D1 GEMS oil pressure, oil pan reseal, front cover

jetpoweredmonkey

Active member
Oct 19, 2018
30
11
Sacramento, California
Hi gang, I have a '96 D1 V8 GEMS here in California, with a rare R380 five speed. I bought it two years ago from the original owner in lovely cosmetic condition and I've been chipping away at all the little problems while driving it. The PO had the engine rebuilt by a machine shop. The owner assembled all the external parts and did an OK job, I've been chipping away at tidying up some of the things that weren't quite up to par.

The truck has always had a delay prior to building oil pressure from a cold start. Recently that got worse, then the oil light came on while coming to a stop, and I could hear lifter clatter so I shut it off immediately. After letting it cool for a while, I restarted and got oil pressure back. I was careful to keep the idle up at stops on this last trip and now I have parked her up for some investigation.

I have the sump and front cover off for inspection. The oil pump looked fine but the front cover is somewhat scored. I am not sure if that is the cause of low oil pressure or not. I will take the cover to a machine shop while it's off and see if they can face the pump area hopefully after building it up a bit. If not I will have to get a new one from the UK at a high cost. I have new oil pump gears and all the gaskets and ancillary bits on hand. While she is apart I have looked through the sump and everything looks good, although I doubt I could see if there was a spun cam bearing etc. I would like to take off a rod cap and see how the rod bearing looks, however I am not sure if the bolts are reusable or not. The factory manual is pretty vague!

I am pretty confident that the lower end is in good order since it has under 40K miles, was built by a reputable shop and the inside is squeaky clean. There was no debris in the sump and there has never been any oil usage. I hope tidying up the oil pump will get me going again. It wasn't replaced during the rebuild because they are not commonly available like the later D1 and D2 front cover.

There is nothing in the manual about the sump gaskets. I've also removed the flywheel inspection plate as there was a wet oil leak in that area. I assumed it was the rear main, but it is bone dry inside the bell housing and on the back of the flywheel. The sump was installed with a cork gasket, and the inspection plate has a rubber strip across the top and was gooped on with RTV. That doesn't look right to me. I would like to replace the rubber strip but can't find a part number or any reference to it anywhere. I'm also not sure whether to use a cork gasket, I've read that the GEMS engine is designed to be run with sealant only. I am pretty sure the leak was coming from the rear main bearing cap as there did not appear to be any sealant under the cork gasket to stop oil traveling along the cap to crankcase joint.

I would love to hear from anyone who has done this job, specifically with regard to what I mentioned:
  • Any info about similar oil pressure problems
  • Should the sump be installed with the cork gasket or sealant
  • What is the part number for the flywheel inspection plate gasket strip
  • How best to seal the sump and inspection plate
 

terryjm1

Well-known member
Jan 23, 2011
685
114
When I took my 96 4.0 apart it only had silicone for the sump gasket. However, my gasket set came with a gasket. I chose to do what the shop manual stated and only used silicone.

On the inspection plate, I don’t really have a good understanding of why it is used.I have taken apart many other older Rover V8 / manual transmission assemblies and never was there such a seal in place. I reused the one that I removed but don’t see any reason for it or sealing the inspection plate at all. I can see the logic of keeping water out of that area, but I’d be more concerned about trapping water inside should it make its way in.

I also not so long ago purchased a 98 D1 that came with a very recently rebuilt 4.0 engine. You can let it idle for hours in the driveway and the oil light does not come on. However, if I drive it on the road for 20 minutes it comes on as soon as I allow the engine to slow to an idle. Oddly, even when the oil light is on, it is the quietest Rover V8 I have ever heard. It has not even the slightest tick. It’s quiet like a new Toyota. I bought the truck as a future project and haven’t yet gotten back to it. It is in storage behind other projects. My first step is to change the oil pressure sensor, although I doubt that is the problem. I look forward to learning your diagnosis.

On the oil pump and low oil pressure condition, my next thought is perhaps a weak pressure relief valve spring. I mostly have worked on old Rover V8 engines with distributor driven oil pumps. In those it was quite simple to increase spring tension. When I get a chance to chase down my low oil pressure problem with the 4.0, if the new pressure switch doesn’t solve the problem, my next step will be to see if the relief valve spring tension can be increased.
 
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Jimmy

Well-known member
Apr 10, 2006
697
44
Aurora, CO
Typical advice would be to attach a mechanical oil pressure gauge before teardown to gather real numbers. Sounds like you're past that, but for any future readers don't skip this step.
 
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jetpoweredmonkey

Active member
Oct 19, 2018
30
11
Sacramento, California
Thanks guys. Yes, I even bought a mechanical oil pressure tester, but did not bother to use it as it was perfectly clear that indeed there was no oil pressure at idle. But normally that should be the first step during diagnosis.

Terry, thanks for the response, I agree, I'm going to clean up the flywheel cover and slap it back on there. It was all gooped up to the trans, that seems silly and needless. I think mounting the sump with sealant will cure my leak issue, which is pretty cool, because aside from one of the transfer case outputs, my Disco will be totally oiltight after this fix...and I have a seal for the transfer box here too! Perseverance pays off.

My guess is that rubber sealing strip must be a gap filler to make sure the plate doesn't admit water from up around the sump area. In any case it does not appear important from an oil sealing perspective.
 

Flyfish

Well-known member
Oct 29, 2004
1,144
103
50
St. Louis
Also make sure you’re using the proper weight oil. I’ve always used Rotella 15/40. I know RPI strongly recommends Valvoline VR1 20/50 racing oil but I can’t speak from experience.
 
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Tugela

Well-known member
May 21, 2007
4,508
319
Seattle
I know RPI strongly recommends Valvoline VR1 20/50 racing oil but I can’t speak from experience.

I can. Good results. 177,000+ miles on my D1 and still running smoothly and quietly. High-zinc 20W50 is also what the indie Rover shops recommended to me. There are other options, as well, however the Valvoline is less expensive than Swepco and others I've also used.
 
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p m

Administrator
Staff member
Apr 19, 2004
14,947
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La Jolla, CA
www.3rj.org
Good call on the oil pressure relief valve. They can get gunked up and jam in semi-open position; the fact that you had low oil pressure and were able to restart the engine and regain it is also in favor of this suggestion.

No gasket on the sump - the manual says a bead of Hylomar or similar non-hardening sealant.
 

jetpoweredmonkey

Active member
Oct 19, 2018
30
11
Sacramento, California
Thanks guys for the additional input. I pulled the relief valve out and found it operating smoothly with no sign of wear or gunk build-up. The relief valve spring measures about 62mm free length which is 2mm longer than the spec in the manual so that seems fine as well.

I had another good look inside the motor from the sump, the cam is in great condition with no sign of wear. Off the top of my head the engine has ~50K miles since rebuilding, or maybe somewhat less than that. I can't rule out a spun bearing of course, but there are no outward signs of it and the internals and oil pan are squeaky clean.

I will see if the machine shop can take on reconditioning of my front cover and if so, I believe I will reinstall and try it again. I have little to lose, if there are still oil pressure issues then the whole works will need to come out for a strip down.

Also in reading up on issues like this, I believe I need to bump up the base idle a bit (was at 750 which I got out of a manual...somewhere...) and change my oil to VR-1 20W50. I've been using Mobil 1 Turbo Diesel Truck 5W/40, which conforms to the manual's oil spec. Mainly I got in the habit of using this because I also use it in my Vanagon, which has an aftermarket thermostatic oil cooler. Running heavier weight oil in that application can cause excessive oil pressure or oil bypass due to the relief valve opening, because oil temps are kept well in check by the thermostatic air oil cooler. The Disco also has a cooler, however it is a water over oil circuit through the radiator, which means the oil is maintained at a higher temp. I hadn't really thought this through fully. The TDT oil has published zinc and phosphorus specs which is another reason why I chose it for these flat tappet engines.

In any case I do think the oil pump is contributing to my issue but is likely not the only problem. This is all good, though, as the condition of the water pump, fan clutch and belt tensioner were all a little suspect (I believe old parts reused when the engine was rebuilt) and I really needed to fix the bad oil pan leak anyway, so very much not a wasted effort. Just crossing fingers that there isn't a bigger problem internal to the engine. I also have a nice shiny new four pass all aluminum radiator to install, after having the AC system reconditioned over the summer, I noticed the temp gauge would creep up a bit while running the system. I have no doubt the new radiator will solve that, and also having the old one out of the way makes it a whole lot nicer to work on the front of the engine.
 

Gordo

Well-known member
When I did my oil pump in my disco i carefully flattened the steel plate cover with super fine wet sand sandpaper on a piece of glass as that was the flattest thing I had on hand. My original cover was not too bad but the steel plate that goes over it bent from grenaded gears and was toast. I had an extra used one on hand. Seemed to work fine. I did put new bearings in mine as I bought it with zero oil pressure. Who knows how long it had been like that. It’s easy to install a mechanical gauge to test it too
 

jetpoweredmonkey

Active member
Oct 19, 2018
30
11
Sacramento, California
Thanks again guys. I took the cover round to the machine shop today. He had a look, and called one of the two top Rover shops in town for their opinion. Both machinist and shop pronounced the wear very minor and said go ahead and run it. I took it past the other excellent shop in town, the owner drives a D2 and is a fanatic. He also said it was perfectly fine, so it is going back together with a new set of gears and we'll give it a go. I'll put the pressure gauge on when I fire her up and see how she looks. Hope to have her back together tonight or tomorrow.
 

Flyfish

Well-known member
Oct 29, 2004
1,144
103
50
St. Louis
Thanks again guys. I took the cover round to the machine shop today. He had a look, and called one of the two top Rover shops in town for their opinion. Both machinist and shop pronounced the wear very minor and said go ahead and run it. I took it past the other excellent shop in town, the owner drives a D2 and is a fanatic. He also said it was perfectly fine, so it is going back together with a new set of gears and we'll give it a go. I'll put the pressure gauge on when I fire her up and see how she looks. Hope to have her back together tonight or tomorrow.
Really nice truck, btw!

Many people suggest to pack the pump with Vaseline or similar so you don’t have any priming issues. Just figured I would mention it.
 

robertf

Well-known member
Jan 22, 2006
4,459
170
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Pressure pot. Pull the lower oil line, slip a 1/2” hose over it, and fill her up. I did that on a new engine and had instant oil pressure
 

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Flyfish

Well-known member
Oct 29, 2004
1,144
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St. Louis
Pressure pot. Pull the lower oil line, slip a 1/2” hose over it, and fill her up. I did that on a new engine and had instant oil pressure
Nice! Then it would be a great tool for filling coolant without needing to burp the air out afterwards.

And if you really want to be ahead of the rover curve, fill both systems with a mixture of oil and coolant, walk inside and beat the dog!
 
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jetpoweredmonkey

Active member
Oct 19, 2018
30
11
Sacramento, California
robertf you nailed it. Some time back my crank pulley came adrift. It woke me up, I thought it was a main bearing. When I attempted to torque it, the bolt spun. Thankfully the design is good and the crankshaft wasn't damaged. I bought a new bolt, torqued it up, no problem. This kind of stuff is what I mean about the PO not quite knowing how to look things over properly when assembling. No biggie.

I have the front cover all rebuilt and packed the pump with assembly grease. New o-ring on the pressure relief valve, new crank seal, new pump gears, new OEM pressure switch. As I'm inspecting the crank and pulley, I see the woodruff key is damaged and sure enough there is a chunk missing out of the pulley next to the keyway. So now's the time to do the key and try to find a pulley.

I went looking for the pulley when it came loose initially but never pulled it off to inspect until now. ERR4922 is the number, which has superseded to ERR7373 which are available in the UK. Can anyone confirm this is the correct pulley?

Next is the crank key. No luck so far on a part number. I have never found a good comprehensive parts diagram web site for these trucks, can anyone point me to one?

Great idea to pressure fill the motor. I thought I would prime the lines and radiator cooler at least.
 

terryjm1

Well-known member
Jan 23, 2011
685
114
I am taking apart a couple 4.0 engines. One is locked and headed to the metal recycler, so the dampener/pulley is surplus. I will let it go cheap if you want something to send out for a rebuild.