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MG MGB Technical - startup of rebuilt engine - oil pressure

Tonight, after many months of work, I finally completed the engine rebuild, installation, prep., etc. on my 69gt.

Being a good boy, I first removed the coil wire and turned the car over looking for oil pressure to build up before I actually try starting the engine for real.

Well, I either get no reading or an excessive reading (~100) at the dash gauge depending on whether or how I wire up the electrical sending unit.

Just turning on the ignition can send the gauge to the top. I'm unsure of the wiring; there are two male connectors, and I have a white/brown wire. I also have another wire candidate (color not original), though I seem to remember it wasn't connected to the other point on the sending unit. Anybody out there know the correct wiring? Haynes shows the white/brown wire and the other going to ground. Which is which or does it matter?

I suspect all is well but I don't want to take any chances. Is it possible that no oil (as you would have initially) could cause high readings?

I read some suggestions on placing a mechanical gauge there. That sounds like a good idea. How do I go about finding/building one of these units?

I also read Paul Hunt's comment about "if you remove the wiring with just the ignition on and the gauge goes from high to zero, then the sending unit is bad". Any body else experience this or can confirm? The unit worked fine before the teardown (but then again my battery was good too--but I had to replace it after the telltale solenoid chatter).

Bill
Bill Schoolfield

Bill. There are normally two oil pump gaskets in the MGB Lower Engine gasket kits. The one that looks like it should be correct is not the one to use for five main applications. Hence, unless I knew I really had good oil pressure, I would not start the engine. Take the oil fitting, the one that the line going to the electrical sending unit attaches to, into a good auto parts store and get a fitting that will fit to it, along with a short rubber line (they had them at the store I went to) and an aftermarket, direct reading guage. Then, attach the direct reading guage to the engine and have an assistant crank the engine over (no spark plugs installed and coil disconnected) for about 30 seconds at a time. You should quickly begin to see oil pressure at the positive reading gauge. If you do not get any reading after several tries, check the oil pump gasket. This will get you started. When you have known good oil pressure, you can check out the car's oil pressure gauge, sending unit, wiring, etc. Les
Les Bengtson

les - what bill said earlier is very true - 2 gaskets for your oil pump come with the gasket set. 1 is for a 3 main engine the other is for the 5 main engine. on mine there was no indication of this and both looked so similar we assumed we got 2 in the set by mistake . Guess which one we used - yep we used the 3 main in a 5 main engine and no oil pressure at all!!! It caused a vacuum leak and oil was not being pumped up. After trying many ideas on how to get pressure we pulled pump and found prelube still inside so we knew pump was not pumping - bench tested and it worked fine then close inspection of gaskets showed minor difference between gasket used and gasket remaining in kit. Looked up diagram for the 3 and 5 main engines and verified they were different gaskets. Look in Moss or VB catalog and diagrams showing pump and gaskets and you will see which is which. If you still have leftovers from your rebuild gasket kit you should be able to tell if the right one was used without droppin yer pan - otherwise - you might want to open her up and check. Good luck - jonny g
jonny g

Even more clearly, the easiest place to find this gauge is at any autozone or
similar. I used one of the large SunPro models when I want to hook up a
temporary manual oil gauge. They're about $30.

Also, you may need to prime your oil pump... I disconnected the oil cooler
top line, held it high in the air, and used a funnel to pour oil down the line
into the block. I also turned the engine backward by hand a couple of revs
during this process.

It also took some time (30, or maybe even 60, seconds) before my
manual gauge started reading the first time. (This is with cranking with
no spark plugs in the block.) After the initial "pressure-up" it would come
up in about 15 seconds.

Another very quick way to see if there is actually any oil being pumped...
removed the oil pressure sensor. *grin* It should squirt out some oil
if it's pumping. When I was trying to get mine started, before I primed
it I did this, only a couple drops came out. Once it started to flow, I
put the sensor back in. :)

Cheers,
Anders
Anders Green

Thank everyone for the replys. I'm going to get the mechanical gauge as suggested. I'm also trying to determine if I did install the wrong gasket. Reading over other posts in the archives about this issue, I believe I installed the correct one. I retrieved the unused one (from the kit) and it has the single large hole with three small ones around it at about 120 degrees apart and one medium sized hole. All holes are circular.

Does this describe the 3 main gasket? If so I'm ok and my problem must be a bad sending unit or perhaps the pump isn't primed correctly. I did prime it, just after assembly but that was awhile ago (several month back). I filled oil from the rear oil plug (the one that the external line connects to).

Bill

Bill Schoolfield

Bill,

Do you still have the name of the thread that describes the gaskets for the 3 and 5 main blocks?

Curt

Curt

The white/brown is the only wire going to the sending unit . The two terminals are actually a single double terminal revited to the sending unit. The ground source is through the threaded fitting on the sending unit. The 5 main oil pump gasket has a D shaped hole, the 3 main gasket does not. I bought a Sun Pro mechanical gauge from Advance for around $12-$15, it has a line and a fitting that fits the sending unit mounting hole. Clifton
Clifton Gordon

Curt,

Are Clifton's comments clear enough. If not search the archives for "oil pump gasket" (all words option). I don't recall which thread it was but I think there are several that describe the differences.

Clifton, sounds like I got the right gasket. Man, that makes feel better! Also sounds like the wiring I recall was correct too. So I'll get the gauge and prime the pump.

Thanks again everyone. You know, 25 years or so ago when I first had my B, I was a poor college student with almost no knowledge of these cars and completely at the mercy of the local mg mechanic (not that he wasn't a decent guy :)).

Today, I own two of these wonderful cars and have done almost all the work on the first restoration, now working on the second. None of this would be possible w/o this site and other like it. Kudos to you all!

Bill
Bill Schoolfield

Bill-
Everybody is talking about the gasket issue and wiring, but nobody is asking the obvious question: Did you prime the oil pump before cranking the engine? Pour a tablespoon of oil down the pushrod wells to lubricate the tappets and another tablespoon of oil into each spark plug hole to lubricate the rings, then oil the rocker arms and valve stems. Next, pour oil into the oil pressure hose connection port on the block. This will fill the main oil gallery and supply oil to the main bearings. You may need to try priming the engine closer to the oil pump. Disconnect the large external oil line at the back corner of the block, fill the port in the block with oil, and then rotate the engine backwards to draw the oil backwards into the oil pump. Once the pump is primed, disconnect the power supply to the fuel pump and turn the engine until your oil pressure gauge gives a reading. Now you may reconnect the electrical power to the fuel pump and start the engine. At this point it is critical that the camshaft and its tappets be properly bedded in to avoid ruining them. Hold the idle of the engine at 2,500 RPM for twenty minutes, occasionally varying engine speed gently between 2,000 and 2,700 RPM. After this process is completed, change the oil and the engine will be ready to be broken in on the road. Drive for 100 miles and change both the oil and the oil filter again, then again at 500 miles to bed in the new cam and lifters, then let it cool and then retorque the head using the proper sequence pattern. You will find some nuts almost tight, some can take almost a quarter turn. Run the car for 100 miles and retorque the head again. You'll find that this time the studs have not lost quite as much torque. Run an additional 400 miles (or 500 total on new engine) and retorque. During this period do not exceed 4,000 RPM or 45 MPH, operate the engine at full throttle, or allow the engine to labor in any gear. Until the next 500 miles (1,000 miles total) has been completed, limit engine speeds to around 4,500 RPM when shifting gears. Cruising on the highway should be limited to no more than 3,500 RPM. Keep varying the throttle opening and engine speed. The secret is to constantly vary the speed and load without creating excess heat through full throttle laboring and high engine speed operation. After 1,000 miles of following this procedure, change the oil and oil filter and refill the sump with a quality oil such as Castrol 20W/50. After another 1,000 miles the engine should be properly broken in and ready for service.
Steve S.

This may be retrospective for Bill, but the best way to prime the system is to pack the oil pump gears with either petrolatum or vaseline during the buildup. It won't affect lubricant qualities, but will provide nearly instantaneous suction resulting in positive pressure throughout the system in 2 or 3 seconds.
In addition to Steve's comments which are all on the mark, one of the most important elements to building a bottom end and camtrain that will go 100,000 hard driven trouble free miles is getting it started and up to optemp and bedding revs as quickly as possible. Prevent flooding which washes lubrication off cyl walls, don't squirt too much lube in the combustion chamber which can foul a plug, and try not to blip the throttle more than absolutely necessary when getting the revs up to the specified cam-bedding speed. I found that a very small squirt of WD40 makes a good starting fluid without inducing backfires or detonation (ever shoot some into an open flame???).
Many years ago when Honda was big into their 15,000 rpm buzz bomb formula engines, I watched a crew prep a brand new engine for a run by preheating both oil and coolant on a parafin cookstove. I figured that maybe there was something to it. Todays oils are so good that preheating them doesn't make much sense unless it's midwinter in Minnesota...
I do preheat the tapwater to a near boil in one of those old timey 2 gallon coffee percolators fitted with a hose bib in place of the spigot, and run a hose from the spout into the radiator to fill the block. I don't use coolant on the initial run, so that if a headgasket should ever go south, or a hose leaks under pressure, there's no cleanup or contamination problems.
Mark Childers

Steve,

Thanks, I did mention above that I had primed the pump but it was some time ago. I will repeat the procedure and follow your guidelines. Thanks for the detailed information. I knew about most of the break in stuff but this is the first time I've seen it mentioned to replace the oil so often early on.

I've spent alot on this engine (money and time), so I want to do everything I can to ensure a proper break in. I hope I didn't do any damage thus far. I probably turned the engine over for no more the 15 secs before I stopped to investigate and ask questions.

Bill

Bill Schoolfield

Curt,

Yes you have used the right gasket. Make sure that the oil in the sump reaches the full mark on the dipstick and just keep cranking - I have known it take up to five minutes of cranking to get pressure - even if the pump is primed.

One problem in using vaseline or grease is that you create a blockage for the oil to flow up the pickup pipe to the pump if you overdo the packing - just a light smear of the lobes is all you should do.

Squirting oil down the rear oil cooler connection usually does the trick.
Chris Betson

One of the reasons for changing oil so often with a new engine is to remove all the tiny wear products which are generated by metal moving against metal for the first time. I think Steve may have overdone it a bit, but not much. I'm a big believer in fresh oil and filters, my 71 GT has 170K miles on the original engine, 32K in the last 2 years.
Paul K

I have added pictures of the oil pump gaskets under the FAQ page of my website. http://www.octarine-services.fsnet.cu.uk/faq.htm
Chris Betson

Whoops! that should be http://www.octarine-services.fsnet.co.uk/faq.htm
Chris Betson

So, it's took me the better part of this weekend to grab my unused gasket, drag out the scanner, hook it up, and figure out how to get the darned image onto comcast's web server. Then I come here to ask someone to look at it and see that someone else is one step ahead of me... Thanks, Chris. A picture is always worth a thousand words.

I guess the bad news is that I have the wrong gasket installed. The good news though, is that I now what my problem is. I guess my next question is how to remove the oil pan with the motor installed. How does one deal with that cross member?

Oh and yes, I too have relied heavily on this web site over the years. Ditto to Bill's comment - Kudos to you all!


Curt

Curt: You can remove the motor mount to body attaching bolts, place a jack with a wide board between the jack and the oil sump so you will not bend the sump, jack the engine high enough to place some 1/2"-1" plywood or wood blocks between the mounts and the body attaching plates. That should give enough room to remove the front sump bolts. I use a 1/4" drive Craftsman 7/16" flex socket. The new Craftsman reversible combination wrenches are also good for access to the front bolts. No need to remove the exhaust, but removing the alternator makes it easier to reach the motor mount bolts on the right side of the engine. Good luck. Clifton
Clifton Gordon

I received similar running-in advice after installing a rebuilt engine in my 73B - a neighbour that races a TR6 mentioned the importance of seatng the camshaft at high revs.

A point of interest is that when I bought a new VW Golf in 2000, the dealer refused to change the oil prior to 8000 km since they had a factory bulletin advising that to do it sooner would delay bedding in of the new engine i.e. they wanted the metallic particles in the oil for a while!

Regards, Barry
B.J. Quartermaine

Gasket swapped out, engine running, oil pressure normal. Amazing...

Clifton, gold star to you. I checked out the archives and saw folks just jacking the flywheel housing. Personally, I never rely on a jack so I went with the blocks under the mounts. 1-bys. Worked like a charm. That plus an air-ratchet and the pan was off and back on before I knew it.

Thanks so much to all.

Curt

Curt

Curt,

Congrat Curt, my experience was a tad more exciting and alarming. I primed the pump, turned the motor over a few time (reverse of normal), removed plugs, disconnected the fuel pump, turned over the ignition and almost immediately I had had oil pressure.

Added the plugs, connected the fuel pump and coil wire, then after a minor advancement of the diz, I had it running.

I was doing the run-in for 20 minutes per Steve S, everything seemed fine, although I wondered about the pressure I had (approx 65). I thought it would be more.

Anyway, my wife, came in the garage and said, whats that spewing all over the place! (sitting in the car I hadn't noticed anything untowards) After shutting down, a quick investigatation showed the problem to be a failed external oil line. Aside from the cleanup, I think all is OK.

My advise to anyone doing an engine rebuild, replace the external oil hoses!! Luckily this happen in the garage and not on the road.

Bill
Bill Schoolfield

This thread was discussed between 05/09/2002 and 09/09/2002

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