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MG MGB Technical - BV8 Exhaust Manifold

I am in the process of removing the exhaust manifolds on our factory V8, the wrap round style ones, prior to having a look at the head gaskets with some professional help this evening. MGB stuff has been invaluable.

All a bit of a struggle to be honest, bring back the 1800, all is forgiven

The exhaust manifold bolts are of 3 lengths but the spares offered are all the same length. Is this correct?

The manifold, I think ends in a straight vertical down pipe level with the sump, not the plate with 3 studs on it shown in the parts diagram - I take it I still have to split it there? I certainly cannot get it out with the small right angled pipe to the Y piece on it, and it looks like it will be a struggle even with that gone!

Any hints on how to get the manifold out (this is still the 'easy' LH one!) ? The paint on the wing is not going to look very good at this rate....

Mike Dixon

The mild-steel tubular 'block huggers' on mine have been a pain for 30 years with cracking in the centre join, two sets with attempted repairs.

You have to remove (or at least pull forwards) the steering rack to get that side off. With the bolts out and the manifold clamp loose you should be able to wiggle/twist the manifold up out of the pipe without undoing anything else, otherwise you have to slacken all the clamps, pull the main pipe with boxes and Y pipe off the intermediate pipes, before you can get those off the manifolds. But see below about falling off!

When new they fit straight on but in use they have warped with the ports turning in towards the middle, which means you can get the bolts out OK but can't get them back in as the holes no longer line up. I welded struts between each adjacent pair which helped with that, but then the outer two end up stepped back from the centre two so they need additional half-thickness single gaskets to pack them out. That complicates installation, I found offering it up with the bolts in, gaskets on the bolts, and a length of thin single-strand wire wrapped once round each bolt kept everything in place. Start each bolt then you can pull the wire out and everything stays in place.

Gaskets are also a pain - singles are a fiddle, double 'tin' LR pairs just don't seal, green and black composite blow out, the only ones that work are the other doubles that are the same construction as the original singles.

All 16 bolts are the same on mine, one bolt in each is partially covered by a tube so a socket won't fit and needs a ring-spanner and a guess at the torque. The back ones are a fiddle, especially the RHS and I think even the other side needed a bit of jiggery-pokery to get a socket on. Hex cap screws may help, but with some manifolds even those are partially covered.

The manifolds end in a plain pipe pointing downwards, a short length or right-angle intermediate pipe pushes up onto the left-hand one and a longer length with three bends pushes up onto the other. A Y piece connects those two ends with the rest of the system. The problem with just pushing on to a vertical pipe is that they wiggle back down again all too easily! The PO said they both dropped off once with him and were pushed along the road until he could stop, so I always kept an eye on mine. One day I thought they looked a bit low, gave them a waggle and both fell off - fortunately at home.

Strap clamps work OK as first image, I noticed some Council workers using stainless 'sign-affix' square head 'channel' bolts when installing a road sign which I thought might be handy and they gave me a handful. The square head locks into the clamp so you only need one spanner when tightening which is easier than getting two up there, and being stainless you can really get some torque on them. The straps being mild-steel do eventually corrode through, which means the joints have to be parted to fit new ones or its tricky getting the ends of new ones close enough to fit the bolt after they have been opened out to fit round a joint. However Clive Wheatley (at one time at least) was showing the ones in the 2nd image which can be opened out and pulled back together much easier, and being stainless should last longer as well.

You mention paint on the inner wing - mine had cooked the paint both sides, the off-side had rusted through and failed the MOT. Me saying RV8s have a much bigger hole there for the pipes to go through got me nowhere! When the engine was out I pop-riveted heat insulation fabric on both sides.

Twice as many cylinders as the 1800, ten times more aggravation!






paulh4

2nd papa: "otherwise you have to slacken all the clamps"

Should read "slacken the middle and rear mounts ..."
paulh4

Amongst other reasons, this is probably the main advantage of the RV8 out through the inner guard style headers.
willy
William Revit

We managed to get the cylinder heads off without taking the manifolds out. I think I will have to remove it though to do the starter motor. I think the hex cap screws might be on the cards though especially as some seem to have been cut down. I will also look at the twin exhaust gaskets as per your MGB stuff


One friend has put the RV8 manifolds on his BV8 - not a simple task or cheap and the pipes still run under the sumps so it still lacks ground clearance - just have to drive more carefully!

I will look out some of those clamps - they look good - I had to cut off one of mine
Mike Dixon

I've been able to remove/refit the starter without taking anything else off - had to do it at least three times! I got to the top bolt with a long 3/8" extension with a U/J part way down, going through between the pipes of the manifold. With the roadster the distributor at the very least has to come out ... but then that's much easier to refit than the V8!

The first time was swapping it for a geared unit after the solenoid was finding it harder to engage without chattering - and it wasn't low voltage feeding it. That lasted about five minutes as the motor was attached to the adapter plates with self-tappers and super-glue and the plate was the wrong way round anyway, so that went back in place of a standard unit. The third time was when I noticed the solenoid wasn't boosting the coil voltage when cranking. The contact was bent right back, obviously never tested at the rebuild. Not that it had problems starting, but once noticed I don't like things not working as they should.

Check the bolt holes in the head are threaded and clear all the way down, may have been problems in the past.
paulh4

Thanks for that - just got the starter off no problem with some help, with just the exhaust loose, which I am not certain helped or not.

Putting the top bolt back in might prove amusing, but so far so good. I think I will go for a hi torque, either WOSP or Powerlite. I did have a WOSP with an intermittent fault last year I sent back. I suspect the guts of them are identical
Mike Dixon

This thread was discussed between 01/04/2025 and 04/04/2025

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