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Excess oil consumption

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ceedub

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After a full engine rebuild on my '73 'B I am using about a litre of oil for every fill up. Because there is blue smoke noticeable after a long down hill ride and a puff after acceleration, I concluded a head problem such as guides or seals. I removed the head and took it to the machine shop yesterday and the machinist informed me that there was nothing wrong with the head and that I need to now look at the piston rings.
My questions are:
1. Is there a trick to removing the pan without removing the engine so I can get the pistons out to check the rings?
2. Is there a possibility that a faulty head gasket could cause an excess consumption of oil?
3. Any other suggestions why I am using so much oil?

The top of the pistons are fairly clean. They are somewhat brown but after the 4500 miles that have been put on the engine I would have thought that they would be blacker than they are.
Thanks for your input.

Ceedub
 
You did not replace guides and seals when doing a full engine rebuild.

I think a leak down check is in order before you do anything else. I vote for head. Have someone else check it if it is still out. In fact I would consider new guides and seals just on general principles. Button it back up and see what happens.
 
I would second the leak down test... but it sounds like the head is already off.
 
New guides and seals installed during the rebuild and the leak down test was done some time ago with no problem noted

Ceedub
 
Was this a professional rebuild , or DIY?

I think the block has to come out to remove the pan.
When the pistons are out, check to make sure the rings are oriented properly.

Let us know what you find.

Dave :savewave:
 
That's a lot of oil. Do all the pistons look the same? ie the same amount of color on them?

Boy, not a clue really. Needs another leak down test if pistons look the same
 
Aside from the good suggestions that the other fellows have offered, were the rings prefitted with a feelers gage in the individual cylinders before assembly? Are the rings of standard material or chrome molly type. Hard rings take a special seating in procedure. It's possible that a ring was broken during assembly, especially if one was to tight. Hopefully not, but don't rule it out.

If the head is already pulled, it's to late, but I agree with those calling for a leak down test. JMHO.
 
Wow, I agree, that's a lot of oil. Given that the guides & seals were replaced, correct parts & they were installed correctly; this almost sounds like someone forgot to install a piston ring(s), or that a standard piston & ring were installed in cylinders that were overbored to the next size. I know this speaks to the other poster's suggestions, which are all good ideas. Were the cylinders overbored? you probably need to mic them to be sure. People make mistakes. You should NOT have that oil consumption.

Eaisest way to drop the pan is to pull the engine. As you know, not really that bad a job in an MGB.

Good luck. Let us know how you make out.

Colin
 
I think one of your orignal questions was if there was a trick to removing the pan with the engine in place?

Yes, you can pull the pan, but you'll need to undo the front engine mounts and jack up the engine a bit (you may be able to lift it on the bellhousing or use a hoist and lift it from the top). I put pieces of 2 X 4 lumber between the mounts and engine to prevent any "slips" of the engine.

The front bolts for the pan are buggers, but if you have patience, you'll get them. I did it last Summer on my '69 with the car on ramps and a floor jack under the bellhousing (plus jack stands, of course).
You may have to play around with different wrenchs (and maybe even bend or modify a wrench to fit).
I'm a relativley non-athletic guy in my late 50s. If I can do it, anyone can.

In the case of my car, I put in new rings, rod bearings (a *must* if you have things apart in my opinion), ground the valves and replaced gaskets and seals. I drove the car 2000 miles last Summer and it used virtually no oil.

G'luck!
 
Nial is correct that you can remove the pan without removing the engine from the car....I don't go so far as undoing the motor mounts but doing so will make the job alot easier......nothing on the engine has to be removed, just do as Nial said & the pan will come off.....get the car high in the air though because there'll be some contortions to get to the front pan bolts.

Sounds like you've either broken a ring, which is easy to do....or you've installed the rings so that one or more ring open ends are directly over other open ends....or you didn't have the correct end gap on your rings....or you might get lucky & its just your cross-hatching job in the cylinders.

What about that cross-hatching? When you spin the crankshaft to look inside all the cylinders do you see good marks?

Was the block bored?

If it wasn't bored, did you check the entire length of each cylinder for 'egg shape'?

Are the pistons new?

Did you install rings in each the cylinders without the pistons to check end gap?
 
Yes, the rings were pre-fitted and correctly gapped. They were standard rings in a 0.040 overbore. The rings were supposed to also be 0.040 over as well. If a ring was broken, shouldn't you see scoring on the cylinder wall? Also, I thought that if it was a ring problem, you would see smoke when under load going uphill which does not occur. Smoke only when going downhill.
The top of #4 piston is darker than the others but not that much.
How can you tell if the rings did not seat?
Thanks all for your replies.

Ceedub
 
Depending on which ring broke & where on the stroke it was, it could be laying in the bottom of the oil pan.

So, you reused the old .040 pistons?

Did you check the diameter of the entire cylinders - top to bottom?

With lots of use, I've found many MGB engines who's cylinders have gone from round, top-to-bottom, to egg-shaped in the middle....if that's the case, you'e rings wouldn't work properly in that egg-shaped part of the cylinder.

Another thing, IMHO, .040is reaching the limit of useable block for street use. I know there are those who build .060 engines, but they always have problems. When I come upon a .040 block, I send it to the scrapyard.

But, then, I'm not the best mechanic on the BCF.
 
what kind of a crankcase venting system does that engine have? Is it possible that something was hooked up improperly and you are getting crankcase pressure when it should be venting?
 
Ron, you picked up on "Smoke only when going downhill." didn't you? I also thought the same thing but assumed he had already checked that as he's already pulled the head. He could have a clogged front side cover.
 
This is a newly machined engine (4500 miles now) and new pistons and new rings. We were careful to alternate end gaps and ensured the correct end gap as well. The cross hatch is quite evident but I'm not sure what a 'glazed' cylinder wall actually looks like which I understand is a symptom of rings not seating.
The crankcase is vented from the side panel to both carbs--standard issue. I checked it and the pipe appears to be clear.
 
When I tore my B engine apart, the compression rings pretty much disentegrated as I was pulling the pistons out. They were cracked all kinds of ways & there was no scoring on the bores. Paul posed a good question earlier: are they chrome moly rings?

Respectfully, if you're going to go to all that trouble jacking the engine & crawling underneath to drop the pan, you're close to pulling the engine anyway, so why not just unbolt it from the transmission & pull it? In my opinion there would be less potential damage to components & it would be safer as well. Should only take an hour or so to pull a MGB engine. You've already got the head off, so it should be even eaiser.

Just my 2 cents.

Colin
 
Colin - it's easier to pull an MGB engine with the transmission intact.

ceedub said:
The crankcase is vented from the side panel to both carbs--standard issue. I checked it and the pipe appears to be clear.
Click to expand...
Inside the front engine cover is a filter that looks like some .004 steel wool....over time, it gets clogged with old, dried oil & doesn't allow the engine to breathe as it should....only way to repair it is to either burn the old mesh out or open the cover & replace it (I usually just burn it out & don't worry about replacing it).

Good to hear it was bored with new pistons - that eliminates all my questions except possible broken ring (if its inside the block).
 
I was wondering about pulling the engine without the transmission. I thought there was a danger of damaging the input shaft if they were separated while still in the car.
 
It really is easier to haul the whole thing out (engine & trans) as a unit. Fiddling around trying to get the input shaft back into the pilot bush with the box in the chassis is a PITA and *that's* usually when the shaft can be damaged/stressed. The few extra minutes/bolts it takes to unhook the trans from the chassis is moot. Twelve bolts, shifter removal, a cable and mebbe a wire or two, it's out. Much better than dangling the bell housing with ropes or whatnot and trying to blindly mate it up while the engine is swinging from a sling... just BAD Juju, IMO. Not sayin' it can't be done, I've done it. Just sayin' it's a LOT easier and safer the "conventional" way.


You could try it once and see. You'll never do it again. :wink:
 
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