Low oil pressure... Cam specs on a 305?

Pressure seems okay when warming up but drops when it is fully warmed up. I can't hear any knocking, no metal in the oil, and the oil pressure gauge is good. My problem is when I bought the motor the guy said it was a 350 with maybe 9k miles (said it was a crate motor, but I'm not so sure now). I finally looked up the numbers on the block and it turns out to be a 305. I really don't care about that part but I put a beefier cam in it (thinking it was a 350) and am wondering if I have too much lift for stock 305 valves, rocker arms, push rods etc. Any ideas? I'm going to cut open the oil filter tomorrow and see what's inside.

I put a Mellings cam with the following specs:

Cam Lift
INT. .298
EXH. .298

Valve lift
INT.447
EXH. .447

Lobe CTR
INT. 110
EXH. 118

Lash Hot
INT. HYD
EXH. HYD

SAE Duration
291 INT.
291 EXH.

.50 Duration
223 INT.
223 EXH.

SAE Timing
BTC 30

 

Anyone out there? I'm really hoping maybe I can just swap cams at most and not have to tear into the motor.??????????????

Does this cam have too much lift for the 305?

 

The HP 305 stock cam is 415/430 lift and 207/213 duration
You should have no problems.
Did you look at the cam bearings?
Cold 45 psi and drops to 25 psi at idle? in gear?

 

Its between 30 and 40 at start up/ idle. When hot at idle almost 0 when I hit the gas it may jump to 10 or 15 if I'm lucky. I haven't looked at the cam bearings yet. I was hoping to see if there were some other things I should check before pulling the motor.

Does vacuum or timing have anything to do with oil pressure?

 

cam is fine, like Ricks Garage said, what is the oil pressure?

Id be pissed if I bought a 305.

 

cam lift and duration have nothing to do with oil pressure. did your oil pressure problem start immediately after the cam swap? when you did the cam swap did you notice excessive sludge buildup in the motor? if everything else appears normal, drop the oil pan and replace the pump. while the pan is down, I would pop off a couple of main and rod caps to take a look at the bearings and crank to see if they are scored. also, what oil are you using? I hope you're not trying to use 5-20 in an old smallblock.

 

I heard the motor run when I bought it but it sat for a while. Before I got the motor in my truck is when I put the cam in so I really don't have a comparison if it was doing this before... rookie mistake I guess. Some people have mentioned the pick up tube being too close to the pan or the gallery plugs behind the timing cover leaking. I guess I'll check these before I end up pulling the motor.

If I cut the filter open and any bearings are worn out will I see it in the filter?

 

0 psi @ idle You need oil pressure to lubricate the rotating parts. No oil and fiction/heat will kill it. Might be as simple as a new oil pump to maintain volume and pressure. How many miles, does it look freshened up?

I run a remanufactured 305 from an 86 Camaro and it holds 40psi. 350 (Larger bore and valves) -vs - 305 (Smaller runners and chambers), no substitute for cubic inches. Vacuum and timing have nothing to do with oil pressure.

 

Yeah this has me stumped but I'm no expert. The only thing that bugs me is there is no obvious signs of bearing wear (metal in oil, knocking, etc). It supposedly only has about 9k miles. If the oil pump was shot it wouldn't get pressure at start up either would it?

 

not true. a worn pump will build pressure with room temperature oil. then heat the oil to 150 degrees, and the molecules in the oil spread apart, which is why cold oil pressure is always higher than when the motor is warm. pump may not be completely shot, just weak. also, what is your idle set at. if you idled the motor way down to make the cam sound more lopey, that could be contributing to your problem.

 

it does not happen that often, but yes the welch plugs behind the cam gear can leak and cause a pressure loss. when i install welch plugs, I normally steak the block to eliminate any chance of them coming back out. What is your pressure when the engine is hot and you are running down the road at 2000-2500 rpm? oil pickup tube could be set too low. another trick is to tack weld the pickup to the pump after you have it installed just to eliminate the thought of it backing out or coming out of position.

 

Oh, I thought if the pump failed it completely failed. Didn't know they could wear slowly. I just rebuilt the carb and it idles MUCH better and much higher. It used to be real lopey before I rebuilt the carb. The carb was flooding REALLY bad before I rebuilt it. Could I still have fuel in my oil after 2 oil changes... I know this can drop oil pressure?

 

You mentioned the oil pick up tube. When we first fired the motor with the new cam there was a weird tap or knock and it turned out the oil pan had been bent just enough so the crank was barely tapping it. I straightened the bottom of the pan and fixed that, but I wonder if this messed up the spacing of the pick up tube. Hmm?

 

I bet you knicked a cam bearing installing the new cam, that bearing has since spunout of its hole and thats why you got no pressure. Stop fucking with it and take it apart before it self destructs.

that or stand on it till it scatters and start over.

 

I'm at the point of standing on it till it blows up and starting over and doing it right.

I let my father in law, who has raced and built Chevy motors his whole life, install the cam so I have to believe he did it correctly... but who knows..

I'm still gonna check the pick up tube and plugs first... can't hurt

 

once you drop the pan shine a light under the cam and take a look, you should be able to see if the bearing is pushed out from there.

I've knicked a bearing or 2 in my time, its not that hard to do so dont blame him if thats the problem,,,, shit happens.

 

Low oil pressure is usually a bearing clearance problem, if so a new pump will have little help. Look for worn bearings and incorrect clearances.

Tig.

 

So I can, I guess, somewhat check the cam bearings from dropping the pan? I was told you had to tear the motor open to actually check the bearings.

I guess to actually check the bearing "clearance" I'll have to pull the motor?

 

If it was mine I would prob go get some cheap 20-50 WT(or thicker) oil & see what it does.
If the pressure rises/changes,its most likely due to a clearance problem with bearings or within pump.......then take it apart.
Good luck,,,

 

A bit of wisdom I found out the hard way, some SBC engines had under size cranks in them from the factory. Plastigage the bearings, it sounds like you got to much clearance.

Toolroomer

 

your not checking the bearing clearence,, your checking to see if the bearing has popped out and riding there like a toilet paper roll on the plunger handle.

I should also point out that you really should be replacing all the bearings at this point anyway, 0 oil pressure has probably done them in.

the stand on it till it blows thing is probably gonna be easier LOL!

 

I guarantee 100% that its the pressure relief valve in the oil pump. A little debris has got the check ball from sealing. Had this happen to me. Just replace the pump and you will be good to go. I ran 3 miles home with 3-5 lbs and 0 oil pressure at idle thinking my gauge was screwed as it made no noise. After pulling a couple of my rod and main caps, the bearings looked brand new. Replaced the pump and have 60 on the freeway and 30 at idle.

 

If you pull the pan you can remove a few main caps and rod caps to :
- check if the bearing inserts are worn into the bronze underlay, which would be worn enough to lower hot oil pressure a lot. Do one cap at a time, and note that the "tangs" go on the same side.
- Inspect the crank journals for scoring or wear

The cam bearings could be worn enough to cause low hot oil pressure (probably not zero) all by themselves, yet still be tight in the block. The cam would have to be removed to allow measuring their inside diameter with a bore gage.

Sadly, it sounds like another case of the easily uttered phrase "just rebuilt" being more bad than good when buying used cars , motorcycles or parts.

 

You could also use a low performance big block oil pump in a small block... And still use the stock sbc oil pickup tube.. 60psi cold and 45-48psi when warmed up..... I'd put in all new bearings also..

 

Don’t give up. Like I said earlier, this sounds like the pump pressure relief valve. It's not uncommon to have a small amount of debris like gasket material to get dropped into your engine on a cam change. Most of the time it will go through the pump and then get trapped in your filter. UNFORTUNATELY the debris most likely got into the valve which will cause 0 pool pressure when warm. I have seen and heard this happen many times. When you pull the oil pan, Pull a couple caps. If the bearings look good, just replace the pump and enjoy many more miles. If the bearings were gone to give 0 oil pressure I would think you'd hear it. I'm betting a new pump and you'll be back in business.

 

Well, I guess I'll get some of these things mentioned checked out. I'm gonna cut open the filter in a bit to see what's inside. Then probably drop the pan and check if the bearings are still in place as well as pick up tube clearance...etc.

Thanks for all the responses. Most of the time no one remembers to say if they fixed their problem or not so I'll try to let you guys (and others in my situation) know what the problem is and how I end up fixing it.

Thanks again.

 

I had this problem with the 305 in my model A. The filter collapsed on it. I swapped out the filter and put in a new pump and it was fine

 

Well, I cut open the oil filter. Everything looks normal there.

I guess the next thing is to drop the pan and check the pump/ pick up tube, bearings, any metal in the pan, etc...

Wish me luck, hopefully this is just a failing oil pump.

 

Pull the by pass spring and piston from the oil pump clean it up and look for foreign object.

Tig.

 

Are you sure your gauge is reading correctly? If oil pressure gets that low, something usually starts rattling.

You could try a new filter and some #40 racing oil to see if it helps before you pull the pan.

If you pull the pan, pull the oil pump and use a rubber tipped air nozzle to blow air into the the pump outlet into the engine block. You can tell if a large amount of air flows anywhere like from the oil galley plugs by the camshaft. I use a screw in plug and stake them in. I also drill a 1/16 hole in them to spray oil on the chain.

I always use Melling High Volume oil pumps. They have larger gears to pump more oil but still have a lower pressure relief valve. It can make up for worn bearings and are used in racing engines where we run an extra .001 clearance on the bearings. If you do this, make certain you get the high VOLUME pump, not the high PRESSURE pump. They come with a new oil pickup tube that is larger than the stock tube.