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MG MGB Technical - Oil Pressure Relief Valve - fitting

On the B engine the oil relief valve is part way down the block at the rear left hand side and is obscured by the exhaust manifold and part of the body structure making removal and replacement extremely difficult. If you have a car hoist removal is relatively straight forward but who has a hoist/lift? Jacking the car up is only of marginal help. Removal is simple but putting the valve back is impossible when lying on the floor.

Apart from removing the inlet and exhaust manifolds (and even with these removed access is limited unless the car is on a hoist) does anyone have practical advice for someone who is not a multi armed contortionist?
R J Marshall

I successfully did this, but afterwards I swore to myself that I
would never, ever, fiddle with the Oil Pressure Relief Valve
while the engine was in situ again!

Note on the cap where the machined threads begin, and mark
the flat that is nearest to it with a permanent felt marker.

Remove the oil pressure spring from the block. Place the cap
against the block and slowly screw it in while noting the exact
position of the marked flat when the threads first engage each
other.

Fabricate a long metal lever from some flat stock, and get
some bits of wood (as wedges). You'll have to experiment
with their exact shapes and sizes. Leverage is your friend.

Replace the oil pressure spring into the block. Place the cap
over the spring - and position the marked flat at just before it
initially engages the threads.

Shove the metal lever and wood wedges between the cap
and the frame rail and work the lever until the cap touches
the block. Twist the cap (with a spanner) to initially engage
the threads. Once the threads are engaged 1-2 rotations,
then it is possible to remove the lever and twist the cap
fully home.

This is easier said than done and will no doubt require many attempts (and failures) and an inordinate amount of patience.

Be sure that all children and neighbors are beyond earshot
as strong cursing often ensues during this process.
Daniel Wong

Actually remove spring, screw cap on, then slowly unscrew until the threads just release, then mark both cap and block. Refit spring, place cap in position just before the threads start to engage, apply pressure, and turn. You shouldn't need anything like two turns for the threads to hold.
PaulH Solihull

It is a fiddle, but do-able. I used the same method as Paul, manifolds removed of course. I have thought of modifying an old cap to be adjustable and also allow the spring to pass through it, though haven't done it yet.
Allan Reeling

Using the method that Daniel and Paul describe doesn't require the removal of either manifold. Of course, it would be a lot easier that way, but taking your time and observing where the relief valve cap threads start to align with the block will make the job so much easier. RAY
rjm RAY

Gentlemen

Thank yopu for your tips. The key question is how do you access the domed nut without removing both manifolds and exhaust or putting the car up on a hoist. I've jacked the car up a few feet and lying on ones back it is impossible to get adequate access. So, how can one do it? (The nearest hoist to where I live is miles away across the rivers and down the highway - a trip which I am loathe to do with a dodgy relief valve).
R J Marshall

Access is better from the engine bay.
Allan Reeling

RJ- So, you're removing the nut to replace a worn spring? How do you know? For me, I use the Moss supplied 3.25" new spring and the spacer disc between the spring and valve. Use your pinkie to pull the relief valve out and clean and polish it up before you reassemble. Sometimes the problem is the valve not seating completely. Just my 2sense. Cheers, Vem
vem myers

This thread was discussed between 04/12/2012 and 08/12/2012

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