Oil pressure panic!!
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,182
Likes: 380
From: Near Los Angeles
Oil pressure panic!!
Hey guys--
I'm about at my witts end and need a bit of help. As you probably know, I recently rebuilt a hp 300. But with only 700 miles I have 38-39 psi at 60mph, with 15/40 oil. Yes, it bothers me A LOT.
Today I dropped the pan and removed one main and one rod cap. The bearings look good, with long pointed streaks of polished areas, and the rest of the bearing surface a dull lead color. No grooves or burns or copper showing. The new melling pump looked good too. All gaskets on the pickup were present, and the screen was not cloged. There was no debris to speak of in the pan.
However, I could see that the pump gears were wearing a groove in the pump cover plate. I could move the release plunger with a screw driver, and it made a squishing/pumping noise, so I assume it is good.
The cam bearings were snug in place, with no bearing surface sticking out. I just don't know what else to do at this point. But with that pressure--12--10 psi coming off the freeway, I don't know how much confidence I could have in this engine. If I had stayed with the 10/30 I had in it, then the pressure would probably be at failure point. I hate to put it back together without having solved the problem. It just kills me to have spent all that $ and to have such a problem.
If anyone can offer a bit of advice, it would be greatly appreciated.
Of course I will put a high volume pump back in it, but that is treating the symptom and not the cause.
I also sliced open the filter to see what was in there. Just minor stuff you'd expect with a new rebuild with new timing gears. Today I am going to plastigauge some of the mains and rods to keep the mechanic honest. Other than all that, the manual gauge is new, an Auto MeteSr with all new lines, coming off where the factory had the big bulbous OEM sending unit.
One note: The ... oil smelled SLIGHTLY of gas. Never a good sign, I know. I have an autolite 4100 rebuilt by Pony Carbs. Because the carb sits 90 degrees to engine on an OffyDP manifold, the mixture screws are up against the valve cover, and Impossible to adjust. I'm thinking the carb is dumping gas, maybe the floats are misadjusted. Anyway, I'll check that and am soon to replace it with a Edlebrock which has the float bowls on the side, making it narrower and easy to adjust.
Heck, I think maybe I just solved my problem.
I'm about at my witts end and need a bit of help. As you probably know, I recently rebuilt a hp 300. But with only 700 miles I have 38-39 psi at 60mph, with 15/40 oil. Yes, it bothers me A LOT.
Today I dropped the pan and removed one main and one rod cap. The bearings look good, with long pointed streaks of polished areas, and the rest of the bearing surface a dull lead color. No grooves or burns or copper showing. The new melling pump looked good too. All gaskets on the pickup were present, and the screen was not cloged. There was no debris to speak of in the pan.
However, I could see that the pump gears were wearing a groove in the pump cover plate. I could move the release plunger with a screw driver, and it made a squishing/pumping noise, so I assume it is good.
The cam bearings were snug in place, with no bearing surface sticking out. I just don't know what else to do at this point. But with that pressure--12--10 psi coming off the freeway, I don't know how much confidence I could have in this engine. If I had stayed with the 10/30 I had in it, then the pressure would probably be at failure point. I hate to put it back together without having solved the problem. It just kills me to have spent all that $ and to have such a problem.
If anyone can offer a bit of advice, it would be greatly appreciated.
Of course I will put a high volume pump back in it, but that is treating the symptom and not the cause.
I also sliced open the filter to see what was in there. Just minor stuff you'd expect with a new rebuild with new timing gears. Today I am going to plastigauge some of the mains and rods to keep the mechanic honest. Other than all that, the manual gauge is new, an Auto MeteSr with all new lines, coming off where the factory had the big bulbous OEM sending unit.
One note: The ... oil smelled SLIGHTLY of gas. Never a good sign, I know. I have an autolite 4100 rebuilt by Pony Carbs. Because the carb sits 90 degrees to engine on an OffyDP manifold, the mixture screws are up against the valve cover, and Impossible to adjust. I'm thinking the carb is dumping gas, maybe the floats are misadjusted. Anyway, I'll check that and am soon to replace it with a Edlebrock which has the float bowls on the side, making it narrower and easy to adjust.
Heck, I think maybe I just solved my problem.
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
I think you may have too, sounds like the fuel leak is thinning out your oil, you said you suspect your carb but i'd check your fuel pump too.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,326
Likes: 48
From: Middle TN
It's probably caused by fuel in the oil.
Oil flow is much more important than pressure.
Put in a new high flow pump and I wouldn't worry to much about pressure especially after you checked the bearings and their ok.
Oil flow is much more important than pressure.
Put in a new high flow pump and I wouldn't worry to much about pressure especially after you checked the bearings and their ok.
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,182
Likes: 380
From: Near Los Angeles
Problem found
Hey guys--
I just wanted to let everyone know that I believe I found the problem. The oil is getting gas in it, somehow, thereby thinning it out and lowering the pressure. I popped off a couple of the bearings and they look normal, however the clearances have opened a bit since the build. The limit in the book is .0015. They are now at a shade under .002, which is well under the limit set for when they need replacing.
Anyway, I put in the HV pump, turned the crank to check clearence, and buttoned up the pan. I also replaced the front cover seal, and put the sleeve on the v. dampener. It had been leaking since the rebuild.
Today I will put it all together and try to find where the gas is coming from--carb or pump. If it is the Carb, it will really not say much for Pony Carburetors who rebuilt it. Buy the end of this week I will replace it with a Edelbrock.
Thanks.
I just wanted to let everyone know that I believe I found the problem. The oil is getting gas in it, somehow, thereby thinning it out and lowering the pressure. I popped off a couple of the bearings and they look normal, however the clearances have opened a bit since the build. The limit in the book is .0015. They are now at a shade under .002, which is well under the limit set for when they need replacing.
Anyway, I put in the HV pump, turned the crank to check clearence, and buttoned up the pan. I also replaced the front cover seal, and put the sleeve on the v. dampener. It had been leaking since the rebuild.
Today I will put it all together and try to find where the gas is coming from--carb or pump. If it is the Carb, it will really not say much for Pony Carburetors who rebuilt it. Buy the end of this week I will replace it with a Edelbrock.
Thanks.
Post Fiend
Joined: Jul 2006
Posts: 6,948
Likes: 44
Chances are that it is not the carb. The carb does not have enough volume in the bowl to create this problem. Fuel would have to sit in a given cylinder and leak down past the rings when the vehicle is not running. While possible is highly unlikely. You would notice fuel leaking through the boosters and this would create a fairly high fuel odor when the vehicle is off.
Once the bowl reached a level where it could no longer leak, the dripping would stop and the problem would be gone. A hot engine would evaporate most of the dripping fuel making this prossibility unlikely. A running engine that is flooding would be difficult to tune, and hard to keep running. The rich condition would drive you nuts and make the engine barely driveable.
That leaves the only other source of fuel and this would be the mechanical fuel pump. This is a common problem with standard off the shelf pumps and is more likely the root of your problem.
Once the bowl reached a level where it could no longer leak, the dripping would stop and the problem would be gone. A hot engine would evaporate most of the dripping fuel making this prossibility unlikely. A running engine that is flooding would be difficult to tune, and hard to keep running. The rich condition would drive you nuts and make the engine barely driveable.
That leaves the only other source of fuel and this would be the mechanical fuel pump. This is a common problem with standard off the shelf pumps and is more likely the root of your problem.
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