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MG MGB Technical - tappet cover pushing oil into air cleaner

Dear Enthusiasts,
I own a 1975 B with a recently rebuilt 1860cc
motor, milled head, fast road camshaft, Mallory dual
point distributor. When I bought the engine the Healey
carbs on it would not fit due to my brake booster, so
I have been driving for 6 months, maybe 1500 miles
with my Stromberg-no problems except sound and power. I
installed a Peco header and Weber 38 outlaw carburetor.
It starved at high speed so we added a Holley red fuel
pump. The problem is-with the weber feeding the engine
oil was seeping from the valve cover cap and pushing from the tappet cover into the air cleaner. I changed
from the alloy valve cover back to stock with breather
elbow connecting to the canister-but today at 75 mph driving home for forty minutes there was a LOT of oil in my air cleaner. The engine must be getting excess
crankcase pressure??? Pleasure when running, now has
good power and excellent note. Weber tech said to run
tappet breather to air filter-looks correct on other
websites. Valve cover venting to charcoal cannister,
anti run on valve connected to base of carb (possible
egr port). Everything looks good but it's not breathing
properly. Oil pressure 65 lbs at speed, does not
overheat hesitate or stall. Any advice greatly
appreciated-sorry to be so long winded (fingered)
Regards, Nestor
Nestor Caryk

Nestor. How many miles does the engine have on it? Have the rings fully seated? It sounds like you have a lot of blow by which is pressurizing the crankcase and blowing out oil. This problem would be related to the cylinder bores and rings, not the carbs, although the Weber may allow you to rev higher and faster than the old Z-S did. Have you had a leak down test done on the cylinders? Might be a worth while first step. Les
Les Bengtson

Nestor,

I experienced similar symptoms when I converted the Stromberg/catalytic-converter system on my 77 B to a Weber DGV and after market "free flow" exhaust. I had excessive blow-by and too much oil in the air cleaner also. My exhaust system was the Pacesetter Ansa copy complete with header. It took quite a bit of trial and error testing of various remedies including re-setting the cam timing, compression tests, vacuum leak hunts, and re-jetting the carb: all to no avail.

I finally took the car to a buddy who rebuilds British cars and has a lot of experience with MG issues. After a test drive the first thing he did was put his hand over the tailpipe. The exhaust was not moving enough air. The muffler shop determined that the intermediate muffler and the final muffler both were obstructed. After junking the Pacesetter and replacing with local parts (only a temporary fix) the blow by problem was solved.

The oily air cleaner was fixed by getting one of the older-style funnel-shaped PCV valves and plumbing it into the manifold with a hose to the front tappet cover. The valve cover is connected to the canister as original.

Doug
D. Cook

Thanks for your input men. I work at a Ford dealership
and have several really good techs trying to help me.
A vented oil cap was suggested due to excessive crank
case pressure. Also, Doug, I have a 2" peco header
feeding into a 1 3/4" anza muffler-sounds great but as
you say may be restrictive. Please restate hoe your
"pcv" vent is directed...from tappet side cover with
pcv valve going into manifold? or air cleaner? Man I
hate to say I'm glad you had the same problem.
Thanks, Nestor
Nestor

Nestor,
Just a suggestion, you could just run a hose from the tappet cover outlet up and over the valve cover to the passenger side of the transmission to vent. It will still toss some oil but it doesn't go in the air filter. If you want to be enviro friendly attach the hose to a catch tank that is vented and empty when needed. What I see that you've done to your engine is increasing the power it can make which causes other things such as the emission systems to be less than efficient than designed for originally.
Cheers.
Kevin

Nestor,

Yes, the hose runs from the tappet cover to the input side of the MG old-style PCV valve which is screwed into the aft hole on the Weber intake manifold. The hose from the center canister outlet goes to the valve cover inlet fitting. The MG PCV valve is a bit more expensive than the ones available in local parts stores but it really works well.

Once I had my blow-by problem solved I tried several different plumbing arrangements and am happiest with this one. The carb stays clean with no oily residue in the venturi. Even when the crankcase ventillation is working properly there is enough oil vapor to make the cleaner and carb dirty if vented through the cleaner.

Currently, I am in the process of changing my cam and have the manifold off the car. The inside of the manifold is also clean with the PCV as above.

Doug
D. Cook

Excessive crankcase pressure implies a problem with the engine that fitting a vented oil filler won't solve. But often they don't seal very well and you do get leakage, I have had to put a 'neck-tie' round the filler neck of mine. But with an alloy cover with no vent you *should* fit a vented oil filler cap or you will have no crankcase breathing. On a 75 the suction for the breathing should come from the carb(s) and be connected to the front tappet cover, and draw through the vented oil filler cap or the canister. Doing away with the canister serves no useful purpose and in fact you lose the function of the anti-runon valve. Rocker cover breather connected to the air filter goes way back to the non-positive crankcase venting systems that were discarded in the early 60s. If your alloy cover has a vent it should be connected to the canister, but if it is not restricted you may get mixture problems.
Paul Hunt

I concur with Doug Cook's recommnedtion for the PCV. If fact I came to the exact same solution for a 73 that I owned about 10 yrs back that I had converted to a DGV setup.
These days I would stick to a good set of rebuilt HS4s.
Andy Blackley

This thread was discussed between 22/04/2004 and 23/04/2004

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