really there.
It's cold and icy here now, when it warms up in a day or two I'll take some measurements. I like the idea about taking the roll pin/gear off of my distributor and see if it meshes with the oil pump shaft. That would take out some of the variables. Worst case (and I dread it) I'll pull the pan and replace the drive shaft. If I'm lucky, I can raise the engine up enough without taking it out of the car.....but I'm not typically a lucky person. :-)

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Originally Posted by Itoldyouso

Very good points, Pat. In fact, I have an MSD distributor for a sbc in the shop that has and adjustable collar. You loosen a couple of set screws to move it up and down. I had never seen that before.

Don

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yep on the big engines with tall decks we cut the collars off the dist and make a slip ring or just buy the msd . i have cut vertex mag dist down for slip rings if the intake has enough meat you can sink the dist well to

Here's an update... I like to see updates on peoples posts, so I figured I'd do it too. Apparently, when my son and I were priming the oil pump the primer slipped up out of the slot in the pump shaft and spun around on the top it. (don't know how the heck that happened, but it did) Anyway, the top of the shaft was mushroomed out a little and it wouldn't slide up inside the distributor gear. The distributor wasn't seating all the way down on the manifold. (how did I miss that? Who knows?) I could have pulled the shaft and put in a new one, but I didn't. I removed the gear from the distributor and drilled it out a teeny bit below the level of the roll pin that holds it on. After that, the distributor almost fell in like it was supposed to. We've got great oil pressure, and it runs like new. Thanks to everyone that offered suggestions, and helped me to pull my head out of my arse long enough to see the obvious. :)