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MG MGB Technical - engine rebuild?

Are there any signs to look for that would indicate it is time for an engine rebuild? The B seems to be running just fine except for oil consumption. I think
I have found the source of leak, but haven't looked into it far enough yet.

I also seem to have lousy gas mileage. My guesstimate is about 15 to 20 mpg. The engine also seems to be a little noisy (clakkity).

I would also like to insdtall an overdrive tranny, but won't pull the engine if i don't need to. I learned from my carb issues this summer, if it ain't broke don't fix it.

Thanks

Ken
70 B
Ken Harris

Ken, that's "If it ain't COMPLETELY broke, don't fix it".

Derek Nicholson

Poorly adjusted rockers could count for noise and poor fuel consumption, give them a check and do a compression check as well..
K Harris

One word of warning if you do start taking it apart it you will do more and it will end up costing more than you originally thought! There are far to many "might as wells" doing something like that. Might as well put in new pistons, might as well get a new cam, might as well lighten the flywheel....

Still you do end up with a brand new engine at the end of it and I must admit doing mine was fun!

You could possibly do just a head job on it in which case no need do take the whole engine out.

How much oil does it actually use? I don't know what normal is but I do know they all use some.

Simon
Simon Jansen

Simon. Yes, i know all too well about the "might as well" gremlin. That is my worry. As for the oil, it uses about 2-3 litres for 250 miles. I think i have found a leak though. it is behind the carbs, on the engine block. There looks to be some sort of "door", but i'm not about to touch the carbs again,until I am sure the season is done for winter.


ken
Ken Harris

Ken,

Sound like the tappet cover. This is a common source for leaks as the seals don't fit very well. Best to glue one onto the cover using gaskit sealant and then put cover into place. Then don't overtighten! Should only take a couple of hours work to sort, most of that taking off the carbs and exhaust manifold for access.

Iain
I D Cameron

Ken-
Converting to an overdrive will require both removal of the transmission and a rebuild. Your oil consumption rate is terrible. I doubt that it's just a leaking rear tappet chest cover.
Steve S.

Have to agree with Steve S. on the oil consumption. There is more going on than a leak.

As for the clatter and the fuel consumption, adjusting the valves may make the engine feel brand new. I recommend you do it whether it is using oil or not.

dave
Dave Braun

Thanks for your respoonses everyone. As for the oil, when i park the car i get an oil patch about the 3-4 inches iin diameter. The only time i get any kind of smoke from the exgaust is if the car has been sitrting for a couple of days or more, then there is a some black smoke on start up, but it goes away quickly. I've had friends follow me and htey say there is a little smoke when shifting, but they say it is a very light blackish smoke. Thet is why i was thinking it is a leak.

Just checked the oil level this morning, and it is halfway between full and empty lines. It was full when we went on a road trip of about 125 miles.

Ken
Ken Harris

Ken,
In addition to the good advice on tuning (tappet adjustment, pressure check etc) above, I'd suggest tappet cover gaskets and a check to ensure the front cover is clear to breath to the carb if that is the setup on your car. From what you say about the puddle when parked you would be leaking a bit over a 125/250 mile run. Might check things like timing cover oil seal as well. They can also drop a bit in quick order.

Then make an assessment on how she runs, economy, oil consumption what have you from a known base data point. Go from there.

Regards
Roger
Roger T

That oil consumption is frightening and there is certainly something far wrong apart from a leak. I would have thought that the first thing to be done is a simple compression test to determine what the state of the pistons and bores actually is. The other thing that I would be checking to determine the state of this motor is the oil pressure which would give a good indication of the state of the bottom end of this engine. Once you have these figures come back to us and we can then give further advice on what best action to take.

Finally with the engine running remove the oil filler cap and race up the engine to determine the extent of fuming and thus piston blow by. Please note that all these tests should be carried out on a hot engine.
Iain MacKintosh

Alright I have done the trests suggested. The oil pressure when moving is around 70, when idling drops to around 50. For the compression test:
Cyl Dry Wet
1 150 165
2 150 165
3 150 170
4 150 160

Upon reviewing the archives I'm guessing these numbers are not that bad. I did notice that when i removed the plugs, #1,2 where fair, 3 getting worse (blackish) and 4 worse still. Before I had my issues with my carbs and did a change the plugs were always llooking perfect per haynes manual, slight tan colour.

Upon recalculating my gas mileage it is not bad after all. right around the 25mpg area.

Ken
70 b
Ken Harris

Those numbers sound pretty good, and don't suggest bad rings or blow-by. But, the oil must be going somewhere. Have you checked/drained your radiator lately? Are you finding any oil in your coolant? On your blackish plug, was the plug oily?

M.D.
M. D.

Well your engine doesn't need rebuilt!! The crank case breathing can often cause considerable oil consumption if not functioning correctly. This was very different for US cars due to emmision stuff, so I can't advise.

As fas as the tappet cover goes, I do know of a car over here that had a SC fitted. His tappet cover gasket had slipped and as a result when running oil was dripping out of this and onto the exhaust giving a smoke screen at times! But, the point is, when the car was not thrashed he was still lossing a lot of oil this way without much obvious sign when inspecting a stainonary car. So while you oil use is very high and may well indicate oil being burnt, don't completely rule out a leak that is worse on the move, especially given the signals you have. A leak would after all be the easiest and cheapest fix, so try it frst!

Iain
I D Cameron

The other place to check its not leaking is the Cam Follower side plate, just behind the exhaust manifold.
K Harris

Same thing I think Ken!
I D Cameron

Sorry Iain that will teach me to pay more attention..
K Harris

Ken, your figures seem to be pretty good so on the face of it there doesn't seem to be much worry there. However please do the test with the oil filler cap removed to see how much blowby there is as the compression rings could be sealing well whilst the oil control rings may not be. You can replace the valve chest gaskets without removing the manifolds and you should of course ensure that there are no external leaks before condemning the engine. Please also make sure that all breather tubes are clear and not kinked in any way.
Iain MacKintosh

Ken-
The black smoke that appears on start-up and then ceases after a short period means that oil is leaking down at least one valve stem and puddling atop a valve. Slight black smoke when shifting is caused by more oil being drawn down the stem by the increased vacuum inside the intake ports when the throttle is closed at higher engine speeds. It's obviously time for new valve stem seals! You'd be surprised at how much oil consumption can be caused by bad ones. As for the small puddle under the car, degrease the engine and try to track it back to its origin. a good flashlight is a useful tool for this task. You may have more than one leak, and its best to get them all at one time.
Steve S.

I drove a 70 B for 17 years. I didn't notice if you checked your engine compression rating. Your engine plate will end in "H" if it's the high compression model. If the engine is the original, you can get about 75K between overhauls. The high compression engines had an extra compression ring and came out of the factory with chrome moly rings and wore the cylinder walls more rapidly. If the engine has been taken care of, your crank will likely only need polishing. The cam will be worn, but likely acceptable.

However, my experience with that vintage of engine was that the cylinder heads needed valve work on about a 2 to 1 ratio to engine overhaul. Of course, that was back when we used leaded fuel. If you're in the 40 to 50K range, I'd recommend considering a valve job on the head. If your compression is that even, it's probably just wear on the valve guides allowing oil through to the cylinders and that would axplain the smoke on startup. Typically, worn guides allow oil to leak down into the cylinders after the engine is turned off and setting. It's not expensive and easy enough to do. Just pull the head, take it to a reputable shop and put it back in place. Be sure (can't stress this enough) to use a quality head gasket or you'll be replacing it in about 2 to 3 months again, follow proper bolt torque procedure, retorque after about 200 miles and adjust the lifters properly as well.
Rick Penland

Ken, if you are seeing black smoke rather than blue that is due to the carbs running rich. Running rich can also increase oil consumption as the excess fuel washes the oil off the cylinder walls so it gets burned, a very rich mixture or heavy use of the choke will also result in raw fuel getting past the rings into the oil pan. This will also delute the oil, thining of the oil by fuel will increase oil consumption.
John H

This thread was discussed between 15/10/2006 and 24/10/2006

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