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MG MGB Technical - Heavy oil use/Rings not seating after rebuild?

Hello everyone, this will be a long entry so here goes:

I had the engine in my 73 B rebuilt 2600 miles ago. I chose to rebuild the engine because it was feeling alittle sluggish and I wanted to gain more performance. The cylinder was bored 30 over, shallow dish pistons used instead of the deeper dish pistons, head was ported and polished, cam was reprofiled to a "fast road" profile. ARP studs were used, and the rotating parts were balanced. I have been using Castrol 15W40 non-synthetic oil for diesel engines upon recommendation from contributors to this forum. The engine has all smog equipment removed except for the absorption canister remains. The front tappet cover vents to the carburetors with no PVC valve.
I ran the cam in on the initial startup at 2000-2500 rpm for 20 minutes, although I was heartbroken to see coolant oozing from above the number 3 sparkplug - the head was visually inspected for cracks, but not magnafluxed. I have found a replacement head of the same casting, and it has been crack tested and found to be OK. The rebuilder of my engine will (thankfully) be transfering the valve train from the cracked head to the replacement. I have temporarily slowed the coolant leak with Marine Tex (Thanks Les Bengston for recommending it in other threads).
I treated the engine lightly in the first 500 miles, but since autocross season was starting, the engine saw hard use shortly after 500 miles, albeit for only short periods of time. Otherwise I drive fairly normally although spiritedly at times:)
Since I will have the head off soon, I thought I would try to address a concern that I have regarding oil consumption. I currently use 1 pint every 200 miles. I cannot see smoke from the tailpipe, and have only minimal drips under the car when parked (less than before the rebuild). The engine is slightly oily underneath, but less than before the rebuild. There is a black substance roughly the consistency of oil that oozes from the area of the head gasket under sparkplugs 2 and 3. From what I understand, only coolant passes through the gasket in this area, and the oil passage is on the other side of the block/head. But the oozing substance is black and thicker than what I would think coolant would be like.
I did compression tests - dry/wet showed:
1 - 162/185
2 - 160/185
3 - 155/180
4 - 170/200
I have attached a photo of the spark plug appearance: there does not appear to be any significant fowling of the plugs.
Looking through the sparkplug holes, I note that the tops of the number 1 and 4 pistons are about half covered with carbon, and are otherwise shiny metal colour. Numbers 2 and 3 pistons are completely covered with carbon. My machinist tells me that when rings do not seat, the pistons remain shiny and don't accumulate carbon.
Do I likely have rings that have not seated? Is there any way to promote ring seating? Do the spark plugs look like the mixtures are too lean, especially 3 and 4? BTW why is a lean mixture a bad thing if the car runs well?
Any help would be appreciated, so that if something can be done with the head off to remedy this, I would like to take the opportunity. Thanks in advance.
Erick Vesterback

Oh and here is the sparkplug photo:

Erick Vesterback

The plugs don't look extreme. Some carbon, no major signs of distress.

2 and 3 normally get a different mixture than 1 and 4 do, due to the siamesed intake ports. So having a different amount of carbon buildup in 1/4 than in 2/3 is perfectly normal and expected.

Your crankcase ventilation system needs to be either stock or very well thought out. It's very easy for a PCV system to suck oil out of an engine and into your intake manifold. The stock system had a restriction orifice to prevent this. Check your PCV system to make sure it's exactly stock.

I don't like the fact that your dry and wet compression numbers are so far apart. That does suggest leakage at the rings.

Your breakin sounds close to reasonable, but possibly not close enough. It's actually quite desirable for a new engine to see hard, though judicious, use. If you baby it, the rings will take forever to seat. Autocross, though, may or may not be 'judicious.' My guess is, it probably wasn't. If you're gonna break it in hard, do it on a straight road. Warm it up, and pull full throttle in third till you hit the speed limit. Slow down using engine braking. Repeat. Let it cool, then repeat the process later.

As for oil, I broke mine in on the cheapest junk available at the dollar store. Worked great. The idea of using diesel oil is interesting - Neat idea. Anyway, Don't use a quality oil to break in a new engine. It won't break in. Friction is your friend at break-in time.

I sure hope it doesn't call for a hone and re-ring!
Sam Good

I think the big difference between the wet and dry compression test is because too much oil was poured into the cylinder for the wet test. The dry test is well up and pretty even. The engine if it is passing oil would be wet enough in the bore already.
Have you got air flowing through the crankcase, I mean is there an air inlet position like a breathing oil cap or charcoal canister.
Is it possible that the dip stick tube is in too far? or wrong dipstick, Try not putting that pint of oil in and see if it uses a second one. If the crank is coming in contact with the oil level in the sump it will use and leak oil. Good luck Denis.
DENIS4

The black ooze may be oil if the crack in the head extends to the top letting oil from the top of the head seep through. The biggest reasons not to run lean is less power, hotter running temp, and holes melted through the pistons. From your spark plug picture you seam to be running lean. Look at the color of the plug lower electrode, you want amedium to light brown, yours appear in the picture to be light gray. Do not judge by the color of the plug body which is coated black, this is common with unleded fuel. The number two plug looks blistered which would be very lean.
John H

Thanks for the replies so far - Sam, if it needs honing and new rings, that just involves jacking the motor up, rmoving the sump and undoing the big ends and pulling the pistons up? Not too difficult?

Denis - I used 5 mL (1 teaspoon) put in with a syringe - would that be too much? I will check into the dipstick position, but if in too far, would that not have the oil level lower by a small amount, not higher?

John - I thought the mixture looked lean, I have already increased the mixture alittle since I took the photo. I am running Bob filters with AAA needles on my HIFs, and they seem to pass the "lift pin" test.

Thanks again for your help.
Erick Vesterback

Erick of coarse your right that would lower the level but the idea was there, and you know what I mean. Anything that can cause too much oil in the sump.
That #4 cylinder worries me, do you have any idea of what the compression pressure should be with your set up. The dry test is so even but #4 so high wet. I would like to see another test without putting any more oil in the bores as they should be wet enough and excess oil dissipated. If it was me I would give the engine a bit longer to bed the rings and dont baby it, plenty of hard pulling. If you decide to pull the pistons and rods you will end up replacing a few parts and its a bit messy doing it in the car, so I would give it a chance.Talk to your engine builder and make sure he is part of the action so he has no excuse to not stand by his work.
Denis
DENIS4

I would pull the head and examine the bores.

Occasionally the reboring will uncover areas of porosity in the cylinder walls that hold oil and the engine will burn excessive amounts forever. The telltale signs are brown streaks or discolouration on the walls.

Also if the honing balls used were excessively coarse, then there may still be considerable cross hatching present on the walls - it it not just the rings that have to bed in!
Chris at Octarine Services

Erick,
Coming at it from another angle, which valve stem seals were used on the head? I rebuilt a B engine once using the factory style seals and had problems with excess oil usage.

I replaced them with the Ford umbrella style, end of problem, lesson learned.
Dave
David Steverson

As far as valve stem seals, I don't believe they are the original style, but I don't remember him talking about Ford umbrella style so I'll check with him on that. Are these actual Ford parts, or parts for the MGB head of a style similar to Ford's?

Point well taken that not only the rings have to bed in, Chris. Would running a bit of a rich mixture help promote bedding in, by thinning down the oil on the cylinder walls? I don't like the idea of using low quality oil to bed in because I'd like to get the best possible lubrication for the bearings.

I agree it is strange that the number 4 compression reading is so high, Denis. Made me wonder if the cam lobe on #4 is different than the others, causing longer compression stroke on that cylinder. I have spoken to the cam profiler about problems I had setting the gaps (centre of heel was much different than alittle before or after the heel centre) and I lost all confidence in him as a result of that conversation.

All in all my rebuild experience hasn't been great, although the engine runs very strong and is actually a pleasure to drive.

Thanks to all who have posted so far.
Erick Vesterback

Erick. I had to tear down a rebuilt engine with about 2K miles on it when the line to the oil cooler sprung a leak at highway speed. Ruined the bearings. However, the cylinder walls still showed a significant cross hatching pattern and the portion of the rings in contact with the cylinder bores still showed blackening from the heat treatment process. Thus, they had still not fully seated. I suspect with modern oils, it will take significantly longer for the rings and bores to fully mate with each other than was common in the past.

As to the valve seals, there is a Ford part which will fit on the MG valves and provides a better oil containment than the rubber O rings. I do not know the part number, but believe it has been mentioned in the past and may be in the archives. If not, someone will post it. However, Peter Burgess, in his book on the MGB engine, states that the rubber O rings are fine on a road going engine. Why not drop him a line and find out his current thoughts?

Les
Les Bengtson

Les, very interesting about the 2k mile engine of yours - I guess the consensus is that the oil is getting by the rings and burning up and leaving via the exhaust. (although valve seals or the crack in the head could be contributing also). I am puzzled by the fact that I don't see any smoke, nor does my wife in times where she has driven behind me, and nobody has commented on my engine smoking during autocross events. Occasionally I see a car driving around town producing lots of blue smoke - I wonder how much oil those cars are going through!

I will check further into the valve seals, and I think it will be interesting to see what things look like when I am at the point of pulling the head. And of course at that time I will post a follow up thread.

Erick
Erick Vesterback

The only problem with the OE valve stem seals are incorrect fitting. If fitted correctly they will last the life of the motor, were as the later seals go hard and become unserviceable. Also the OE seals still allow the small amount of oil that the modern bronze guides require , where mushroom seals are too efficient when new. I have been using OE seals for over fifty years in the motor trade and never had an oil use issue. I am only talking about BMC engines.
DENIS4

The "improved" seal is actually an MGC part which fits the top of the valve guide and has a sprung lip seal on the valve stem.

I fit them to inlet valves only, leaving the exhaust with no seal.

Sufficient oil works its way down to lubricate the inlet valve guides.

The "O" rings only stop oil running down from the top of the valve assembly and do nothing to control the oil splashing about between the springs.

Many times I have seen the "O" rings fitted incorrectly on the stems and not in the caps under the collets!
Chris at Octarine Services

This thread was discussed between 26/09/2007 and 01/10/2007

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