Serp Oil pressure issue, just want to run this by....
Discussion
Original Problem:
Gauge reading 10 ish PSI cold and no more than 20-25 when warm around town etc.
pressure light on at hot idle.
Original oil 20/50 (bit thick for my liking)
Diagnosis, pressure release/pump
Strip down, and pump out.
New big ends as surfaces wiped (Clearance is now 1.5 thou)
Mains OK. (Clearance is 1 thou)
Pump cover OK, very very very light scoring
other side of pump/case is scored but not what I would call excessive.
Pump rotor new with rebuild 5k miles ago (allegedly)
Reassemble.
new pressure release spring/shim sprng with 2 m8 washers
10/40 oil
15-20pi cold Idle/ 40psi cold 3k
Great, put coolant in finish off everything an run up.
coolant up to cycle temp,
5psi hot idle/25-30psi hot 3k
Oil light on constantly at idle
New diagnosis,
chain case scored excessively, needs machining or new case
New pump.
All car gauge readings confirmed with external mechanical gauge.
Boggling me at the moment, as this is most bizarre. Thoughts appreciated, sometimes you can look at a problem too hard and miss something truly obvious.....
J
Gauge reading 10 ish PSI cold and no more than 20-25 when warm around town etc.
pressure light on at hot idle.
Original oil 20/50 (bit thick for my liking)
Diagnosis, pressure release/pump
Strip down, and pump out.
New big ends as surfaces wiped (Clearance is now 1.5 thou)
Mains OK. (Clearance is 1 thou)
Pump cover OK, very very very light scoring
other side of pump/case is scored but not what I would call excessive.
Pump rotor new with rebuild 5k miles ago (allegedly)
Reassemble.
new pressure release spring/shim sprng with 2 m8 washers
10/40 oil
15-20pi cold Idle/ 40psi cold 3k
Great, put coolant in finish off everything an run up.
coolant up to cycle temp,
5psi hot idle/25-30psi hot 3k
Oil light on constantly at idle
New diagnosis,
chain case scored excessively, needs machining or new case
New pump.
All car gauge readings confirmed with external mechanical gauge.
Boggling me at the moment, as this is most bizarre. Thoughts appreciated, sometimes you can look at a problem too hard and miss something truly obvious.....
J
Edited by tofts on Sunday 29th May 01:55
So, I spent a few more hours on the car the other day, lapped and polished the oil pump rotor/housing, reassembled the beast as I spoke to my machinest and we both came to the conclusion that the scoring is well below excessive.
Oil pressure now getting slightly better but still not brilliant, so I changed to 20-50 oil out of curiosity and absolutely no difference what so ever which is when I started having a good think.
So having no more luck, I downed tools and had a good think. There are only so many places oil can leak, so I made a list for the entire oil system what I have checked, and what I can't check. process of elimination. Whatever remains, must therefore be the cause..... SO:
Oil pick up
NO. Blocked?
Gasket on oil pickup
NO. letting air in?
Gallery through crank case
Porous, other leaks? No, pulled vacuum on bottom of strainer to front of engine.
Front case gasket
NO. Leaking?
behind pressure relief valve
NO. Pressure seal brand new, no leaks
NO. Valve not sticking, valve not scored, new spring, new seal. valve moves in body fine when under tension.
pump low pressure side
NO. Scored, not excessive.
pump high pressure side
NO. Scored, but not enough to worry about
NO. Pump to case clearance less than 2 thou
front of pressure relief valve
NO. Valve not sticking, valve not scored, new spring, new seal. valve moves in body fine when under tension.
NO. Oil filter restricted? If so, pressure gauge would be high.
NO. pressure gauge leaking?
out of oil filter
NO. Filter new, as above
pressure light switch
NO, not leaking
main gallery
POSSIBLE: is end gallery plug leaking?
mains, big ends, cam
NO. Mains are all less than 1 thou
NO. Big ends are brand new bearings, and I checked 1 bearing, which is 1.5 thou
POSSIBLE: Cam, cam bearings, unable to check, dismantle top of engine (great....)
head gasket
NO. Leaking? no evidence external, no oil in water or vice versa
head gallery
NO. gallery to rocker leaking? With engine running, rockers have a small amount of oil being delivered, correct.
rocker shaft
NO. Excessive wear? removed ends of rocker to check for wear. None to speak of, rockers in good shape, correct small oil cut out.
the only two things that I can fathom are causing the problem, are really unlikely but it must be one of them as everything else is perfect (well, nearly)
So, i went down the garage this evening, put on some loud music and set to work. At half past 12 at night!
Hour later, this is what I find....
That folks, is the most unusual cam lobe I have ever seen. Also know as a SLIPPED CAM BEARING?! Its amazing there was any pressure at all!
I have never seen one this bad before! and its really really REALLY lucky that no piston damage or coil binding of valve spring has occurred, as the lifter has been running over this and the lobe! And could have increased valve lift by about another 1/4 of an inch or more on that cylinder, thankfully being hydraulic has probably saved it!
Thankfully, I have found it, but sadly to change all of the cam bearings, means taking the engine out. Can do most of them in situ, but its not recommended.... Shall speak to the gent that owns the car in the morning and deliver my findings, not the best of news but at least the problem is now found.
J
Oil pressure now getting slightly better but still not brilliant, so I changed to 20-50 oil out of curiosity and absolutely no difference what so ever which is when I started having a good think.
So having no more luck, I downed tools and had a good think. There are only so many places oil can leak, so I made a list for the entire oil system what I have checked, and what I can't check. process of elimination. Whatever remains, must therefore be the cause..... SO:
Oil pick up
NO. Blocked?
Gasket on oil pickup
NO. letting air in?
Gallery through crank case
Porous, other leaks? No, pulled vacuum on bottom of strainer to front of engine.
Front case gasket
NO. Leaking?
behind pressure relief valve
NO. Pressure seal brand new, no leaks
NO. Valve not sticking, valve not scored, new spring, new seal. valve moves in body fine when under tension.
pump low pressure side
NO. Scored, not excessive.
pump high pressure side
NO. Scored, but not enough to worry about
NO. Pump to case clearance less than 2 thou
front of pressure relief valve
NO. Valve not sticking, valve not scored, new spring, new seal. valve moves in body fine when under tension.
NO. Oil filter restricted? If so, pressure gauge would be high.
NO. pressure gauge leaking?
out of oil filter
NO. Filter new, as above
pressure light switch
NO, not leaking
main gallery
POSSIBLE: is end gallery plug leaking?
mains, big ends, cam
NO. Mains are all less than 1 thou
NO. Big ends are brand new bearings, and I checked 1 bearing, which is 1.5 thou
POSSIBLE: Cam, cam bearings, unable to check, dismantle top of engine (great....)
head gasket
NO. Leaking? no evidence external, no oil in water or vice versa
head gallery
NO. gallery to rocker leaking? With engine running, rockers have a small amount of oil being delivered, correct.
rocker shaft
NO. Excessive wear? removed ends of rocker to check for wear. None to speak of, rockers in good shape, correct small oil cut out.
the only two things that I can fathom are causing the problem, are really unlikely but it must be one of them as everything else is perfect (well, nearly)
So, i went down the garage this evening, put on some loud music and set to work. At half past 12 at night!
Hour later, this is what I find....
That folks, is the most unusual cam lobe I have ever seen. Also know as a SLIPPED CAM BEARING?! Its amazing there was any pressure at all!
I have never seen one this bad before! and its really really REALLY lucky that no piston damage or coil binding of valve spring has occurred, as the lifter has been running over this and the lobe! And could have increased valve lift by about another 1/4 of an inch or more on that cylinder, thankfully being hydraulic has probably saved it!
Thankfully, I have found it, but sadly to change all of the cam bearings, means taking the engine out. Can do most of them in situ, but its not recommended.... Shall speak to the gent that owns the car in the morning and deliver my findings, not the best of news but at least the problem is now found.
J
Edited by tofts on Sunday 29th May 02:01
No worries.
I have spoken at length with the owner about the way forward, and it has been decided to pull the engine and check/replace all camshaft bearings. The engine was only rebuilt 5k miles ago, and I have to wonder weather it was rebuilt for the same problem, which has now reappeared. Not being able to know for sure, some investigatory work in to the exact cause of failure is necessary to prevent possible occurrence.
If the block has been damaged then it will have to be welded and machined IF possible, otherwise new block.....
Wait and see by the end of the week...
I have spoken at length with the owner about the way forward, and it has been decided to pull the engine and check/replace all camshaft bearings. The engine was only rebuilt 5k miles ago, and I have to wonder weather it was rebuilt for the same problem, which has now reappeared. Not being able to know for sure, some investigatory work in to the exact cause of failure is necessary to prevent possible occurrence.
If the block has been damaged then it will have to be welded and machined IF possible, otherwise new block.....
Wait and see by the end of the week...
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