Its not hard to install an MGB top (aka hood), but it is kind of fiddly. I have been selling Robbins tops for years and they are probably the best top available, now that Coventry (the OEM) has stopped making them. I have installed dozens of them. I guess its time to do a write-up.
Disregarding any needed repairs to the bows, it takes about 3.5-4 hours to install a new hood. Plan for a whole afternoon if you have not done it before. If you have the option, plan to do the job on a nice sunny day. It will help with the stretching. If no sunny days are available, I have had great success using a small space heater placed on the rear bulkhead. Fold the seats out of the way, remove the bulkhead top carpet and run the cord so it won’t get caught in the door. Fire up the heater, roll up the windows, pull the top into place and throw a blanket on top to keep the heat in. Let the whole affair cook for a while and the top will be much easier to work with.
(Seriously, though. Be safe and sensible. Don’t melt things or set anything on fire. If you do, its your fault, not mine. I told you not to.)
First of all, inspect your top bows for fit and operation. Its pointless to install a new top on bows that don’t work.
There are three types of bows. This write-up will be for the latest design, the Folding top, by far the most common. If I get one of the others in the shop, I will add more info and pics.
Early cars came with either Scissors tops or a Stow-Away tops. Scissors tops are not particularly well-liked and should only be used if you have an early car and want to keep it original. They are a hassle.
If the bows drop into a rectangular socket and are not bolted to the header rail, you’ve got a Stow-Away top. Its possible to use a Stow-Away hood on a later car and its possible to install a later Folding hood onto an earlier car. Some people like the option of removing the top in the summer to gain the extra space and Stow-Away tops make that easy.
’71 and later cars came with a Folding top. If your bows screw to the car body and doesn’t have a weird inwards-folding scissor-like deal above the doors, its a Folding top. Additionally, there is also the choice of fixed or zip-out window. That is completley up to you. Fixed windows tend to stay nice and taught, which improves visibility. Zip out windows let you zip the window out for better ventilation (shade and breeze), but the window tends to remain a bit wavy when zipped in place, as there is less tension over time. Your choice, they install exactly the same.
Once you know what top to order, be sure to order a new header seal. Also, have a look at the aluminum strip that holds the header seal. If yours is beat up, order one of those too.
If you still have a top on the car, check it for operation. Make sure it goes up and down smoothly and ends up centered on the windscreen. Check the shape of the bows, they should be smoothly convex as they go from side to side, not flat across the top from having boxes piled on top. If you need to adjust or fix things, now would be a good time to razor blade the old top off. Starting from just aft of the wing window, where the inner snap flap joint is, cut up through the sewn seams, then straight across the top to the other side. Don't worry about the part left on the header. We are just looking at the bows now. If you have a Folding top, the rear bow may be attached to the hood with little cloth strips called listing. Slice that off too. Extract the anchor bar from the rear edge of the old top and save it.
I prefer to remove the bows for cleanup, but you can do it in place. If you are at all on the fence about whether you need to sand and paint your bows, err on the side of paint. You will be staring at them for 5-10 years before you get another chance.
(I say 5-10 years for a couple of reasons. A top will last exposed to the weather and still be perfectly functional for at least 5 years. With decent care and a carport or breathable cover, you can extend the life of at top for another 5 years, easy. Anything beyond 10 years, I consider to be “free top” territory. You heated garage folks can get decades of use, but unfortunately that is not the norm.)
I will continue as if you have Folding bows. In the case of stow-away bows you can clean them up at your leisure since they are not attached to the top. The installation and fitting at the header are the same for all hoods.
Remove your bows from the car by holding them about half way erected and by then removing the three screws (#3 Pozidriv, not Philips!) per side. This is easiest with two people. There may or may not be a plate for a tonneau bar clamped behind the bows. If the six long screws are buggered up, or any of the captive nuts in the body are missing or loose, now is the time to replace or fix them. If there are any cracked welds or loose rivets on the bows, now is the time to fix them.
Remove the remnants of the old top from the header. This may or may not help you in installing the new one, depending if it was done right by Previous Guy™. At each end, there should be a single counter-sunk screw (#2 Pozi) with a flush trim washer. Unscrew and save. If this screw is missing, which is common, you will need to source #6 counter sunk sheet metal screw with a suitable flush trim washer. Flush washers have a larger surface area than a similarly sized regular countersunk washer and are preferable. There will be two hard plastic bumpers with flat headed sheet metal screws. Sometimes hood material is under the edge of these. If so, loosen the screws to free up the material. There are a dozen or so 1/8" pop rivets holding the aluminum strip to the bottom of the header rail. Drill these out with an 1/8" drill bit. If your header rail has been drilled out to take larger pop rivets or *gasp* sheet metal screws, by Previous Guy™, just get a new header, or locate a used one from your local club/FleaBay. Larger fasteners make the header seal want to push out and its generally not worth the trouble to repair a buggered header. If the holes in the aluminum strip are all wallowed out from repeated installations or the seal retaining lip is all bashed up for whatever reason, buy a new one. They are cheap.
At the top of the driver's side end of the header is a small hole. Shake the remnants of all the dead pop rivets out of the header via this hole, so it doesn’t sound like a rain stick every time you put your hood up or down. You can open this hole up a size or two with a uni-bit to make dead rivet extraction easier. Clean off any old adhesive with adhesive solvent. Also clean off the rear bow where the listing will be glued, especially if it is covered with dead glue and old listing. 3M General Purpose Adhesive Remover is your friend. If you want to paint your bows with satin black paint, now is the time. Don't forget to clean and paint the anchor bar as well, if it needs it. If you elect to repaint your bows, let the paint cure a couple of days, so that it won't be affected by solvents in the new glue. If you had to drill out the little access hole to a larger size, you can find little flush plastic plugs to fill the hole at the hardware store. The plug will not be visible under the new top, but the edge of a large hole might be.
Now, Gather ye your supplies.
You will need some good contact cement. Either buy a small can of brush-on DAP Weldwood or opt for a spray-can of Weldwood or 3M Extra Strength (not Super 77 or anything marked as reposition-able). It must have a "spider-web" vertical spray pattern, not a generic round aerosol pattern. Spray adhesive is faster to use, but you can also make a bigger mess in less time if you have not used it before. Brush-on takes longer between coats, but is far more idiot-proof. Your call.
Pick up a small roll of 4-6" masking paper, or newspapers, and a roll of masking tape.
Grab a box of cheap single-edged razor blades. Top material is tough stuff and you will go through more than a few.
Get a supply of 1/8" aluminum pop rivets. You will want four of the longer, 3/8" ones for double-thick areas, but shorter 1/4" ones will suffice for the rest.
Obviously, you will need a pop-rivet tool.
You will need a #2 Pozidriv screwdriver (Ugh, fine, a #2 Phillips, under duress or if you have to use new domestic screws, don’t get me started) and a small awl or scribe.
You will also need a 1/8” hole punch and a Durable DOT snap installer tool. You can buy a crappy one at your local fabric store or you can beg/bribe your local upholstery guy to crimp the final two snaps on for you with his awesome commercial one.
Pro-tip: spring for a can of 3M adhesive remover, about $16 for a quart. It is not only great for cleaning up contact cement, it is good for all kinds of clean up jobs in the shop. Also, it won't eat your car's paint. You will find that it becomes your second most-reached-for can o' stuff, right after your favorite penetrating oil, which is Kroil.
Install your bows back onto the car and make sure they operate correctly, nice and straight, and the header ends up centered side-to side on the windscreen. Leave the bows erect, but not latched.
Take a look at the front corner area of the new top. This is the most important part and how this is installed will determine 98% of how good your top looks once finished. There is the main stretch of material that goes across the header. Parallel to the top of the door glass flap, there is a shorter, double-thick flap with a scalloped front corner, next to the edge binding. Finally there is a small, thin strip hanging out at a funny angle. Once you have located these parts, we can talk about how they go on the car. Over the years, I have seen almost every possible combination that these bits can be attached to a header, and most of them are wrong.
It might help to connect the back part of the top to the car at this point.
Bear in mind that you can NEVER fold an MGB hood while the rear is hooked and snapped to the car. It will stress the seams of the top and you will put a permanent kink right in the middle of the rear quarter windows. While installing the top, you will get very good at hooking and unhooking the back of the top. Once you know how an MGB top goes on and off, you can help spread the Good Word to keep others from damaging theirs.
Begin rant here.
If you are not sure how to correctly fold the top, take a few minutes and google it. John Twist of University Motors has a video. Other folks have videos. The owner’s manual has instructions. Get someone in your MG club to show you how. Seriously, just do a quick fold to save 20 seconds because you are in a hurry and now you have to look at creased windows or worse for ten long years.
OK, I’m back.
The anchor bar should have a slight concave shape to match the deck of the car. Its easy to bend, so take this last chance to get it right. Slide the anchor bar into its slot in the back corner of the top, tapered edge facing the rear. Work it all the way across through the top, keeping it up over the folded internal seams until it is completely inside the top, then work it back from the other end so that it ends up centered. The bar should be on top of the internal flaps, visible at the two openings for the anchors and no bar ends peeking out.
Fit the rear edge of the top to the car, sliding the anchor bar into the two chrome anchors. From either corner, just behind the doors, pull the lower edge of the top forward so that the stainless tongues can slip into the stainless sockets on the car. Only now can you snap the Lift-the-Dot snaps onto their studs, four on each side. With a new top, you may have to pull rather hard to get all the LTDs to line up. This is OK, the top is tough and has more ability to stretch than you think it does. After its been on your car for a while, it will change shape to fit your car, just like your favorite jeans.
Reach up inside the top and move the rear bow so that it lays in the seam above the back window. Don’t worry about the thin listing material at this time, just make sure the bow is in place in the seam.
With the door windows rolled down, pull the top material forwards so that you can see how it will fit on the car. It might help to sit inside the car to see how it must fit. Look at the frontmost corner of the flap that hangs over the window. There is a bound tab sticking forward at the innermost edge. This will take a DOT snap and connect to the stud at the top of the windshield post. Outboard of this tab, there is a double-thick section that has a little scalloped cut at the front edge (this is important) and a sewn longitudinal corner. Outboard of that is the drip rail tapering down at the front end to a single bound edge. The way that this Great Conjunction of Stuff fits at the outer corner of the header is key to top fit.
The double-thick section gets screwed to the bottom of the header with the single sheet-metal screw and flush washer in what I call the Big Stab. Once you have located this section and poked your awl into the single screw hole, you are kind of committed, although there is a little wiggle room which we will cover later on. You don’t get a lot of error correction that will not be visible once its finished, so take your time and get it right. Its better to waste half an hour looking at this from every possible angle than to start off wrong and end up with a mangled flap with a bunch of extra holes.
1) From the inside, the window flap/snap-tab will want to be tight up against the top edge of the door glass. However, it can’t be so tight against the glass that the snap flap can’t reach around inside to reach the stud on the windscreen post. The tab generally will end up with a slight jog as it stretches around the top edge of the wing window frame. If you get this flap too tight, you will likely have problems with the wing window hitting the drip rail.
2) Viewed from the outside, follow the line along the top of the drip rail. You will want this line to visually flow right down into the leading edge of the wing window frame. Not so far forward that the drip rail meets up with the windscreen frame, it will be difficult to put up. Not so loose that the line bonks into the top the wing window frame, it will not fit correctly on the header.
3) Viewed from the side, the bottom of the drip rail will be at the same level as the double-thick section behind it as it wraps underneath the header. If you can see the double-thick section past the drip rail edge, you need to pull more side-to-side to bring the drip rail lower. However, too much pull side-to-side will leave the drip rail hanging too low and the wing window will hit it every time the door is opened or closed, wearing a hole into the drip rail edge.
4) The taped edge of the drip rail just sort of folds under at the front corner of the header. Too much tension forward will leave the taped edge loose with nowhere to go. Not enough tension and the leading edge of the header will not be covered, and your angled flap will not end up in the right place. It will look goofy.
Keeping all of that in mind, free the back of the top from the car. First the LTD snaps, then the forward tongue tab, then the anchor bar, and let it flop back onto the boot.
Lift the header up to about half-mast so that you can get at its underside. Being careful not to let the bows collapse onto the top, bring the top up into place and hold the three sections on one side approximately where they should go. With this bottom view, it will become clear where the things will have to end up.
At the front edge of the header is a lip that I call the lip. At the outer ends of the the lip you will see a section where the lip tapers off and meets up with a weld as it turns back to meet the rounded end of the header. This area is where all the action happens.
The double-thick section has a scalloped corner cut out to clear the edge of the weld on the header and it should tuck right up behind the tapered end of the lip. Holding the edge of the drip rail against the outer corner of the header, you should be able to fold the double-thick section down around the end of the header onto its bottom edge, pulling forward to just shy of the weld. Finally, the thin flappy strip will now line up exactly with the inside edge of the lip of the header. (Over time, the hood material will tend to shrink. This strip keeps tension on the material to stop if from pulling up from the header at the corners.)
Once you have determined the correct location of the corner of the hood, its time for the Big Stab. Using your awl, poke a small hole through the double-thick section into the original screw hole and secure it with the screw and flanged finish washer.
Now, do the same thing on the other side! You will need to stretch the top quite a bit laterally to accomplish this, but it will work. This is the same way the factory installed the hoods, starting well over 50 years ago. They did not spend a huge amount of time custom fitting each top to each car. They installed the hood to the header using the pattern of the hood itself as an installation guide, trusting that the hood was fabricated correctly. There is enough stretch and shrink in the material that the rest of the hood will fit well enough as long as it is mounted to the header correctly.
OK, now we have the two screws in place. The hood should be in the right spot. Reattach the back of the hood to the car, erect the top, and this time clip the header into place. Yes, its kind of scary having all that tension on two little screws. That’s what the flush washer is for. It spreads the load so that it is pulling along a wide section, not just a single screw head or a plain flush washer with a sharp edge. You should be able to pull the hood into what looks like the correct place by pulling along the drip rail and the front edge.
This is 98% of your hood fit right here, so take the time to get it right!
What we are looking for is the line of the drip rail lining up with the front of the wing window frame, and the lower edge of the drip rail being flush with the bottom of the header and the double-thick section. At this point, you should be close, like within 1/8” from the right spot, likely within manufacturing tolerance for MGBs at least. If you need to adjust side-to-side by a small amount to get the drip rail perfect, the extra hole will be hidden by the flush washer. If you did not pull the top forward enough, that is OK, the extra holes will be hidden under the flap in later steps.
Hooray! The hard part is done! Now it is just following the steps and some detail work.
Unlatch the hood to release the tension and flip up the front of the material as far as you can. You can use masking tape to hold it back onto itself. If you want to cover things with masking paper, now is when to do it. Put some across the top of the windscreen, the wing windows and, if you tend to be sloppy, across the front seats as well. You are going to apply glue to the front 1-1/4” or so of the header and the corresponding area of the inside of the hood. Its OK put glue forward of that on the hood, it will get cut away, but don’t go any farther back or the glue will be visible from the inside. You will note that the front edge of the hood matches the shape of the header very well. Its not just extra material. This is by design and is to give you a reference that will help you pull the hood evenly forward.
Let the glue dry until it smooth and just a little tacky. You may need to apply additional coats on the cloth. See the instructions on your adhesive.
Now, plan ahead for your next move, so that you can work quickly. Its going to take less than a minute. You are going to pull the hood material forward at each corner, so that the material at the "hump” at the shoulder at the end of the header is taught and even, and your drip rail in the correct location fore-and-aft, and then pull downward so that the material will stick to the header. Quickly move to the other side of the car and do the same thing. Once your corners are down, you can move inwards and pull the front of the hood forward so that it has even tension across the front. Use the shape of the material as a guide to keep the tension even. As you move towards the center, you won’t have to pull as hard as you did at the start to keep things even. If you get a wrinkle or a spot of uneven tension, don’t panic. You should be able to pull the material back up and correct it, though you may have to re-apply adhesive. Once your hood looks good across the front, go back and rub it down good and hard, so that the adhesive bonds well.
You might want to take a break and have a beer/cup of coffee and let the glue cure and the material stretch into place a bit. Think how good its gonna look!
Unlatch the clamps and unhook the back of the hood. Again. Fold the hood back just to where you can get at the lower side of the header. Don’t crumple your quarter windows!
Take a little sandpaper or coarse Scotchbrite and scuff the surface, top and bottom, of the little scalloped corner, as well as the shiny side of the flippy flap, starting 1/2” from the seam. This will help give the contact cement better adhesion. Apply contact cement to the bottom of the header, from the line of holes forward up under the lip, as well as under the scalloped edge flap. Don’t apply it to the entire surface or it will show. Check the glued surface of the loose top material. If you did the previous gluing right, the glue line should follow the shape of the header fairly well, if you think it needs more glue, now’s the time. Let it all dry completely.
Once the glue is dry, press the scalloped edge down into place. Pull the flippy flap inwards and press it into place along the corner of the lip. It should fit flush behind the lip, well into the corner and cover the loose end of the scalloped edge.
Working with you fingers, fold the front edge of the hood over the lip and press it into place. Don’t just tug it all at once. Work it tightly from the outside and roll it over the lip. Once over the lip, press it tightly into the corner and then onto the lower surface. As you near the ends of the header, you will need to cut three little darts into the back side of the hood, so that it will lay down flat and not form a wrinkle. Two will be near the welded longitudinal seam and the other an inch or so from the end. Cut the darts on the riveting surface, not so far they extend up onto the lip. The taped edge will be exposed on the outside for about an inch, then dive under the lip and end up fairly close to a rivet hole.
Using your awl, poke holes through the hood material to line up with the existing holes. Pop rivet the aluminum strip down over the material, using longer rivets for the thick sections at the ends. Trim the hood material flush with the rear edge of the aluminum strip.
Install the header seal by folding the hidden bead into the aluminum retainer and poking the exposed edge into place with a screwdriver. The ends of the seal are cut at an angle to match the shape of the header. If you are not sure, leave it a little long and trim it after it is clamped onto the windscreen frame.
Hook up the rear of the hood to the car and clamp the header into place. Be aware that the header seal is supposed to sit in front of the lip on the windscreen frame, not on top of it. You might have to poke it into place when you first clamp it down until it “learns” where it should sit.
Pull the snap tabs tightly forward over the DOT snap stud and using your awl, make the location to install the snap. Punch the hole and install a snap at each tab.
If you have a stow-away frame, your done! If you have a folding frame, you have one more step: glue the listing.
Crawl inside the car and make sure the rear bow is sitting in between the listing flaps. If you need to just shove the listing into place with your finger. You can push the bow up or down a little bit to get it nestled nicely in the welded seam. You can have a friend give helpful advice as to what looks best. I generally try to get it right in the middle of the seam, but some cars want to be a bit high or low. Tape the front listing out of the way. Apply contact cement to the face of the rear flap and to the bow, up to the front edge. It does not need to wrap all the way around the front. In fact its easier to trim it just in front of the flat inner face of the bow. When the glue is ready, pull the rear listing around towards the front and press it into place. Razor blade off the extra material, holding the blade at an angle so that it trims off smoothly. Now, glue up the front flap of the listing. You are going to want to wrap the glue pretty far around the back on this one, but you don’t have to go completely all the way around to the seam, just mostly. When the glue is ready, wrap the front listing around the back, pressing it tightly into place. Carefully trim the listing up around the back as far as you can reasonably get without slicing your hood open. It does not have to be completely flush with the back edge. All that surface area is probably stronger than the thread its made of. Its not going anywhere and no one can see back up there anyway. You just don’t want it falling down in a couple of years.