Visit our Twitter feed for more great content
MGExp

MG Engine Swaps Forum

Rover 3.9 variation in oil pressure

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
My rover V8 conversion has done about 15 month now and behaved well with 45 lb oil pressure cruise and 25 lb idle hot. Went on a short club run today and it was good going there. On the way home I gave it a bit of a squirt through the gears and all good but as I slowed the oil pressure dropped with the revs to about 10-15lb. Reving the engine there was no or little increase and the engine sounded and felt harsh. I was almost home so I coasted on light throttle up my long drive and into the shed but as I did so the pressure went back to normal and its now dead smooth again. Oil is clean and full on the stick and although its stinking hot here at the moment the drive home was only 18km. I am thinking a stuck relief valve that freed itself or a slipping oil pump drive peg. It only got hot enough for the fans to come on as I got to my shed so not cooked, First time I have taken it to high revs although it has done several long trips at highway speed. The engine has a remote filter but no oil cooler.
Any other thoughts? Faulty spin on filter? but it has to be something intermittent. I will start with the easy bits first but I wont know if its fixed unless I find something obvious. It would have been easier to find if it was still playing up, but if it was it could also be a disaster. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
allanreeling ALLAN R
RANDLAY, TELFORD, Shropshire, UK   GBR
Sounds more likely a sticking relief valve. If there was a problem with the oil pump drive you would have lost ignition.
That " squirt through the gears" will have lifted the valve and it stuck open for a time.



soonerv8

mgv8glen Avatar
mgv8glen Gold Member Glenn Towery
Dover, DE, USA   USA
I will 2nd the stuck OPRV, if the pump shaft was spinning in the oil pump gear the pressure would probably stay low all the time. FWIW, your oil pressure is too high! & you are putting too much load on the cam bearing, (high wear point) another week link of the BPOR engine. 30 lb oil press is all you need & I have 2 different rover engines that have over 300,000 miles on each them with only 30 lbs of oil pressure ???? GM only had 30lbs.oil pressure with all the 215 engines they made????

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
Rule of thumb is 10psi/1000rpm, but if you have 50psi at 5K that's pretty good. My guess is that you had all the oil in the top end of the engine and were sucking some air at the pickup. Try putting a little more oil in it. You can run a bit over the full mark without worry. If you have a spare pan see how much it will hold before it goes 1/4" deep at the shallow end of the sump.

Jim

hpmowog Avatar
hpmowog Karl Keiger
It could also be a bad oil pressure sending unit. I had an SD1 with the 3.5 that had erratic oil pressure indicated on the gauge. I thought the oil pump was going out, but when I temporarily hooked up a mechanical gauge, it read perfectly steady.

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Thanks fellers I have taken it all in. Have driven the car from cold a few times since the problem and its been OK. I ran this engine in on Penrite running in oil then changed to 20/50, Its now done 3500 km so will swap to Pentite Classic Light that I use in my other cars. This should lower the cold oil pressure and flow better. The pump has a new Flowtech base with side entry and not easy to get at. Weather has been terrible for the last 3 weeks 40c+ and 47 one day so not great for climbing under and getting oily. This week is great with low 30s, but just coming to our hottest time of the year.
Jim your advice has me thinking. I have small breathers on the rocker covers , filter one side, restricted vacuum the other. No sign of breathing heavy but may be a bit of pressure in the sump slowing oil return ??? Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd, Florence, KY, USA   USA
Dennis, it's common for oil to be retained in the top of the engine during high speed operation, which was why 7 qt oil pans were developed. (Imagine a 1/4 mile engine needing that much oil because gravity doesn't bring it back to the pan fast enough! Skidpads are even worse. It also helps explain all the work that is done to the inside surfaces of racing engines.)

If you are having fun in the twisties there's going to be less oil available to the pickup and air can get in. Once it does it can take a little while to be pumped back out.

Typically the shallow part of the pan will be about 1/4" below the crank. If you have a windage tray you can keep most of the oil from getting crank whipped but starts and stops will cause some. Depending on how you drive you may want to consider a modified oil pan. Usually passive traps (lips) and such are sufficient, but a widened sump is a good way to increase capacity without hurting ground clearance.

Jim

allanreeling ALLAN R
RANDLAY, TELFORD, Shropshire, UK   GBR
Dennis if you had pressure in the crankcase you would probably see oil seepage at the front crank oil seal. I had that when I first ran my 3.9. It stopped as soon as I increased the breathing.
Jim's point about bottom end "starvation" is interesting. My 3.9 came out of a L R Discovery and the sump pan was much bigger than the one on my Vitesse engine. Also when I built the 3.9 I did a bit of work on the valley to aid oil return. I know people who have polished the valleys too.



soonerv8


Attachments:
P1000221.JPG    61.3 KB
P1000221.JPG

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
My flux oil pressure has settled down with the classic light oil. Its a lot lighter cold and appears the 20/50 was, as Jim suggested "hanging up ". I have tried to recreate the situation but its now doing what it should.
The only difference is hot idle is a bit lower at about 18lb. Thanks .again Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster