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MG MGB GT V8 Factory Originals Technical - manifold bolts

As these bolts are somewhat awkward, any recommendations for using studs or Hex head and in what positions.


The original bolts and thick washers were in pretty bad shape when I rebuilt my engine, the bolts were rusted and pitted. I used Allen-head cap screws on all the exhaust manifold bolt locations, and new thick washers. I believe the bolts are 3/8" UNC x 7/8" long. I got mine at an industrial hardware liquidator company called Blue Collar Supply here in Sacramento, California. They were black oxide coated, so they looked right on the Rover V-8 engine.

Getting replacement thick washers was a problem, these are not usually available at a normal auto parts store. I remembered that similar washers were used on old Chevy smallblock V-8s (I had helped a friend install an engine in a '58 Corvette a couple of years before). I went to the local Chevy dealership and was able to order the washers, and they fit perfectly. They were shiny plated, but I bead blasted them and sent them out to a gunsmith friend of mine who was able to give them a black finish to match the cap screws.

I got a 3/8" square drive Allen socket to match the cap screws from Snap-On. It is really short and will fit in between the screw and the side of the engine bay pretty well.

Several points to remember when replacing exhaust manifold bolts:
1. Use exhaust manifold gaskets (Part # GEG 692) especially if you have the OEM cast iron manifolds - the factory installation did not use them. They will cushion the manifolds and reduce chance of cracking.

2. Use Copaslip or Felpro Grey Bolt Prep on all the bolts when installing, and torque to 13 foot pounds ONLY!!!

3. Make sure that there is sufficient clearance between the old Rover engine number boss and the exhaust manifold (at least 1/8" when the engine is cold). This boss is between the center cylinders on the LH side of the engine. MG had to grind off this boss to clear the factory manifolds, they re-stamped the engine number at the back near the bell-housing flange.

4. Make sure that the A-pipe ends can enter the exhaust manifold flanges easily without bending or forcing them. Any stress on the exhaust flanges can crack them.

Remember that the factory exhaust manifolds are NLA and cost a mint now. I found a set at Beers of Houghton for 500 UKP!! That's why we need to do all we can to protect them from cracks.

Hope this helps,
Paul Kile
Paul Kile

The MGOC sells Allen bolts, and I have seen them in use, but in only in seven out of the eight positions on each side! Ths is because the 3rd bottom bolt from the front on the left (2nd on the right) is so hidden behind the pipe that you cannot even get an Allen key in. As the others are not particularly difficult anyway it seems to defeat the object somewhat.

Paul Hunt

I managed to get all the Allen bolts in with no problems with the stock cast iron manifolds. Tubular headers may pose different problems due to their curvature. I like the Allen bolts because I was able to get a driver that allowed the use of my 3/8" drive torque wrench on the bolts
Paul Kile
Paul Kile

Just a thought, I am using stainless button head capscrews. Slightly larger bearing surface on the head, doesn't stick out as far, and uses a smaller hex key. Also a little less likely to stick.
Jim Blackwood

The idea of using studs is to prevent stripping threads in head but probably not suitable for replacing all bolts.

The other problem I have is the rack shaft re first bottom bolt on right hand manifold. I've ground an Allen key to access Hex bolt.

I've also ground down an old spanner to deal with the bolts Paul H refers to, but as Paul K mentions a torque wrench is really required.

Thanks for suggestions I will see if they can be applied under the bonnet.


I have Hex head(Allen Key) bolts fitted, access can be had to all the bolts, with a cut down Allen key fitted into a socket.
The torque required to tighten standard bolts or Hex bolts is not much, can't remember the figures off the top of my head. Over torque was the main problem with cracking over the OE manifold on factory V8's.
Keith Rowson


Allen bolts on my manifolds

The Factory torque on the manifold bolts was 13 foot-lbs. This was on the original MG installation with no manifold gaskets used. With gaskets in place, I used the later Rover spec of 16 foot-lbs. I also made sure I used Copaslip on the bolt threads.

Paul Kile

PS - I wonder how many guys named Paul are out there with Factory V-8s?
Paul Kile

Been delayed with manifolds due to replacing slave on midget.

Paul K - mispent youth probably, but would copaslip play havoc with torque setting, another reason for trying a stud.

Also anyone tried the sport gasket from Rimmer's?


Paul Kyle you canít count yourself among the guys named Paul that have factory V8s because your manifolds are torqued to 16 foot-lbs.

I just couldnít resist! Iím looking forward to seeing yours in a show sometime.
George Champion

"Also anyone tried the sport gasket from Rimmer's?"

Don't know what this is but I have seen three different types so far, listed in the order I have used them:

'Thick' metal-faced, one per port - good compressability but being thick they reduce the clearance to the inner wing, they are also a bit of a fiddle to get lined up.

Green composition, one per pair of ports - thin (better clearance), easy to locate, but they crack both between the ports and, more importantly, between manifold and head.

'Thin' metal-faced, one per pair of ports - reasonable compressability, being thinner they give better clearance to the inner wing, easy to line up.

Paul Hunt

There is an all steel gasket.

Fits one per pair of ports and is actually three layers of spring steel like valley gasket. Seems to be very effective and reusable - I had the manifolds off at least 6 times one the one set of gaskets.

They are a range rover part and may have been superseded.

I've been using cap head bolts in all 8 holes per side without too much difficulty.

I have a new pair of manifolds to fit at some point which have the bolt holes cut as slots were the manifold covers the bolt hole. You put a bolt in the head and slide the manifold onto it - should make holding the gaskets easier.


Dave Brooke

Paul H.,
I used the Rover thick metal faced gaskets, one per port. The trick to putting these in is to install the manifold with the upper bolts first, running the bolt through the gasket bolt hole while holding the gasket up above the manifold. You then rotate the gasket down until the lower hole lines up, then put the lower bolts in.

Some American Buick gaskets have the lower bolt holes slotted, so you can install the lower bolts as well, then rotate the gasket to engage the bolt.

Paul in Surrey,
I assume that the torque settings given in the manual take into account that some sort of anti-seize is to be used on the bolts, since anti-seize is specified for these bolts elsewhere in the book. I believe that most torque settings assume that the bolts in question are to be lightly lubricated, unless they specifically say install them dry.

I'm afraid my car is not totally genuine, since the Abingdon air is long gone from the tires! Hope to attend some shows next season, since I need to take care of the second gear synchro problem (a result of a subcontractor error in rebuilding the tranny!). I'm waiting for the winter to pull the engine and trans, I don't relish doing the job in the Sacramento summer (which I'm sure pales in comparison to a Yuma summer!)

Paul Kile
Paul Kile

My Buick gaskets are not slotted. I used a trick I read somewhere be using a rubber band around the top and bottom bolts to hold the gasket in place for each port until the bolts have been started. Wouldnít be nice if the gaskets were made as a single piece per side as they are on Chevrolets?

Paul Kyle you may have something there. How many people would buy a novelty item of genuine Abingdon air? I heard Detroitís solution to air pollution is to have it pumped into tires of production cars.

George Champion

"since the Abingdon air is long gone from the tires"

Not that they ever had it, of course ...
Paul Hunt

This thread was discussed between 03/08/2001 and 16/08/2001

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