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BJ8 Oil Pressure

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dlamb43

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Oil pressure drops to "0" when hot at idle!!! Help!! Startup cold is 50-60 lbs. drops to 35 lbs when cruising hot, but drops to zero at adle after a good run. Engine is running great with no feel of loss of power, and I'm not burning any oil and only lose a healthy drip from the rear cover. Any ideas?? I'll run a compression test next week. Thanks David Lamb "Actor 430"
 
How many miles on the engine?
1. First, I would check to see if the rocker arm is squirting oil. It should only have a small drip from each rocker. The rocker arm can be rebuilt by Rocker Arm Specialists.
2. However, more than likely and depending on the answer to my question, your bearings, rod and main, are worn. You can pull the oil pan and check a rod bearing. If worn, you will see copper. If not you will see a silver color on the inside of the bearing.
It may be time for an engine overhaul anyway.
 
I hate to be the bearer of bad news, BUT .... those are exactly the symptoms of worn rod and main bearings.
Im sure others that KNOW this engine better than I, will be chiming in here sooner or later.
there could be an oil pressure relief valve issue or an oil type issue. I know most of the members recomend useing a certain brand and viscisity oil in thier engines along with specific filter brands.

Me not having THIS engine I couldnt recomend any.
 
David -

Try putting a washer or two behind the oil pressure release spring - to give a little extra length to the spring.

It sounds to me like the oil pressure release valve/plunger or the spring has worn slightly and is reaching the full extent of its travel when the oil is hot and thin.

Fixing this will take you about 5 minutes, its a relatively common problem in the BMC C-series motor when they have lots of miles on them.

If the washer fixes your problem, you can then order a new spring and valve/plunger from Moss or whoever and that will fix your problem.

/bcforum/images/%%GRAEMLIN_URL%%/driving.gif
 
Thanks shorn,aweman,and Alan!! Will check the oil pressure relief (release?) valve (when I locate it!!!), do the washer thingy, keep fingers crossed and HOPE. PO spent about 40 grand on mechanical work a Healey Werks about three years ago, but I cannot find any receipts for bottom end parts or labour!!! Sooo....it's probably my turn..rodsand mains eh? Cheers, David (actor 430)
 
Thanks shorn,aweman,and Alan!! Will check the oil pressure relief (release?) valve (when I locate it!!!), do the washer thingy, keep fingers crossed and HOPE. PO spent about 40 grand on mechanical work at Healey Werks about three years ago, but I cannot find any receipts for bottom end parts or labour!!! Sooo....it's probably my turn..rods and mains eh? Cheers, David (actor 430)
 
I don't agree you should start whipping out the rods and crank. Most of these engines are now running on thinner oil which means lower oil pressure by definition.

If you can't hear any knocking noises under load at low speed or at high speed and if you have some oil pressure, say 35 psi hot at around 2000 rpm, then I would say just carry on driving.

If you are an average owner of 53 years old, it may out-last you /bcforum/images/%%GRAEMLIN_URL%%/smile.gif !
 
Well maybe Richard, but I would only feel comfortable with a reading of 10 PSI Per 1000RPM so a showing at idle which is about 900RPM should show pretty close to 10 PSI pressure. If not I would be looking for the problem.--Fwiw--Keoke
 
David:
As I stated, I would try a number of things before instaling new rod and main bearings.
The first bieng the oil pressure relief valve spring tension.
Then make sure the guage is working properly.
IF you cant get the oil pressure up to "Normal" levels, I myself WOULD NOT wait for the engine to start ratteling before replacing those bearings.
A rod bearing loose enough to make noise CAN BE {and usualy results in} real trouble.
I.E. Scored crankshaft {requiring turning of the crankshaft}.
IF one becomes loose enough it CAN come apart and MIGHT punch a hole in the block. {Usualy requires a relativedly high R.P.M. to do this}
In any case ANY of the above failures are an expensive proposition.
Rebuilding the bottom end of an engine is not all that expensive IF the crankshaft journals dont need to be machined.
Kerry
 
Lots of opinions on the subject of low oil pressure. Most of the fixes are good. I would suggest setting personal priorities. By this I mean you need to examine where your Healey is headed. Complete re-build in a year or two? Just want to keep her going? First let me state that oil pressure under 10#s is not good and you should do something to get it closer to at least 20#s, hot, @ low RPM. Each engine is different. I replaced the oil relief plunger. The new one was about 3-5 .000" bigger in diameter, new spring tension was difficult to compare. I may have seen a 5# increase. You could place spacers behind the spring but that would be a temporary fix. The rocker assembly seems easy to diagnose and then fix. Take the valve cover off after heating up the engine and see if the oil is gushing. The fix is in-expensive, fast turn around and easy to install. If you are still not satisfied, next you will be heading for the bearings. Pull the pan with the engine in place. Replace rod bearings at least. You should also go after the mains. There is a thread on this forum describing how to get the mains out and in with the crank in place. I would not wait; you need to get to the source of pressure loss
 
Thanks to all for the input! What a forum, I could have used your help years ago planning a career! Will keep you posted on results of tests. Cheers, Actor 430
 
The pressure relief valve is more or less irrelevant in this context. It is a relief valve to prevent excessive pressure, ie it opens over 50-60 psi. It will have no effect on the low end pressure unless it is stuck open, which is unlikely. If the spring gets weaker it just means it will open at a lower pressure, say 40, but not 10.
 
Richard -

Actually it is dependent on how the valve and spring have failed. The spring won't weaken (this was never my assumption), but if a coil has broken (it happens) or the plunger has worn into the spring, or if the plunger's diameter has worn, you will get the symptoms described.

All I'm saying is this repair takes 10 minutes to fix and is a good place to start when trying to diagnose low pressure. Better to do that than rip the car apart to replace the rocker and the bearings if you ask me.

It's always best to start with the easy stuff first before ripping your motor apart.
 
Alan, er.. your original post was talking about a worn/weaker spring and that has no effect on low oil pressure. The relief valve is there to protect the oil pump and filter from high pressures under cold conditions.

I agree about checking for the broken spring though.

Originally I was just trying to stop David whipping out the innards, as most were suggesting, if its not that bad. ie no funny noises. If the engine is that worn then it probably needs a full rebuild and that, to me anyway, is a major and expensive decision.

PS. your little avatar man with the gear stick is the best /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Yes Richard, the relief valve has a direct affect on the pressure. The more tension on the spring [Adding Shims] the higher the pressure. Consequently, if you raise one end of the pressure spectrum the other, low ,end must follow. However, this is not to be construed as a cure for the overall problem, it is at best an interim route to some piece of mind until you can resolve the actual problem.---Keoke
 
Sorry Keoke, you are wrong. Up to say 40 psi from the pump all the oil goes through the engine because the valve is shut and as far as the engine is concerned the valve need not be there. Over 40 psi the valve opens and limits the excessive pressure going to the engine. The spring tension just alters the opening pressure, say 30,40 or 50, but it will have NO effect at 10 bar.

Apologies if this appears pendantic. I just think the technical advice should be sound.

Richard
 
Richard -

Many of the springs I've seen are worn on the sides and have severely weakened spring rates as a result, and I have also seen them broken as a result. The springs wear because they rub against the side of the interior of the oil gallery over time. This is why you should always replace this spring and plunger assembly with each rebuild, if not more often.

If the spring is broken, you will have little or no oil pressure, esp. if the oil is warm.

Alan
 
I'm not experienced enough to resolve this one!! Soooo.. I guess the first thing is to change the oil just in case it may have broken down. Then replace the pressure relief spring since shimming it may (re Keoke) give a false reading and thus false sense of security, then pull the pan and have a look and then do the rods (and WCS mains!) Funny but I hear nothing out of the ordinary and she pulls just fine!. Cheers, David
 
Richard3000 said:
Sorry Keoke, you are wrong. Up to say 40 psi from the pump all the oil goes through the engine because the valve is shut and as far as the engine is concerned the valve need not be there. Over 40 psi the valve opens and limits the excessive pressure going to the engine. The spring tension just alters the opening pressure, say 30,40 or 50, but it will have NO effect at 10 bar.

Apologies if this appears pendantic. I just think the technical advice should be sound.

Richard
Click to expand...

IF you have not experienced the problem and its interim solution then do not knock it we all know how the valve works and have used the techique many times.--Keoke- /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
Richard3000 said:
Sorry Keoke, you are wrong. Up to say 40 psi from the pump all the oil goes through the engine because the valve is shut and as far as the engine is concerned the valve need not be there. Over 40 psi the valve opens and limits the excessive pressure going to the engine. The spring tension just alters the opening pressure, say 30,40 or 50, but it will have NO effect at 10 bar.

Apologies if this appears pendantic. I just think the technical advice should be sound.

Richard
Click to expand...
In an "ideal" world your statements could be true. In the real world, the spring DOES lose tension, takes a shorter set. The spring OD also wears down from constant friction between spring & plunger which reduces the spring wire cross section & tension. Lastly, the plunger seating surface & it's seat in the block can become distorted by carbon build up so that a perfect seal is not made. In other words, the relief valve lets off "some" pressure well below it's intended design level. This leakage is most noticeable at low oil flow, idle conditions.
D
 
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