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MG MGB Technical - Rocker arm oiling, and PCV routing

Hi,

1) With the fuel pump fixed (see another thread), I was able to start up the rebuilt engine today.

2) Oil pressure was approximately 60 psig on the gage, but I have a question.

3) When I looked in the oil filler cap there was not much oil splashing forth and about like in a Detroit V8. I use to set tappets on some late 1950 V8's and use to have to have rags layed along the edges to catch the oil when setting them in a run condition.
So, my question is, "is this low oil flow to the the rocker arm assembly normal in the MGB's." It is oiling but not like I expected, for example the cast iron floor is wetted only, but no "glaring" oil on it.

4) Paul Hunt, with the engine running I was able to confirm that, as you said, the 3/8 dia port on the firewall side of the carburetor is on the atmospheric side of the throttle plate, and effectively a PCV valve. With increased RPM, the flow into this port increases.

5) A picture in the Haynes manual seems (not clearly) to show a hose running from the tappet cover breather pipe into this port. And this is what you are saying is correct. However the diameter of the breather pipe is 1/2 inch and diameter of the carburetor stub is 3/8 inch so the hose must be a factory formed hose. Remember that this engine had the air pump removed and the breather pipe was opened, which ment that the engine was not breathing well, and I have surmised was some of the reason for the engine being so ground up inside.

6) I must get some crankcase circulation, and I like your idea of installing an oil filler cap with a filter in it and pulling the air in there, down into the crankcase, and back up the breather pipe, and to the carburetor.

7)How ever I am still sorting out what to do with the metered hose at the back of the carburator, which was attached to that canister. My problem is that I do not know the routing inside of the canister. The three hoses attached to the top of the canister are still there: one from the carburetor bowl, one for the gas tank, and a larger one from the rear of the rocker arm cover. Now the question:

"If I set up a PCV system as you suggested, will not the gas vapors collected in the canister be sucked into the engine via the metered hose at the rear of the rocker arm cover."

8) The run-on valve and the hose into the bottom of the canister is still attached, but the large 1.0 diameter out of the bottom of the run-on valve, which use to connect into the air pump,somewhere, is simply dangling free, that is, opened. I am not sure what to do here. There is another approx 3/16-1.4 ID hose running from the intake manifold to the run-on valve which at the moment I have disconnected. I do not have the run-on valve circuit sorted out yet.

9) Further, after the engine warmed up and I turned it off it wanted to diesel, so it looks like I must solve that problem yet. I only ran the car for approximately 45 minutes, while timing it, etc. I had meter timed the distributor before starting the engine so it was at TDC and it did int "diesel" until I advanced it to 8-9 degrees. I am not sure where to set the timing. I may have it a bit too advanced.

10) Paul, wasn't it you that earlier suggested that I block off the gas tank vent at the canister and purchase a vented gas cap---from a MGA---I think.

11) Regarding the PCV routing the reason I suggested attaching the breather pipe to the air cleaner is because that was the common practice for years in the older Detroit V8's. The routing was (A) from the air cleaner into one rocker arm cover via a cap filled with some kind of metal, or nylon wool (B) down into the crank case (C) up to the other rocker arm cover (D) through a PCV valve mounted in the cover, and (E) into the base of the carburetor.

12) I had thought this routing would work well on the MGB, that is, (A) from the air cleaner to the breather pipe (B) down into the crankcase (C) up into the rocker arm area (D) out the back existing rear rocker arm pipe, and (E) into the carburetor. I had considered removing or opening the metering hole at the rear rocker arm port.

13) But I see no reason why your routing would not work, that is to (A)intake through a wool filled oil filler cap (B) down into the crankcase (C) up and out the breather pipe via the lifter cover area, and (D) into the carburetor.

14) The EGR valve was also disconnected. I do not see any port on the carburetor to connect it to. They usually connect above the throttle plate often throug a slit, as compared to a round hole. There is only one vacuum port at the base of the carburetor, and this appears to be the vacuum advance port.

15) Thanks for your help! It is nice to have someone to lean on, while sorting out this emission control and PCV routing stuff, especially with poor documentation, and after some mechanic buggered some stuff up, which I am fairly certain lead to premature engine failure.

16) The engine is not idling smoothly, and it appears a carburetor rebuild is needed. The idle air adjustment that the mechanic removed from the side of the carburetor is probably part or all of the reason for the rough idle. I see that I may be able to order this idle air control from Moss for in the $40 range.

17) The temperature gage is not working. It is probably the tranducer.

Layne Wilson

Layne Wilson

Layne, run on or dieseling is common in MGB engines.
Stan Best

Yes, and I suspect that it is is caused by your poor idling. In order to avoid dieseling you must achieve an even idle at no more than 800rpm and you will probably find that difficult until you have fixed all your plumbing. Your timing at 8/9 degrees seems about right.
Iain MacKintosh

Hi,

1)In paragraph #4 above I wrote, "--the 3/8 port on the firewall side of the carburetor is on the atmospheric side of the throttle plate--"

2) What I ment to say was "--is a metered port on the intake side of the throttle plate--"

Layne
Layne Wilson

Layne - There were no EGR valves used on the MGBs. You may be refering to the gulp valve and if the rest of the AIR system is removed, there is no need for the gulp valve. Cheers - Dave
David DuBois

Dave - EGR valves *were* used on MGBs, at the same time as the Zenith was fitted. Gulp valves were fitted with the air pump from 1968.

Layne - the breather port *should* be on the atmospheric side of the butterfly, which is why your earlier comment that the flow *increased* with increased rpm bothered me. The breather port should exhibit a relatively constant but low level of vacuum when measured between the butterfly and the piston, as that is the characteristic of the constant depression carb. When the butterfly is opened more of the vacuum from the inlet side of the butterfly appears on the piston side, but that in itself causes the piston to rise which lets more air in from the filter side, which balances the vacuum again. I don't have a Zenith to check, I can only say that what you described as the port *is* what Haynes shows as the breather.

3. There *should* be quite a lot of oil splashing about under the rocker over, if I want to run my engine with the cover off I raise to back of the car to level the engine or it makes a terrible mess.

7. Yes.

8. The 1" dangling pipe is the breather and ventilation inlet port open to atmosphere.

9. The anti-runon valve will totally stop dieselling and running-on but the emissions plumbing has to be complete and no blockages or open ports other than at the bottom of the valve. I assume North American spec cars were prone to running-on as UK cars never got this valve. It has become more common in the UK with the introduction of unleaded. I tried an after-market valve which lets air into the servo hose but it made no difference at all, eventually I plumbed it like the North American system so it acted on the carb float chambers and it is 99.9% successful. The aftermarket valve *may* be better screwed directly into one of the blanked-off ports of the inlet manifold, with the right engineering, as unscrewing one of the big plugs does stop the engine.

10. Gas cap and filler neck from a pre 1970 MGB. may be the same as MGA, don't know.

14. The Zenith (for the MGB) shouldn't have a vacuum advance port, this was on the inlet manifold. Haynes shows an EGR valve port on the engine side, facing up and across the rocker cover (if it were long enough).
Paul Hunt 2

This thread was discussed between 02/10/2006 and 03/10/2006

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