MGB Tappet breather to Weber downdraft

[Celtic 77]

I have a 77 B with a Weber downdraft and am trying to organize the multitude of various hoses. There is a clear plastic line from the tappet cover to the Weber. When i take the air cleaner off, there is a lovely mist of oil that I assume is being sucked into the carb to reburn. Is this necessary? Too bad this mist couldn't have been redirected to the rocker panels! Final question: There is a water line from the rear of the cylinder head to the heater pipe that I assume was for the old Zenith. I want to use either as rubber plug on each end since it seems to be just redundant. I will ultimately have one straight heater pipe from the heater to the radiator hose. Thoughts?

 

[Joe Reed]

That hose from the tappet cover to the air filter was originally used with a PCV valve - which doesn't exist with the Weber - to provide a slight vacuum to reduce pressure in the crankcase. As you've found, most Weber users plumbed it into the air filter to hopefully still provide at least a bit of negative pressure. Inside that front tappet cover is a steel-wool type of matrix that is supposed to separate out the oil vapor, allowing it to drain back into the engine. If you're actually seeing an oil mist at the carb either that matrix is missing or, more likely, you're getting too much pressure into the crankcase via worn piston rings.
You can replace that heater hose with one going direct from the radiator hose to the heater and eliminate that small hose, which was used in conjunction with the water choke on the original ZS. Sounds as if your Weber is not equipped with a water choke. You can do what I did....remove the two screws from that fitting on the rear of the head, used that as a pattern to make a simple blanking plate and gasket and install that on the head.

 

[Celtic 77]

That hose from the tappet cover to the air filter was originally used with a PCV valve - which doesn't exist with the Weber - to provide a slight vacuum to reduce pressure in the crankcase. As you've found, most Weber users plumbed it into the air filter to hopefully still provide at least a bit of negative pressure. Inside that front tappet cover is a steel-wool type of matrix that is supposed to separate out the oil vapor, allowing it to drain back into the engine. If you're actually seeing an oil mist at the carb either that matrix is missing or, more likely, you're getting too much pressure into the crankcase via worn piston rings.
You can replace that heater hose with one going direct from the radiator hose to the heater and eliminate that small hose, which was used in conjunction with the water choke on the original ZS. Sounds as if your Weber is not equipped with a water choke. You can do what I did....remove the two screws from that fitting on the rear of the head, used that as a pattern to make a simple blanking plate and gasket and install that on the head.

Excellent help. Thanks for that. Great info...

 

[Celtic 77]

FYI all... While shopping for door seals, I came upon Northwest Import pars in Portland Oregon. Good prices and they actually supply a blanking plate and gasket for the rear fitting on the head. $19.00! Well worth it.

 

[Alski99]

Steve at Northwest Import Parts provides great customer service. They have good prices, and fast service.

Al Hayward
‘77 MGB roadster
Brooklands Green