MG MGB and MGB GT Tech Talk
Hello, I have 2 questions:
1. My oil pressure on my engine (from cold) is 60psi. I have just had the engine rebuilt and a new oil pump fitted, based on this should I expect a higher value than this?
2. Is there a way of testing the fuel gauge, only I have connected it up with half the tank full and the gauge reads 'over full'. What else could be wrong.
Thanks for all your help
Thanks for your response,
I will need to check the value when hot, what should it be? I have fitted a new gauge so would assume that it is working ok. With regard to the relief spring I haven't changed, should this have been changed with the engine refurbishment? Will 60 PSI harm the engine? I bought the car as an unfinished project and sadly never saw the engine run before.
I will have to check the wire to the sender (removing it) also. There is a voltage regulator on in between the sender and the gauge but it is very old.
Many thanks
Alex,
60 psi won't hurt the engine. As Ernie pointed out, other factors may have as much impact on the reading you are getting as the engine itself. The previous engine in my roadster never read above 60 psi after a rebuild and provided many years of service (still is in another car). The current engine (also a fresh rebuild) does run around 75 psi when cold, 60 plus when hot.
Steve
60 is more than adequate and in spec but it's not a good reflection on the engine builder.
Assuming the relief spring and plunger are OK, and TBH they don't go weak of their own accord - for instance it's 200,000m + since my engine had it's first 20 thou rebore, a new set of shells on a standard crank, and an oil pump, and it still pumps 60-70lbs + on hot tickover with the original spring and plunger still fitted - there are really only two things which can cause low pressure, an undersize crank, meaning too much clearance, or a weak oil pump.
MGB oil pumps are very durable and although it's remotely possible you have a faulty one I'd be more inclined to suspect the crank.
What you might be able to do about it is another matter.
The actual spec for a B engine is 50-80lbs running and 10-25lbs on idle but those have to be regarded as bare minimums in engines built from mass produced components, a modern professional rebuild should be to much closer tolerances, the equivalent of a blueprinted engine to the original, and as such pump much more.
If I had built it I would take it back and find out what the problem was, whether your builder is as conscientious I don't know.
There is a related thread here which you migh find interesting.
http://www.mgexperience.net/phorum/read.php?1,1921337,page=1
Alex,
I have some questions. What weight of oil are you using? Then the big question, I have a 79 LE that was bought new in Canada which means the speedometer is not in MPH and the oil gauge in not in PSI they are both in K's. That said, if you are in the UK, you should also have the same gauges meaning if you are at 60k you would have to convert that to psi a reduction of about 30%. If that IS true then you have a real problem. Then I for one would be suspect that the engine was not rebuilt. It would be interesting to hear from you as to what gauges you have US or UK. Let me know.
Please put the year of your car in your profile - that will tell us whether you have an electric or mechanical gauge.
If it is an electric gauge, the first thing I'd check is the sending unit. They are reliable, but after 40 years anything can go out of calibration. You may well have more than 60 PSI if your sender hasn't been changed in the last few years.
You also didn't mention the weight of the oil you are using, and what the pressure is at different RPM. Does it decrease much when it warms up.
If it is a solid 60 PSI at all RPM, that is an indication that your relief valve is tripping at 60 PSI. No big deal - replace the spring on the relief valve. If you have less than 60 PSI at idle, and it rises to 60 at speed, then I'd say your bearing clearances are excessive (or your pump has low output).
I have some more information.
When I first start the engine the oil pressure goes up to 69 PSI. Then when the engine is warm, with the choke back in (not being used) and at 1200 RPM (the carburettors haven't been tuned yet) I am getting a reading of 58 PSI.
I would be a bit surprised if it was an engine fault as I reassembled it myself and checked the big end bearings during assembly. I didn't (probably foolishly) change the spring in the relief valve at the time. Do you think its worth getting this changed?
Could I be loosing pressure elsewhere, for example if there was a slight leak at the oil cooler etc? The oil I have used is a 20W50 oil from Halfords (not an expensive one, but as it has to be disposed of shortly...)
Many thanks,
'Had rebuilt' and 'reassembled it myself' are not quite the same thing now are they :P
When you say you checked the big end bearings what did you use for that, was it sufficiently accurate to make such measurements. Did you similarly check the mains too ?
Did you actually have it reground at all ?
The relief valve spring is not so hard to change but personally I wouldn't invest too much hope in it being the problem, worth a try all the same.
As regards oil I have only ever used cheap 20w50 - Halfords included - changed every 3000 miles with the filter each 6000. 300,000 miles on a standard crank is ample justification of that policy and allows me I believe to say with some confidence that the oil itself will not be anything to do with your low pressure ;)
Now we know the fuller story it seems to me you really have two fairly simple choices:
1. Live with it.
2. Strip it down again to see if you a scuffed shell or something similar.
If you had a leak somewhere sufficient to lose that amount of pressure believe me you would know about it !
thanks for your help, to answer your question the Crank was reground, cylinders rebored, head skimmed, new pistons etc, etc. Oh and the gauge is mechanical (but is new so wouldn't expect that to be at fault).
Hi Alex,
A better test is the hot oil pressure (as its winter by hot I mean blank off the oil cooler with cardboard, go for a drive on the motorway, get in some stop start traffic get the temperature gauge at least halfway) and then see what the oil pressure is. With a low idle (cooling fan, lights on, heater blower on, clutch in) I can get readings as low as 28 PSI which I am assured means something is wrong internally. I must have an excess clearance or possibly an internal leak on a casting or something.
Good luck,
Cheers