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MG MGB Technical - MGB excessive crankcase pressure?

Hey everyone I have a 1968 mgb roadster that has a 1976 engine in it. The problem I am having is that the smog equipment has been removed, the head has caps in it for the smog rails, the gulp valve has been removed, the tappet cover vent tube is not connected to anything and the engine is over pressured. The engine does not leak oil at all when sitting but while it is running after about 5-10 minutes it pressurizes and sends oil out burning it and sending tons of smoke into the cab. I took the oil filler cap off of the valve cover while it is running and it blows tons of smoke out of it (and also out of the tappet cover)it has a lot of pressure blowing out of both. I am not sure what should be capped off or where the hoses should go. any help with this would be great, the engine runs great other than these problems. I tried hooking the tappet cover straight to the intake today and that made a strong suction instead of pressure in the valve cover but then started blowing smoke out of the exhaust after running on the freeway. I tried to research it and i see that the pcv valve could be an issue I just tried to take it off and saw that the hole was blocked with carbon but have not tried to test drive since unblocking because some sites have said that it can be blocked off and i have no idea what the pcv valve does or how it works. Thank you all in advance for your help
Scot Hamm

Here are some pictures it is dark but I wanted to take them and add them tonight. This is my current attempt with the tappet cover hooked straight to the intake manifold with negative pressure instead of positive pressure in the valve cover


Scot Hamm

6


Scot Hamm

pic 7


Scot Hamm

pic 2


Scot Hamm

pic 3


Scot Hamm

pic 4


Scot Hamm

pic 5


Scot Hamm

Hi Scot

Try blanking off the pcv valve and vent the breather tube from crankcase to atmosphere and see if problem goes away.
We have had pcv valved Bs and other cars burn oil if too much air enters the system and engine can then suck everything into engine....eg dipstick loose.

Peter
Peter Burgess Tuning

A 68 engine would have had a PCV valve, but they stopped in 69 so a 76 shouldn't have one.

But if it is blowing tons of smoke and pressure out of the oil filler cap and tappet chest cover with the oil filler cap removed as you say then you have massive blow-by, either a damaged piston or broken rings. Almost certainly a head off job, maybe a compression test first to see which cylinders are affected.
Paul Hunt

If you look at the pic labeled pic 7 I am referring to the mushroom looking metal thing with a vacuum hose coming out of the top of it as the pcv valve. I bought the motor off a guy on ebay who was converting his B to a V8 and he said it was a 1976 so that is assumption as well(it was a rubber bumper car)Is the mushroom looking thing a pcv valve? if not what is it? I will try and do a compression test in the next few days but the engine runs great other than when it smokes.
Scot Hamm

Scott. You need to get out your factory workshop manual, both for your model year and the model year of the engine, and begin to learn what you have and how the various systems hooked up.

"Is the mushroom looking thing a pcv valve? " No, it is an exhaust gas recycle (EGR) valve. You do not seem to have a positive crankcase ventilation valve on your set up. You, also, seem to have the tube off the rocker arm cover not connected to anything. It should have been connected to a charcoal cannister on the original car and is the source of positive pressure, filtered air for the later model emissions control systems.

You seem to have put together a "bitsa"--bits of this, bits of that. What happened to your old GF engine (the one which should have come with the car)? While much of the basic engine should fit into your car, various parts from the old engine (front plate, rocker arm cover, intake and exhaust manifolds, carbs and linkage, etc. need to be pulled off the old engine and assembled to your new engine if the system is going to work as your 68 was intended to do. Part of that work will include checking out the "mushroom" style PCV valve on your original SU intake manifold and ensuring its diaphragm is in good condition so that it will work properly.

Right now you do not have either a functional 68 engine system, nor a functional 75 and later engine system. The 68 style system would be easier to set up and administer and I would recommend you use that as your model. When the current engine is properly set up, then would be the time to start looking for problems. Right now, the problem solving is verging on the overwhelming. Cut down your variables and let us see what happens.

Les
Les Bengtson


Thank You guys I just checked and the compression are
cyl#1 134
cyl#2 70
Cyl#3 125
Cyl#4 130

The motor had to be Frankensteined to get it to run the old block was shot so the car sat 5 years until i could find a donor engine. I ended up having to take the timing gear, plate, and front engine mounts from the 68 and install them onto the current engine. I am hoping to find out what is causing cylinder 2 to be so low I am going to get a leak down tester to test the valves later this week. I am hoping its not the piston or cylinder. I do not mind eliminating the smog system all together. Is it ok to cap off the egr with a blank gasket (gasket material with no holes cut?
Scot Hamm

Thanks for the heads up on that Les. Lots of good advice there.

Peter
Peter Burgess Tuning

Scott. Your photos show the Z-S carb with its combined intake/exhaust manifold. There should be a catalytic converter attached to the exhaust manifold. This system is, quite bluntly, junk and should be scrapped. Install the intake and exhaust manifolds from the 68 along with the HS-4 carbs. The 68 exhaust manifold has the provision for the PCV valve and the system works quite well. (I have a 68 GT myself.) Attach the line (hose) from the front tappet cover to the PCV valve on the 68 intake manifold. Remove the later model rocker arm cover and install the one off the 68. At that point, you can begin your trouble shooting process.

As for the low compression, that is either piston/rings, bad bore (which would lead to excessive oil consumption) or a bad valve/valve seat. John Twist once told me not to bother with leak down tests as any car that requires a leak down test already requires the cylinder head to be removed. Hence, a waste of time and money to pay for a leak down test. When the head is removed, you will want to have it crack inspected--about 90% are cracked and need to be replaced from actual observation and testing.

Put your engine in the proper conformation, then find out what the problems are with it and correct them as you find them.

Les
Les Bengtson

Peter. Was posting as you were. Always good to hear from you my friend. Les
Les Bengtson

I can't really make out what is connected to what, and I'm not familiar with the Zenith other than pictures.

The port on the back of the rocker cover did originally go to the charcoal cannister, but it is the fresh-air inlet to the crankcase, not a source of positive pressure. Without the canister you need to put a small K&N filter on that port, otherwise dirty air will be drawn into the crankcase by the ventilation system.

Suction on the crankcase should come from the carb, connected to the front tappet chest cover. That uses the constant depression function of the Zenith (and SUs from 1969) to apply a constant low level of suction to the crankcase. Item 4 in the attached is that suction pipe.

With 70psi in No.2 that is almost certainly the source of the massive blow-by, piston or rings.


Paul Hunt

I borrowed my dads leak down tester today and confirmed it is either the piston or the rings in cylinder 2. I wont be able to work on it for a while because I am going in for knee surgery and don't want to have it torn down while I'm in recovery. Who knows, maybe I will just convert to a V8 or Rotary engine it'll probably be close to the same amount as rebuilding the complete motor. It is so old that I'm sure if I go in to re-ring it ill find more and more that needs to be done internally. Thank You all for your help

Scot
Scot Hamm

Scott, are you going to try and register your B as a '68 model? If so, the '76 engine will require you to have it pass the smog specifications for a '76 car. A huge PITA. It would appear, from your photos, that your crankcase vent hose is being run directly to your intake manifold. This will cause the engine to burn an incredible amount of oil due to the lack of a PCV valve in the line. RAY
rjm RAY

since the car is a 68 and has been registered as a 68 the motor does not need to be checked the pic of the crankcase vent running to the intake manifold was recently done in attempt to try and fix the problem of blow by. unfortunately I found that the rings are bad in cylinder 2.
Scot Hamm

Hey everyone this will be the last post I put on this page just wanted to let you know that there is a hole/ gouge in the cylinder and what i was referring to as cylinder 2 may be cylinder 3 it is the one that is 2nd away from the firewall. Thank You all again for the help! until next time God Bless!
Scot Hamm

Indeed that is 3. They number from the water pump end.
Paul Hunt

Scot.
You may be able to sleeve that engine.
Any good engine shop can help with advice.
SANDY

Sandy. I have seen minor damage to cylinder walls clean up when bored oversize. But, the main impression that I have gotten from this conversation is that Scot is looking for a quick and easy fix, has little knowledge of what he is doing, and does not want to put the effort into learning. He, also, tends to jump to conclusions without any real evidence to back up those conclusions.

Yes, this situation is easily (well, relatively easily) corrected and the result would be, most likely, a good example of an early Mark II, chrome bumper car. But, it will require money, hard work, and a great deal of learning to make that happen.

If Scot wants to do that, we are here to assist him. But, if not, I have better uses of my time than trying to convince him of what it would be best to do. That must come from him to be a proper learning, and growing, experience.

Les
Les Bengtson

Les what do you suggest? I am on a tight budget right now maybe in 5 years things will be different. I am currently looking for a quick fix because I am shy on funds. I was very discouraged when I found the cylinder was gouged it was the same cylinder and same thing that happened to my first engine around 10 years ago. I know this sounds crazy but the car still runs ok other than blowing smoke can I use JB weld on the cylinder wall to fill it in? I am worried that even if I fix the cylinder it will happen again I have had 3 motors and they have had the same problem in the same cylinder.
Scot Hamm

"I have had 3 motors and they have had the same problem in the same cylinder."

I have the greatest difficulty in believing that, unless you are doing something radically wrong somewhere, which is probably going to be impossible for us to guess at.
Paul Hunt

JB weld on a cylinder wall would be like putting a band-aid on a razor cut while standing in the shower with the water running.
A total waste of time.
Please supply photo of those gouges so we can supply further help.
Sandy
SANDY

Scot,

One option you might consider (with limited funds) is to find another car perhaps in a scrap yard (or Craig's List) with accident damage, or rusted shell. Do a few reasonable tests on the engine like compression, and oil pressure, etc. and make an offer. You could also end up with a spare gearbox in the mix.

Regards,

Larry C. '69 midget & '74 B/GT
Larry C '69 Midget

This thread was discussed between 20/04/2015 and 28/04/2015

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