Hi Chris,
Since we are covering a number of topics, I will try to insert my
comments into your text.
> As usual with this car, nothing is as it seems.
> Here's some more surprises. The engine has about 6K miles
> on it. Complete re-build. The only thing not done was to install
> hardened valve seats.
Should be A-OK, but definitely isn't. Valve seats won't affect this
crankcase pressurisation. Shouldn't have any effect anyway unless you
drive long and hard and fast.
> If there was too much pressure in the crankcase, then I
> would suspect other gaskets would leak too (?)
It's likely that others would leak, but this tappet cover is
notoriously difficult to get tight.
>What do you think about this to check for too much pressure - If I
disconnect the
> valve (rocker) cover tube (remove the cap I put on to seal) with the
> tappet cover still connected to the carbs, if the crankcase pressure
> was high, there should be no measurable vacuum (measured with a
> gauge) at the valve cover tube with the engine idling ?????? Any
> thoughts ?
Right. If there is no vacuum, which there should be, then pressure in
engine is equal to or higher than atmospheric pressure. But it should be
lower, since the carbs are sucking away at it via the tappet cover.
That's why I was asking about compression test to see if there might be
ring blow-by. Which we hope there is not.
I'm due for a valve adjustment, spark plug replacement,
> and wires & cap replacement - I'll do the compression test at the
> same time. Unfortunately, having owned five Alfas and two Toyota
> Supras (7M), I'm very familiar with leaky head gasket symptoms :-)
> So far, none have surfaced and car has good power.
> One thing I cannot seem to cure is a chronic high idle problem - I keep
fixing
> it and a few hundred miles later it comes back (?) Seems like a
> vacuum leak, but I just can't find it.
It may be that this engine is just running better and better, hence
idling faster, as it wears in. It's only 6,000 miles since rebuild, so
that could still be happening. Have you tried lifting the carb pistons
to see if idle speed rises/drops/stays steady? That's the test for carb
adjustment.
> I've never tried opening the tappet cover with the valve
> cover still plugged. I've tried opening the valve cover with the
> tappet cover still connected to the carbs and opening both to
> atmosphere - both produce the leak. I was originally going to leave
> the tappet cover connected to the carbs and open the valve cover
> tube (and install an small air filter on the valve cover tube), but
> the high idle problem (and the leak) precluded doing this.
Just take off the filler cap and see what happens. There should be a
slight suction into the engine. You could, very carefully, hold a piece
of plastic wrap over the hole and see if it bulges out or sucks in.
> Someone else just E-Mailed me about a single piece cover
> that he used to finally cure his leak. What I'm actively looking
> for is a cover from an older car that has a gasket channel. On my
> car, the rear cover (with the gasket channel) hasn't leaked a drop
> !!!
>
> Thanks Again For The Time, Skip
>
> P.S. 250M miles for mains. That's impressive. I can't imagine
> 150K for any MGB engine. What's the record out there for an MGB
> engine without the head being removed ????
That was a number that John Twist cited, for his wife's car. But he
qualified it by saying that the life of the mains is related to the
condition of the big-end bearings.
Bob
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